לוח שנה משולב

The sinking of organic particles in the ocean and their degradation by marine microorganisms drive one of the most conspicuous carbon fluxes on Earth, the biological pump. Yet, the mechanisms determining the magnitude of the pump remain poorly understood, limiting our ability to predict this carbon flux in future ocean scenarios. Current ocean models assume that the biological pump is governed by the competition between sinking speed and degradation rate, with the two processes independent from one another. In this talk, I will demonstrate that contrary to this paradigm, sinking itself is a primary determinant of the rate at which bacteria enzymatically degrade particles in the ocean. By combining video microscopy and microfluidic experiments to directly observe and quantify bacterial degradation of individual organic particles in flow, I will show that even modest sinking speeds of 8 meters per day enhance degradation rates more than 10-fold. I will further discuss the molecular mechanism behind the sinking-enhanced degradation, as well as possible ways by which bacteria can slow the sinking of particles. Finally, using the results obtained from a mathematical model, I will show that the coupling of sinking and degradation may contribute to determining the magnitude of the vertical carbon flux in the ocean, and will outline major open questions in the field.

Nonoscillatory coding and multiscale representation of very large environments in the bat hippocampus

Abstract: The hippocampus plays a key role in memory and navigation, and forms a cognitive map of the world: hippocampal ‘place cells’ encode the animal’s location by activating whenever the animal passes a particular region in the environment (the neuron’s ‘place field’). Over the last 50 years of hippocampal research, almost all studies have focused on rodents as animal models, using small laboratory experimental setups. In my research, I explored hippocampal representations in a naturalistic settings, in a unique animal model – the bat. My talk will outline two main stories: (i) In rodents, hippocampal activity exhibits ‘theta oscillations’. These oscillations were proposed to support multiple functions, including memory and sequence formation. However, absence of clear theta in bats and humans has questioned these proposals. Surprisingly, we found that in bats hippocampal neurons exhibited nonoscillatory phase-coding. This highlights the importance of phase-coding, but not oscillations per se, for hippocampal function across species – including humans. (ii) Real-world navigation requires spatial representation of very large environments. To investigate this, we wirelessly recorded from hippocampal dorsal CA1 neurons of bats flying in a long tunnel (200 meters). Place cells displayed a multifield multiscale code: Individual neurons exhibited multiple place fields of diverse sizes, ranging from 0.6 to 32 meters, and the fields of the same neuron differed up to 20-fold in size. Theoretical analysis showed that the multiscale code allows representing large environments with much better accuracy than other codes. Thus, by increasing the spatial scale, we uncovered a neural code that is radically different from classical spatial codes. Together, these results highlight the power of the comparative approach, and demonstrate that studying the brain under naturalistic settings and behavior enables discovering new unknown aspects of the neural code.

There is Chemistry in Social Chemistry
Abstract: Non-human terrestrial mammals constantly sniff themselves and each-other, and based on this decide who is friend or foe. Humans also constantly sniff themselves and each-other, but the functional significance of this behavior is unknown. Given that humans seek friends who are similar to themselves, we hypothesized that humans may be smelling themselves and others to subconsciously estimate body-odor similarity, and that this may then promote friendship. To test this hypothesis, we recruited non-romantic same-sex friend dyads who had initially bonded instantaneously, or so called click-friends, and harvested their body-odor. In a series of experiments, we then found that objective ratings obtained with an electronic nose, and subjective ratings obtained from independent human smellers, converged to suggest that click-friends smell more similar to each other than random dyads. To then estimate whether this similarity was merely a consequence of friendship, or a driving force of friendship, we recruited complete strangers, smelled them with an electronic nose, and engaged them in non-verbal same-sex dyadic interactions. Remarkably, we observed that dyads who smelled more similar had better dyadic interactions. In other words, we could predict social bonding with an electronic nose. This result implies that body-odor similarity is a causal factor in social interaction, or in other words, there is indeed chemistry in social chemistry.

Chromosomal instability is one of the major hallmarks in cancer driving numerical and structural chromosome aberrations. Cancer cells can use the chaotic background of chromosome instability to generate ordered genomic events leading to accelerated tumor formation or drug resistance. I will show how chromothripsis, the catastrophic shattering of a chromosome and random religation of its pieces, can promote resistance to therapy. Using cancer cells and patient samples, I identified that chromothripsis drives the formation and evolution of extrachromosomal DNA (ecDNA) elements that can amplify genes conferring drug resistance. I will then discuss how transient centrosome amplification can induce a burst of chromosomal instability in vivo. This triggers the formation of random aneuploidies (changes in chromosome numbers) with cancer initiating cells carrying a specific aneuploidy signature leading to accelerated tumorigenesis. This work has uncovered aneuploidy as a direct driver of cancer and enables a better understanding of the involvement of specific aneuploidies in cancer.

Functional ultrasound imaging (fUS) is an emerging neuroimaging tool capable of measuring brain-wide vascular signals linked to neuronal activity with a high spatial-temporal resolution (100 µm, 10 Hz) in real-time. This technology is portable, affordable and adaptable to many species, and has already found applications in areas ranging from basic research to the clinic. Focusing on fundamental neuroscience, I will outline some of the recent technical advancements of fUS, such as the capacity to image the entire rodent brain while manipulating specific neuronal circuits with optogenetics. I will exemplify how promising this imaging technique is for shedding new light on the brain-wide circuits underlying behavior, as fUS is one of the few methods that enables imaging of activity deep in the brain of behaving mice.
Zoom link: https://weizmann.zoom.us/j/95406893197?pwd=REt5L1g3SmprMUhrK3dpUDJVeHlrZz09
Meeting ID: 954 0689 3197
Password: 750421

Thermodynamics requires a system to equilibrate with its thermal environment, alias a bath. However, our results over the years have shown that, surprisingly, nonintrusive observations of a quantum system may heat or cool it, thus preventing the equilibration [1,2]. Recently, we have shown that also the bath state, which is considered immutable in thermodynamics, is dramatically changed by a quantum probe and its observations [3]. These effects stem from the unavoidable entanglement between quantum systems and baths even when they are weakly coupled, thus undermining the tenets of thermodynamics in the quantum domain. Most remarkably, we have recently demonstrated that probe observations can render thermal bath states nearly pure [4]. The implications are far reaching, most prominently the ability to reverse the time arrow of the entire system-bath compound, by causing its quantum coherent oscillation. This raises the question: Is thermodynamics, which rests on the concept of a bath, compatible with quantum mechanics? It may appear necessary to assume that a quantum working medium in a heat machine is dissipated by a bath [5,6]. Yet, most recently, we have shown that heat machines can be perfectly coherent, non-dissipative devices realized by nonlinear interferometers fed by few thermal modes [7], so that baths are redundant. Finally, I will discuss the ability of observers to commute information to work [8] and speculate on the role of observers in physics [9].

References to our work
1. Nature 452, 724 (2008).
2. PRL 105,160401 (2010).
3. NJP 22, 083035 (2020).
4. Arxiv 2108.09826 (2021)
5. Nat. Commun. 9, 165 (2018).
6. PNAS 115, 9941 (2018); PNAS 114, 12156 (2017).
7. Arxiv2108.10157 (2021).
8. PRL 127, 040602 (2021).
9. G.Kurizki and G. Gordon, “The Quantum Matrix” (Oxford Univ. Press, 2020).