Publications

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 510 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 ZIPs effects on neuronal and behavioral plasticity.

From infancy we learn to comply with societal norms. However, overt compliance is not necessarily accompanied by a change in internal beliefs. The neuromodulatory processes underlying these different phenomena are not yet understood. Here, we test the role of oxytocin in controlling overt compliance versus internalization of information delivered by a social source. After intranasal oxytocin administration, participants showed enhanced compliance to the erroneous opinion of others. However, this expression was coupled with a decrease in the influence of others on long-term memories. Our data suggest that this dissociation may result from reduced conflict in the face of social pressure, which increases immediate conforming behavior, but reduces processing required for deep encoding. These findings reveal a neurobiological control system that oppositely affects internalization and overt compliance.

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.

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.

Memories are more easily disrupted than improved. Many agents can impair memories during encoding and consolidation. In contrast, the armamentarium of potential memory enhancers is so far rather modest. Moreover, the effect of the latter appears to be limited to enhancing new memories during encoding and the initial period of cellular consolidation, which can last from a few minutes to hours after learning. Here, we report that overexpression in the rat neocortex of the protein kinase C isozyme protein kinase Mz (PKMz) enhances long-term memory, whereas a dominant negative PKMz disrupts memory, even long after memory has been formed.

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.

A young woman was filmed during 2 d of her ordinary life. A few months and then again a few years later she was tested for the memory of her experiences in those days while undergoing fMRI scanning. As time passed, she came to accept more false details as true. After months, activity of a network considered to subserve autobiographical memory was correlated with memory confidence rather than with accuracy. After years, mainly regions of the temporal pole displayed this pattern. These results might reflect a slow process of increased reliance on schemata at the expense of accuracy.

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.

We measured long-term memory for a narrative film. During the study session, participants watched a 27-min movie episode, without instructions to remember it. During the test session, administered at a delay ranging from 3 h to 9 mo after the study session, long-term memory for the movie was probed using a computerized questionnaire that assessed cued recall, recognition, and metamemory of movie events sampled approximately 20 sec apart. The performance of each group of participants was measured at a single time point only. The participants remembered many events in the movie even months after watching it. Analysis of performance, using multiple measures, indicates differences between recent (weeks) and remote (months) memory. While high-confidence recognition performance was a reliable index of memory throughout the measured time span, cued recall accuracy was higher for relatively recent information. Analysis of different content elements in the movie revealed differential memory performance profiles according to time since encoding. We also used the data to propose lower limits on the capacity of long-term memory. This experimental paradigm is useful not only for the analysis of behavioral performance that results from encoding episodes in a continuous real-life-like situation, but is also suitable for studying brain substrates and processes of real-life memory using functional brain imaging.

Scientists currently study memory from many different perspectives: neurobiological, ethological, animal conditioning, cognitive, behavioral neuroscience, social, and cultural. This book aims to help initiate a new science of memory by bringing these perspectives together to create a unified understanding of the topic. The book began with a conference where leading practitioners from all these major approaches met to analyze and discuss sixteen concepts crucial to our understanding of memory. Each of these sixteen concepts is addressed in a different part of the book, and in the sixty-six chapters that fill these parts, a leading researcher addresses the chapter's concept by clearly stating his or her position on it, elucidating how it is used, and discussing how it should be used in future research. For some concepts, there is general agreement among practitioners from different fields and levels of analysis, but for others there is general disagreement and much controversy. A final chapter in each part, also written by a leading researcher, integrates the various viewpoints offered on the part's concept, then draws conclusions about the concept.

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.

The mitogen-activated protein kinase (MAPK) signaling cascades (including the extracellular signal-regulated kinases [ERKs], the c-Jun N-terminal kinases [JNKs], and the p38 stress-activated protein kinases) are abundant in neurons in the mature central nervous system (1). Originally, these cascades were discovered as critical regulators of cell division and differentiation in nonneuronal cells, raising the question: What role would these cascades play in nondividing, terminally differentiated neurons in the adult brain?

Researchers may have seen the signature of a memory in the making. In monkeys that learnt to associate two stimuli, single neurons changed their responses before, during or after learning became evident.

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.

