Biomedical subjects

Holger Wiese

Publications and source records attributed to Holger Wiese.

12 recordsLinked to original sources

PubMed2006

Frontal positivity discriminates true from false recognition.

Lesion studies have indicated a presumably recollection-based involvement of the prefrontal cortex in the discrimination of true and false recognition. ERP studies of word list recognition, on the other hand, generally did not yield such effects in the time range associated with recollection processes which might relate to variables like study-test shifts of context. The present study aimed to further explore ERP correlates of true and false recognition, using an experimental procedure which emphasized recollection of item-specific information. Young healthy subjects performed a word recognition task, in which items previously presented (targets), semantically related distractors (lures), and unrelated new items (distractors) had to be classified as old or new followed by a remember/know judgment for old items. Items were presented visually during both study and test. Correct old responses to targets elicited significantly more pronounced positive waveforms in comparison to correct rejections of distractors (old/new effect) between 400 and 700 ms after stimulus onset at all left and central electrode positions. A significant old/new effect for false alarms to lures was observed only at the left parietal electrode. ERPs associated with hits and false alarms to lures were similar at parietal but differed at frontal electrode positions. This pattern of results suggests a differential processing of true and false recognition in frontal and posterior brain regions when item-specific recollection is facilitated. Our findings support the assumption of monitoring processes in parallel to the recollection of item-specific information in recognition memory, which might become affected by illusory sensory information generated by posterior areas.

Adult↗

PubMed2005

Self-initiated movements in chronic prefrontal traumatic brain injury: an event-related functional MRI study.

Electrophysiological studies found traumatic lesions of the prefrontal cortex (PFC) to affect the preparation of self-initiated movements. However, a precise localization of the observed effects has not been reported yet. Moreover, previous reports did not account for effects of lesion location. Therefore, the present study utilized functional MRI to investigate the influence of predominantly left or right hemispheric PFC lesions on movement preparation in chronic traumatic brain injury (TBI) patients. 18 TBI patients with MRI-defined contusions of the PFC as well as 18 healthy control subjects matched for age and gender were examined. Patients were divided into subgroups of predominantly left or right hemispheric lesions. During functional image acquisition, subjects performed self-initiated abductions of their right index finger. Neuropsychological tests of attention and working memory, which are supposed to modulate preparatory processes, were conducted. Patients with predominantly left contusions demonstrated enhanced activity of the dorsal lateral premotor cortex in comparison to healthy control subjects. In predominantly right lesioned patients, reduced activity within the right caudate head was observed. Compared to predominantly left lesioned patients, neuropsychological tests yielded reduced task performances in the right lesion subgroup. In line with previous electrophysiological research, imaging results of the present study are interpreted to represent altered preparatory networks in chronic prefrontal TBI patients. Since attentional and working memory functions are supposed to modulate preparatory processes, differences between the patient subgroups are suggested to result from the more pronounced cognitive impairments in the right-lesioned group.

Adult↗

PubMed2005

On the neural basis of focused and divided attention.

Concepts of higher attention functions distinguish focused and divided attention. The present study investigated whether these mental abilities are mediated by common or distinct neural substrates. In a first experiment, 19 healthy subjects were examined with functional brain imaging (fMRI) while they attended to either one or both of two simultaneously presented visual information streams and responded to repetitive stimuli. This experiment resembled a typical examination of these mental functions with the single task demanding focused and the dual task conditions requiring divided attention. Both conditions activated a widespread, mainly right-sided network including dorso- and ventrolateral prefrontal structures, superior and inferior parietal cortex, and anterior cingulate gyrus. Under higher cognitive demands of divided attention, activity in these structures was enhanced and left-sided homologues were recruited. In a second experiment investigating another 17 subjects with almost the same paradigm, it was accounted for that in most dual task investigations of focused and divided attention the single tasks are easier to process than their combined presentation. Therefore, the task difficulty of focused attention tasks was increased. Almost the same activity pattern observed during division of attention was now found during focusing attention. Comparing both attentional states matched for task difficulty, differences were found in visual but not in prefrontal or parietal cortex areas. Our results suggest that focused and divided attention depend on largely overlapping neuronal substrates. Differences in activation patterns, especially in prefrontal and parietal areas, may result from unequal demands on executive control due to disparate processing requirements in typical tasks of focused and divided attention: Easier conditions begin with mainly right-sided activity within the attention network. As conditions become more difficult, left-lateralized homologue areas activate.

Adult↗

PubMed2005

Prefrontal cortex activity in self-initiated movements is condition-specific, but not movement-related.

