Cerebral response to pyramidal tract stimulation in wood rats and its relation to laboratory rats.

The cerebral response evoked by stimulation of the bulbar pyramidal tract in wood rats, like that of laboratory rats, consisted of a small alpha wave, almost obscured by a very large, superimposed r wave. The alpha wave behaved like a purely antidromic response, whereas the r wave behaved like a postsynaptic response, including a marked variability in amplitude on repeated trials. The contralateral forepaw and hindpaw motor sites mapped onto the somatic sensory foci for these two paws; further examination showed that the somatic sensory and motor representations were largely superimposed. An incipient sagittal fissure 1.5 mm lateral to the midline marked the boundary between limbic and neocortex. Because of their structural similarities and their differences in somatic sensory and motor organization, wood rats and laboratory rats are prime subjects for comparative study of the role of amalgamated and separate sensory and motor cortices in regulating movement and behavior.