Fig 5. Cortical brain mapping of the RA-MS response group elicited by tapping the tendons of the degloved forelimb organized by individual muscle sensory response.

(A) An overview of the left cortical hemisphere in the rat. Cytochrome oxidase delineated borders and barrel patterns of primary somatosensory cortex (black lines and grey shading): F = forepaw barrel subfield; H = hindpaw barrel subfield; V = vibrissae; Bp = buccal pad; L = lower lip, O1 & O2 = oral modules 1 & 2; L = chin/lower lip; B = body; S2 = second somatosensory area. The dashed box denotes the area of interest enlarged in (B) through (U). Scale bars = 500 μm; R = rostral; L = lateral. (B-U) The shapes of the labeled points refer to location or compartment: X = Shoulder; Square = Proximal Anterior Compartment; Triangle = Proximal Posterior Compartment; Circle = Distal Anterior Compartment; Diamond = Distal Posterior Compartment. We find that the muscles with the smallest overall representational area (the distal flexors and distal extensors) appear to project only to the transitional zone area that is rostral and medial to the S1 forepaw representation. In contrast, the proximal and middle muscles (except the triceps) and the extensor digitorum, each having a larger overall representational area, appear to project to transitional zone areas surrounding the S1 forepaw representation (A-D, F and O). Note: Although not evident in the composite overlays, the receptive fields for the RA-MS-type response group are separate from S1 (Fig 4B–4H).