Biomedical subjects

Guy Vingerhoets

Publications and source records attributed to Guy Vingerhoets.

14 recordsLinked to original sources

PubMed2005

Trial pacing in mental rotation tasks.

Functional imaging of mental rotation has revealed a wide variety of cortical activation patterns besides the consensus on parietal involvement. Some insight has been gained on the role of motor cortex, but the differential activation of other brain regions has received little attention. A previous fMRI study using a blocked substraction design [D'Esposito et al., NeuroImage 6 (1997) 113-121] has shown an effect of trial pacing on the observed activation pattern of a simple visuospatial task requiring mental rotation. In this study, we want to assess if trial pacing can help clarify some of the diversity in the observed cortical activation patterns associated with fMRI blocked designs of mental rotation so far, especially when comparing mental rotation of different stimuli. We used two different stimuli, i.e. hands and tools, that have been used in previous mental rotation studies. Our results revealed a bilateral involvement of lateral premotor and parietal cortex irrespective of trial pacing, but there was a marked influence of trial pacing on the observed activation of occipital and other frontal regions. Stimulus type specific activation patterns were entirely limited to the fixed-paced design. We conclude that trial pacing is a vital aspect when developing and interpreting the related imaging results of a blocked subtraction design. Fixed-paced designs may be more sensitive for duration effects. A self-paced trial schedule may be more appropriate to isolate the neural substrate of the cognitive component of interest or to exclude response time differences as a confounding factor.

Adult↗

PubMed2005

Stimulus pacing affects the activation of the medial temporal lobe during a semantic classification task: an fMRI study.

Our purpose was to explore the influence of stimulus pacing in blocked functional MRI studies on the activation pattern elicited by a semantic retrieval task. Twenty-two participants performed both a fixed-paced and a self-paced functional MR imaging experiment in which a semantic categorization (animal/object) task was contrasted with a perceptual (small/capital letter string) categorization task. Group and single-subject ROI analyses were computed. In both the fixed-paced and self-paced experiments, semantic categorization contrasted with perceptual categorization elicited a cerebral network generally accepted to be involved in semantic processing comprising left inferior prefrontal, left lateral temporal, paracingular and right cerebellar areas. Our main finding was that the self-paced stimulus modality additionally yielded significant activation in the medial temporal lobe (MTL) structures including the hippocampus and the parahippocampal gyrus. More elaborative single-subject ROI analyses revealed MTL activation in 86% of the subjects for the self-paced design, but only in 21% of subjects for the fixed-paced design. The discussion focuses on possible explanations for this finding. We conclude that a self-paced as opposed to a fixed-paced semantic retrieval paradigm is able to detect significant MTL activation in groups as well as in single-subjects. This offers opportunities for the application of such a design in clinical practice.

Adult↗

PubMed2005

Impaired intentional content learning but spared incidental retention of contextual information in non-demented patients with Parkinson's disease.

We investigated the incidental and intentional learning performance of 29 patients with idiopathic Parkinson's disease (PD) and 20 healthy volunteers. Measures of incidental and intentional memory were assessed with a spoken verbal recall task followed by a temporal word order task, a picture recall task followed by a spatial picture location task, and a written word recall task followed by a judgement of word frequency task. A multivariate analysis of variance and appropriate post hoc tests revealed significant differences for all intentional learning variables. In all cases, PD patients performed worse than normal controls. No group differences were found for the incidental retention of contextual information. The results indicate that PD patients have a selective problem of intentional learning, whereas incidental learning of contextual information remains intact. Elaborate processing, attentional and organizing strategies in the systematic encoding, and recollection of information have been attributed to dorsolateral prefrontal activation. Preferential dysfunction of dorsolateral prefrontal cortex-associated memory processes is consistent with the previously reported uneven patterns of dopamine loss in the striatum of patients with idiopathic PD showing most severe dopamine depletion in the portion of the caudate nucleus that is anatomically connected to the dorsolateral frontal cortex.

