Publications

Memory consolidation can be promoted via targeted memory reactivation (TMR) that re-presents training cues or context during sleep. Whether TMR acts locally or globally on cortical sleep oscillations remains unknown. Here, we exploit the unique functional neuroanatomy of olfaction with its ipsilateral stimulus processing to perform local TMR in one brain hemisphere. Participants learned associations between words and locations in left or right visual fields with contextual odor throughout. We found lateralized event-related potentials during task training that indicate unihemispheric memory processes. During post-learning naps, odors were presented to one nostril in non-rapid eye movement (NREM) sleep. Memory for specific words processed in the cued hemisphere (ipsilateral to stimulated nostril) was improved after local TMR during sleep. Unilateral odor cues locally modulated slow-wave (SW) power such that regional SW power increase was lower in the cued hemisphere relative to the uncued hemisphere and negatively correlated with select memories for cued words. Moreover, local TMR improved phase-amplitude coupling (PAC) between slow oscillations and sleep spindles specifically in the cued hemisphere. The effects on memory performance and cortical sleep oscillations were not observed when unilateral olfactory stimulation during sleep followed learning without contextual odor. Thus, TMR in human sleep transcends global action by selectively promoting specific memories associated with local sleep oscillations.

Recollection of personal events is a major activity of the human mind and is considered essential for maintaining the cohesiveness of the self-concept. Yet evidence from cognitive psychology and brain research converge to raise doubts concerning the veridicality of the events recalled. Furthermore, even information encoded and recalled correctly seems to be prone to significant and long-lasting distortion by exposure to new input at the time of retrieval. A major source of such new input is inter-personal. From early infancy, we tend to look to others as a primary source of information and may reevaluate our own perceptions, preferences, and memories when they contradict a larger consensus. Circuits in our brain can modify our memory in response to such information even under conditions in which our original memory is accurate and our confidence is strong. Part of what we believe we know is in fact a product of the amalgamation of the internal representations originating in multiple brains. Personal memory may hence be considered conceptually as a node in a highly distributed multi-dimensional memory space, in which the contribution of the individual is only part of an informational syncytium that transcends the personal. This may provide our species with a phylogenetic advantage ensuring that, on one hand, accumulated information can be fitted to the real-time requirements of the locale, but on the other hand, that the storage capacity and availability of information markedly exceeds the capacity and the life span of the individual brain. In consequence, however, individuals may be unreliable narrators of their own history.

The complexity of the human brain and the difficulties in identifying and dissecting the biological, social and contextual underpinnings of mental functions confound the study of the etiology and pathophysiology of mental disorders. Large-scale computer simulation of the human brain was recently proposed as a method to circumvent some of these difficulties. In this two-part paper, we discuss selected conceptual and pragmatic issues pertaining to the mental illness simulation in general and computer simulation in particular. We address the merits and limitations of two generic types of simulation vehicles, biological simulation in animal models (Part I) and virtual simulation in computer models (Part II), in the study of mental disorders in humans. We point to the need to tailor the vehicle and method of simulation to the goal of the simulation, and suggest future directions for maximizing the utility of mental illness simulation. We argue that at the current state of knowledge, the biological-phenomenological gap in understanding mental disorders markedly limits the ability to generate high-fidelity biological and computational models of mental illness. Simulation focusing on limited realistic objectives, such as mimicking selected distinct biological and phenomenological attributes of specific mental symptoms, may however serve as a useful tool in exploring mental disorders.

[No abstract available]

The ζ-inhibitory peptide (ZIP) is considered a candidate inhibitor of the atypical protein kinase Mζ(PKMζ). ZIP has been shown to reverse established LTP and disrupt several forms of long-term memory. However, recent studies have challenged the specificity of ZIP, as it was reported to exert its effect also in PKMζknock-out mice. These results raise the question of what are the targets of ZIP that may underlie its effect on LTP and memory. Here we report that ZIP as well as its inactive analog, scrambled ZIP, induced a dose-dependent increase in spontaneous activity of neurons in dissociated cultures of rat hippocampus. This was followed by a sustained elevation of intracellular calcium concentration ([Ca²⁺]i) which could not be blocked by conventional channel blockers. Furthermore, ZIP caused an increase in frequency of mEPSCs followed by an increase in membrane noise in patch-clamped neurons both in culture and in acute brain slices. Finally, at 5–10 μM, ZIP-induced excitotoxic death of the cultured neurons. Together, our results suggest that the potential contribution of cellular toxicity should be taken into account in interpretation of ZIP’s effects on neuronal and behavioral plasticity.

We review reports of brain activations that occur immediately prior to the onset or following the offset of to-be-remembered information and can predict subsequent mnemonic success. Memory-predictive pre-encoding processes, occurring from fractions of a second to minutes prior to event onset, are mainly associated with activations in the medial temporal lobe (MTL), amygdala and midbrain, and with enhanced theta oscillations. These activations may be considered as the neural correlates of one or more cognitive operations, including contextual processing, attention, and the engagement of distinct computational modes associated with prior encoding or retrieval. Post-encoding activations that correlate with subsequent memory performance are mainly observed in the MTL, sensory cortices and frontal regions. These activations may reflect binding of elements of the encoded information and initiation of memory consolidation. In all, the findings reviewed here illustrate the importance of brain states in the immediate pen-encoding time windows in determining encoding success. Understanding these brain states and their specific effects on memory may lead to optimization of the encoding of desired memories and mitigation of undesired ones. (C) 2014 Elsevier Ltd. All rights reserved.

Flexible mnemonic mechanisms that adjust to different internal mental states can provide a major adaptive advantage. However, little is known regarding how this flexibility is achieved in the human brain. We examined brain activity during retrieval of false memories of a movie, generated by exposing participants to misleading information. Half of the participants suspected the memory manipulation (Distrustful), whereas the other half did not (Naïve). Distrustful displayed more accurate memory performance and a brain signature different than that of Naïve. In Distrustful, the ability to differentiate true from false information was driven by a qualitatively distinct hippocampal activity for endorsed items, consistent with the view that hippocampal encoding allows recollection of a specific source. Conversely, in Naïve, BOLD differences between true and false memories were linearly correlated with accuracy across participants, suggesting that Naïve subjects needed to reinstate and evaluate stored information to discern true from false. We propose that our results lend support to models suggesting that hippocampal activity can exhibit different computational schemes, depending on memorandum attributes. Furthermore, we show that trust, considered as a subjective state of mind, may alter basic hippocampal strategies, influencing the ability to separate real from false memory.

