Organization of some brainstem and limbic connections of the hypothalamus

Electrophysiological and anatomical studies allow the formulation of some features of organization of the lateral hypothalamus: (1) The HVM is the major source of modulatory inpur to the lateral hypothalamus; (2) There is a high degree of convergence of afferent paths in the lateral hypothalamus resulting in the same type of postsynaptic firing pattern, whether it be inhibition or excitation; (3) The response to afferent activation is usually quite simple, consisting of either a brief excitatory period or a fifty to several hundred millisecond inhibition. Complex firing patterns in a response to afferent stimulation are rare; (4) Descending hypothalamic output activates two classes of neurons in the midbrain; (a) an output with a strong synaptic drive acting upon cells which are not spontaneously active and which do not respond to arousing stimuli, and (b) an output with moderate to weak synaptic drive acting upon cells that are spontaneously active and excited by peripheral arousing stimuli.