Pre- and postnatal lead-exposure in monkeys: effects on activity and learning set formation.

Rhesus monkeys were pre- and postnatally exposed to 0, 350, or 600 ppm lead acetate in the diet. Blood lead levels of the mothers were less than 1, 24.4, and 37.4 micrograms/100 g blood, respectively, while those of the offspring were substantially higher, at least in the early stages of development. At the age of 12-15 months the animals were tested for group activity levels in an unfamiliar environment. No substantial lead-related alterations of activity occurred neither for group activity nor for the activity of individual animals. There were, however significant dose-related impairments of pattern discrimination learning set formation, while in simple discrimination learning during the early training phases deficits were seen in the high lead group only. Emotional alterations of these animals may account for this result, whereas true cognitive deficits are likely to underly the impairment of learning set formation seen in the low lead group. It is concluded that the effects of lead in cognitive tasks are not secondary to changes of general activity level.