Tactile responses in the mouse perirhinal cortex show invariance to physical features of the stimulus
Sensory processing in the cortex follows a hierarchical structure, transforming fine-grained stimulus features into abstract, invariant representations. These transformations have typically been characterised in visual pathways ranging from primary visual cortex to inferotemporal cortex. Less is known about how stimulus representations are formatted in other modalities and downstream regions such as the perirhinal cortex (PER), which receives processed sensory input from all modalities and is involved in object recognition. To address this, we investigated neural activity along the somatosensory hierarchy in awake, head-fixed mice receiving tactile whisker stimulation on either side of the face. PCA and stimulus-baseline decoding analyses revealed that PER activity was similar across stimulated sides, while this was not the case in primary somatosensory cortex (wS1). We also performed decoding analyses for the side of stimulation and the stimulus movement direction and found that wS1 and secondary somatosensory cortex could reliably decode both features. In contrast, PER was shown to be invariant to both features. We also clustered neurons based on their response dynamics, which indicated that the majority of PER neurons did not encode the basic stimulus features. These findings demonstrate that PER is a critical node in the somatosensory processing hierarchy, encoding tactile information in an invariant and abstract format. Together, these insights contribute to a more refined understanding of how perceptual processing in PER contributes to the various cognitive processes it is utilised for. Significance StatementSensory information is processed in stages that transform detailed signals into complex, stable representations. The perirhinal cortex (PER) is at the apex of these stages and is involved in recognizing objects, a cognitive process that requires both perceptual and memory-based processing. While PERs role in the latter is established, evidence for the former is conflicting. To investigate this, we recorded PER activity in mice passively experiencing simple tactile stimulation with two pairs of feature combinations. Along the cortical somatosensory hierarchy invariance of stimulus representation emerged in PER, while individual features were represented in earlier cortices with high fidelity. This suggests that PER contributes to the formation of invariant representations of sensory stimuli that is a foundation for object recognition.