Dissertation Abstract

An Anatomical and Physiological Investigation of Lateral Hypothalamic Enhancement of Visuo-Motor Responses in Cats

The results of brain stimulation and lesion studies have demonstrated that the lateral hypothalamus plays a role in the neural processes underlying sensory attention. The present experiments were undertaken to help define the role of the lateral hypothalamus in directing visual attention and to elucidate neuroanatomical substrates for lateral hypothalamic interaction with visual-attentive processes.

Stimulation of behaviorally-identified sites in the lateral hypothalamus of cats enhanced visuo-motor responses to previously ineffective visual stimuli. The introduction of a moving visual target into the contralateral, but not ipsilateral, visual hemifield of a hypothalamically-aroused cat produced an immediate orienting response, persistent smooth-pursuit visual-tracking, and facial-following movements.

Recordings of eye-movement frequency during optokinetic stimulation revealed that concurrent lateral hypothalamic excitation enhanced the efficiency of visual following over a wide range of stimulus velocities. Furthermore, the lateral hypothalamic arousal reversed habituation seen after repeated optokinetic stimulation.

Several cortical and subcortical areas have been implicated in the control of visual attention and eye movements. One area which could mediate lateral hypothalamic enhancement of visuo-motor responses is the pulvinar-lateral posterior complex. Following injections of either horseradish peroxidase-in-solution or crystalline-horseradish peroxidase into the pulvinar-lateral posterior complex, retrogradely-labelled cells were found in four separate areas of the hypothalamus: the dorsal hypothalamus, ventromedial-perifornical hypothalamus, and two distinct subnuclei within the posterior lateral hypothalamus.

Crystalline-horseradish peroxidase implants placed in the posterior-lateral hypothalamic areas which project to the pulvinar-lateral posterior complex revealed afferents from several visual areas: the anterior and middle suprasylvian gyri, the pretectal nuclei, the superior colliculus, and the medial terminal nucleus.

These data support the hypothesis that the lateral hypothalamus directs behavioral responses, in part, by regulating the utilization of sensory information relevant to the orientation to and capture of prey.

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