Biomedical subjects

Karel Deblaere

Publications and source records attributed to Karel Deblaere.

6 recordsLinked to original sources

PubMed2004

Visual extinction for motion.

PURPOSE: To alert clinicians to the heretofore undescribed visual behavioral phenomenon of visual extinction limited to motion. METHODS: Neuro-ophthalmological, neuropsychological and neuroimaging assessment of a 57-year-old man with vague visual complaints. RESULTS: Extinction limited to visual motion perception in the left hemifield was demonstrated. The visual defect was attributed to a lesion involving the right occipito-temporo-parietal region in the presence of a left posterior infarction. CONCLUSION: The importance of clinical examination for detection of this specific higher-order visual defect is stressed. The present observation may be helpful in understanding the effects of attention on visual perception and may have important implications for rehabilitation of patients with visual neglect.

Cerebral Infarction↗

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

Painful isolated Horner's syndrome caused by pontine ischaemia.

PURPOSE: To alert ophthalmologists to the possibility of brainstem ischaemia in patients with isolated Horner's syndrome. DESIGN: Observational case report. METHODS: Neuro-ophthalmological and neuroimaging assessment of a 59-year-old woman presenting with an isolated Horner's syndrome after an episode of headache. RESULTS: Horner's syndrome was pharmacologically localised to a first- or second-order sympathetic neuron on the right. Magnetic resonance imaging (MRI) showed a small ischaemic lesion at the transition between pons and midbrain, lateral to the anterolateral system involving the sympathetic tract on the right side. CONCLUSION: An isolated Horner's syndrome may be the presenting sign of a brainstem infarction. This case report stresses the importance of a rational approach to Horner's syndrome and the need to order accurate MRI.

Brain Ischemia↗

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↗