Advisor: Mark Bear

Date and time: October 31st at 3pm 

Location: Singleton Auditorium 46-3002, or on zoom (link: https://mit.zoom.us/j/91638779625)

Talk title: Dissecting the Cortical Circuitry Underlying Stimulus-Selective Response Plasticity

Abstract:

Visual recognition memory is a fundamental process which enables animals, from mice to humans, to efficiently navigate their world and ignore unimportant familiar stimuli in favor of novel, potentially behaviorally salient stimuli. One manifestation of visual recognition memory is stimulus-selective response plasticity (SRP), a robust and lasting modification of primary visual cortex (V1) in mice that occurs as a result of passively viewing visual stimuli. SRP is readily observed as a pronounced increase in the magnitude of visual evoked potentials recorded from neocortical layer 4 in response to phase-reversing grating stimuli, and other methods of recording cortical activity reveal additional signatures of this form of plasticity. SRP is highly selective for stimulus features such as stimulus orientation, spatial frequency, and contrast, and may provide a means for investigating how the cortex mediates recognition memory more broadly. Originally hypothesized to be a relatively straightforward case of thalamocortical Hebbian plasticity onto principal cells in layer 4, SRP is now understood to be substantially more complex, involving some form of intracortical or corticothalamic processing. In recent years efforts have focused on determining how SRP is expressed across different cell types and layers of V1 in order to better understand how the circuitry of V1 might mediate SRP. In this talk, I first provide a broad overview of SRP and its relation to visual recognition memory, with a focus on what is known about its mechanisms. Next, I explore the role of inhibition in SRP, and present evidence that SRP expression can be explained by the differential recruitment of two distinct classes of inhibitory cells: parvalbumin-positive (PV+) and somatostatin-positive (SOM+) interneurons. Finally, I investigate how SRP is expressed across the cortical layers of V1. Using 2-photon calcium imaging, I measure the somatic and dendritic responses of different populations of excitatory cells across multiple layers of V1 in order to gain a clearer picture of how SRP is expressed by the cortical circuit more broadly.