Effects of the cholinergic agonist nicotine on reorienting of visual spatial attention and top-down attentional control.

The cholinergic agonist nicotine facilitates detection of invalidly cued trials in location-cueing paradigms and reduces the associated neural activity in human inferior parietal cortex. By using functional magnetic resonance imaging we test the hypothesis that the nicotinic modulation of attentional reorienting may result from reduced use of top-down information derived from prior cues. In a within subjects design non-smoking volunteers were given either placebo or nicotine (Nicorette 2 mg gum) prior to performing a cued target discrimination task. Attention was either validly (80%) or invalidly (20%) cued to the right or left visual hemifield. The difference in reaction times to invalidly and validly cued targets is termed the 'validity effect' and indicates the costs for attentional reorienting. Nicotine reduced the validity effect and reorienting-related neural activity in right inferior parietal cortex. Further regions consistently modulated in their activity by nicotine were the right middle temporal gyrus, left middle frontal gyrus, left parahippocampal gyrus and right cerebellum. The effects of nicotine upon top-down modulation were investigated by comparing occipital activity when attending to the right vs. left visual hemifield under placebo and nicotine. If nicotine reduced the use of top-down information attentional modulation in occipital cortex should be smaller under nicotine as compared with placebo. Even though an attention-related modulation of neural activity was observed in the fusiform and middle occipital gyrus we found no evidence for differences in attentional modulation under placebo and nicotine. Our data support a role of nicotinic cholinergic receptors in facilitating several subcomponents of attentional reorienting via modulation of right inferior parietal, temporal and frontal brain activity. In contrast, the findings in the occipital cortex do not support the hypothesis that the effects of nicotine on attentional reorienting are due to reduced reliance on top-down information derived from prior cues.