Effect of muscarinic blockade on the speed of attention shifting and learning

The study aimed to investigate to what extent blockade of muscarinic receptors affects the speed of endogenous versus exogenous attentional shift times, and how it affects learning induced improvements of attention shift times. Subjects viewed an array of 10 moving clocks and reported the time a clock indicated when cued. Target clocks were indicated by peripheral or central cues, including conditions of pre-cuing. This allowed assessing shift times when attention was pre-allocated, when peripheral cues triggered exogenous attention shifts, and when central cues triggered endogenous attention shifts. In study 1, each subject participated in 2 sessions (scopolamine/placebo), whereby the order of drug intake was counterbalanced across subjects, and subjects were blinded to conditions. Scopolamine/placebo was administered before a psychophysical experiment was conducted. In study 2, the effect of muscarinic blockade on learning induced improvements of attention shift times was investigated. Here scopolamine/placebo was administered immediately after the first (of two) psychophysical sessions, whereby a given subject either received scopolamine or placebo pills. Confirming previous results, we show that pre-cuing resulted in the fastest shift times, followed by exogenous cuing, with endogenous attentional shifts being slowest. Scopolamine application increased attentional shift times across all 3 conditions compared to placebo, but in a dose dependent manner. Additionally, blockade of muscarinic receptors immediately after the first session reduced learning dependent improvement of attention shift times. These results demonstrate that muscarinic receptors play an important role in attention shifting, and they contribute to learning of attention shifting.