19.11.2015: Mario Dipoppa

Testing canonical microcircuits in mouse visual cortex

Mario Dipoppa, University College London, UK

In mouse primary visual cortex, visual responses of excitatory Pyramidal (Pyr) neurons are modulated by non-visual information such as locomotion. This modulation has been suggested to arise from a canonical microcircuit where Vasoactive Intestinal Peptide (Vip) interneurons inhibit Somatostatin-expressing (Sst) that in turn disinhibit Pyr neurons. On the other hand, size tuning of Pyr neurons has been suggested to be mediated by Sst neurons in another canonical microcircuit. The role of Parvalbumin (Pvalb) interneurons in these circuits has not yet been determined. To test these microcircuits and their mutual interactions we measured how locomotion affects neural activity and spatial integration in all these three types of interneurons.

We used two-photon calcium imaging in mice that were head-fixed and free to run on an air-suspended ball while visual stimuli of different sizes were presented. We used mouse transgenic lines expressing red fluorescence protein in specific class of interneurons to identify them. We found that running increases spontaneous activity in Vip and Sst cells, and on deep Pvalb cells. It has the opposite effect on superficial Pvalb cells. Furthermore, running increases visual responses to all stimulus sizes in Pvalb, to large stimuli in Sst cells and to small stimuli in Vip cells. Increase of spontaneous activity and visual responses by running in Sst neurons is not consistent with the disinhibitory microcircuit.    During rest, Sst neurons are more surround suppressed than during running. This suggests a revision of Sst-mediated surround suppression microcircuit during the resting state.