Aged↗

PubMed2005

What is said or how it is said makes a difference: role of the right fronto-parietal operculum in emotional prosody as revealed by repetitive TMS.

Emotional signals in spoken language can be conveyed by semantic as well as prosodic cues. We investigated the role of the fronto-parietal operculum, a somatosensory area where the lips, tongue and jaw are represented, in the right hemisphere to detection of emotion in prosody vs. semantics. A total of 14 healthy volunteers participated in the present experiment, which involved transcranial magnetic stimulation (TMS) in combination with frameless stereotaxy. As predicted, compared with sham stimulation, TMS over the right fronto-parietal operculum differentially affected the reaction times for detection of emotional prosody vs. emotional semantics, showing that there is a dissociation at a neuroanatomical level. Detection of withdrawal emotions (fear and sadness) in prosody was delayed significantly by TMS. No effects of TMS were observed for approach emotions (happiness and anger). We propose that the right fronto-parietal operculum is not globally involved in emotion evaluation, but sensitive to specific forms of emotional discrimination and emotion types.

Adult↗

PubMed2005

Lateralized anterior mesiotemporal lobe activation: semirandom functional MR imaging encoding paradigm in patients with temporal lobe epilepsy--initial experience.

PURPOSE: To prospectively demonstrate anterior mesiotemporal lobe (MTL) activation in healthy volunteers by using a semirandom memory-encoding paradigm and to prospectively compare lateralized functional magnetic resonance (MR) imaging activation with intracarotid amobarbital procedure (IAP) memory test results in patients with temporal lobe epilepsy (TLE) who were scheduled to undergo surgery. MATERIALS AND METHODS: The study was approved by a local ethics committee, and written informed consent was obtained from all subjects. Eight healthy volunteers and 18 patients with TLE who were scheduled for surgery were included in the functional MR imaging study involving the use of a memory-encoding paradigm with variable epoch lengths. Subjects were instructed to memorize new pictures that were mixed among pictures that they had seen before. Data analysis entailed computations of the contrast between the MTL activation induced by the new pictures and the MTL activation induced by the old pictures and of the lateralization index, defined as the relative difference in the number of activated voxels between the left and right MTLs. Lateralization indexes were compared between the patients and the volunteers and statistically correlated with the patients' IAP memory test results. To study deviations from perfect correspondence between the functional MR imaging- and IAP-derived lateralization indexes, orthogonal regression analysis was applied. Proportional relations for the patients with left-sided TLE and for those with right-sided TLE were calculated separately. RESULTS: The memory paradigm consistently activated the posterior and anterior MTL structures in both the healthy volunteers and the patients. Regression analysis revealed that functional MR imaging activation was stronger than the IAP results when it was lateralized to the contralateral MTL. This analysis also revealed a significant (P < .001) correlation between the functional MR imaging results and the IAP results in the patients with right-sided TLE but not in those with left-sided TLE (P > .1). CONCLUSION: The functional MR imaging memory-encoding paradigm consistently yielded MTL activation in the volunteers and the patients with TLE, but lateralized functional MR imaging activation was in concordance with the IAP results in only those patients with right-sided TLE.

Adult↗

PubMed2005

Relation between neurocognitive impairment, embolic load, and cerebrovascular reactivity following on- and off-pump coronary artery bypass grafting.

