Ellen Seiss

The Neurophysiology of Response Competition: Motor Cortex Activation and Inhibition following Subliminal Response Priming

Some widely used tasks in cognitive neuroscience depend on the induction of a response conflict between choice alternatives, involving partial activation of the incorrect response before the correct response is emitted. Although such conflict tasks are often used to investigate frontal-lobe-based conflict-monitoring processes, it is not known how response competition evolves in the motor cortex. To investigate the dynamics of motor cortex activation during response competition, we used a subliminal priming task that induced response competition while bypassing preresponse stage processing conflict. Analyses of movement-related EEG potentials supported an interaction between competing responses characterized by reciprocal inhibition. Inhibitory interactions between response channels contribute to the resolution of response conflict. However, the reciprocal inhibition at motor cortex level seemed to operate independent of higher level conflict-monitoring processes, which were relatively insensitive to response conflict induced by subliminal priming. These results elucidate how response conflict causes interference as well as the conditions under which frontal-lobe-based interference control processes are engaged.

Proprioception-Related Evoked Potentials: Origin and Sensitivity to Movement Parameters

Reafferent electroencephalography (EEG) potentials evoked by active or passive movement are largely dependent on muscle spindle input, which projects to postrolandic sensory areas as well as the precentral motor cortex. The origin of these proprioception-related evoked potentials has previously been studied by using N20-P20 source locations of the median nerve somatosensory evoked potential as an landmark for postcentral area 3b. As this approach has yielded contradictory findings, likely due to spatial undersampling, we applied dipole source analysis on two independently collected sets of high-density EEG data, containing the proprioception-related N90 elicited by passive finger movement, and the N20-P20 elicited by median nerve stimulation. In addition, the influence of movement parameters on the N90 was explored by varying amplitude/duration and direction of passive movements. The results showed that the proprioceptive N90 component was not influenced by movement direction, but had a duration that covaried with the duration of the movement. Sources were localized in the precentral cortex, located on average 10 mm anterior to the N20-P20 sources. The latter result supports earlier claims that the motor cortex is involved in the generation of proprioception-related EEG potentials.

Executive control in the Simon task: A dual-task examination of response priming and its suppression

Executive control processes are supposed to regulate behaviour and to resolve conflicts in information processing. Recently, Stürmer and colleagues (Stürmer et al., 2002; Stürmer & Leuthold, 2003) reported electrophysiological findings in a Simon task that indicated control over a location-based processing route that mediates response priming. Importantly, when a response conflict occurred on a given trial, a suppression of response priming on the immediately following trial was demonstrated. The present study examines boundary conditions of such control in the Simon paradigm by comparing single-task with dual-task performance. In four experiments a second task, alternating trial-by-trial with the Simon task, was systematically manipulated in its control demands. Whereas reaction time (RT) analysis of single-task conditions revealed the absence of location-based response priming in the Simon task, such priming reappeared when the second task required an overt response. In contrast, working memory load as such did not touch the Simon effect. Therefore, not the response conflict itself but capacity-limited response monitoring processes seem to be critical for executive control in the Simon task and the suppression of response priming.

Does focused endogenous attention prevent attentional capture in pop‐out visual search?

To investigate whether salient visual singletons capture attention when they appear outside the current endogenous attentional focus, we measured the N2pc component as a marker of attentional capture in a visual search task where target or nontarget singletons were presented at locations previously cued as task-relevant, or in the uncued irrelevant hemifield. In two experiments, targets were either defined by color or by a combination of color and shape. The N2pc was elicited both for attended singletons and for singletons on the uncued side, demonstrating that focused endogenous attention cannot prevent attentional capture by salient unattended visual events. However, N2pc amplitudes were larger for attended and unattended singletons that shared features with the current target, suggesting that top-down task sets modulate the capacity of visual singletons to capture attention both within and outside the current attentional focus.

Effects of attentional filtering demands on preparatory ERPs elicited in a spatial cueing task

OBJECTIVE We used ERP measures to investigate how attentional filtering requirements affect preparatory attentional control and spatially selective visual processing. METHODS In a spatial cueing experiment, attentional filtering demands were manipulated by presenting task-relevant visual stimuli either in isolation (target-only task) or together with irrelevant adjacent distractors (target-plus-distractors task). ERPs were recorded in response to informative spatial precues, and in response to subsequent visual stimuli at attended and unattended locations. RESULTS The preparatory ADAN component elicited during the cue-target interval was larger and more sustained in the target-plus-distractors task, reflecting the demand of stronger attentional filtering. By contrast, two other preparatory lateralised components (EDAN and LDAP) were unaffected by the attentional filtering demand. Similar enhancements of P1 and N1 components in response to the lateral imperative visual stimuli were observed at cued versus uncued locations, regardless of filtering demand, whereas later attentional-related negativities beyond 200 ms post-stimulus were larger the target-plus-distractor task. CONCLUSIONS Our results implicate that the ADAN component is linked to preparatory top-down control processes involved in the attentional filtering of irrelevant distractors; such filtering also affects later attention-related negativities recorded after the onset of the imperative stimulus. SIGNIFICANCE ERPs can reveal effects of expected attentional filtering of irrelevant distractors on preparatory attentional control processes and spatially selective visual processing.

Cognitive Functioning and Work Success in Adults with Dyslexia

Dyslexic adults completed questionnaires designed to investigate relationships between cognitive functioning, especially executive aspects, and work success. The study was designed to determine whether quantitative support could be provided for the model of adult dyslexic success derived from the work of Gerber and his colleagues (Gerber, Ginsberg, & Reiff, 1992). A planning/metacognitive awareness scale and a cognitive failures scale were used as measures of cognitive skill. Personal success was assessed with job satisfaction and work-based self-efficacy scales, and societal success was determined by assessing the salary level, promotion in the current profession and academic qualifications. Correlational analyses indicated that people with dyslexia with higher levels of planning and metacognition reported higher levels of job satisfaction and self-efficacy. However, these measures were not related to societal success. The findings are discussed in terms of avenues for further investigation of factors leading to more positive outcomes for dyslexic individuals and ways to increase the likelihood of dyslexic adults achieving success in the workplace.

