Hypothalamic influences upon activity of units of the visual cortex.

Electrical stimulation of critical sites within the hypothalamus of cats elicits a well coordinated attack upon a rat.' A cat will attack a rat in preference to other objects2 and the choice of object (in some instances, the experimenter) can be determined by the site stimulated.! Vision is used by the cat in locating its target and, under certain experimental conditions, opening of the mouth prior to biting depends on vision.4 The mechanism whereby specific hypothalamic stimulation elicits such a critical use of vision is unknown. If the visual selection of attack objects, visually guided approach by a cat to a rat, and visually guided opening of the mouth prior to biting, were due to hypothalamic influences upon the visual system, then one would expect hypothalamic stimulation to modify the activity of the visual system. It has been shown that stimulation of attack sites within the hypothalamus modifies visual cortical potentials evoked by stimulation of the optic tract or optic radiations, and that the direction of the change is in the opposite direction to that induced by stimulation of the midbrain reticular formation.6 In the present study individual units of the visual cortex were examined to see if their activity was altered by stimulation of the hypothalamus. These visual units are sensitive to movement and particular shapes and orientations of the stimulus as well as to light flashes and steady lights. If the units responded to previously optimal stimuli in a different fashion during hypothalamic stimulation, the possibility that these changes were involved in the cats visually selecting a target remains open.