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Pood-deprived neonatal rats actively ingest milk that is infused into their mouths through intraoral cannulas. This ingestion is accompanied by behavioral activation. The involvement of various brain regions in ingestion and activation was examined by making transections along the neuraxis from ;the olfactory bulbs to the anterior pons in 2-day-old rats. Following a 24-hr deprivation period, a series of oral milk infusions was given, and milk intake and activity were measured. Intake was severely reduced only in animals with diencephalic transections. Cuts in front of or behind the diencephalon resulted in normal or slightly decreased intake. In contrast, activity tended to decline as the level of the transection became more caudal. Thus ingestion and its accompanying behavioral activation could be separated neuroanatomically. These results suggest that two brain mechanisms are involved in the ingestive response of the infant rat, one in the diencephalon and another caudal to the mesencephalon. However, behavioral activation appears less discretely organized, involving most of the neuraxis.

Electrical stimulation of the brain is an effective reinforcer in simple learning situations when trials are separated by as much as 15 min. In this experiment 13 rats with electrodes in lateral hypothalamus were trained on a position discrimination with trials separated by 24 hr., and subsequently on reversal problems. 11 Ss learned the original discrimination; 6 of 10 /Ss tested completed 1 reversal; and all 6 tested Ss completed a 2nd reversal. 1 S was tested further and completed 7 reversals. Clearly, in the successful cases, reinforcing properties of electrical stimulation were sufficient to induce learning of a discrimination problem even though trials were separated by 24 hr.

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