OBJECTIVES: To evaluate the effect of on-pump and off-pump coronary artery bypass grafting (CABG) on postoperative cognitive impairment and cerebrovascular reactivity, with attention for the perioperative high-intensity transient signals (HITS). DESIGN: A prospective comparative study. SETTING: Urban university hospital. PATIENTS: Candidates for cardiac surgery. METHODS: Measurement of HITS as a reflection of embolic load was performed in 50 patients (on-pump CABG, n = 32; off-pump CABG, n = 18). To measure cognitively induced cerebrovascular reactivity, cerebral blood flow velocity (BFV) was measured preoperatively in 66 patients, early postoperatively (after 6 days) in 63 patients, and late postoperatively (after 6 months) in 44 patients during five cognitive tasks. In the same session, seven standardized neuropsychological tests were administered. RESULTS: A higher embolic load was found in the on-pump group (p < 0.01). In the on-pump group, aortic cannulation was the most important HITS-prone surgical maneuver. Repeated-measures multivariate analysis of variance (using surgical technique as between-subjects factor and significant differences between both groups as covariates) on the group data revealed no significant differences in neuropsychological performance and BFV immediately after surgery or at 6 months after surgery, compared with preoperative performance. No main effect of surgery was found for neuropsychological performance and BFV. No significant correlations were found between the number of HITS and the degree of postoperative neuropsychological impairment. Individual comparisons revealed that 60% (59.4% in the on-pump group; 61.1% in the off-pump group) of the patients undergoing CABG showed evidence of cognitive impairment soon after surgery. In 24.2%, the cognitive sequelae persisted at 6 months follow-up (31.8% in the on-pump group; 9.1% in the off-pump group). The cognitive impairment index (sum of impaired neuropsychological tests) showed a significant difference after 6 months between both surgery groups with fewer neurocognitive tests that remained impaired in the off-pump group. CONCLUSIONS: In off-pump surgery, significantly fewer HITS were observed. On an individual level, more favorable results in neuropsychological test performance were demonstrated in the off-pump group after 6 months. The number of HITS showed no correlation with degrees of early and late postoperative neuropsychological impairment.

Age Distribution↗

PubMed2004

Lessons for neuropsychology from functional MRI in patients with epilepsy.

This contribution aims to review the major findings of pre- and postsurgical functional magnetic resonance imaging (fMRI) in patients with refractory epilepsy from a neuropsychological perspective. We compared the contribution of fMRI with the intracarotid amytal procedure (IAP) with respect to functional mapping of language and memory in patients with therapy-resistant epilepsy. We conclude that using comprehensive language paradigms, fMRI has been able (1) to provide estimates of the degree of language lateralization including the degree of involvement of the nondominant hemisphere, (2) to provide information on the location of its activated network during expressive and receptive language, and (3) to help delineate eloquent language regions in the vicinity of the surgical target, thus preventing postoperative complications. The contribution of the frequently observed nondominant hemisphere activation to language should be explored and its clinical relevance determined. Evidence from fMRI studies is accumulating that reorganization of cognitive and motor function favors the activation of contralateral homotopic areas, although this process is far from understood. The exact functional contribution of atypical areas of activation should be investigated critically. In the presurgical evaluation process, detailed and reliable localization of language and memory functions of the individual patient is mandatory and should be the ultimate goal in the development of comprehensive clinical fMRI protocols.

Amobarbital↗

PubMed2003

Multilingualism: an fMRI study.

To investigate the hypothesis that in multilingual speakers different languages are represented in distinct brain regions, 12 multilingual right-handed men performed a word fluency task, a picture naming task, a comprehension reading task, and their respective control tasks in three languages (Dutch, French, and English) while whole-head functional magnetic resonance imaging (fMRI) was applied. In general, all language tasks revealed predominantly overlapping regions of activation for the different languages. Cerebral activation during use of the foreign languages showed a tendency toward a more extensive recruitment of the areas activated in the native language and the activation of a greater number of regions. Word generation in the foreign languages elicited additional bilateral inferior frontal activation, including Broca's area and left middle temporal gyrus activation; in the native language, additional postcentral activation was found. Picture naming in the foreign languages recruited additional inferior-lateral and medial frontal regions predominantly on the left, and more posterior right hemispheric activation in the mother tongue. During comprehension reading there was more activation in medial posterior regions in the native language. Our results suggest that the performance of language tasks in different languages engages largely the same cerebral areas but that the brain, to perform at a comparable proficiency level, engages more neural substrates for later acquired languages. Our findings do not support the view that languages learned later in life entail more right hemispheric involvement. Finally, a consequent effect of language exposure was found for reading, where increased familiarity engages more occipital activation whereas decreased familiarity appears to be associated with increased left hemispheric inferior frontal activation.

