Layer 2/3 Pyramidal Neurons Control the Gain of Cortical Output

Initial anatomical and physiological studies suggested that sensory information relayed from the periphery by the thalamus is serially processed in primary sensory cortical areas. It is thought to propagate from layer 4 (L4) up to L2/3 and down to L5, which constitutes the main output of the cortex. However, more recent experiments point toward the existence of a direct processing of thalamic input by L5 neurons. Therefore, the role of L2/3 neurons in the sensory processing operated by L5 neurons is now highly debated. Using cell type-specific and reversible optogenetic manipulations in the somatosensory cortex of both anesthetized and awake mice, we demonstrate that L2/3 pyramidal neurons play a major role in amplifying sensory-evoked responses in L5 neurons. The amplification effect scales with the velocity of the sensory stimulus, indicating that L2/3 pyramidal neurons implement gain control in deep-layer neurons. [Display omitted] •Cortical layer 2/3 (L2/3) input evokes both excitatory and inhibitory currents in L5•L2/3 input has a net excitatory effect in L5•L2/3 input amplifies sensory-evoked responses in L5•L2/3 input modulates the gain of sensory-evoked responses in L5 Quiquempoix et al. investigated the role of the canonical cortical layer 2/3 (L2/3)-to-L5 pathway in sensory processing by deep-layer neurons of the mouse somatosensory cortex. They show that the recruitment of this pathway plays a major role in amplifying sensory-evoked responses in L5 neurons.