Temporal processing of intervals in the range of seconds or more is cogniti
vely mediated, whereas processing of brief durations below 500 msec appears
to be based on brain mechanisms outside cognitive control. To elucidate th
e critical role of various neurotransmitters in timing processes in humans,
the effects of 3 mg of haloperidol, a dopamine receptor antagonist, 11 mg
of the benzodiazepine midazolam, and 1 mg of scopolamine, a cholinergic rec
eptor antagonist, were compared in a placebo-controlled double-blind experi
ment. In addition, changes in cortical arousal, semantic memory, and cognit
ive and motor skill acquisition were assessed. Temporal processing of long
durations was significantly impaired by haloperiodol and midazolam, whereas
processing of extremely brief intervals was only affected by haloperidol.
The overall pattern of results supports the notion that temporal processing
of longer intervals is mediated by working-memory functions and, therefore
, any pharmacological treatment, irrespective of the neurotransmitter syste
m involved, that produces a deterioration of working memory, may interfere
with temporal processing of longer intervals. Temporal processing of interv
als in the range of milliseconds appears to depend on the effective level o
f dopaminergic activity in the basal ganglia.