NB & CNS Seminar - Stelios Smirnakis | Tuesday, May 7, 2024 at 4 pm

Date: Tuesday, May 7, 2023

Reception: 3:30 pm

Time: 4 pm

Location: Chen 100

Speaker: Stelios Smirnakis, Associate Professor

Neuroscience

Harvard University

We used two-photon imaging to record from granular and supragranular layers in mouse primary visual cortex (V1) under spontaneous conditions and applied an extension of the spike time tiling coefficient (STTC; introduced by Cutts and Eglen J Neurosci 2014) to map functional connectivity architecture between pyramidal neurons within and across layers. We found that a significant fraction of intra- and inter-layer neuronal pairs exhibit statistically significant functional connections extending to distances of 1mm or more. As expected, neuronal pairs with similar tuning functions exhibit a significant bias towards higher inter-neuronal correlations; however, this bias is small, suggesting that functional connectivity in V1 microcircuits remains largely promiscuous. In contrast, internal state modulations, as reflected by changes in pupillary diameter or aggregate population neuronal activity, appear to play a stronger role in shaping inter-neuronal correlations. First-order functional connectivity groups of individual pyramidal neurons determine the hub structure of area V1 columns; all layers examined exhibit strong small-world characteristics and network robustness. The probability of firing of layer 2,3 (L2,3) pyramidal neurons can be estimated as a function of cofiring activity across their first-order layer 4 (L4) functionally connected "partners", which constitute their "putative input" groups. The functional form of these response functions conforms well to ReLU, reaching up to firing probability one for some units. Interestingly, L2,3 neurons with different "putative input" group size behave differently with respect to their ability to transmit synchronous patterns of activity from L4 to L2,3, as well as with respect to how they couple to internal state modulations, reminiscent of choroists vs soloists (Okun et al. Nature 2015). In general, information transmission is best viewed as progressing from neuronal ensemble to neuronal ensemble; functional connectivity analysis allowed us to identify such candidate ensembles and show that they exhibit high sensitivity, precision, and specificity for L4 to L2/3 neuronal activity transmission. A tentative hypothesis is proposed under which such information encoding ensembles are regulated by a small number of individual interneurons. In summary, functional connectivity analysis under spontaneous activity conditions reveals a modular neuronal ensemble architecture both within and across granular and supragranular layers of mouse primary visual cortex. Furthermore, modules with different degrees of connectivity appear to obey different rules of engagement and communication across the area V1 columnar circuit. A preliminary comparison with functional connectivity analysis performed under stimulus conditions will be also discussed.