EFFECTS OF CHRONIC HALOPERIDOL ON REACTION-TIME AND ERRORS IN A SUSTAINED ATTENTION TASK - PARTIAL REVERSAL BY ANTICHOLINERGICS AND BY AMPHETAMINE

The attentional and motor-disruptive effects of low doses of haloperid ol were studied in a sustained attention task performed by rats. Five separate groups (n = 7 or 8) of rats were trained to react to a 0.125- sec visual stimulus by executing a nose-poke response within 3 sec of stimulus presentation. Each group of rats received its own dose (0.0, 0.02, 0.04, 0.08 or 0.12 mg/kg) of haloperidol daily for 3 months, and from the 1st week onward dose-effects on reaction time were quite sta ble across time. Haloperidol treatment disrupted the sustained attenti on task performance by decreasing the number of behavior-initiated sti mulus presentations, decreasing the number of reinforcers earned, incr easing the proportion of errors of omission and increasing reaction ti me to the target stimulus. Testing of challenge drugs began after 23 d ays of haloperidol treatment. Scopolamine (0.1 and 0.2 mg/kg), benztro pine (1.0, 3.0 and 6.0 mg/kg) and d-amphetamine (0.25, 0.5, 1.0 and 2, 0 mg/kg) ameliorated haloperidol-induced reaction time slowing, wherea s only benztropine and amphetamine lessened haloperidol-induced errors of omission. The 2,0-mg/kg dose of amphetamine by itself produced a s ignificant increase in errors of omission without affecting reaction t ime. Haloperidol effectively normalized this amphetamine-induced disru ption in attention, The results are consistent with a dopaminergic inv olvement in the expression of both attention and motor processes.