Mice lacking a certain neurotransmitter receptor have trouble forgetting scary experiences. This finding uncovers a fear-regulating feedback loop in the brain that might be at work in humans, too.

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.

We demonstrate that the NMDA receptor is involved in taste learning in the insular cortex of the behaving rat and describe two facets of this involvement. Blockage of the NMDA receptor in the insular cortex by the reversible antagonist APV during training in a conditioned taste aversion (CTA) paradigm impaired CTA memory, whereas blockage of the NMDA receptor in an adjacent cortex or before a retrieval test had no effect. When rats sampled an unfamiliar taste and hence learned about it, either incidentally or in the context of CTA training, the tyrosine phosphorylation of the NMDA receptor subunit 2B (NR2B) in the insular cortex was specifically increased. The level of tyrosine phosphorylation on NR2B was a function of the novelty of the taste stimulus and the quantity of the taste substance consumed, properties that also determined the efficacy of the taste stimulus as a conditioned stimulus in CTA; however, blockage of the NMDA receptor by APV during training did not prevent tyrosine phosphorylation of NR2B. We suggest that tyrosine phosphorylation of NR2B subserves encoding of saliency in the insular cortex during the first hours after an unfamiliar taste is sampled and that this encoding is independent of another, necessary role of NMDA receptors in triggering experience-dependent modifications in the insular cortex during taste learning. Because a substantial fraction of the NR2B protein in the insular cortex seems to be expressed in interneurons, saliency and the tyrosine phosphorylation of NR2B correlated with it may modulate inhibition in cortex.

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.

Mechanisms that are recruited in long-term potentiation (LTP) may operate in certain types of learning. Research restricted to the molecular or cellular level cannot provide one with an answer to the question whether LTP plays a role in learning; the nature of the representation in the circuit and the effect of LTP on this representation must be addressed. Similarities exist between properties of LTP and learning and memory, that is, rapid induction, stimulus specificity, associativity, and endurance. Such similarities may be also detected in non-neuronal systems. Furthermore, there is no reason to assume that properties displayed by the molar activity of a system will be displayed by the individual components of that system. This chapter proposes that one needs a neuronal circuit that encodes a specific, identified internal representation. That neuronal circuit should also sustain LTP. In the meantime, LTP remains an intriguing model capable of unveiling molecular components of neuronal plasticity.

In conditioned taste aversion (CTA) and taste-potentiated odor aversion (TPOA) individuals learn to associate taste or odor with poisoning. This leads to subsequent aversion to that taste or odor. In nature, the poisoning is due to toxins in the foodstuff; in the laboratory, ip injection of LiCl is usually used to elicit transient malaise. Protein tyrosine phosphorylation is modulated in the course of action of the signal transduction pathways that regulate cellular differentiation and growth. It became apparent that tyrosine phosphorylation also plays a key function in neuronal activity and plasticity. Protein tyrosine phosphorylation, as a posttranslational modification, can persist for only seconds to possibly minutes or hours. Therefore, even when considered as a mechanism of cellular memory, protein tyrosine phosphorylation per se cannot instantiate long-term changes. The observation that protein synthesis is necessary for memory consolidation is construed as indicating that modulation of gene expression is required for the formation of long-term memory.

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

The Ca²⁺/calmodulin (CaM)-activated adenylate cyclase has been implicated as playing an important associative role in classical conditioning in both Aplysia and Drosophila. Studies of the cyclase in mammalian cerebral cortex have suggested that Ca²⁺/CaM sensitivity is confined to a subpopulation of total cyclase activity. We investigated the properties of cyclase from Aplysia, rat, and bovine central nervous system membranes by using CaM-Sepharose chromatography. Although only a minority of total cyclase activity bound to the CaM column, both bound and unbound fractions of cyclase from all three species showed comparable stimulation by Ca²⁺ in the presence of CaM. When solubilized bovine membranes were first depleted of most of their endogenous CaM by prior chromatography, binding to the CaM column was substantially increased and Ca²⁺ stimulation of the unbound fraction was somewhat reduced. However, this reduction in Ca²⁺ sensitivity resulted from the loss of Ca²⁺ sensitivity during prior chromatography, rather than from the more efficient separation of Ca²⁺-sensitive and -insensitive forms. This finding, together with the fact that we never observed any enrichment for Ca²⁺ sensitivity in the bound fraction over the level in the starting preparation, suggests that the vast majority of the cyclase present in solubilized central nervous system membranes is Ca²⁺/CaM-sensitive.

