Learning in Monkeys Exposed Perinatally to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

TCDD is an extremely toxic chemical pollutant which bioaccumulates in maternal adipose tissue, and is transferred to the developing organism during gestation and lactation. Long-term cognitive deficits have been reported following perinatal exposure to polychlorinated biphenyls, which are structurally and toxicologically similar to TCDD. In the current study, monkeys exposed to TCDD perinatally were later tested in two cognitive paradigms, discrimination-reversal learning (RL) and delayed spatial alternation (DSA). RL detected effects; whereas DSA, as analyzed, did not. RL consisted of a series of simple spatial reversals, followed by spatial reversals with color and shape as irrelevant cues, then by color reversals and finally by shape reversals. TCDD-exposed monkeys exhibited retarded learning of the shape reversals. The deficit was most pronounced on the first reversal following overtraining. There were no group differences on the spatial or color reversals. However, the number of trials the TCDD-exposed monkeys individually took to learn the spatial reversals was positively correlated with TCDD concentration in body fat. Conversely, the number of trials they took to learn the color reversals was negatively correlated with TCDD in body fat.