The hippocampus is known to be involved in encoding and retrieval of episodes. However, real-life experiences are expected to involve both encoding and retrieval, and it is unclear how the human hippocampus subserves both functions in the course of a single event. We presented participants with brief movie clips multiple times and examined the effect of familiarity on the hippocampal response at event onset versus event offset. Increased familiarity resulted in a decreased offset response, indicating that the offset response is a novelty-related signature. The magnitude of this offset response was correlated, across hippocampal voxels, with an independent measure of successful encoding, based on nonrepeated clips. This suggests that the attenuated offset response to familiar clips reflects reduced encoding. In addition, the posterior hippocampus exhibited an increased onset response to familiar events, switching from an online familiarity signal to an offline novelty signal during a single event. Moreover, participants with stronger memory exhibited increased reactivation of online activity during familiar events, in line with a retrieval signature. Our results reveal a spatiotemporal dissociation between novelty/encoding and familiarity/retrieval signatures, assumed to reflect different computational modes, in response to the same stimulus.

Humans are strongly influenced by their environment, a dependence that can lead to errors in judgment. Although a rich literature describes how people are influenced by others, little is known regarding the factors that predict subsequent rectification of misleading influence. Using a mediation model in combination with brain imaging, we propose a model for the correction of misinformation. Specifically, our data suggest that amygdala modulation of hippocampal mnemonic representations, during the time of misleading social influence, is associated with reduced subsequent anterior-lateral prefrontal cortex activity that reflects correction. These findings illuminate the process by which erroneous beliefs are, or fail to be, rectified and highlight how past influence constrains subsequent correction.

Protein kinase M zeta (PKMζ), an atypical isoform of protein kinase C (PKC), has been implicated in long-term maintenance of neuronal plasticity and memory. However, the cellular machinery involved in these functions has yet to be elucidated. Here, we investigated the effects of PKMζ overexpression on the morphology and function of cortical neurons in primary cultures. Transfection with a plasmid construct expressing the PKMζ gene modified the distribution of spine morphologies and reduced spine length, while leaving total spine density and dendritic branching unchanged. A significant increase in magnitude but not frequency of miniature excitatory post synaptic currents was detected in the PKMζ overexpressing cells. These results suggest that PKMζ is involved in regulation of dendritic spine structure and function, which may underlie its role in long-term synaptic and behavioral plasticity.

That human evolution amalgamates biological and cultural change is taken as a given, and that the interaction of brain, body, and culture is more reciprocal then initially thought becomes apparent as the science of evolution evolves (Jablonka and Lamb, 2005). The contribution of science and technology to this evolutionary process is probably the first to come to mind. The biology of Homo sapiens permits and promotes the development of technologies and artefacts that enable us to sense and reach physical niches previously inaccessible. This extends our biological capabilities, but is also expected to create selective pressures on these capabilities. The jury is yet out on the pace at which critical biological changes take place in evolution. There is no question, however, that the kinetics of technological and cultural change is much faster, rendering the latter particularly important in the biography of the individual and the species alike. The capacity of art to enrich human capabilities is recurrently discussed by philosophers and critics (e.g., Arsitotle/Poetics, Richards, 1925; Smith and Parks, 1951; Gibbs, 1994). Yet less attention is commonly allotted to the role of the arts in the aforementioned ongoing evolutional tango. My position is that the art of cinema is particularly suited to explore the intriguing dialogue between art and the brain. Further, in the following set of brief notes, intended mainly to trigger further thinking on the subject, I posit that cinema provides an unparalleled and highly rewarding experimentation space for the mind of the individual consumer of that art. In parallel, it also provides a useful and promising device for investigating brain and cognition.

Encoding of real-life episodic memory commonly involves integration of information as the episode unfolds. Offline processing immediately following event offset is expected to play a role in encoding the episode into memory. In this study, we examined whether distinct human brain activitytime-lockedtotheoffsetofshortnarrativeaudiovisualepisodes could predict subsequent memory for the gist of the episodes. We found that a set of brain regions, most prominently the bilateral hippocampus and the bilateral caudate nucleus, exhibit memory-predictive activity time-locked to the stimulus offset. We propose that offline activity in these regions reflects registration to memory of integrated episodes.

Are specific distributed coactivations in the brain during memory retrieval a signature of retrieval outcome? Here we show that this is indeed the case. Widespread brain networks were reported to be involved in the retrieval of long-term episodic memories. Although functional coactivation among particular regions occurs during episodic memory retrieval, it is unknown to what extent it contributes to the accuracy and confidence of recollection. In this study we set out to explore this question. Participants saw a narrative documentary movie. A week later they underwent an fMRI scan during which they either accepted or rejected factual or fictitious verbal statements concerning the movie. Correct vs. incorrect responses to factual statements were more common and were provided with higher confidence than those made to fictitious statements. Whereas activity in the retrieval network correlated mostly with confidence, coactivations primarily correlated with memory accuracy. Specifically, coactivations of left medial temporal lobe regions with temporal and parietal cortices were greater during correct responses to factual statements, but did not differ between responses to fictitious statements. We propose that network coactivations play a role in recovering memory traces that are relevant to online retrieval cues, culminating in distinct retrieval outcomes.

In this conversation, the world-renowned neurobiologist Yadin Dudai discusses the latest advances in memory research, specifically the discovery of memory 'erasure' associated with the inhibition of an enzyme called PKMzeta. The conversation tackles the reductionist method in scientific inquiry, the mind/brain dilemma, the problematics of animal models in memory research, and the therapeutic implications of this groundbreaking discovery.

We report here that ZIP, a selective inhibitor of the atypical protein kinase C isoform PKMζ, abolishes very long-term conditioned taste aversion (CTA) associations in the insular cortex of the behaving rat, at least 3 mo after encoding. The effect of ZIP is not replicated by a general serine/threonine protein kinase inhibitor that is relatively ineffective toward PKMζ, is independent of the intensity of training and the perceptual quality of the taste saccharin (conditioned stimulus, CS), and does not affect the ability of the insular cortex to re-encode the same specific CTA association again. The memory trace is, however, insensitive to ZIP during or immediately after training. This implies that the experience-dependent cellular plasticity mechanism targeted by ZIP is established following a brief time window after encoding, consistent with the standard period of cellular consolidation, but then, once established, does not consolidate further to gain immunity to the amnesic agent. Hence, we conclude that PKMζ is not involved in short-term CTA memory, but is a critical component of the cortical machinery that stores long- and very long-term CTA memories.

