Effects of chronic lead exposure on learning and reaction time in a visualdiscrimination task

Long-Evans rats exposed chronically to lead (Pb) acetate (0, 75, or 300 ppm ) were tested as adults on an automated, three-choice visual discrimination task as parr of a larger study designed to elucidate the cognitive effects of developmental Pb exposure. Median adult BPb levels for the groups were <5, 20, and 36 mu g/dl. The pattern of results suggested a linear effect, w ith increasing lead dose producing progressively slower learning and an inc reased incidence of "impaired" individuals. This latter measure proved to b e slightly more sensitive than the former, suggesting individual difference s in susceptibility to ph neurotoxicity. Additional analyses revealed that the impairing effect of Pb was seen in both the chance and post-chance lear ning phases, indicating that the: deficit was not Limited to (but could inc lude) attentional function. Reaction time on incorrect trials was reduced i n the 300-ppm group. whereas no Pb effect was seen for correct trials. The present findings suggest that chronic developmental Pb exposure produces an associative deficit as well as a tendency to respond rapidly, but does not affect information-processing speed. (C) 2000 Elsevier Science Inc. All ri ghts reserved.