Functional reorganization of cat somatic sensory-motor cortex (SmI) after selective dorsal root rhizotomies

Conscious tactile sensibility has been hypothesized to take origin with activity in the lemniscal system, in general, and somatosensory cortex (Sin|), in particular, due to the highly specific functional and synaptic organization of these structures13, t4. Sml neurons, for example, have been found to respond with distinct properties to discrete somatic modalities of stimulation of local peripheral receptive fields (RFs) 12. Recent evidence, however, necessitates a re-evaluation of this interpretation of the mode of function of these ascending structures. Overlapping connections from widespread and/or multiple RFs have been observed to project, in intact animals, to neurons in spinal cord2,16 and dorsal column nuclei (DCN) 3. These anomalous connections are more readily observed in DCN4, ll and Sml 1° of the cat when specific, dominant input pathways are acutely interrupted, and in chronically deafferented cat spinal cord 1, DCN4,11, rat thalamus and SmP 5. This report describes a functional reorganization in Sml of adult cats within 8-55 days of selective dorsal root section. The data were obtained from 6 adult cats during 18 recording sessions. The animals were intubated under ketamine analgesia (Ketaset) (10 mg/kg i.m.), paralyzed with gallamine triethiodide (Flaxedil) (4.5 mg/kg/h, IV), and artificially respirated with an analgesic mixture of 65 ~ N20/35 ~ Oz. Anesthesia during surgery was obtained by the addition of 1.5 ~ halothane (Fluothane). The medial left post-cruciate region of Sml (predominantly receiving caudal body afferent input v) was exposed, and a chronic recording chamber was implanted over the cortex 10. Upon completion of the control recordings from 5 cats, the right hindlimbs and tails of 3 cats (2 of which were also studied as controls) were selectively deafferented via intradural dorsal root rhizotomies. All of the dorsal roots caudal to