Whether olfactory working memory involves verbal representations or neural images of odor per se remains unclear. This study investigated whether verbal representation influences performance in an olfactory delayed-match-to-sample task and used monorhinal presentation to generate hypotheses as to the underlying anatomy of this mechanism. The main findings were that (a) nameable odorants were easier to remember than hard-to-name odorants and (b) the nameability effect was more pronounced when the evaluation was done across nostrils. Considering these results within a proposed model implies dual representation in olfactory working memory: All odors, nameable and hard to name, are represented both perceptually and verbally.

Several recent functional neuroimaging studies have reported robust bilateral activation (L > R) in lateral posterior parietal cortex and precuneus during recognition memory retrieval tasks. It has not yet been determined what cognitive processes are represented by those activations. In order to examine whether parietal lobe-based processes are necessary for basic episodic recognition abilities, we tested a group of 17 first-incident CVA patients whose cortical damage included (but was not limited to) extensive unilateral posterior parietal lesions. These patients performed a series of tasks that yielded parietal activations in previous fMRI studies: yes/no recognition judgments on visual words and on colored object pictures and identifiable environmental sounds. We found that patients with left hemisphere lesions were not impaired compared to controls in any of the tasks. Patients with right hemisphere lesions were not significantly impaired in memory for visual words, but were impaired in recognition of object pictures and sounds. Two lesion-behavior analyses - area-based correlations and voxel-based lesion symptom mapping (VLSM) - indicate that these impairments resulted from extra-parietal damage, specifically to frontal and lateral temporal areas. These findings suggest that extensive parietal damage does not impair recognition performance. We suggest that parietal activations recorded during recognition memory tasks might reflect peri-retrieval processes, such as the storage of retrieved memoranda in a working memory buffer for further cognitive processing.

The brain endocannabinoid system has been shown to play a role in memory, though the extent to which this role generalizes over different types and processes of memory is not yet determined. Here we show that the cannabinoid receptor 1 (CB1) plays differential roles in acquisition, extinction and reconsolidation of conditioned taste aversion (CTA) memory in the rat insular cortex, which contains the taste cortex. Activation of the CB1 receptor in the insular cortex inhibits acquisition and reconsolidation but not extinction, whereas blockade of the CB1 receptor promotes memory and blocks extinction of CTA, while having no apparent effect on reconsolidation. The CB1 ligands used in this study were incapable of substituting the unconditioned stimulus in CTA training. All in all, the data raise the possibility that the state of activity of the CB1 receptor in the insular cortex contributes to the encoding of hedonic valence that enters into association with taste items.

This part presents five chapters on the concept of transfer. The first chapter discusses the inclusion of the concept of transfer in molecular and cellular neuroscience. The second considers transfer in animal learning. The third discusses transfer as the most central concept in learning and memory. The fourth discusses the relationship between retention and transfer and the conditions yielding specificity or generality of transfer. The fifth chapter presents a synthesis of the chapters in this part.

Tinnitus, the perception of sound in the absence of external acoustic stimulation, is a common and devastating pathology. It is often a consequence of acoustic trauma or drug toxicity. The neuronal mechanisms of tinnitus are neither yet fully understood nor are effective treatments available. Using a novel behavioral paradigm for measuring tinnitus in the rat based on tone-guided navigation, we show here that the development of long-term noise-induced tinnitus, the most prevalent and clinically important form of human tinnitus, can be abated by local administration of the NMDA antagonist "ifenprodil" into the cochlea in the first 4 days following the noise insult but not afterwards. This suggests that long-term tinnitus undergoes a consolidation-like process, resembling the ontogeny of items in long-term memory. Furthermore, this finding paves the way to potential therapeutic strategies for the prevention of chronic tinnitus once the noise insult had taken place.

Reconsolidation is a putative neuronal process in which the retrieval of a previously consolidated memory returns it to a labile state that is once again subject to stabilization. This study explored the idea that reconsolidation occurs in spatial memory when animals retrieve memory under circumstances in which new memory encoding is likely to occur. Control studies confirmed that intrahippocampal infusions of anisomycin inhibited protein synthesis locally and that the spatial training protocols we used are subject to overnight protein synthesis-dependent consolidation. We then compared the impact of anisomycin in two conditions: when memory retrieval occurred in a reference memory task after performance had reached asymptote over several days; and after a comparable extent of training of a delayed matching-to-place task in which new memory encoding was required each day. Sensitivity to intrahippocampal anisomycin was observed only in the protocol involving new memory encoding at the time of retrieval.

The interactions among experience, emotion, and memory are considered to be instrumental in the ontogeny and maintenance of acquired emotional and behavioral disorders (e.g., phobias). Here we address the question whether an anxiety-like state can associate with taste to produce conditioned taste aversion (CTA). We have used an anxiogenic agent, the 5-HT _2C receptor agonist meta-chlorophenylpiperazine (mCPP), to induce an anxiety-like emotional state in rats after consumption of an unfamiliar tastant. The anxiogenic agent induced CTA. The mCPP-induced CTA could be prevented by concomitant administration of ethanol, which is known to reverse mCPP-induced anxiety-like behavior, at a concentration that had no effect on CTA memory. In contrast, ethanol did not prevent LiCl-induced CTA. Administration of mCPP before the consumption of the tastant had no effect on the preference for that tastant. Taken together, these results indicate that anxiety-like state can serve as the unconditioned stimulus in CTA training. This finding may be relevant to the ontogeny of pathologies involving food aversion.

Long-term fear memory in the medaka fish (Oryzias latipes) regains transient sensitivity to a consolidation blocker immediately after memory reactivation in retrieval ('reconsolidation'). Here we show that reconsolidation occurs in fresh long-term memories but not in remote memories, and that the apparent amnesia induced by blockade of reconsolidation can be reinstated by an unpaired reinforcer, a procedure that has no effect on amnesia induced by blockade of consolidation. Extinction memory also undergoes post-reactivation reconsolidation, the blockade of which exposes the previously acquired fear. Hence in medaka, the process manifested in reconsolidation seems itself to consolidate; moreover, even when the post-reactivation application of the consolidation blocker is still able to disrupt the memory, the conditioned fear does not seem to go away permanently.

