Cutaneous reflexes and pathways affecting them in the monkey, Macaca mulatta

Cutaneous reflexes of decerebrate monkeys were studied in terms of threshold and receptive field before and after various lesions of the cord and brain stem. They were more severely depressed than in the decerebrate cat. This was true of extensor as well as flexor reflexes. They were released by lesions of the dorsolateral funiculi of the cord below the level of these lesions and further inhibited above that level. They were severely depressed blow the level of lesions of the ventrolateral funiculi with the exception of digital reflexes, which were lowered in threshold with no change of receptive field. In each of these cases a unilateral lesion had bilateral effects. Ventrolateral lesions induced no change in cutaneous reflexes above the level of the lesion. Spinal transection usually abolished all cutaneous reflexes below the lesion except the digital, which was altered in pattern, lowered in threshold, and unchanged in receptive field. In some instances high threshold cutaneous reflexes were elicited from small reflexoginous zones immediately after transection (ephaptic period) and disappeared after 30–60 min. Chronic lesions of descending spinal paths resulted in spinal compensation with considerable preservation of flexor and extensor cutaneous reflexes after spinal transection. Extensive lesions of the vestibular nuclei had little effect upon cutaneous reflexes but did abolish ascending effects on proprioceptive reflexes following transection of the cord (Schiff-Sherrington phenomenon). Pontomedullary lesions abolished the ascending effects of dorsolateral lesions. Midline lesions at either medullary or medullopontine levels released cutaneous reflex activity. Animals decerebrated at a level high in the medulla displayed far more active skin reflexes than those decerebrated at midcollicular level. We concluded that descending paths inhibitory to skin reflexes arise in the reticular formation above the level of the lower medulla, probably in the medial portion of the pons and upper medulla and course down the dorsolateral funiculi, that paths mediating facilitation of these reflexes arise in nuclei of the brain stem extending into the lower medulla and run down the ventrolateral funiculi, and that ascending pathways of facilitation follow the dorsolateral funiculi.