From an invariant sensory code to a perceptual categorical code in second somatosensory cortex

A crucial role of cortical networks is the conversion of sensory inputs into perception. In the cortical somatosensory network, neurons of the primary somatosensory cortex (S1) show invariant sensory responses, while frontal lobe neuron responses correlate with the animal’s perceptual behavior. But, where in the cortical somatosensory network are the sensory inputs transformed into perceptual behavior? Here, we report that in the secondary somatosensory cortex (S2), neurons with invariant sensory responses coexist with neurons whose responses correlate with the animal’s perceptual behavior. These distinct neural responses exhibit analogous timescales of intrinsic fluctuations, suggesting that they belong to the same hierarchical processing stage. Furthermore, during a non-demanding control task, the sensory responses remained unaltered while perceptual responses vanished. Conclusively, the S2 population responses exhibit intermediate dynamics between S1 and frontal lobe neurons. These results suggest that the conversion of touch into perception crucially depends on S2.