TOP-DOWN AND BOTTOM-UP MECHANISMS OF V1 ACTIVITY GENERATION DURING SLEEP

Sleep is divided into rapid-eye-movement (REM) sleep, characterized by awake-like high frequency desynchronised activity, and non-REM (NREM) sleep, characterized by slow wave activity. How these diverse types of activity are produced and structured are disputed, with both bottom-up and top-down hypotheses being proposed. In the primary visual cortex (V1), layer 2/3 pyramidal (PYR) neurons possess anatomically segregated dendritic compartments with distinct sources of input: basal dendrites, that primarily receive feedforward and local inputs; and apical dendrites, that receive inputs from higher cortical areas and higher thalamic nuclei. The sources of input which drive V1 activity during sleep and how this varies over substates is unknown. One candidate source of top-down inputs is the RSC as it's one of the densest feedback pathways to V1, and its activity has been found to be increased during REM sleep. Here we characterise apical and basal dendritic calcium activity in sparsely-labelled V1 PYR neurons using 2-photon calcium imaging during visual stimulation, and subsequent sleep states. We aim to test the hypothesis that the balance of activity of the apical vs. basal dendrites shifts during sleep in favour of greater top-down activation. Additionally, by recording RSC🡪V1 axon activity and V1 somas simultaneously using dual color 2-photon calcium imaging, we aim to identify whether RSC boutons and V1 somas activity increases during REM and if they’re correlated. Together, these experiments test whether V1 activity during different sleep states is predominantly driven by top-down or by bottom-up inputs and whether the RSC modulates V1 during REM.