Adult↗

PubMed2003

Cerebral hemodynamics during discrimination of prosodic and semantic emotion in speech studied by transcranial doppler ultrasonography.

Simultaneous measurement of blood flow velocity (BFV) in the middle cerebral arteries was achieved by transcranial Doppler ultrasonography in 36 right-handed volunteers who were instructed to identify the emotion conveyed by prosody or semantics of a number of sentences. The tasks were performed under 2 levels of interference: neutral versus discordant affective value of the modality that had to be ignored. A multivariate analysis of variance showed a significant bilateral increase in BFV during the discordant conditions reflecting increased attentional demand. A significant left-hemispheric lateralization of BFV was observed as emotional semantics were labeled. When attention was shifted to affective prosody, the lateralization effect disappeared as a result of a marked increase in right-hemispheric BFV.

Adult↗

PubMed2003

Neurostimulation for refractory epilepsy.

Neurostimulation is an emerging treatment for refractory epilepsy. To date the precise mechanism of action remains to be elucidated. Better insight in the mechanism of action may identify seizure types or syndromes that respond to such a treatment and may guide the search for optimal stimulation parameters and finally improve clinical efficacy. In the past ten years some progress has been made through neurophysiological, neuroanatomical, neurochemical and cerebral blood flow studies in patients and animals undergoing vagus nerve stimulation (VNS). Interesting results have been found in VNS-treated patients that underwent evoked potential measurements, cerebrospinal fluid investigation, neuropsychological testing and PET, SPECT and fMRI testing. Desynchronisation of abnormal synchronous epileptic activity is one of the hypotheses on the mode of action that might primarily be responsible for an anti-seizure effect. There is however increasing evidence from research and clinical observation that VNS might establish a true and long-term anti-epileptic effect. It has been shown that VNS influences neurotransmission in the brain and provokes long-term changes in cerebral blood flow in areas crucial for epileptogenesis such as the thalamus and medial temporal lobe structures. Deep brain stimulation (DBS) for epilepsy has regained interest. Central nervous system structures known to play a key role in the epileptogenic network such as the thalamus and subthalamic nucleus have been targeted. Another approach is to target the ictal onset zone such as the medial temporal lobe. At Ghent University Hospital 10 patients have been treated with long-term amygdalohippocampal DBS. Several hypotheses have been raised for the mechanism of action of DBS for refractory seizures. Seizure reduction may be due to a microlesion caused by electrode insertion or by provoking a reversible functional lesion due to the effect of electrical current on hyperexcitable tissue. Neurophysiological techniques such as evoked potentials monitoring and intraoperative single unit potential recordings may guide correct electrode placement, individual DBS titration and elucidation of the mechanims of action of DBS for epilepsy.

Animals↗

PubMed2002

Motor imagery in mental rotation: an fMRI study.

Twelve right-handed men performed two mental rotation tasks and two control tasks while whole-head functional magnetic resonance imaging was applied. Mental rotation tasks implied the comparison of different sorts of stimulus pairs, viz. pictures of hands and pictures of tools, which were either identical or mirror images and which were rotated in the plane of the picture. Control tasks were equal except that stimuli pairs were not rotated. Reaction time profiles were consistent with those found in previous research. Imaging data replicate classic areas of activation in mental rotation for hands and tools (bilateral superior parietal lobule and visual extrastriate cortex) but show an important difference in premotor area activation: pairs of hands engender bilateral premotor activation while pairs of tools elicit only left premotor brain activation. The results suggest that participants imagined moving both their hands in the hand condition, while imagining manipulating objects with their hand of preference (right hand) in the tool condition. The covert actions of motor imagery appear to mimic the "natural way" in which a person would manipulate the object in reality, and the activation of cortical regions during mental rotation seems at least in part determined by an intrinsic process that depends on the afforded actions elicited by the kind of stimuli presented.

