CALLOSAL TRANSFER OF IMPULSES ORIGINATING FROM SUPERFICIAL AND DEEP NERVES OF CAT FORELIMB

  • 1 January 1976
    • journal article
    • research article
    • Vol. 114  (2) , 155-177
Abstract
In 18 chloralose-anesthetized, curarized cats the callosal transfer of somatic information originated in exteroceptive and proprioceptive receptors was studied. Several cutaneous and deep nerves of the forelimb were prepared and stimulated with graded intensities, to activate selectively afferent fibers of the different groups of Lloyd''s classification. Simultaneous records were taken (and averaged on-line by means of a multichannel analyzer) from the distal end of a cut dorsal rootlet (C7-C8), from the cerebral cortex (SI, SII or area 3a) and from the somesthetic callosal region (SCR). The low-threshold afferent fibers (Group II) of cutaneous origin had a wide projection to the SCR, with the maximal density in its middle portion. Some of the fastest cortico-callosal impulses were relayed monosynaptically at cortical level. Plots of the amplitude of cortical and callosal responses as a function of stimulus strength showed that both central responses have the same threshold and exhibit a parallel, sharply-rising amplitude increase. Impulses elicited in afferent fibers of higher threshold (Group III) did not enhance the cortical and callosal positive waves provoked by Group II afferent volleys. Afferent fibers of deep origin sent a wide projection to the SCR, although less substantial than that of cutaneous fibers. Stimulation of the deep radial nerve elicited mass responses in the whole SCR, provided the strength of stimuli was high enough to engage the Group II fibers. Only in the central portion of the SCR were small potentials recorded in response to pure Group I volleys of the DRN [deep radial nerve].

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