Relationships between sensory-evoked synaptic input and long-range target-related spiking output of cortical layer 5

Abstract

Even the simplest stimuli evoke highly heterogeneous responses in thousands of neurons in the related primary sensory areas of the mammalian neocortex. This intracortical (IC) representation of the stimulus is integrated by specific output populations in cortical layer 5 (L5), which transmit the results of cortical sensory information processing to several distant brain areas. How local IC activity is transformed into cortical output, and whether the transformations are related to the specific long-range targets is unknown. Here we combined injections of retrograde tracer agents with in vivo recordings and computational modeling to determine relationships between local synaptic input and sensory-evoked responses of individual L5 neurons with identified subcortical targets. We found that cortico-subcortical (CS) neurons in L5 of rat primary somatosensory cortex (S1) are subdivided into four disjoint projection types, which are embedded into the cortical circuitry in a target-related manner. Our results demonstrate that several CS output channels, in parallel, transform IC activity into target-related spiking patterns, potentially to extract disjoint features from the same stimulus