Keywords: Biochemistry & Molecular Biology; Medicine, Research & Experimental

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 phosphatase, and protein kinase on protein phosphorylation. Among these inhibitors, Zn²⁺ was found to affect the incorporation of ³²P into specific bands and phydroxymercuribenzoate was found to be most suited for freezing the activity of both kinases and phosphatases. Cyclic AMPdependent protein kinase (cAMPdPK) activity was present in both supernatant (S₂) and paniculate (P₂) fractions, with the majority (6085%, depending on the homogenization medium) being associated with S₂, as determined by phosphorylation of exogenous synapsin I. cAMPdPK 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 subunit of the cAMPdPK, RII. 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 cAMPdPK, 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 (8090%, 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⁺/calmodulindependent kinase were detected in S₂. The 45kilodalton protein was a major substrate in this fraction too, as was pp37.

Protein phosphatases1, 2A and 2B have been identified in membrane and soluble fractions of Drosophila melanogaster heads. Similarities between Drosophila and mammalian protein phosphatase1 included specificity for the β subunit of phosphorylase kinase, sensitivity to inhibitor1 and inhibitor2, inhibition by protamine, retention by heparinSepharose and selective interaction with membranes. In addition, an inactive form of protein phosphatase1, termed protein phosphatase1_I, was detected in the soluble fraction that could be activated by preincubation with MgATP and mammalian glycogen synthase kinase3. Inhibitor2 partially purified from Drosophila had an identical molecular mass to its mammalian counterpart, and recombined with mammalian protein phosphatase1 to form a hybrid protein phosphatase1_I. Similarities between Drosophila and mammalian protein phosphatase2A included preferential dephosphorylation of the α subunit of phosphorylase kinase, insensitivity to inhibitors1 and 2, activation by protamine, exclusion from heparinSepharose and apparent molecular mass. A Ca²⁺dependent calmodulinstimulated protein phosphatase (protein phosphatase2B) 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.

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 wholebody 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 Drosophila memory mutant rutabaga (rut) has been previously shown to have a defective subpopu-lation (or functional state) of the enzyme adenylate cyclase. We report here that the reduced adenylate cyclase activity is also associated with a defective responsiveness of the enzyme to forskolin. Forskolin activation isotherms of the enzyme in normal membranes reveal low- and high-affinity forskolin-interacting components; the residual enzyme in the mutant shows a smaller proportion of the high-affinity response. In addition, in mutant membrane preparations, forskolin fails to shift the K_m of the enzyme for free Mg²⁺ and for MgATP, in contrast to the situation in the normal tissue. The defect in the responsiveness to forskolin in rut is even more pronounced in a Lubrol-solubilized enzyme preparation, and is due to intrinsic properties of the cyclase system rather than to the absence (or presence) of a soluble, or detergent solubilized, factor in rut. The reduced forskolin responsiveness maps to the X chromosomal segment 12F5-6 to 13A1-5, within the region previously reported to span the locus that controls both the abortive memory and the lack of Ca²⁺-stimulation of adenylate cyclase in rut¹⁷. The possible relevance of the findings to postulated molecular mechanisms of short-term memory formation is discussed.

Adenylate cyclase in washed, crude membrane fractions prepared from the Drosophila conditioning mutant, rutabaga, displays an altered responsiveness to Ca²⁺. The results are of interest since the modulation of adenylate cyclase activity by Ca²⁺ has recently been suggested to play a role in molecular events that underlie memory formation.

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.

Several lectins (concanavalin A, wheat germ agglutinin, wax bean agglutinin, and phytohemagglutinin) induce aggregation and precipitation of deoxycholatesolubilized benzodiazepine receptors from calf cerebral cortex. These receptors were also retained on columns of immobilized lectins. Photoaffinity labeling of the soluble benzodiazephine receptors prevented their interaction with lectins. Periodate treatment caused inactivation of benzodiazepine receptors which was partially prevented by diazepam and/or γaminobutyric acid. The possible association of the drugbinding site and the carbohydrate moiety is discussed.

