Distinct response dynamics to whisker stimulation in barrel and perirhinal cortex

Hierarchical processing has been shown to underlie complex functions such as invariant object coding. The perirhinal cortex (PER) is a higher-order region that sits at the apex of such processing streams and is involved in object recognition. Although it receives tactile information from barrel cortex (wS1) and secondary somatosensory cortex (S2), it is unclear how PER neurons respond to such stimuli. To address this, we performed population recordings of the barrel and perirhinal cortices of head-fixed mice while an object deflected their whiskers. Both ipsi- and contralateral stimulations were performed, as PER receives interhemispheric projections from the contralateral wS1. Of the responsive units in each region, the majority were positively modulated in wS1 and negatively modulated in PER. The corresponding population dynamics were visualised using PCA. For both stimulation types, the first whisker deflection in the trial produced a large deviation in PC space, with weaker deviations to successive deflections. This occurred in both regions, but with qualitatively distinct trajectories. To explore this further, we used K-means to cluster neuron response dynamics. Through this, we found transient inhibitory responses in wS1, but not in PER. Conversely, PER featured a mode of inhibition that lasted the entire stimulation duration, which was absent in wS1. Together, these findings provide a step towards understanding how tactile stimuli is represented in PER.