Biomedical subjects

Evelijne M Bekker

Publications and source records attributed to Evelijne M Bekker.

4 recordsLinked to original sources

PubMed2006

Task-dependent exogenous cuing effects depend on cue modality.

Task-dependent exogenous cuing effects on reaction time in detection and discrimination tasks have been ascribed to delayed withdrawal of attention in discrimination tasks. Alternatively, these differences may be due to cue-induced response inhibition in detection tasks. Unimodal and crossmodal versions of the Posner paradigm were examined with short cue-target intervals. Targets above or below fixation required either detection or discrimination responses. Cuing effects were determined for the target-elicited P1 component and for the lateralized readiness potential (LRP). Task-dependent cuing effects on reaction time were found in the unimodal but not in the crossmodal version, but not for the P1 component. The LRP data indicated that inhibition of return in the unimodal detection task had a premotoric locus. These findings suggest that inhibition in the unimodal detection task resulted from speeded motor inhibition triggered by the visual cue.

Acoustic Stimulation↗

PubMed2005

Disentangling deficits in adults with attention-deficit/hyperactivity disorder.

CONTEXT: A lack of inhibitory control has been suggested to be the core deficit in attention-deficit/hyperactivity disorder (ADHD), especially in adults. This means that a primary deficit in inhibition mediates a cascade of secondary deficits in other executive functions, such as attention. Impaired stopping has been claimed to support the inhibition hypothesis. However, executive functions such as inhibition and attention are hard to disentangle. OBJECTIVE: To use event-related potentials in adult patients with ADHD to show that impaired stopping is associated with abnormalities of attention. DESIGN: The stop signal task was presented to 24 adults with ADHD combined subtype and 24 controls. Stop event-related potentials are distorted by overlap from event-related potentials to other stimuli in close temporal proximity, but we applied a method (Adjar level 2) to effectively remove this overlap. RESULTS: In line with an inhibitory control deficit, the stop signal reaction time was longer in adults with ADHD (F(1,46) = 7.12, P<.01) whereas there was no significant difference for go stimulus reaction time. Overlap-free stop event-related potentials revealed smaller stop P3s in adults with ADHD (F(1,44) = 4.20, P<.05). In children with ADHD, this has been interpreted to reflect deficient inhibitory control. However, controls were also found to have larger early responses in the auditory cortex (N1) when stop signals resulted in successful stops, relative to failed stops, signifying increased attention (F(1,23) = 11.88, P<.01). This difference was completely absent in adults with ADHD. CONCLUSIONS: Disturbed attentional processing of the stop signal contributed to impaired stopping in adults with ADHD. This finding may have implications for treatment.

Adolescent↗

PubMed2005

Source analysis of the N2 in a cued Go/NoGo task.

Previous source analyses of event-related potential (ERP) data elicited in Go/NoGo tasks have suggested that the anterior cingulate cortex (ACC) plays an important role in response inhibition. So far, however, source models were derived for the difference wave Go stimulus minus NoGo stimulus. This difference wave is confounded with motor- and attention-related activity. To avoid these confounds, we alternatively derived source models for NoGo stimuli only. The problem of the NoGo-N2 being superimposed on a positive deflection was addressed in two ways. First, a baseline correction was applied using the time points just preceding and succeeding the NoGo-N2. Second, a separate source model was derived at the maximum amplitude of this positive deflection. Subjects were presented with a cued version of the continuous performance task (CPT; ABX). In a second study, the probability of the Go stimulus was gradually increased to heighten subjects' tendency to respond and, as a consequence, to enhance the amplitude of the NoGo-N2. The source models of the NoGo-N2 consistently indicated bilateral dipole pairs in medial frontal regions. This is in accordance with a generator in the anterior cingulate cortex.

Adult↗

PubMed2005

The pure electrophysiology of stopping.

In the stop-signal task, subjects should withhold their response in a choice reaction time task when a stop-signal, usually a tone, is presented. Successful stops have been associated with event-related potentials (ERPs) featuring a larger frontocentral positivity relative to failed stops. The functional interpretation of this stop-P3 has been disputed, because stop-ERPs are distorted by overlap from ERPs elicited by preceding go-stimuli. We effectively removed confounding potentials with the 'adjacent response filter method (ADJAR)'. Confirming an interpretation in terms of response inhibition, the stop-P3 remained and overlap removal resulted in a more anterior distribution. As a new finding, the N1 was larger on trials with successful stops, which suggests that inhibitory performance at least partly depended on the ability to switch attention to the stop-signal. Finally, the parietal P3 tended to peak earlier for successful than for failed stops. This is in line with the Horse Race Model, which states that faster stop-processes have a higher chance of winning the race against the go-process.

Adolescent↗