Effects of parachlorophenylalanine and amphetamine on habituation of orienting.

Parachlorophenylalanine significantly reduced the orienting response to the first presentation of a tone but did not alter the size of responses to subsequent tone presentations nor the rate of habituation. In contrast amphetamine did not alter the orienting response but significantly impaired habituation. It was concluded that there was little evidence for a serotonergic involvement in behavioral habituation, although a role for the catecholamine system could not be excluded.