Past events

The vomeronasal system is a chemosensory system devoted to processing cues from other organisms. In my talk I will describe a set of studies from our lab that aim to reveal how chemosensory information is represented by neuronal activity in the AOB (accessory olfactory bulb), the first brain region receiving vomeronasal inputs. After reviewing some of our published work on basic aspects of stimulus representations, I will describe unpublished work in which we explore neuronal correlates of behavioral imprinting, reproductive-state dependent processing, and changes in the genetic background of the subject organism. Taken together, these studies point at a high degree of stability of stimulus representations at the level of the AOB. Finally, I will show that despite its presumed role in processing innately relevant cues, the vomeronasal system has considerable capacity to form novel stimulus response associations, providing further support for the idea that responses to innately relevant cues can be dramatically altered as a result of experience.

One of the fundamental functions of the brain is to integrate incoming sensory stimuli, perceive and associate these integrations with internal representations, and make fast and reliable decisions and actions. Although these processes have been extensively studied, we are still missing a comprehensive understanding of the exact spatiotemporal dynamics at a mesoscale level, i.e. at the neuronal population level spanning many cortical and sub-cortical areas. In my opinion, the key to understanding these processes is to measure from large populations of neurons within a single trial as a subject performs a complex behavior. In my talk, I will present a variety of evidence from behaving mice backing up this claim. In one of the projects, we imaged calcium signals from the whole dorsal cortex of mice performing a whisker-based texture discrimination task with a short-term memory component. Mice use different behavioral strategies to solve the task either deploying an active strategy — engaging their body and whiskers towards the approaching texture — or passively awaited the touch. Based on this strategy, short-term memory was located in frontal secondary motor cortex (M2) in active mice whereas in a newly identified posterior area (P) in passive mice. Optogenetic perturbation of these areas impaired performance specifically in the associated strategy. In some cases, mice overcame the perturbation by switching to the alternative strategy. Thus, depending on behavioral strategy within single trials, cortical population activity is routed differentially to hold information either frontally or posteriorly before converging to similar action. Additional projects, using different tasks, neuronal subtypes and during learning highlight the importance of observing and dissecting mesoscale dynamics during complex behaviors.

According to the long-lasting computational scheme each neuron sums the incoming electrical signals via its dendrites and when the membrane potential reaches a certain threshold the neuron typically generates a spike. We present three types of experiments indicating that each neuron functions as a collection of independent threshold units, where the neuron is activated following the origin of the arriving signals. In addition, experimental and theoretical results reveal a new underlying mechanism for the fast brain learning process, dendritic learning, as opposed to learning which is based solely on slow synaptic plasticity. The learning occurs in closer proximity to the neuron, dendritic strengths are self-oscillating, and weak synapses play a key role in the dynamics.

Retinal prostheses represent an exciting development in science, engineering, and medicine – an opportunity to exploit our knowledge of neural circuitry and function to restore or even enhance vision. However, although existing retinal prostheses demonstrate proof of principle in treating incurable blindness, they produce limited visual function. Some of the reasons for this can be understood based on the exquisitely precise and specific neural circuitry that mediates visual signaling in the retina. Consideration of this circuitry suggests that future devices may need to operate at single-cell, single-spike resolution in order to mediate naturalistic visual function. I will show large-scale multi-electrode recording and stimulation data from the primate retina indicating that, in some cases, such resolution is possible. I will also discuss cases in which it fails, and propose that we can improve artificial vision in such conditions by incorporating our knowledge of the visual system in bi-directional devices that adapt to the host neural circuity. Finally, I will briefly discuss the potential implications for other neural interfaces of the future.