Recent reports have revitalized the debate on whether, for each item in memory, consolidation occurs just once, or whether, upon their activation in retrieval, items in memory undergo reconsolidation. Further, it has been recently reported that following retrieval in the absence of reinforcer, the activated memory can either reconsolidate or extinguish, depending on the training history. This raises the question whether consolidation, extinction and reconsolidation share neuronal mechanisms, and moreover, whether reconsolidation recapitulates consolidation. In conditioned taste aversion (CTA), consolidation depends on protein synthesis in the central nucleus of the amygdala, whereas extinction depends on protein synthesis in the basolateral nuclei of the amygdala. Here we show that inhibition of protein synthesis in either of these nuclei has no effect on CTA memory under conditions that initiate reconsolidation. This implies that reconsolidation does not recapitulate consolidation, and that consolidation, reconsolidation and extinction are different processes.

Consolidation is the progressive postacquisition stabilization of long-term memory. The term is commonly used to refer to two types of processes: synaptic consolidation, which is accomplished within the first minutes to hours after learning and occurs in all memory systems studied so far; and system consolidation, which takes much longer, and in which memories that are initially dependent upon the hippocampus undergo reorganization and may become hippocampal-independent. The textbook account of consolidation is that for any item in memory, consolidation starts and ends just once. Recently, a heated debate has been revitalized on whether this is indeed the case, or, alternatively, whether memories become labile and must undergo some form of renewed consolidation every time they are activated. This debate focuses attention on fundamental issues concerning the nature of the memory trace, its maturation, persistence, retrievability, and modifiability.

Practice makes perfect, but the role of repetitions in skill learning is not yet fully understood. For example, given a similar number of trials on a given task, it is debated whether repeating and non-repeating items are learned by the same neural process. When one is given training with both types of items - does one learn two separate skills, or only one? Here we show, using a mirror reading task, that practice trials with trial-unique words, and practice trials with repeated words, count towards learning to a different degree. There was no interaction between the time-course of learning repeated and unique words even within the same individuals given mixed training. While repeated words were learned faster than unique words, the repetitions-dependent gains diminished with training beyond a small number of repetitions. Moreover, the gains in performance could not be accounted for solely by the number of repetitions, as assumed by power-law models of learning; rather, the passage of time was a critical factor. Finally, our results suggest that although both repeated and new words were learned by both declarative and procedural memory mechanisms, even a single repetition of specific words could lead to the establishment of a selective differential representation in memory. The results are compatible with the notion of a repetition-sensitive process, triggered by specific repeating events. This 'repetition counter' may be a critical trigger for the effective formation of procedural as well as some type of declarative memory.

Ample data indicate that cAMP-response element-binding protein (CREB) is essential for the formation of long-term memory in various species and learning systems. This implies that activated CREB could delineate neuronal circuits that subserve items in memory, while leaving open the possibility that the specifics of CREB activation itself contribute to the specificity of the internal representation encoded by the relevant circuit. We describe here the differential activation of CREB in the rat brain as a function of two related yet distinct forms of aversive conditioning: conditioned taste aversion (CTA) and conditioned context aversion (CCA). We found that CTA induces strong CREB activation in the insular cortex (IC) and the lateral septum (LS), but not in the parietal cortex (PC) and the medial septum (MS). In contrast, CCA results in strong activation in the PC and MS, but not in the IC and LS. These findings are congruent with a model that links differential pattern of activity within the LS and the MS with the acquisition of elemental versus contextual conditioning and, more generally, with the notion that CREB activation delineates learning-dependent circuits as a function of the type of cognitive process engaged.

The study of experimental extinction and of the spontaneous recovery, of the extinguished memory, could cast light on neurobiological mechanisms by which internal representations compete to control behavior. In this work, we use a combination of behavioral and molecular methods to dissect subprocesses of experimental extinction of conditioned taste aversion (CTA). Extinction of CTA becomes apparent only 90 min after the extinction trial. This latency is insensitive to muscarinic and β-adrenergic modulation and to protein synthesis inhibition in the insular cortex (IC). Immediately afterwards, however, the extinguishing trace becomes sensitive to β-adrenergic blockade and protein synthesis inhibition. The subsequent kinetics and magnitude of extinction depend on whether a spaced or massed extinction protocol is used. A massed protocol is highly effective in the short run, but results in apparent stagnation of extinction in the long-run, which conceals fast spontaneous recovery, of the preextinguished trace. This recovery can be truncated by a β-adrenergic agonist or a cAMP analog in the insular cortex, suggesting that spontaneous overtaking of the behavioral control by the original association is regulated at least in part by β-adrenergic input, probably operating via the cAMP cascade, long after the offset of the conditioned stimulus. Hence, the performance of the subject in experimental extinction is the sum total of multiple, sometimes conflicting, time-dependent processes.

In the behaving rat, the consumption of an unfamiliar taste activates the extracellular signal-regulated kinase 1-2 (ERK1-2) in the insular cortex, which contains the taste cortex. In contrast, consumption of a familiar taste has no effect. Furthermore, activation of ERK1-2, culminating in modulation of gene expression, is obligatory for the encoding of long-term, but not short-term, memory of the new taste (Berman et al., 1998). Which neuro-transmitter and neuromodulatory systems are involved in the activation of ERK1-2 by the unfamiliar taste and in the long-term encoding of the new taste information? Here we show, by the use of local microinjections of pharmacological agents to the insular cortex in the behaving rat, that multiple neurotransmitters and neuromodulators are required for encoding of taste memory in cortex. However, these systems vary in the specificity of their role in memory acquisition and in their contribution to the activation of ERK1-2. NMDA receptors, metabotropic glutamate receptors, muscarinic, and β-adrenergic and dopaminergic receptors, all contribute to the acquisition of the new taste memory but not to its retrieval. Among these, only NMDA and muscarinic receptors specifically mediate taste-dependent activation of ERK1-2, whereas the β-adrenergic function is independent of ERK1-2, and dopaminergic receptors regulate also the basal level of ERK1-2 activation. The data are discussed in the context of postulated novelty detection circuits in the central taste system.

