Assessing the aversiveness of intracranial stimulation.

A comparison was made between rats' performance to escape intracranial stimulation in a shuttle-box, two-lever box and a single-lever Sidman avoidance situation. The former two tasks also provided concurrent rate-independent measures of the rewarding properties of ICS. The rate-independent measures of aversion (latency to escape ICS) obtained in the shuttle-box and two-lever task were significantly correlated with each other but were not significantly correlated with the lever-press rates on Sidman avoidance. A number of animals that would not lever-press to initiate ICS would perform the locomotor response very vigorously to initiate the same ICS suggesting that even rate-independent lever-press measures may not accurately reflect the motivational characteristics of ICS. These data are discussed in the context of the problem as to why animals escape rewarding ICS and it is suggested that the escape behaviour is an independent phenomenon which merits further study in its own right.