Sudden sensory events trigger modality-independent responses across layers in the mouse neocortex

Sudden sensory events trigger widespread electrocortical responses and noticeable changes in an animals behavior. It remains unclear, though, how this "surprise" signal is generated via afferent sensory input and represented by neuronal ensembles. Using in vivo electrophysiology, here we recorded the activity of different cortical areas across layers in awake head-fixed mice, while presenting sensory stimuli of different modalities and saliencies. When brief, salient stimuli were delivered at long intervals, we found prominent responses across cortical areas regardless of the stimulus modalities, resembling those observed in human electroencephalography. These responses were larger and emerged earlier in the infragranular layer than in the granular layer of the primary sensory cortex. At short inter-stimulus intervals, in contrast, only modality-specific responses were observed in the corresponding primary sensory cortex. These results indicate that sensory information travels through multiple ascending pathways, in particular, supra-modal surprise signals via non-classical sensory pathways to the cortex.