Adult↗

PubMed2002

Reliability and validity of day-to-day blood flow velocity reactivity in a single subject: an fTCD study.

To evaluate the within-subject variability of repeated task-induced blood flow velocity (BFV) change, we measured the haemodynamics of the anterior and middle cerebral arteries of the same volunteer on 20 consecutive working days during the performance of mental arithmetic with transcranial Doppler ultrasonography. BFV changes with the arithmetic condition were compared against a resting and a counting condition. Absolute BFV data showed equally increased velocities during rest and arithmetic activity as compared to counting. The findings suggest that the resting state might not be the ideal reference paradigm to evaluate task-induced haemodynamic changes. Selecting the counting condition as the more valid baseline measure, we obtained relatively stable lateralisation indices for the MCA with 1 of 10 measurements outside the 95% confidence interval. Reproducibility was poorer in the ACA, with 3 outliers. A strategy that calculates the average of multiple short activation epochs within the same session appears to improve the reliability of the lateralisation index.

Adult↗

PubMed2002

Short-term and long-term neurocognitive outcome in on-pump versus off-pump CABG.

OBJECTIVE: Neuropsychological dysfunctions are considered to be important complications of coronary artery bypass graft surgery (CABG). We examined the frequency of neuropsychological abnormalities occurring in patients undergoing CABG with (on-pump) and without (off-pump) cardiopulmonary bypass. METHODS: Neuropsychological assessment with seven cognitive tasks was performed one day before, 6-7 days after (n=49) and 6 months after (n=35) surgery. The subgroup undergoing on-pump surgery (n=30 at 7 days and n=22 at 6 months) was demographically comparable to the off-pump subgroup. The on-pump group included more multiple vessel disease. RESULTS: Repeated measures multivariate analysis of variance (using surgical group as a between-subjects factor) on the group data revealed no significant differences neither immediately after surgery nor at 6 months after surgery, compared with the preoperative performance. There were no significant differences between the on-pump and off-pump groups in post-operative neuropsychological performance soon after surgery. A significant difference was found between the two groups 6 months after surgery, with more favorable results for the off-pump group. Individual comparisons revealed that 59% of the patients of both groups undergoing CABG showed evidence of cognitive impairment soon after surgery. In 11% of the patients (all on-pump), the cognitive sequelae persisted at follow-up. CONCLUSION: This study showed no short-term difference between the on-pump and off-pump CABG groups. The long-term cognitive outcome revealed more favorable results for the off-pump group. Although a preference to operate multiple vessel disease with classical cardiopulmonary bypass (CPB) has to be considered, the present study shows evidence for a different pattern of early decline and late recovery of cognitive functions in patients undergoing CABG with and without CPB.

Aged↗

PubMedDate not supplied

Vagus nerve stimulation for refractory epilepsy: a transatlantic experience.

Vagus nerve stimulation (VNS) is an alternative treatment for medically or surgically refractory epilepsy. The long-term efficacy and safety of VNS were evaluated in a large patient series at Ghent University Hospital and Dartmouth-Hitchcock Medical Center. Between March 1995 and February 2003, seizure frequency and type as well as prescribed antiepileptic drugs and side effects were prospectively assessed in 131 patients treated with VNS in either center. Patients with a minimum follow-up duration of 6 months were included in the efficacy and safety analysis. A total of 118 of 131 implanted patients had a minimum postimplantation follow-up period of 6 months (mean, 33 months). The mean age of these patients was 32 years and the mean duration of refractory epilepsy was 22 years. The mean reduction in monthly seizure frequency in all patients was 55% (range, 0-100; SD = 31.6). Seven percent of patients were free of seizures with impaired consciousness, 50% of patients had a seizure frequency reduction of more than 50%, and 21% of patients were nonresponders. Fifteen patients reported stimulation-related side effects such as hoarseness or gagging. In a large patient series from two geographically distinct epilepsy centers located in two different continents, VNS proved to be efficacious and safe during long-term follow-up.

Adolescent↗