In conditioned taste aversion (CTA) organisms learn to avoid a taste if the first encounter with that taste is followed by transient poisoning. The neural mechanisms that subserve this robust and long-lasting association of taste and malaise have not yet been elucidated, but several brain areas have been implicated in the process, including the amygdala. In this study we investigated the role of amygdala in general, and the cAMP response element- binding protein (CREB) in the amygdala in particular in CTA learning and memory. Toward that end, we combined antisense technology in vivo with behavioral, molecular and histochemical analysis. Local microinjection of phosphorothioate-modified oligodeoxynucleotides (ODNs) antisense to CREB into the rat amygdala several hours before CTA training transiently reduced the level of CREB protein during training and impaired CTA memory when tested 3- 5 d later. In comparison, sense ODNs had no effect on memory. The effect of antisense was not attributable to differential tissue damage and was site- specific. CREB antisense in the amygdala had no effect on retrieval of CTA memory once it had been formed and did not affect short-term CTA memory. We propose that the amygdala, specifically the central nucleus, is required for the establishment of long-term CTA memory in the behaving rat; that the process involves long-term changes, subserved by CRE-regulated gene expression, in amygdala neurons; and that the amygdala may retain some CTA- relevant information over time rather than merely mediating the gustatory trace during acquisition of CTA.

The muscarinic antagonist scopolamine blocks conditioned taste aversion (CTA) when microinjected bilaterally into the rat insular cortex shortly before the exposure of the rat to a novel taste (the conditioned stimulus, CS) in CTA training. Scopolamine has no effect when microinjected shortly after the exposure to the novel taste or shortly before the application of the malaise-inducing agent (unconditioned stimulus, UCS). Scopolamine does not affect sensory, motor and retrieval mechanisms required for performing the CTA task, and does not block CTA when injected into another cortical area. The effect of scopolamine is independent of the taste used as CS. Furthermore, microinjection of scopolamine into the insular cortex shortly before the pre-exposure to a new taste in a latent inhibition paradigm, impairs the attenuation of CTA by that pre-exposure. Other muscarinic antagonists, pirenzepine and AF DX-116, have an effect similar to that of scopolamine. Comparison of the dose-dependency curves of the muscarinic antagonists suggests a predominant role in CTA for M2 subtype receptors. Carbachol, a muscarinic agonist, also impairs the encoding of taste in the insular cortex, but the results are confounded by the ability of that ligand to induce seizures. Our findings suggest that cholinergic neuromodulation participates in processing the CS in the gustatory cortex in CTA, either by encoding novelty at the cellular level, or by instructing the neural circuits to store the novel taste representation.

Rats were trained to discriminate an aqueous compound of an odor and taste (amyl acetate and NaCl) from the components of the compound before removal of one olfactory bulb and the contralateral ventrolateral frontal cortex. In postoperative tests, experimental rats performed much more poorly than nonlesioned controls or controls which had all lesions made in the same hemisphere. However, there were no significant differences among groups on tests for detection of amyl acetate and NaCl. These results provide evidence that integration of taste and smell in the production of flavor occurs in the ventrolateral frontal cortex.

Protein tyrosine phosphorylation is a major signal transduction pathway involved in cellular metabolism, growth, and differentiation. Recent data indicate that tyrosine phosphorylation also plays a role in neuronal plasticity, We are using conditioned taste aversion, a fast and robust associative learning paradigm subserved among other brain areas by the insular cortex, to investigate molecular correlates of learning and memory in the rat cortex, In conditioned taste aversion, rats learn to associate a novel taste (e.g., saccharin) with delayed poisoning (e.g., by LiCl injection), Here we report that after conditioned taste aversion training, there is a rapid and marked increase in tyrosine phosphorylation of a set of proteins in the insular cortex but not in other brain areas. A major protein so modulated, of 180 kDa, is abundant in a membrane fraction and remains modulated for more than an hour after training, Exposure of the rats to the novel taste alone results in only a small modulation of the aforementioned proteins whereas administration of the malaise-inducing agent per se has no effect, To the best of our knowledge, this is the first demonstration of modulation of protein tyrosine phosphorylation in the brain after a behavioral experience.

We have investigated the effect of systemic treatment with drugs that affect the cAMP cascade on the sensory response and sensory fatigue in an identified mechanosensory neuron of Drosophila. Forskolin, an activator of adenylate cyclase, decreases the sensory response of the neuron. H7, an inhibitor of protein kinase, inhibits sensory fatigue. Octopaminergic ligands facilitate sensory fatigue. These results, together with our previous neurogenetic analysis of sensory fatigue in Drosophila (Corfas and Dudai 1990), corroborate the hypothesis that the cAMP cascade is involved in the generation and modulation of sensory fatigue.

"Dudai attempts to achieve two goals: to write a textbook on the neurobiology of learning and memory that is accessible to advanced undergraduate and graduate students, and to provide a reference text for neuroscientists interested in this field. In general, the book achieves both aims . . . . well written, extensively referenced, and thoughtful--an excellent acquisition for any upper division undergraduate or university library with clientele interested in the biology of behavior." --Choice". . . Dudai's book represents a well-written and superbly illustrated up-to-date introduction to the neurobiology of memory which can serve as a valuable supplement to the more clinically orientated textbooks." --International Journal of Geriatric Psychiatry"The product of a broad and intelligent understanding of the neurobiology of learning. The author has taken a bold step in incorporating many disparate views with his own, and has produced a stimulating and valuable guide to a theory of the neural basis of memory." --Journal of Nervous and Mental Diseases

Upon tactile stimulation of it thoracic bristle(s), Drosophila cleans with a patterned set of leg movements the field covered by the stimulated bristles. We demonstrate that this cleaning reflex undergoes habituation and dishabituation. Repeated monotonous stimulation of the bristles by controlled air puffs leads to decrement, and finally to disappearance, of leg response. Spontaneous recovery of the response takes place in a time-dependent manner. Restoration of response can also be obtained by application of a high-frequency stimulus directed to other bristles. A mutant, rut, which is defective in learning and in adenylate cyclase activity, can habituate and dishabituate, but habituation is abnormally short-lived. As opposed to both nonassociative and associative learning paradigms used in Drosophilia to date, the cleaning reflex lends itself to some aspects of cellular analysis, since single sensory neurons that mediate the input and motor neurons that mediate the behavioral output are identifiable. The modified reflex should therefore be useful in establishing the effects of single gene mutations that affect behavioral plasticity on the development and properties of identified neurons that contribute to discrete modifiable behaviors.

