Translaminar recurrence from layer 5 suppresses superficial cortical layers

The role of translaminar feedback projections between layer 5 and layers 2/3 in sensory processing remains unclear. Here, the authors show that ascending projections from layer 5 suppress superficial layers, and that this translaminar feedback sharpens feature selectivity in the primary auditory cortex. Information flow in the sensory cortex has been described as a predominantly feedforward sequence with deep layers as the output structure. Although recurrent excitatory projections from layer 5 (L5) to superficial L2/3 have been identified by anatomical and physiological studies, their functional impact on sensory processing remains unclear. Here, we use layer-selective optogenetic manipulations in the primary auditory cortex to demonstrate that feedback inputs from L5 suppress the activity of superficial layers regardless of the arousal level, contrary to the prediction from their excitatory connectivity. This suppressive effect is predominantly mediated by translaminar circuitry through intratelencephalic neurons, with an additional contribution of subcortical projections by pyramidal tract neurons. Furthermore, L5 activation sharpened tone-evoked responses of superficial layers in both frequency and time domains, indicating its impact on cortical spectro-temporal integration. Together, our findings establish a translaminar inhibitory recurrence from deep layers that sharpens feature selectivity in superficial cortical layers.

Automated summary

The authors demonstrate that translaminar feedback projections from layer 5 suppress activity in superficial layers and enhance feature selectivity in the primary auditory cortex.