Biomedical subjects

Pieter Vandemaele

Publications and source records attributed to Pieter Vandemaele.

5 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↗

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

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↗