Extending our previous research concerned with the reception of callosal messages by the cortical somatosensory areas of the cat, the present experiments were devoted to studying what kind of somesthetic information is transmitted through the fibers of the corpus callosum (CC). By recording electrical activity through coaxial macroelectrodes and tungsten microelectrodes directly from the CC of chloralose-anaesthetized cats, a set of fibers was identified in the rostral part of this commissure (somesthetic callosal region, SCR, extended from the rostrum to the stereotaxic plane A 14, caudad) through which callosally-projecting cells of somatosensory areas re-transmit messages originated in the contralateral body surface. On measuring the amplitude of the mass potentials (slow positive or biphasic inflections, carrying unresolved multispike activity) elicited by stimulation of different regions of the body surface, and on exploring with macroelectrodes the rostrocaudal extent of SCR, it was found that: i) shocks applied to the whisker regions and to the forelimbs (both to paws and to proximal segments) elicit in CC the strongest mass potentials, which can be recorded from the widest extent of SCR; ii) shocks delivered to other trigeminal (orbital or jaw regions) or segmental (trunk or hindlimb) skin elicit the weakest responses; iii) a certain somatotopy of body surface representation seems to exist in SCR, since trigeminal, fore— and hindlimb responses are best elicitable in its rostral, middle and caudal part, respectively. Direct stimulation of somatosensory areas evokes in SCR asynaptic, short-1atencied (0.4-0.6 msec) positive potentials. Stimulation of the thalamic ventrobasal complex evokes in the same region post-synaptic mass potentials (latency at the onset, 1.5—2 msec) similar to those elicited by peripheral shocks. On recording with microelectrodes from SCR, 43 spontaneously active fibers were isolated, all reactive to electrical and physiological stimulation of peripheral receptive fields (PRF) located in trigeminal (31 fibers) segmental (10 fibers) and in both trigeminal and segmental regions (2 fibers). The PRF and the reactivity of almost all fibers sampled were lemniscal in character and similar to those of cortical somatotopic neurones.
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Con il contributo del Ministero per i Beni e le Attività Culturali