Functional and Structural Properties of Highly Responsive Somatosensory Neurons in Mouse Barrel Cortex

Abstract

Sparse population activity is a well-known feature of supragranular sensory neurons in neocortex. The mechanisms underlying sparseness are not well understood because a direct link between the neurons activated in vivo, and their cellular properties investigated in vitro has been missing. We used two-photon calcium imaging to identify a subset of neurons in layer L2/3 (L2/3) of mouse primary somatosensory cortex that are highly active following principal whisker vibrotactile stimulation. These high responders (HRs) were then tagged using photoconvertible green fluorescent protein for subsequent targeting in the brain slice using intracellular patch-clamp recordings and biocytin staining. This approach allowed us to investigate the structural and functional properties of HRs that distinguish them from less active control cells. Compared to less responsive L2/3 neurons, HRs displayed increased levels of stimulus-evoked and spontaneous activity, elevated noise and spontaneous pairwise correlations, and stronger coupling to the population response. Intrinsic excitability was reduced in HRs, while we found no evidence for differences in other electrophysiological and morphological parameters. Thus, the choice of which neurons participate in stimulus encoding may be determined largely by network connectivity rather than by cellular structure and function.

Higher-order thalamocortical projections selectively control excitability via NMDAR and mGluRI-mediated mechanisms

“…Using an unbiased classification, we clustered L2/3 pyramidal neurons in two groups, one with broad and dense apical tufts, and another with slender tufts (Figure 1). The morphological characteristics of these populations are very similar to previously reported BT and ST neurons 8,9 . Our experiments show that the extent and density of their dendrites were good indicators of the synaptic connectivity with the axons that overlapped with them (Figure 2), which is in line with Peters’ rule stating that synaptic connections are proportional to the axo-dendritic overlap 12 .…”

“…L2/3 BT neurons) with POm afferents are associated with higher-than-average levels of plasticity 25,59,60 . However, there is no indication that the BT neuronal subtypes should generally display higher levels of activity in vivo 9 .…”

“…However, there is no indication that the BT neuronal subtypes should generally display higher levels of activity in vivo 9 .…”

Coexistence of state, choice, and sensory integration coding in barrel cortex LII/III

“…2b). Consistent with previous studies (O 'Connor et al 2010;Mayrhofer et al 2015;Barz et al 2021), we found that a small fraction of neurons were highly responsive to tactile stimulation (~10 %; Fig. 2c).…”

“…As described in previous work, we found that evoked activity in L2/3 is somatotopically organized (Woolsey and Van der Loos 1970;Clancy et al 2015), sparsely distributed in the population (O'Connor et al 2010;Mayrhofer et al 2015;Barz et al 2021) and adapting rapidly in most neurons (Gerdjikov et al 2018). Increasing stimulation frequency of a single whisker increases monotonically population response (Gerdjikov et al 2010(Gerdjikov et al , 2018Mayrhofer et al 2015).…”