Behavioral effects of cyclic dosing with methylmercury in pigeons.

The present experiments examined the effects of cyclic dosing with methylmercury (MeHg) on some psychological functions in pigeons. A delayed sequence discrimination task involving order competency and a feeding task involving perceptual motor skill were tested in pigeons dosed with 2.0 mg/kg, 0.5 mg/kg, or no MeHg (the control group) during cycles of brief daily MeHg exposure and extended behavioral testing. Performance in the sequence discrimination and the feeding task was affected after a cumulative dose of only 20 mg/kg in the 2.0 mg/kg group. Sequence discrimination recovered within three months after dosing when MeHg was stopped, but feeding skill did not recover over the remainder of the experiment (about 4 1/2 months later). A cumulative dose of 86 mg/kg in the 0.5 mg/kg group had no observable effect on either task.