Absence of gaze direction effects on EEG measures of sensorimotor function

OBJECTIVE Gaze direction is known to modulate the activation patterns of sensorimotor areas as seen at the single cell level and in functional magnetic resonance imaging (fMRI). To determine whether such gaze direction effects can be observed in scalp-recorded electroencephalogram (EEG) measures of sensorimotor function we investigated somatosensory evoked potentials (SEPs) and steady state movement related cortical potentials (MRPs). METHODS In two separate experiments, SEPs were elicited by electrical stimulation of the median nerve (experiment 1) and steady state MRPs were induced by 2 Hz tapping paced by an auditory cue (experiment 2), while subjects directed their gaze 15 degrees to the left or to the right. RESULTS Gaze direction failed to produce any appreciable differences in the waveforms of the SEPs or MRPs. In particular, there was no effect on peak amplitude, peak latency and peak scalp topography measures of SEP and MRP components, or on spatial or temporal parameters of dipole models of the underlying cortical generators. Additional frequency domain analyses did not reveal reliable gaze-related changes in induced power at electrode sites overlying somatosensory and motor areas, or in coherence between pairs of parietal, central and frontal electrodes, across a broad range of frequencies. CONCLUSIONS EEG measures of sensorimotor function, obtained in a non-visual motor task, are insensitive to modulatory effects of gaze direction in sensorimotor areas that are observable with fMRI.

Motor Planning in Chronic Upper-Limb Hemiparesis: Evidence from Movement-Related Potentials

Background Chronic hemiplegia is a common long-term consequence of stroke, and subsequent motor recovery is often incomplete. Neurophysiological studies have focused on motor execution deficits in relatively high functioning patients. Much less is known about the influence exerted by processes related to motor preparation, particularly in patients with poor motor recovery. Methodology/Principal Findings The current study investigates motor preparation using a modified response-priming experiment in a large sample of patients (n = 50) with moderate-to-severe chronic hemiparesis. The behavioural results revealed that hemiparetic patients had an increased response-priming effect compared to controls, but that their response times were markedly slower for both hands. Patients also demonstrated significantly enhanced midline late contingent negative variation (CNV) during paretic hand preparation, despite the absence of overall group differences when compared to controls. Furthermore, increased amplitude of the midline CNV correlated with a greater response-priming effect. We propose that these changes might reflect greater anticipated effort to respond in patients, and consequently that advance cueing of motor responses may be of benefit in these individuals. We further observed significantly reduced CNV amplitudes over the lesioned hemisphere in hemiparetic patients compared to controls during non-paretic hand preparation, preparation of both hands and no hand preparation. Two potential explanations for these CNV reductions are discussed: alterations in anticipatory attention or state changes in motor processing, for example an imbalance in inter-hemispheric inhibition. Conclusions/Significance Overall, this study provides evidence that movement preparation could play a crucial role in hemiparetic motor deficits, and that advance motor cueing may be of benefit in future therapeutic interventions. In addition, it demonstrates the importance of monitoring both the non-paretic and paretic hand after stroke and during therapeutic intervention.

Monitoring long-term effects of mild traumatic brain injury with magnetic resonance spectroscopy: a pilot study.

This pilot study explores the metabolic changes associated with persistent postconcussion syndrome (PCS) after mild traumatic brain injury (mTBI; >12 months after injury) using magnetic resonance spectroscopy. We hypothesized that those mTBI participants with PCS will have larger metabolic differences than those without. Data were collected from mTBI participants with PCS, mTBI participants without PCS and non-head-injured participants (all groups: n=8). Magnetic resonance spectroscopy metabolite profiles within the dorsolateral prefrontal cortex showed a reduced creatine/choline ratio in mTBI patients compared with control participants. This data provides initial evidence for residual metabolic changes in chronic mTBI patients, but there was no conclusive relationship between these metabolic changes and PCS symptom report. Creatine is involved in maintaining energy levels in cells with high or fluctuating energy demand, suggesting that there may be some residual energy impairment in chronic mTBI.

Movement-related changes in cortical excitability: a steady-state SEP approach.

This study explored the use of steady-state somatosensory evoked potentials (ssSEPs) as a continuous probe on the excitability of the somatosensory cortex during the foreperiod and the response time of a cued choice reaction time task. ssSEPs were elicited by electrical median nerve stimulation at the left and right wrist, using a stimulation frequency of 22.2 Hz. Scalp-recorded ssSEPs were analysed by means of dipole source analysis to achieve optimal separation of left and right hemisphere ssSEPs. The time course of ssSEP modulation at the source level was extracted by means of a wavelet transform. In addition to the extraction of ssSEPs, the analysis included the derivation of lateralized attention and movement-related potentials, i.e. the attention-directing anterior negativity (ADAN) and the lateralized readiness potential (LRP). The results revealed a time course of ssSEP modulation remarkably similar to the time course of ADAN and LRP. The time course was characterized by a reduction of ssSEP amplitude at latencies just following the peak latency of the ADAN (approximately 400 ms) and the peak latency of the LRP (approximately 1200 ms). This reduction was greater for contralateral than for ipsilateral movements. The study demonstrates that ssSEP methodology represents a feasible approach to the measurement of movement-related changes in cortical excitability, which may be used to resolve ambiguities in the interpretation of lateralized event-related brain potentials.