Large Unresponsive Zones Appear in Cat Somatosensory Cortex Immediately After Ulnar Nerve Cut

Abstract

Abstract:The organization of the primary somatosensory cortex innervated by the ulnar nerve was studied before and immediately after ulnar nerve transection in 11 cats electrophysiologically mapped under Nembutal or Ketamine anesthesia. The cortex was reexamined a second time beginning 42 hr after nerve transection in four cats anesthetized with Nembutal. One additional sham-operated control was also mapped. The region of cortex formerly served by the ulnar nerve remained largely unresponsive to somatic stimulation independent of the type of anesthetic used during recording. Nonetheless, animals anesthetized with Ketamine had more new responsive sites in deafferented cortex following nerve cut than cats anesthetized with Nembutal. New responses, when observed, were evoked by stimulation of a region of skin adjacent to the region served by the ulnar nerve. These findings suggest that the immediate response to deafferentation of somatosensory cortex is a limited acquisition of novel responses restricted to a region immediately adjacent to cortex containing normal afferent input.Resume: Zones et endues de non-reponse apparaissant dans le cortex somesthesique du chat immediatement apres la section du nerf cubital. Nous avons Studie l'organisation du cortex somesthesique primaire innerve par le nerf cubital avant et immediatement apres la section du nerf cubital chez 11 chats cartographies au point de vue 61ectrophysiologique sous anesth6sie au Nembutal ou a la ketamine. Le cortex a tt& reaxamine une seconde fois 42 heures apres la section nerveuse chez 4 chats anesthesies au Nembutal. Un chat controle ayant subi une operation factice a aussi ete cartographie. La region du cortex desservie anterieurement par le nerf cubital est demeuree en grande partie insensible a la stimulation somatique, quel qu'ait ete le type d'anesthesie utilise pendant l'enregistrement. Cependant, les animaux anesthesies a la ketamine avaient plus de sites sensibles nouveaux dans le cortex desafferentie suite a la section nerveuse que les chats anesthesies au Nembutal. Quand de nouvelles reponses etaient observees, elles etaient provoquees par la stimulation d'une region de la peau adjacente a la region innervee par le nerf cubital. Ces observations suggerent que la reponse immediate a la desafferentiation du cortex somesthesique est une acquisition limitee de reponses nouvelles, restreintes a la region immediatement adjacente au cortex contenant l'infux afferent normal.

Sensitivity of neurons in somatosensory cortex (S1) to cutaneous stimulation of the hindlimb immediately following a sciatic nerve crush

“…G ilbert and W iesel, 1992;D arian-Sm ith and Gilbert, 1995;Rosier et al, 1995;Schm idt et al, 1995), auditory cortex (Robertson and Irivine, 1989) and som atosensory cortex (M etzler and M arks, 1979;M erzenich et al, 1983;Rasm usson and Turnbull, 1983;Kelahan and D oetsch, 1984;Wall and Cusick, 1984;Rasmusson and N ance, 1986;Calford andTweedale, 1988, 1991a, b;Cusick et al, 1990;Turnbull and Rasm usson, 1990;Byrne and C alford, 1991;Kolaric et al, 1994;Li et al, 1994;D oetsch et al, 1996;Silva et al, 1996;Faggin et al, 1997;Schroeder et al, 1997). T hese studies indicate that a general feature of cor tical plasticity within prim ary sensory neocortex is the m utability of functional boundaries that separate sensory representations.…”

Functional organization of tactile inputs from the hand in the cuneate nucleus and its relationship to organization in the somatosensory cortex

“…For example, for locations within about 8 cm from the tip of the forepaw, areas of most fields at each level were about 300-500 mm 2 or less (Mountcastle, 1957;Iwamura and Spencer, 1975;Iwamura and Tanaka, 1978;Golovchinsky, 1980). Similarly, many studies in cats illustrate CN and S-I cortical receptive fields on the forepaw and forelimb, and visual comparisons indicate considerable overlap in the sizes of these fields (e.g., cuneate: Dykes et al, 1982;Pettit and Schwark, 1996;Dykes and Craig, 1998;cortex: Iwamura and Tanaka, 1978;Felleman et al, 1983;Li et al, 1994;Myasnikov et al, 1994). Studies in raccoons also indicate overlap in the sizes of digit and palm fields at CN and VPL levels; however, within this overlap the median size of fields in VPL was two to three times larger than the median size of CN fields (Rowinski et al, 1981;Warren et al, 1986).…”

The Proprioceptive Senses: Their Roles in Signaling Body Shape, Body Position and Movement, and Muscle Force

“…It suggests that the cortical representation of each body part has an inhibitory surround maintained by small-fiber input which, if removed, leads to an expansion of the representation. Illusory increases in size may not appear to be so dramatic when a large part of the body is anesthetized or removed (227,258). While these immediate distortions of body size with local anesthesia have been linked to loss of input from small-diameter afferents (e.g., Refs.…”