We have quantitatively analyzed the effect of the mutation rut, which lesions a Ca²⁺-stimulated subpopulation (or functional state) of adenylate cyclase, on acquisition, consolidation and retention of an olfactory associative memory in Drosophila. The classical conditioning paradigm developed by Tully and Quinn (1985) was employed. Our data indicate that rut reduces acquisition and short-term memory in this paradigm, yet does not abolish consolidation of residual memory into an anesthesia-resistant form. Assuming that the rut behavioral defect is not due to altered neuroanatomy, the data also suggest that the adenylate cyclase activity lesioned by rut is only one of the molecular processes required for acquisition and short-term memory. These different postulated processes seem to act in parallel but are probably recruited sequentially; the mechanism involving rut⁺ gene product is necessary for response prior to other mechanisms which do not require rut⁺. It is also suggested, on the basis of the present results combined with previous data, that processes which do not require Ca²⁺-activated cyclase can not fulfill the partial role of this enzyme during acquisition but can partially compensate for its absence in later phases of memory formation.

Abstract: We have characterized protein phosphorylation in vitro in subcellular fractions from Drosophila melanogaster heads. Optimal conditions for the incorporation of ³²P into proteins, and its dependence on ATP, divalent cations, and cyclic nucleotides have been determined, as well as the effect of inhibitors of ATPase, protein phospha‐tase, and protein kinase on protein phosphorylation. Among these inhibitors, Zn²⁺ was found to affect the incorporation of ³²P into specific bands and p‐hydroxymercuri‐benzoate was found to be most suited for freezing the activity of both kinases and phosphatases. Cyclic AMP‐depen‐dent protein kinase (cAMP‐dPK) activity was present in both supernatant (S₂) and paniculate (P₂) fractions, with the majority (60–85%, depending on the homogenization medium) being associated with S₂, as determined by phosphorylation of exogenous synapsin I. cAMP‐dPK catalyzed the phosphorylation of at least 18 endogenous polypeptides in S₂ and at least 10 endogenous polypeptides in P₂. These proteins could be classified on the basis of the extent of stimulation of phosphorylation by cyclic nucleotides, dependence on cyclic nucleotide concentration, and rate of phosphorylation. A phosphoprotein of 51 kilodaltons (pp51) was a major component of the S₂ and P₂ fractions and displayed properties expected from the regulatory sub‐unit of the cAMP‐dPK, R‐II. A phosphoprotein doublet of approximately 37 kilodaltons (pp37) was stimulated to the largest extent by cAMP in the P₂ and S₂ fractions. The phosphorylation of several proteins in both fractions was significantly lowered by the mammalian Walsh inhibitor of cAMP‐dPK, whereas in some cases the stimulation of phosphorylation of the same proteins by exogeneous cAMP was relatively small. Phosphoproteins from two learning mutants known to be deficient in cAMP metabolism, dnc and rut, were analyzed for their extent of phosphorylation in the presence of a stable cAMP analogue; no significant differences from normal were detected, suggesting that the genetic defect in cAMP metabolism is not accompanied by constituent abnormalities in phosphorylated substrates in the adult fly, and that the physiological defects in these mutants result from aberrations in the interaction of the cAMP cascade with normal substrates. The majority of Ca²⁺/calmodulin kinase activity (80–90%, depending on the homogenization procedure) was associated with S₂ as revealed by phosphorylation of exogenous synapsin I. Two endogenous substrates for this kinase in P₂ had molecular masses of approximately 45 and 87 kilodaltons. At least 11 substrates for the Ca²⁺/calmodulin‐dependent kinase were detected in S₂. The 45‐kilodalton protein was a major substrate in this fraction too, as was pp37.

Protein phosphatases‐1, 2A and 2B have been identified in membrane and soluble fractions of Drosophila melanogaster heads. Similarities between Drosophila and mammalian protein phosphatase‐1 included specificity for the β subunit of phosphorylase kinase, sensitivity to inhibitor‐1 and inhibitor‐2, inhibition by protamine, retention by heparin‐Sepharose and selective interaction with membranes. In addition, an inactive form of protein phosphatase‐1, termed protein phosphatase‐1_I, was detected in the soluble fraction that could be activated by preincubation with MgATP and mammalian glycogen synthase kinase‐3. Inhibitor‐2 partially purified from Drosophila had an identical molecular mass to its mammalian counterpart, and recombined with mammalian protein phosphatase‐1 to form a hybrid protein phosphatase‐1_I. Similarities between Drosophila and mammalian protein phosphatase‐2A included preferential dephosphorylation of the α subunit of phosphorylase kinase, insensitivity to inhibitors‐1 and ‐2, activation by protamine, exclusion from heparin‐Sepharose and apparent molecular mass. A Ca²⁺‐dependent calmodulin‐stimulated protein phosphatase (protein phosphatase‐2B) that was inhibited by trifluoperazine was identified in the soluble fraction. The remarkable similarities between Drosophila protein phosphatases and their mammalian counterparts are indicative of strict phylogenetic conservation and demonstrate that the procedures used to classify mammalian protein phosphatases have a wider application. Characterisation of the Drosophila phosphatases will facilitate genetic analysis of dephosphorylation systems and their possible roles in neuronal and behavioural plasticity in Drosophila.

Two conceptual revolutions, which occurred a long time ago, shaped theface of modern research in the life sciences. The first was the mechanisticrevolution, the cornerstones of which were formulated mainly by Rene Descartesin the seventeenth century. Animals, said Descartes, are machines governed bythe same laws that govern any other physical object under the Sun. (Man, headded, has in addition a soul, that resides in the machine and interacts withit.) It is Descartes’ mechanistic views that paved the way to thereductionistic approach characterizing most, if not all, of the work carried outtoday in biology laboratories. The second major revolution culminated twocenturies later. The living world is not static, but undergoes continuousalterations and innovations; species were not created as such in the beginningof time but evolved from ancestral forms. Man is no exception. The clear-cut,poetic events of the third, fifth and sixth days of creation, as depicted inGenesis, were thus replaced by a seemingly cold and dry scientific alternative.For this revolution, the main responsibility lies with Charles Darwin —although he was not the first to initiate it.

