Bitzidou M, Bale MR, Giusto E, Maravall M

In the world around us natural stimuli unfold over time and their temporal patterning is key to making sense of them. Physical features in these stimuli are concatenated in a particular order that defines a sequence. To explore which sequence properties are used for discrimination and which brain regions participate in sequence recognition, we trained mice in a sequence discrimination task. Mice distinguish between “words” constructed from distinct whisker vibrotactile stimuli assembled in different orders and have to respond to one of them. Optogenetic inactivation of cortical population activity was performed to determine the cortical sites where tactile information is processed. Inactivating the somatosensory barrel cortex (S1BC) and secondary somatosensory cortex (S2) abolished sequence discrimination on interspersed light-on trials. Suppression of posterior parietal cortex (PPC) had no detectable effect, while suppression of primary motor cortex (wM1) disinhibited lick responses. These results suggest that the sensory input used for sequence recognition flows through S1BC and S2, but that sequence selectivity is learned in higher areas.