[Activity of hypothalamic neurons during elaboration of a defensive conditioned reflex].

During elaboration of conditioned defensive reflex to combinations of acoustic and electro-cutaneous stimuli in alert rabbits 44% out of 86 neurones in the ventromedial nucleus and 42% out of 40 cells in the perifornical nucleus of the hypothalamus elaborated conditioned responses. 71% of ventromedial neurones and 53% of perifornical cells (out of those that were conditioned) showed inhibitory responses while the rest demonstrated an activation. In half of the neurones that showed conditioned responses it was possible to elaborate differentiation and extinctive inhibition. Significant conditioned responses appeared following 20-30 pairings of sound and electro-cutaneous stimulation. Their extinction took place after 10-20 non-reinforcements. A correlation was found between conditioned activity of neurones in the ventromedial nucleus groups and changes in heart-rate. Different roles of lateral and medial nuclear groups of the hypothalamus in conditioning were shown. This may point to their participation, along with other brain structures, in the formation of respectively vegetative and motor components of the integrative behaviour.