Nicotinic antagonist effects on functional attention networks.

Cholinergic neurotransmission has been implicated in memory and attention. We investigated the effect of the non-competitive nicotinic antagonist mecamylamine on three components of attention processes (i.e. alerting, orienting and executive control) in 12 healthy male subjects whilst performing the Attention Network Task (ANT) in a magnetic resonance imaging (MRI) scanner. Participants received 15 mg mecamylamine in a single blind and placebo- controlled randomized procedure 90 min prior to obtaining functional MRI data. Our results confirm previous reports of beneficial effects of cueing (alerting and orienting) and detrimental effects of conflict (executive control) on reaction times when performing the ANT. The functional MRI data confirmed distinct neural networks associated with each of the three attention components. Alerting was associated with increased left temporal lobe activation while orienting increased bilateral prefrontal, right precuneus and left caudate activation. Executive control activated anterior cingulate and precuneus. Mecamylamine slowed overall response time and down-regulated brain activation associated with orienting and to some extent brain activation associated with executive control when compared to placebo. These findings are consistent with nicotinic modulation of orienting attention by cueing and executive control when responding to conflicting information. The latter nicotine antagonist effect may be mediated via cholinergic modulation of dopamine neurotransmission in mesolimbic pathways.