EFFECTS OF SCOPOLAMINE ON DISCRIMINATED RESPONDING IN THE RAT

¹ Walter Reed Army Institute of Research, Washington, D. C.

Thirsty rats were trained to make a different lever response to each of two auditory stimuli in order to obtain a water reward. Periods of silence intervened between stimulus presentations and no lever responses were rewarded during these silent periods. Scopolamine in doses of from 0.2 mg/kg up to 1.0 mg/kg was administered before the start of selected sessions to test its effects on discriminated responding. The administration of scopolamine for all subjects resulted in a) an increase in the number of incorrect responses to the stimuli, b) a large increase in the number of lever-presses in the silent periods, and c) an increased tendency for subjects to make successive responses on the same lever rather than to alternate responses between the two levers.

When lever-responses were no longer reinforced with water, and scopolamine administered before each of these extinction sessions, a relatively high rate of responding persisted even after 40 such extinction sessions. This persistence of response did not continue, however, when responses on the preferred lever were punished with an aversive electric shock.

Some other experimental procedures were briefly summarized which investigated further the decreased tendency for animals to alternate lever-responses under scopolamine.