It is well known that anti-histamines have significant CNS side effects such as sleepiness and impaired psychomotor performance, which might induce traffic accidents. There are some reports about the effects of anti-histamines on a car driving performance, but the mechanism has not been understood yet. We examined the changes of the regional cerebral blood flow (rCBF) during a simulated car driving after oral administration of sedative anti-histamine by positron emission tomography (PET). Right-handed, healthy male volunteers (n=7, age 20-25 y. o. ) performed a car driving on a simulated game after oral administration of d-chlorpheniramine (6mg) and placebo. Their rCBF was examined during 1) rest with closed eye, 2) playing a game (active driving) by PET with H2 15O. After oral administration of placebo, the significant increase of rCBF was found in the occipital lobe (Brodmann Area 17, 18, 19), parietal lobe (BA 7) and cerebellum during active driving compared with the resting condition(p<0. 001). Compared to placebo, d- chlorpheniramine produced the significant increase of rCBF in the frontal lobe (BA 6, 8, 9, 11) and temporal lobe (BA 21) during active driving(p<0. 005). It suggests that more attention to visual perception, decision and sensori- motor control is needed after administration of anti- histamines than placebo
