Effect of internal and external cues on the heart rate of the rat.

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Abstract
The HR [ heart rate] of rats placed in a Skinner box where they press on a bar for water reinforcement increased linearly with length of pretrial water deprivation. The HR recorded in the same rats while they remained in their living cages 2 hours before being placed in the Skinner box showed a lower but parallel increase related to duration of deprivation. However the HR recorded in similar conditions on a 2nd group of rats who were never placed in the bar-pressing situation was much lower and showed no increase with the prolongation of water deprivation. These variations in HR are interpreted as an activation effect depending on the interaction between an internal state of deprivation and the related meaning of external cues.