Activity of the prefrontal cortex (PFC) has been observed in previous block-design brain imaging studies of self-initiated movements. However, the meaning of these activations remained unclear. A functional MRI experiment was carried out, which utilized an epoch and an event-related analysis approach to the data. We hypothesized that event-related activity of the PFC would argue for a contribution to movement preparation. In contrast, epoch-, but not event-related activity pointed to tonic activations, probably reflecting enhanced attentional states or working memory processing. Twenty-one subjects were examined with 845 T2*-weighted images. During active phases, subjects were instructed to perform self-initiated movements of the right index finger with intertrial intervals of about 8 s. On single subject level, epoch- and event-related regressors were entered into a combined model, estimating the exclusive contribution of either regressor. For statistical inference on multisubject level, random effects analyses were performed. For the epoch regressor, activity within the right dorso- and ventrolateral prefrontal cortex, the bilateral insula, and the right inferior parietal lobe was observed. The event-related regressor detected activity within the right inferior parietal lobe, ventral from the activity found with the epoch regressor. The present results indicate a condition-, but not a movement-related function of the PFC in self-initiated movements. Furthermore, anatomically distinct regions within the inferior parietal cortex seem to be involved in condition-specific and movement-related processes. The observed condition-specific activations are suggested to reflect attentional or working memory processes, supervising task performance, rather than movement preparation or initiation.

Adult↗

PubMed2005

Reorganization of motor execution rather than preparation in poststroke hemiparesis.

BACKGROUND AND PURPOSE: The aim of the present study was to examine movement-related potentials (MRPs) in patients in the "chronic" stage after cortical stroke with recovered hemiparesis compared with healthy control subjects. METHODS: Right index finger MRPs were derived from 12 patients > or =1 year after infarction in the territory of the left middle cerebral artery as well as from 12 control subjects. MRP components were compared between groups. RESULTS: In the patient group, the component directly preceding movement onset (negative slope [NS]) was significantly reduced over the lesioned hemisphere contralateral to the movement. Furthermore, increased motor potentials (MPs) were observed over the contralesional hemisphere during movement execution. No changes in the early MRP (Bereitschaftspotential) reflecting movement preparation were found. CONCLUSIONS: Because the NS is supposed to be generated by the primary motor cortex, the decreased component over the lesioned hemisphere is interpreted to represent impaired contralateral M1 functioning in stroke patients. Contralesional activity has been reported as a probable sign of brain plasticity by functional imaging studies. Our results broaden these findings, giving new insights into the temporal course of movement-related brain activity in recovered cortical stroke patients. The data point to a functional reorganization of motor execution rather than preparation in poststroke hemiparesis.

Aged↗

PubMed2005

Sparse imaging and continuous event-related fMRI in the visual domain: a systematic comparison.

Continuous image acquisition as used in most functional magnetic resonance imaging (fMRI) designs may conflict with specific experimental settings due to attendant, noisy gradient switching. In sparse fMRI, single images are recorded with a delay that allows the registration of the predicted peak of an evoked hemodynamic response (HDR). The aim of this study was to assess validity and sensitivity of single-trial sparse imaging within the visual domain. Thirteen subjects were scanned twice. Either continuous or sparse image acquisition was applied while participants viewed single trains of flashlights. Sparse fMRI results were compared to continuous event-related fMRI results on single- and multisubject level regarding spatial extent, overlap, and intensity of activation. In continuously recorded data, the variability of the HDR peak latency was examined because this measure determined the timing of sparse image acquisition. In sparse fMRI, the sensitivity was analyzed considering different numbers of averaged trials. Sparse imaging detected the core activity revealed using continuous fMRI. The intensity of signal changes detected by continuous or sparse fMRI was comparable. The HDR peak latency was stable across sessions, but intersubject and regional variability might have affected the power of sparse fMRI. In sparse imaging, adding trials resulted in extension of activation and improvement in statistical power. The comparison with established continuous fMRI confirms the validity of sparse imaging. Conventional event-related data acquisition and analysis provided more comprehensive results. However, only sparse fMRI offers the opportunity to apply stimuli and record further biosignals free of scanner-related artifacts during intervals without image acquisition.

Adult↗

PubMed2004

Movement preparation in self-initiated versus externally triggered movements: an event-related fMRI-study.

In the present study, we used fMRI to investigate whether event-related preparatory processes of self-initiated and externally triggered movements differ. Twenty subjects were examined with 1000 T2*-weighted images in two consecutive sessions. During the first session subjects performed self-initiated abductions of the right index finger. For the second session subjects were instructed to perform the movements in response to visual cues. Number and timing of movements were matched between conditions. For statistical inference on multisubject level, random effects analyses were performed. Significantly enhanced activity during self-initiated compared to externally triggered movements was found within the left SMA, the left pre- and sensorimotor cortex, the right putamen, the left anterior cingulate gyrus, and the left inferior parietal lobe. The significantly increased activity during self-initiated in comparison to externally triggered movements might represent differential demands of the two conditions on the neuronal motor net during movement preparation, reflecting utilization of precise knowledge when to move in self-initiated movements. Our results emphasize a possible role of the primary motor cortex for movement preparation as observed in electrophysiological studies, but do not support a specific involvement of the dorsolateral prefrontal cortex as suggested by former block design studies.

Adult↗

PubMed2004

Recovery of movement-related potentials in the temporal course after prefrontal traumatic brain injury: a follow-up study.

