Since emotional reactions in the higher vertebrates depend on individual experience and are aroused in man, in addition, by complex symbols, one would expect that the hypothalamus could be excited from the cortex. In experiments with topical application of strychnine on the cerebral cortex, the transmission of impulses from the cortex to the hypothalamus was demonstrated. Moreover, the responsiveness of the hypothalamus to nociceptive stimulation is greatly increased under these conditions. Even more complex and obviously cortically induced forms of emotional arousal could be elicited in monkey A on seeing monkey B (but not a rabbit) in emotional stress. A previously extinguished conditioned reaction was restored in monkey A and was associated with typical signs of emotional excitement including sympathetic discharges.

It seems to follow that by and large an antagonism exists between the paleo -- and the neocortex as far as emotional reactivity is concerned, and that the balance between the two systems determines the emotional responsiveness of the organism. In addition, the neocortical hypothalamic relations play a great role in primates, as Mirsky's interesting experiment on the ``communication of affect'' demonstrates. But even in relatively primitive laboratory animals such as the rat, sex activity closely identified with the hypothalamus and the visceral brain is enhanced by the neocortex. MacLean stressed correctly the importance of the visceral brain for preservation of the individual and the species, as evidenced by the influence of the limbic brain (including the hypothalamus) on emotions related to fight and flight and also on sexual functions. It should be added that in man neocortical hypothalamic interrelations probably play a role in the fusion of emotional processes with those underlying perception, memory, imagination, and creativity.