Scopolamine effects on rCBF during human eyeblink conditioning

The purpose of this study was to examine the effects of the anticholinergic scopolamine on regional cerebral blood flow (rCBF) during classical conditioning of the human eyeblink response, a simple form of learning and memory. In ten healthy young female research volunteers (mean age = 26.7 ± 0.9 years S.E.M.), a 0.4 mg scopolamine dose was administered intravenously one hour before rCBF was measured with H215O positron emission tomography. Scans were obtained during unpaired (control) and paired (conditioning) presentations of a binaural tone (conditioned stimulus) and an airpuff (unconditioned stimulus) to the right eye. The control conditions consisted of explicitly unpaired presentations of the tone and airpuff before (control) and after (extinction) pairings of tone and airpuff. As expected, scopolamine impaired the acquisition of the eyeblink response compared to untreated subjects. Regions that showed significant relative increases in rCBF during classical conditioning included the lateral occipital cortex bilaterally, the right anterior and posterior cingulate, and the right cerebellum. Regions that showed significant relative decreases in rCBF during classical conditioning included the thalamus, the left putamen, and the left cerebellar cortex, replicating in part our previous findings in unmedicated young subjects. Interestingly, areas of the cerebral cortex, (e.g., the auditory cortex) were not activated in the present study, as they were in the prior study. These findings may be attributable to the effect of scopolamine.