Contralateral and ipsilateral projections of cerebral somatic areas to the medulla oblongata of cat.

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Summary Single electrical shock stimuli delivered alternatively to various somatic areas of paralyzed cats evoked electrical activities, contralaterally and ipsilaterally, in the territories of: the spinal trigeminal nucleus (V), the posterior funicular nuclei (PF), the reticular formation (RF), ventral region of the lateral funiculus, the anterior funiculus, and the lateral pyramidal tract. In the territories of V and PF at the inferior olivary level the initial latencies of the contralateral responses were mostly less than 2 or 4 msec, while those of the ipsilateral responses ranged widely from 2 msec or less to over 10 msec. In the territories of V at the pyramidal decussation level the initial latencies of the contralateral responses were mostly 2 msec or less, while those of the ipsilateral responses were almost 4–10 msec. On the contrary, in the territories of PF at this level, no latency difference was seen between the contralateral and the ipsilateral responses. The initial latencies were 2 msec or less at both sides. At the inferior olivary level, the latencies of the responses in the contralateral RF and in the interior part of the ipsilateral RF were mostly 4 msec or less, while those in the lateral part of the ipsilateral RF were mostly 2–10 msec. It is confirmed that somatic areas send many fibers directly though the contralateral RF to the contralateral territories of V and PF. It also seems possible that somatic areas appear to send many fibers ipsilaterally to the interior part of RF from which fibers terminate transsynapti-cally to the territories of V and PF, although the possibility that direct ipsilateral fibers of very small diameter might exist is not excluded.