Neurobiology graduate student Jennifer Li (Glickfeld Lab) will present Subthreshold mechanisms underlying rapid adaptation in visual cortex on Zoom, Thursday, February 11 at noon.
Please email DGSA David Gaines for connection information.
Abstract: Adaptation is a fundamental feature of visual processing that enables the nervous system to adjust to features of our surrounding environment. Previous studies have addressed mechanisms underlying adaptation in in response to relatively constant stimuli presented for tens of seconds or more. However, the statistics of natural scenes suggests that in most animals, visual input is changing at much higher rates. Our lab has identified a form of rapid adaptation in primary visual cortex (V1) where presentation of a brief, 100 ms grating stimulus is sufficient to suppress responses for seconds. We sought to identify the mechanisms contributing to this phenomenon by measuring various features of subthreshold cellular activity that have previously been implicated in changes associated with adaptation. We recorded from single layer 2/3 V1 neurons in vivo in awake mice and measured subthreshold membrane potential, stimulus-evoked excitation (EPSCs), and stimulus-evoked inhibition (IPSCs) while presenting pairs of 100 ms static gratings. We find that membrane potential changes following the first grating do not predict changes in spike output (n=5 cells). Instead, rapid adaptation leads to a reduction in both EPSC and IPSC amplitudes in response to the second grating (n=7 cells). Additionally, this reduction appears to be orientation-selective—synaptic inputs are most suppressed when these pairs of stimuli are matched in orientation versus orthogonal. We find that changes in synaptic inputs mirror the degree, selectivity, and time course of the effects of rapid adaptation on the spike output of these neurons. Altogether, this suggests that the lasting suppression of responses in V1 is primarily due to suppression of the inputs that cells receive. Thus, our data identify a synaptic mechanism that contributes to history-dependent encoding of visual stimuli at naturalistic time scales. Ongoing and future experiments will use layer-specific optogenetic manipulations to determine whether reduction of inputs is selective to feedforward or recurrent pathways within V1 to better understand the broader circuit context of these changes.