Fourteen monkeys were given on different days 10 mg. of methyl-phenidate (Ritalin) and 5 mg. of amphetamine.
The day and night activity of eight was recorded by means of a special cage. Of these eight, three had a bilateral leucotomy and five were intact.
Both drugs caused a decrease in daytime locomotion, but a marked increase in small tic-like movements and fidgeting. The effect of amphetamine was the more marked and prolonged.
Methyl-phenidate in contrast to amphetamine had no effect on the sleep pattern of any of the monkeys.
A double dose (20 mg.) of methyl-phenidate given to two intact and two leucotomized monkeys failed in both cases to produce the same effects as amphetamine.
Histological studies of the brains of the leucotomized monkeys showed that pathways from the frontal lobe to the dorso-medial nucleus of the thalamus and in the reverse direction had been interrupted in addition to pathways from the orbital area of the frontal lobe and the globus pallidus to the posterior hypothalamus.
The increase in locomotion after leucotomy is probably due to the interruption of these pathways, particularly those to the hypothalamus.
The effect of the drugs on both the intact and operated monkeys would indicate the posterior hypothalamus as a possible “target area”.
It is suggested that testing the effects of drugs on primate behaviour can supply information useful in psychiatry.