OBJECTIVE: The movement-related potential (MRP) is an EEG measure related to self-initiated movements, consisting of the Bereitschaftspotential (BP), the negative slope, and the motor potential. Since in a former study the BP was reduced in acute prefrontal traumatic brain injury (TBI) patients, the present study examined the MRPs' course in follow-up examinations. METHODS: Right index finger MRPs of 22 patients with contusions of the prefrontal cortex were recorded 12, 26, and 52 weeks after TBI and compared to controls. RESULTS: Within the patient group, a significant increase of the BP in the temporal course after TBI was observed. MRPs 12 and 26 weeks after TBI did not differ significantly from the control group. One year after TBI, significantly enhanced BPs were found. CONCLUSIONS: In the temporal course after prefrontal TBI, a recovery of the initially reduced BP was observed. The enhanced BP areas 1 year after TBI might represent the need for increased cognitive resources during movement preparation, supporting a recovered, but less effective neuronal network. SIGNIFICANCE: The present study represents the first longitudinal follow-up study of MRPs after prefrontal brain lesion. The observed changes reflect the plastic capacity of the brain, reorganizing the neuronal network function.

Adult↗

PubMed2004

Impaired movement-related potentials in acute frontal traumatic brain injury.

OBJECTIVE: Focal brain lesions due to traumatic brain injury (TBI) do not only lead to functional deficits in the lesion area, but also disturb the structurally intact neuronal network connected to the lesion site. Therefore we hypothesized dysfunctions of the cortical motor network after frontal TBI. The movement related potential (MRP) is an EEG component related to voluntary movement consisting of the Bereitschaftspotential (BP), the negative slope (NS), and the motor potential (MP). The aim of our study was to demonstrate alterations in the movement related cortical network in the acute stage after TBI by comparing our patients' MRPs to those of a healthy control group. METHODS: EEGs of 22 patients with magnetic resonance imaging defined contusions of the prefrontal cortex were recorded within 8 weeks after TBI. We further recruited a healthy control group. The paradigm consisted of self-paced abductions of the right index finger. RESULTS: Compared to healthy controls, the BP in the patient group was significantly reduced and its onset delayed. Moreover, an enhanced contribution of the postrolandic hemisphere ipsilateral to the movement and a reduced contribution of the left frontal cortex, ipsilateral to the lesion in the majority of the patients, were observed during motor execution (MP). CONCLUSIONS: Anatomical connections between the prefrontal cortex and the supplementary motor area (SMA) are known to exist. We suggest that prefrontal lesions lead to reduced neuronal input into the SMA. This deficit in the preparatory motor network may cause the reduced BPs in our patients. Moreover, an increased need for attentional resources might explain the enhanced motor potentials during movement execution. In conclusion, we demonstrated altered MRPs in the acute stage after frontal TBI, which are a consequence of disturbed neuronal networks involved in the preparation and execution of voluntary movements.

Adolescent↗

PubMed2004

[Reduced contralateral preponderance of the movement-related potential during execution of self-initiated movements in acute prefrontal traumatic brain injury].

OBJECTIVES: An enhanced ipsilateral motor potential after prefrontal TBI is known. Our aim was to examine, whether this contributes to movement initiation or execution. METHODS: EEGs of 22 patients and 28 healthy controls were recorded. Subjects performed self-initiated movements of their right index finger. From the resulting movement-related potentials difference curves of corresponding left and right hemispheric electrodes were calculated. RESULTS: We observed significantly reduced difference curves at parietal electrodes P3 - P4 in the patient group during movement execution, but not at movement initiation. CONCLUSIONS: Our results point to compensatorily enhanced monitoring processes during movement execution following TBI. This is provided by enhanced activity of the ipsilateral postrolandic cortex, leading to the reduced preponderance observed in the present study.

Adult↗

PubMed2004

[Quantification of acute muscle pain after whiplash injury using computer-aided pressure algesimetry].

OBJECTIVE AND METHOD: The present study utilised the PC-interactive pressure algesimetry to quantify cervical pain after whiplash injury. Pressure painfulness of the splenius and trapezius muscles was investigated in patients with an acute cervical syndrome after whiplash injury and compared to that of healthy subjects. RESULTS: Pressure painfulness of neck and shoulder muscles was significantly increased in whiplash patients. The trapezius muscles were more painful left than right, probably due to the seat belt position. CONCLUSIONS: The computer-interactive pressure algesimetry enables a standardised, rater-independent quantification of cervical pain due to whiplash injury.

Acute Disease↗

PubMed2003

Sparse imaging of the auditory oddball task with functional MRI.

Cortical reactions to rare task-related stimuli have been studied with electrophysiological methods in the assessment of the P300 component as well as in functional imaging studies with regard to oddball tasks. While functional magnetic resonance imaging studies using auditory stimuli have to deal with interference between auditory stimuli and scanner noise, the aim of our study was to assess auditory target processing with the sparse imaging method. Single volumes of echo-planar imaging were acquired 4 s following the onset of the stimuli of interest. In keeping with previous studies, target stimuli activated the insula, superior temporal gyrus, cingulate gyrus, middle frontal gyrus, parietal cortex and the cerebellum. Our results encourage the application of the sparse imaging method in experiments on cognitive processing elicited by auditory stimulation in a silent environment.

Acoustic Stimulation↗