Abstract: Adenylate cyclase in homogenates of Drosophila melanogaster is heterogeneous with respect to its affinity toward MgATP and its subcellular distribution. K_m values for MgATP range, under similar assay conditions, from ∼10⁻⁵M to ∼10⁻³M, depending on the body region and on the subcellular localization of the enzyme. The majority of the enzyme in whole‐body preparations is particulate, but various body regions differ in the relative proportion of the soluble enzyme. The memory mutant rutabaga lacks up to 35% of the total particulate activity. Even ligands that stimulate directly the catalytic subunit are incapable of bringing the activity of the mutant's enzyme to normal levels. The defect is differentially pronounced in various body parts and is associated with an altered responsiveness of the enzyme to Mg²⁺, to Ca²⁺, and to forskolin. It is suggested that rutabaga is lesioned in a subpopulation, or a functional state, of adenylate cyclase, which may play a role in memory formation.

The history of psychology has been closely intertwined with interest in such phenomena as giftedness, creativity, genius, precocity, and high levels of achievement; particular attention has focused for many years on the study and measurement of intelligence.

Two proteolytic activities that degrade [Leu⁵]enkephalin were found in Torpedo californica electric organ. One is a soluble aminopeptidase that degrades enkephalin at the Tyr¹-Gly² peptide bond, and the second is an endopeptidase that degrades enkephalin at the Gly³-Phe⁴ peptide bond. The aminopeptidase is inhibited by low concentrations of puromycin and bestatin. More than 60% of the endopeptidase is associated with the particulate fraction and is almost completely inhibited by low concentrations of captopril (SQ 14225) or SQ 20881 (potent inhibitors of angiotensin converting enzyme). Thiorphan and phoshoramidon (potent enkephalinase inhibitors) are much less effective. The pattern of cleavage and inhibition of the particulate endopeptidase thus resembles that of angiotensin converting enzyme.

1. 1. [³H]Octopamine binds to a particulate preparation from heads of Drosophila melanogaster at a level of 0.5 ± 0.1 pmol/mg protein, with an apparent dissociation constant of 6.0 ± 0.9 × 10^-9M at 26°C. The binding is reduced or abolished by heat, trypsin, detergents, sulfhydryl reagents and EDTA. 2. 2. Low concentrations of MgCl₂ or CaCl₂ increase binding but high ionic strength is inhibitory. 3. 3. Low concentrations of dihydroergotamine, phentolamine, clonidine, chlorimipramine and chlorpromazine, but not of serotonin and propranolol, displace the labeled biogenic amine from its binding sites. 4. 4. The stable GTP analogue, guanosine-5′-(β-γ-imido)triphosphate (Gpp(NH)p), at the μM range, decreases the maximal number of the high-affinity [³H]octopamine-binding sites. 5. 5. The properties of the [³H]octopamine-binding sites are compared to the properties of octopamine receptors as revealed by stimulation of adenylate cyclase in insects, including Drosophila.

The hydrodynamic behaviour of benzodiazepine receptors solubilized by deoxycholate from calf cerebral cortex reveals two molecular forms. The Stokes radii are 46.5 Å and 67.2 Å, and the sedimentation coefficients are 10.9 S and 14.6 S. The calculated apparent molecular weights and frictional ratios suggest either two nearly globular proteins of ca. 200K and 400K daltons each, or two ca. 300K daltons proteins which differ significantly in their degree of asymmetry. The benzodiazepine binding site is located on ca. 51K daltons component(s) in both forms.

Antibodies specific for benzodiazepines were raised in rabbits by immunization with a conjugate of a benzodiazepine deriva-tive, Ro 7-1986/1, with bovine serum albumin. The presence of anti-Ro 7-1966/1 antibodies in the sera was demonstrated by a radioimmunoassay using the radioligand [³h]flunitrazepam ([³h]FNZ). The antibodies displayed a high-affinity for [³H]FNZ (kd = 0.073± ^0.003nM) and cross-reacted with a broad spectrum of benzodiazepine derivatives. Benzodiazepine levels in samples of sera and urine of benzodiazepine-treated humans were deter-mined. Due to the high sensitivity of the assay only minute volumes (microliter quantities) of body fluids are employed and, therefore, no extraction of the drugs is required. Nitrazepam and diazepam levels as low as 20 picograms can be easily observed. Intoxicating levels of benzodiazepines can be detected by a single measurement in less than 10 min. This radioimmunoassay is advantageous for pharmacokinetic studies, toxicological examinations and forensic medicine due to its high sensitivity, wide-range specificity and technical simplicity.

The study describes, for the first time, detection of a putative, high-affinity octopamine receptor by direct binding studies with a radiolabeled ligand. Crude membranes prepared from heads of Drosophila melanogaster bind [³H]octopamine at a level of 0.4 pmol per mg protein with an apparent K_d of 5 nM. Low concentrations of dihydroergotamine, phentolamine and chlorpromazine, but not of propranolol and serotonergic ligands, were potent displacers of [³H]octopamine binding. The [³H]octopamine binding assay may prove useful in assessing the potency of novel octopaminergic ligands.

Benzodiazepine receptors are present in high concentration in the chick retina. Their pharmacological properties are similar to those of the benzodiazepine receptors present in the brain. The retina receptors appear prior to, as well as during, the period of synaptogenesis. In the newborn chick retina the receptors are localized in the inner synaptic layer, probably on or close to synaptic connections.

1. 1. High ionic strength markedly reduces the ability of oxotremorine to displace [³H]quinuclidinyl benzilate ([³H]QNB) from muscarinic binding-sites in Drosophila head homogenate and alters the shape of the oxotremorine binding isotherm, but has only a small effect on the binding of [³H]QNB itself. 2. 2. Guanosine-5′-(β,γ-imido)) triphosphate (Gpp(NH)p) reduces the ability of oxotremorine and carbamylcholine to displace [³H]QNB and alters the shape of their binding isotherms, but has no significant effect on the binding of the labeled ligand itself. 3. 3. The results demonstrate that in vitro properties of [³H]QNB-binding-sites in Drosophila are similar to those of mammalian muscarinic receptors and suggest that Drosophila muscarinic sites are associated with a nucleotide-mediated effector system.

