Raccoon forelimb motorsensory cortex: II. Somatosensory inputs to single neurons

Somatosensory input to 431 neurons in MsI has been studied in unanesthetized, paralyzed raccoons (Procyon lotor). The type of sensory input to neurons in lateral sigmoid gyrus (cytoarchitectonic area 4) and in posterior sigmoid gyrus (areas 4 and 3a) was not significantly different. Of these neurons, 36% were activated by superficial cutaneous stimulation (touch, tap or hair deflection) and 26% by deep stimulation (pressure or joint movement). Mute neurons (not driven by any form of peripheral stimulation tested, or vaguely driven) comprised 38% of the sample. Only 4% of anterior sigmoid gyrus (area 6) neurons responded to superficial or deep stimulation; 96% were mute. The majority of MsI neurons had small (less than or equal to 20 cm2) peripheral receptive fields (PRFs). There was a statistically significant trend for PRF size to decrease along the proximal-distal axis of the forelimb. The area of MsI digit PRFs was significantly larger than the area of SmI digit PRFs. Comparing the data for raccoon MsI with information from the literature for cats and monkeys suggests that the type and amount of somesthetic afferent input to forelimb MsI is related to the behavioral uses to which each animal puts the forelimb.