Donald C. Goodman

Functional localization in the cerebellum of the albino rat

Abstract In thirty-seven intact, unanesthetized albino rats, thirty-nine points in cortex and subjacent white matter of the cerebellum were stimulated (60-cycle sinewave) by means of permanently implanted electrodes. Stimulus strengths of 0.05 to 0.25 ma evoked slow, tonic movements which were chiefly bilateral and reciprocal in nature. Stimulation of the vermis on either side of the mid-line from central lobule caudally to nodulus elicited limb responses of ipsilateral flexion and adduction and contralateral extension and abduction (vermal-zone postural pattern). From the paravermal area (2 mm wide, longitudinal zone adjacent to vermis), a limb posture was evoked which was a mirror-image of that obtained from the vermis (paravermal-zone postural pattern). Limb movements following stimulation of hemispherical cortex lateral to the paravermal area were in general similar to those responses obtained from the vermis (lateralzone postural pattern). Therefore, the present experiment supports the longitudinal corticonuclear zone theory of cerebellar function. Nevertheless, there are differences between the responses obtained in the rat and those reported in the literature on other mammals. These differences concern chiefly the consistent inclusion of the contralateral limbs in the postures evoked from the paravermal and lateral cortical zones of the rat cerebellum. The theory is suggested and discussed that bilateral and reciprocal control of posture by the cerebellar hemispheric cortex is phylogenetically an old organization of cerebellar function and that the regulation of ipsilateral movements by the hemispheric cortex of the cerebellum represents a more recent specialization of cerebellar function.

Retinofugal projections of Caiman sklerops

Abstract The retinofugal projections of the South American alligator, Caiman sklerops , were traced utilizing the Nauta-Gygax method. The results of this study confirm earlier work on the alligator which described direct retinal connections to the lateral geniculate nucleus of the thalamus, the nucleus lentiformis mesencephali of the pretectum and the optic tectum and basal optic nucleus of the midbrain. Contrary to observations in the literature, projections to the dorsolateral anterior nucleus of the thalamus and posterior dorsal nucleus of the pretectal region were not observed. The present study described for the first time in this species: an uncrossed optic tract component to the lateral geniculate body and the optic tectum; a small bundle of decussated optic tract fibers which recrosses in the posterior commissure and appears to terminate in the ipsilateral pretectal region; and contralateral connections to the nucleus geniculatus pretectalis. No direct retinohypothalamic connections were observed. The retinofugal projections were compared with those described for other reptilian species (turtle, lizard and snake) examined with modern experimental methods. Similarities and differences were consistent with the taxonomic classifications represented by these four reptilian species at the subclass and superorder levels. A pattern of retinofugal projections common among nonmammalian vertebrate species is discussed. A possible relationship in the cayman of the newly described uncrossed retinotectal connections to binocular vision is suggested.

Motor functions and their anatomical basis in the forebrain and tectum of the alligator

Abstract Loci in the forebrain and optic tectum of unanesthetized and unrestrained South American alligators, Caiman sklerops , were stimulated by means of permanently implanted electrodes. Stimuli of 0.20–0.60 mamp applied to the dorsolateral portion of the corpus striatum initiated ipsilateral locomotory movements that were flexible in nature; i.e., modifiable by external environmental situations. They were coordinated and occurred after a latent period of 1–5 sec. Stimulation of the dorsal pallium caused no overt motor responses. Nevertheless, some of the experiments suggested that the dorsal pallium may exert an influence on motor function and that this influence is probably limited to a class of responses associated with the head region. Stimulation of the lateral portion of the optic tectum produced ipsilateral circling movements, whereas stimulation of the medial tectal region caused circling in the contralateral direction. Stimulation at midline regions evoked a forward progression. The locomotory responses evoked from the optic tectum occurred immediately after the application of the stimulus. The observed movements were rigid and stereotyped in character and were not modified by nuances in the external environment. These data do not support the commonly held idea that the optic tectum, with its stereotyped responses, plays a dominant role in reptilian behavior.