A putative benzodiazepine receptor was solubilized from calf cortex by the use of sodium deoxycholate as an 10.9S entity containing subunits of which at least part are of 51 K molecular weight. The solubilized receptor retains its high affinity for [³H]flunitrazepam. The affinity for various other drugs, including benzodiazepines and xanthine derivatives, was also not significantly altered. GABAergic modulation of the receptor affinity for [³H]flunitrazepam was diminished but still detectable.

The development of the cholinergic system in the rat hippocampal formation was studied following lesion of the septal region at an age of 2-4 days postnatal (i.e. the lesion was performed prior to the establishment of the septohippocampal connections). The steep increase in acetylcholinesterase (AChE) level, that under normal conditions take place during the second and the third week postnatal, was not observed in early lesioned animals, and AChE level at maturity was about 30% of control. AChE level of adult-lesioned animals was about 15% of control, suggesting an age-dependent plasticity in response to the lesion. Early deafferentation did not seem to alter the pattern of development of muscarinic binding sites as measured by specific binding of [³H]quinuclidinyl benzilate ([³H]QNB). Total [³H]QNB bound per hippocampus of adult, early-lesioned animals was about 70% of control, but this reduction could be accounted for by the atrophy observed in the hippocampal formation following early lesion. Binding of [³H]QNB per protein in early lesioned animals did not differ from normal. Thus the development and the level of muscarinic binding sites in the hippocampal formation do not seem to depend upon normal establishment of presynaptic contacts.

1. 1. The toxicity of cholinergic drugs injected to Drosophila was compared with the ability of the drugs to displace α-[¹²⁵I]bungarotoxin and [³H]quinuclidinyl benzilate binding and to inhibit acetylcholinesterase in vitro. 2. 2. Nicotine and mecamylamine were highly toxic; high concentrations of the latter ligand had no effect on the putative cholinergic receptors and on acetylcholinesterase in vitro. 3. 3. Carbamylcholine, curare, oxotremorine and dexetimide displayed substantial toxicity; α-bungaro-toxin was not found to be more toxic upon injection than small, non-cholinergic positively-charged proteins. 4. 4. The muscarinic antagonists atropine and scopolamine displayed low toxicity; decamethonium and hexamethonium displayed high LD₅₀ values and induced a marked catatonia at sublethal doses. 5. 5. Properties of putative cholinergic receptors in Drosophila are discussed.

The hippocampal formation of the rat contains two types of membrane-bound cholinergic binding sites, as revealed by specific binding of [³H]quinuclidinyl benzilate (QNB) or of α-[¹²⁵I]bungarotoxin (α-Btx). The sites differ in pharmacological profile, sensitivity to detergents and ontogenesis. The major binding site (about 17 pmol per adult hippocampus) is of a muscarinic nature, and binds [³H]QNB with an on-rate of 2 × 10⁶ M^-1 sec^-1 and an apparent K_D of 0.4 nM. This binding is displaced by low concentrations of muscarinic ligands but not of nicotinic ligands. The earliest increase in binding level is detected at about day 4 postnatal and a sharp increase in total binding takes place between days 10 and 15. Total binding continues to increase gradually about 3-fold until an age of about 7 weeks, at a rate resembling that of acetylcholinesterase. α-Btx-binding sites (about 0.6 pmol per adult hippocampus) display a nicotinic profile with an on-rate constant for α-[¹²⁵I]Btx of 6 × 10⁴ M^-1 sec^-1 and an apparent K_D of 2 nM. Ontogenesis of these sites clearly differs from that of muscarinic sites and acetylcholinesterase. Absolute binding reaches mature levels at an age of 12-14 days postnatal, and binding per tissue protein is higher during the first postnatal days than at maturity. It appears that the level of toxin-binding sites attains mature values vefore the major synaptogenetic events in the area are completed.

The powerful muscarinic antagonist [³H]quinuclidinyl benzilate (QNB) specifically binds to homogenates of Drosophila melanogaster head at a level of 65 ± 6 fmol/mg protein, with an apparent dissociation constant of 0.15–0.7 nM. The half‐life of the ligand‐receptor complex at 25°C is 30–40 min. Binding is inhibited by low concentrations of muscarinic ligands but not by low concentrations of nicotinic ligands, anticholinesterases or non‐cholinergic drugs. Binding‐sites are membrane bound and are inactivated by trypsin and by Triton X‐100. Part of the activity (

α-[125I]Bungarotoxin specifically binds to homogenates of Drosophila melanogaster head at levels of 0.3–0.8 pmol/mg protein. The dissociation constant calculated from rates of association and dissociation of toxin · receptor complex, is 0.6 · 10−9M. Ca2+, and to lesser extent Na+, inhibit the reaction. α-[125I]Bungarotoxin binding is inhibited by low concentrations of unlabelled toxin, nicotinic ligands and eserine, but not by low concentrations of muscarinic ligands, decamethonium or an organophosphate. The receptor is membrane bound and can be partially released into 100 000 × g supernatant by a combination of 1 M NaCl and 1% Triton X-100. Most of the activity in the supernatant sediments after further centrifugation at 200 000 × g for 2 h. Toxin binding sites are distinct from acetylcholinesterase molecules as revealed by pharmacological, biochemical and genetic techniques. The gene for the toxin-binding nicotinic receptor in Drosophila is apparently not located adjacent to the gene for acetylcholinesterase.

Acetylcholinesterase (AChE) preparations obtained from electric organ tissue of Electrophorus electricus subsequent to tryptic digestion and/or autolysis had sedimentation coefficients of about 11 S and molecular weights of 320,000-350,000. These values did not significantly decrease upon prolonged autolysis. The major polypeptide in 11 S AChE had molecular weights of 82,000 ± 6,000 and 59,000 ± 4,000. The ratios of these two components was a function of the degree of autolysis of the tissue from which the enzyme was purified. In less autolysed tissue the principle component was the 82,000 one, while after prolonged autolysis the 59,000 component predominated. The appearance of the 59,000 component was accompanied by the appearance of polypeptides of ∼25,000. It is proposed that autolysis and/or proteolysis cleave the 82,000 polypeptide chain of native AChE into fragments of 59,000 and ∼25,000 which are retained in the quaternary structure of the enzyme unless it is denatured. Possible models for the quaternary structure and arrangement of disulfide bridges in 11 S AChE are discussed.