Abstract
Mouse primary somatosensory barrel cortex (wS1) processes whisker sensory information, receiving input from two distinct thalamic nuclei. The first-order ventral posterior medial (VPM) somatosensory thalamic nucleus most densely innervates layer 4 (L4) barrels, whereas the higher-order posterior thalamic nucleus (medial part, POm) most densely innervates L1 and L5A. We optogenetically stimulated VPM or POm axons, and recorded evoked excitatory postsynaptic potentials (EPSPs) in different cell-types across cortical layers in wS1. We found that excitatory neurons and parvalbumin-expressing inhibitory neurons received the largest EPSPs, dominated by VPM input to L4 and POm input to L5A. In contrast, somatostatin-expressing inhibitory neurons received very little input from either pathway in any layer. Vasoactive intestinal peptide-expressing inhibitory neurons received an intermediate level of excitatory input with less apparent layer-specificity. Our data help understand how wS1 neocortical microcircuits might process and integrate sensory and higher-order inputs.
Highlights
Thalamic input is of critical importance for neocortical function, but the distribution of synaptic input onto distinct cell-types located in different cortical layers remains incompletely understood
When analyzing POm input to SST neurons, we found small peak excitatory postsynaptic potentials (EPSPs) amplitudes and slopes across layers (Figure 6C), which remained small after normalization to the L5A excitatory neurons (Figure 6C, Table 3 and Table 4)
Our data suggest that ventral posterior medial (VPM) and POm input to excitatory and PV neurons is much stronger than the thalamic input to SST neurons, with vasoactive intestinal peptide (VIP) neurons receiving an intermediate level
Summary
Thalamic input is of critical importance for neocortical function, but the distribution of synaptic input onto distinct cell-types located in different cortical layers remains incompletely understood. Primary sensory cortical areas receive thalamic input from primary sensory thalamic nuclei - for example the lateral geniculate nucleus innervates primary visual cortex, the medial geniculate nucleus innervates primary auditory cortex and the lateral and medial portions of the ventral posterior nucleus innervate primary somatosensory cortex. The primary sensory thalamic input to primary sensory areas is arranged in topographic maps, for example retinotopy in visual cortex, tonotopy in auditory cortex, and somatotopy in somatosensory cortex. The primary sensory thalamic input is thought to drive sensory processing in the recipient cortex (Reinhold et al, 2015), and it is of critical importance to investigate thalamic input onto specific classes of neurons distributed across cortical layers
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