Scopolamine Reduces Electrophysiological Indices of Distractor Suppression: Evidence from a Contingent Capture Task.

Limited resources for the in-depth processing of external stimuli make it necessary to select only relevant information from our surroundings and to ignore irrelevant stimuli. Attentional mechanisms facilitate this selection via top-down modulation of stimulus representations in the brain. Previous research has indicated that acetylcholine (ACh) modulates this influence of attention on stimulus processing. However, the role of muscarinic receptors as well as the specific mechanism of cholinergic modulation remains unclear. Here we investigated the influence of ACh on feature-based, top-down control of stimulus processing via muscarinic receptors by using a contingent capture paradigm which specifically tests attentional shifts toward uninformative cue stimuli which display one of the target defining features In a double-blind, placebo controlled study we measured the impact of the muscarinic receptor antagonist scopolamine on behavioral and electrophysiological measures of contingent attentional capture. The results demonstrated all the signs of functional contingent capture, i.e., attentional shifts toward cued locations reflected in increased amplitudes of N1 and N2Pc components, under placebo conditions. However, scopolamine did not affect behavioral or electrophysiological measures of contingent capture. Instead, scopolamine reduced the amplitude of the distractor-evoked Pd component which has recently been associated with active suppression of irrelevant distractor information. The findings suggest a general cholinergic modulation of top-down control during distractor processing.

Prism Adaptation Alters Electrophysiological Markers of Attentional Processes in the Healthy Brain.

Neglect patients typically show a rightward attentional orienting bias and a strong disengagement deficit, such that they are especially slow in responding to left-sided targets after right-sided cues (Posner et al., 1984). Prism adaptation (PA) can reduce diverse debilitating neglect symptoms and it has been hypothesized that PA's effects are so generalized that they might be mediated by attentional mechanisms (Pisella et al., 2006; Redding and Wallace, 2006). In neglect patients, performance on spatial attention tasks improves after rightward-deviating PA (Jacquin-Courtois et al., 2013). In contrast, in healthy subjects, although there is evidence that leftward-deviating PA induces neglect-like performance on some visuospatial tasks, behavioral studies of spatial attention tasks have mostly yielded negative results (Morris et al., 2004; Bultitude et al., 2013). We hypothesized that these negative behavioral findings might reflect the limitations of behavioral measures in healthy subjects. Here we exploited the sensitivity of event-related potentials to test the hypothesis that electrophysiological markers of attentional processes in the healthy human brain are affected by PA. Leftward-deviating PA generated asymmetries in attentional orienting (reflected in the cue-locked N1) and in attentional disengagement for invalidly cued left targets (reflected in the target-locked P1). This is the first electrophysiological demonstration that leftward-deviating PA in healthy subjects mimics attentional patterns typically seen in neglect patients. Significance statement: Prism adaptation (PA) is a promising tool for ameliorating many deficits in neglect patients and inducing neglect-like behavior in healthy subjects. The mechanisms underlying PA's effects are poorly understood but one hypothesis suggests that it acts by modulating attention. To date, however, there has been no successful demonstration of attentional modulation in healthy subjects. We provide the first electrophysiological evidence that PA acts on attention in healthy subjects by mimicking the attentional pattern typically reported in neglect patients: both a rightward attentional orienting bias (reflected in the cue-locked N1) and a deficit in attentional disengagement from the right hemispace (reflected in the target-locked P1). This study makes an important contribution to refining current models of the mechanisms underlying PA's cognitive effects.

Cortical processing of head- and eye-gaze cues guiding joint social attention.

Previous fMRI experiments showed an involvement of the STS in the processing of eye-gaze direction in joint attention. Since head-gaze direction can also be used for the assessment of another person's attentional focus, we compared the mechanisms underlying the processing of head- and eye-gaze direction using a combined psychophysical and fMRI approach. Subjects actively followed the head- or eye-gaze direction of a person in a photograph towards one of seven possible targets by moving their eyes. We showed that the right posterior superior temporal sulcus (STS) as well as the right fusiform gyrus (FSG) were involved in both processing of head- as well as eye-gaze direction. Another finding was a bilateral deactivation of a distinct area in the middle STS (mSTS) as well as the left anterior STS (aSTS), that was stronger when subjects followed eye-gaze direction than when they followed head-gaze direction. We assume that this deactivation is based on an active suppression of information arising from the distracting other directional cue, i.e. head-gaze direction in the eye-gaze direction task and eye-gaze direction in the head-gaze direction task. These results further support the hypothesis that the human equivalent of the gaze sensitive area in monkeys lies in more anterior parts of the STS than previously thought.