Layer 4 organization and respiration locking in the rodent nose somatosensory cortex

Rodents and other mammals acquire sensory information by precisely orchestrated head, whisker, and respiratory movements. We have, however, only limited information about integration of these signals. In the somatosensory domain, the integration of somatosensory information with other modalities is particularly pertinent for body parts such as eyes, ears, and nose, which serve another modality. Here we analyzed the nose/nostril representation in the rodent somatosensory cortex. We identified the representation of the nose/nostril in the rat somatosensory cortex by receptive field mapping and subsequent histological reconstruction. In tangential somatosensory cortical sections, the rat nostril cortex was evident as a prominent stripe-like recess of layer 4 revealed by cytochrome-c oxidase reactivity or by antibodies against the vesicular glutamate-transporter-2 (identifying thalamic afferents). We compared flattened somatosensory cortices of various rodents including rats, mice, gerbils, chinchillas, and chipmunks. We found that such a nose/nostril module was evident as a region with thinned or absent layer 4 at the expected somatotopic position of the nostril. Extracellular spike activity was strongly modulated by respiration in the rat somatosensory cortex, and field potential recordings revealed a stronger locking of nostril recording sites to respiration than for whisker/barrel cortex recoding sites. We conclude that the rodent nose/nostril representation has a conserved architecture and specifically interfaces with respiration signals.NEW & NOTEWORTHY We characterized the rodent nose somatosensory cortex. The nostril representation appeared as a kind of "hole" (i.e., as a stripe-like recess of layer 4) in tangential cortical sections. Neural activity in nose somatosensory cortex was locked to respiration, and simultaneous field recordings indicate that this locking was specific to this region. Our results reveal previously unknown cytoarchitectonic and physiological properties of the rodent nose somatosensory cortex, potentially enabling it to integrate multiple sensory modalities.