Abstract: Adenylate cyclase in Drosophila melanogaster heads is stimulated 56fold by low concentrations of octopamine. The octopamine stimulation is inhibited by low concentrations of the αadrenergic ligands phentolamine and dihydroergotamine and of chlorpromazine, but not by low concentrations of the βantagonist propranolol and by the αantagonist yohirnbine. dTubocurarine enhances the octopamine effect. Tyramine, norepinephrine, and epinephrine also stimulate the cyclase, probably via the octopamine receptor. Serotonin and dopamine stimulate Drosophila adenylate cyclase 1.31.4fold; at least the latter putative neurotransmitter seems to interact with a receptor distinct from the octopamine receptor. Prolonged incubation with dopamine in vitro abolishes adenylate cyclase basal activity as well as responsiveness to guanyl nucleotides, NaF, and putative neurotransmitters.

Administration of the muscarinic agonist oxotremorine led to a decrease in the number of muscarinic receptors, as determined by specific binding of [³H]quinuclidinyl benzilate ([³H]QNB), in several rat brain regions both during development and at maturity. In contrast, administration of the muscarinic antagonist scopolamine led to an increase in the number of [³H]QNB-binding sites in various brain regions. Scopolamine also prevented the decrease in the number of [³H]QNB-binding sites induced by administration of an organophosphorus drug. The results are compatible with the hypothesis that the number of brain muscarinic receptors, or at least of a sub-class of them, is regulated by their transmitter.

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.

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.

It has been suggested that cholinergic receptors in insects are neither nicotinic nor muscarinic but of a mixed nature, and hence differ from 'classic' vertebrate receptors. However, recent evidence indicates that insects also contain distinct nicotinic and muscarinic binding-sites with properties resembling those of vertebrate receptors. The study of these macromolecules sheds light on the phylogenesis of cholinergic systems and may offer new possibilities for biochemical, genetic and toxicologic research.

Cholinergic nicotinic receptors in rat brain were demonstrated by the use of the potent nicotinic antagonist [¹²⁵I]α-bungarotoxin ([¹²⁵I]α-Btx). Biochemical studies on binding of [¹²⁵I]α-Btx to rat hippocampal homogenates revealed saturable binding sites which are protected by nicotine, d-tubocurarine and acetylcholine but not by atropine or oxotremorine. The hippocampus and hypothalamus displayed relatively high [¹²⁵I]α-Btx specific binding whereas the cerebellum was devoid of specific binding. Other regions displayed intermediate binding levels. Analysis of the regional distribution of [¹²⁵I]α-Btx binding by autoradiography of frontal brain sections revealed high labeling in the hippocampus, hypothalamic supraoptic, suprachiasmatic and periventricular nuclei, ventral lateral geniculate and the mesencephalic dorsal tegmental nucleus. It is suggested that the limbic forebrain and midbrain structures as well as sensory nuclei are the main nicotinic cholinoceptive structures in the brain.

Acetylcholinesterase (acetylcholine hydrolase, E.C. 3.1.1.7) (AChE) is a widely distributed enzyme (Nachmansohn, 1959; Koelle, 1963) present, in particular, in excitable membranes of nerve and muscle, but also at other sites, such as the erythrocyte membrane (Mendel et al., 1943) and cobra venom (Zeller, 1948). The function of AChE in the postsynaptic membrane of cholinergic synapses is believed to be termination of synaptic transmission by the hydrolysis of acetylcholine (ACh), but its role in, for example, extrajunctional membranes, presynaptic membranes, and erythrocyte membranes has not been established. The evidence that AChE is usually a membrane-bound enzyme is based on subcellular fractionation and on electron microscopy combined with histochemical studies (Whittaker et al., 1964; Karlin, 1965; Bloom and Barrnett, 1966; Rodriguez de Lores Arnaiz et al., 1967; Israël et al., 1970; Nachmansohn, 1970). However, the exact relationship of the enzyme to the membrane has not been clarified (Hall and Kelly, 1971; Cohen et al., 1972).

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.