Network‐selectivity and stimulus‐discrimination in the primary visual cortex: cell‐assembly dynamics

Abstract

Visual neurons coordinate their responses in relation to the stimulus; however, the complex interplay between a stimulus and the functional dynamics of an assembly still eludes neuroscientists. To this aim, we recorded cell assemblies from multi-electrodes in the primary visual cortex of anaesthetized cats in response to randomly presented sine-wave drifting gratings whose orientation tilted in 22.5° steps. Cross-correlograms divulged the functional connections at all the tested orientations. We show that a cell-assembly discriminates between orientations by recruiting a 'salient' functional network at every presented orientation, wherein, the connections and their strengths (peak-probabilities in the cross-correlogram) change from one orientation to another. Within these assemblies, closely tuned neurons exhibited increased connectivity and connection-strengths than differently tuned neurons. Minimal connectivity between untuned neurons suggests the significance of neuronal selectivity in assemblies. This study reflects upon the dynamics of functional connectivity, and brings to the fore the importance of a 'signature' functional network in an assembly that is strictly related to a specific stimulus. Apparently, it points to the fact that an assembly is the major 'functional unit' of information processing in cortical circuits, rather than the individual neurons.

High noise correlation between the functionally connected neurons in emergent V1 microcircuits

“…Indeed, this investigation extends the work on ensembles (Miller et al 2014;Reid et al 2015;Bharmauria et al 2015b), wherein authors have shown that same ensembles are active in response to the stimulus and even at spontaneous oscillations. We have already reported that a signature microcircuit is activated in such an ensemble that is strictly related to the presented stimulus (Bharmauria et al 2015b).…”

“…Indeed, this investigation extends the work on ensembles (Miller et al 2014;Reid et al 2015;Bharmauria et al 2015b), wherein authors have shown that same ensembles are active in response to the stimulus and even at spontaneous oscillations. We have already reported that a signature microcircuit is activated in such an ensemble that is strictly related to the presented stimulus (Bharmauria et al 2015b). Reid et al (2015) documented that within the sequential 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 activation of ensembles in a Hebbian assembly, neurons fire with repeating firing patterns in an ensemble called 'doublet pathways'.…”

“…The current experiments were done on anaesthetized cats and we have already shown that the disclosed functional connections are strongly related to the presented stimulus rather than the spontaneous fluctuations in the brain -the proportion of connections was more at stimulus conditions than at 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 spontaneous activity; the gamma power was high at stimulus presentation than at spontaneous oscialltions (Bharmauria et al 2014;Bharmauria et al 2015a, Bharmauria et al 2015b Graf et al 2011;Cossell et al 2015). One may also argue that high noise correlation between the connected neurons in current investigation might be attributed to the artificial binning of spikes in wider resolution windows, but if it were the case we would not have obtained such trendy difference between the connected and the unconnected pairs.…”

“…Moreover, we also report that, Rsc between neurons is independent of the presented orientation and the neurons may or may not exhibit connections from one orientation to another irrespective of the strength of Rsc. We suggest that the "inherent" temporal spiking pattern between neurons confers them almost equivalent Rsc along the presented orientations (Miller et al 2014;Reid et al 2015;Bharmauria et al 2015b), but on occasions it may not be possible to reveal it through CCGs as the firing rate varies from one orientation to another. This study also relates to another recent study by Shimono and Beggs (2014), wherein they revealed such functional links in small clusters (3-6 neurons) using transfer entropy.…”

Information and the Origin of Qualia

“…There is a growing conviction that it is ensembles of neurons that are key to the link between neuronal dynamics and their function in information processing, rather than individual cells (Harris, 2005; Buzsáki, 2010; Bharmauria et al, 2016). Some recent evidence for the existence of these ensembles/networks is discussed later.…”