Chronic low-level lead exposure in monkeys does not affect simple reaction time

Simple visual reaction time was measured in a group of adult monkeys (Macaca fascicularis) dosed continuously with lead from birth onward, and in matched controls. Blood lead concentrations had been stable for 6 years at 33 micrograms/dl at the time of testing. The monkey was required to make contact with a stainless steel bar to initiate a trial, and release it at the onset of a visual cue. Delays between one and 13 sec were interposed between the initiation of the trial and the onset of the cue light in a semi-random manner over the course of each session. Reaction times did not differ between groups. Reinforcement was then made contingent upon progressively shorter reaction times until performance deteriorated to a specified level. Treated monkeys were able to respond as rapidly as controls. Simple reaction time proved insensitive to impairment by lead exposure, in contrast to other measures of performance tested in this group of monkeys.