Cell-type specialization of layer 5 excitatory neurons in tactile behavior

Abstract

Layer 5 is the canonical output layer of sensory cortex. The two most numerous neural constituents of Layer 5 are pyramidal tract (PT) and intratelencephalic (IT) neurons. These output cell classes combine diverse sets of inputs and project to distinct locations across the brain, suggesting differing roles in sensory information processing. Here, we investigated the representation of touch and whisker motion in these two cell types within primary somatosensory cortex (S1) using optogenetically targeted single unit electrophysiology during whisker-guided object localization. PT neurons (N = 32) had much higher spike rates than IT (N=26) during behavior. Individual members of both were modulated by, but average population firing rates were stable between quiet and whisking periods. PT neurons showed greater absolute spike rate changes, but less relative modulation than IT neurons to whisking kinematic features. Touch-excited PT (N = 18) and IT neurons (N = 8) rapidly adapted to active touch. Both populations encoded the azimuthal position of touched objects, with IT neurons more sharply tuned to position. However, position was more precisely decodable from PT population activity, due to greater evoked spikes per touch. A consequence of these characteristics is that PT neurons, with their higher firing rates, may be more effective participants in rate-based neural codes, while IT neurons, with their sharp modulation, may be more effective in timing or synchrony-based codes.