PubMed Health⌕ Search

Biomedical subjects

M Regard

Publications and source records attributed to M Regard.

At least 19 recordsLinked to original sources
PubMed2006

Lateralized and frequency-dependent effects of prefrontal rTMS on regional cerebral blood flow.

Repetitive transcranial magnetic stimulation (rTMS) is a means to study the function and connectivity of brain areas. The present study addressed the question of hemispheric asymmetry of frontal regions and aimed to further understand the acute effects of high- and low-frequency rTMS on regional cerebral blood flow (rCBF). Sixteen healthy right-handed men were imaged using H(2)(15)O positron emission tomography (PET) immediately after stimulation. High (10 Hz)- and low (1 Hz)-frequency suprathreshold short-duration rTMS was applied over either the left or right dorsolateral prefrontal cortex (DLPFC). Slow and fast rTMS applied over the left DLPFC significantly increased CBF in the stimulated area. Compared to baseline, slow rTMS induced a significant increase in CBF contralateral to the stimulation site, in the right caudate body and in the anterior cingulum. Furthermore, slow rTMS decreased CBF in the orbitofrontal cortex (OFC, ipsilateral to stimulation side). Fast rTMS applied over the right DLPFC was associated with increased activity at the stimulation site, in the bilateral orbitofrontal cortex and in the left medial thalamus compared to 1-Hz rTMS. These results show that rCBF changes induced by prefrontal rTMS differ upon hemisphere stimulated and vary with stimulation frequency. These differential neurophysiological effects of short-train rTMS with respect to side and frequency suggest hemisphere-dependent functional circuits of frontal cortico-subcortical areas.

Adult↗
PubMed2005

Attention and interhemispheric transfer: a behavioral and fMRI study.

When both detections and responses to visual stimuli are performed within one and the same hemisphere, manual reaction times (RTs) are faster than when the two operations are carried out in different hemispheres. A widely accepted explanation for this difference is that it reflects the time lost in callosal transmission. Interhemispheric transfer time can be estimated by subtracting RTs for uncrossed from RTs for crossed responses (crossed-uncrossed difference, or CUD). In the present study, we wanted to ascertain the role of spatial attention in affecting the CUD and to chart the brain areas whose activity is related to these attentional effects on interhemispheric transfer. To accomplish this, we varied the proportion of crossed and uncrossed trials in different blocks. With this paradigm subjects are likely to focus attention either on the hemifield contralateral to the responding hand (blocks with 80% crossed trials) or on the ipsilateral hemifield (blocks with 80% uncrossed trials). We found an inverse correlation between the proportion of crossed trials in a block and the CUD and this effect can be attributed to spatial attention. As to the imaging results, we found that in the crossed minus uncrossed subtraction, an operation that highlights the neural processes underlying interhemispheric transfer, there was an activation of the genu of the corpus callosum as well as of a series of cortical areas. In a further commonality analysis, we assessed those areas which were activated specifically during focusing of attention onto one hemifield either contra- or ipsilateral to the responding hand. We found an activation of a number of cortical and subcortical areas, notably, parietal area BA 7 and the superior colliculi. We believe that the main thrust of the present study is to have teased apart areas important in interhemispheric transmission from those involved in spatial attention.

Adult↗
PubMed2002

Neurological and neuropsychological outcome after SAH.

The fact that neurological status and physical integrity alone do not sufficiently assess the overall state of patients after aneurysmal subarachnoid hemorrhage (SAH) gives rise to the necessity for complementary neuropsychological investigation. Neuropsychological work-up should also cover an emotional state, psychosocial adjustment and competence in everyday life of the patients. In our prospective study we investigated 82 patients three months and one year after SAH and early clipping of the aneurysm. For the evaluation of postoperative neurological functions the Glasgow Outcome Scale (GOS) was used. For the neuropsychological assessment we used standardized measures of verbal and figural learning and memory, verbal and figural fluency, speed of information processing, visuospacial abilities and affective function. One year after SAH 95.6% of patients with Hunt&Hess Grade 1 and 2 on admission showed good neurological results (GOS 4 and 5). However, only 30.1% (18 of 63 patients with a favourable neurological outcome--GOS 4 and 5) did not show any neuropsychological deficit. Localization of the ruptured aneurysm significantly correlated with cognitive measures. The best cognitive outcome was shown in patients with aneurysms on the anterior communicating artery (ACoA) followed by posterior communicating artery (PCoA) and those located on the internal carotid artery (ICA) on the right side.

Aneurysm, Ruptured↗
PubMed2001

Spatial- and verbal-memory improvement by cold-water caloric stimulation in healthy subjects.

We investigated the effects of unilateral cold-water vestibular stimulation on healthy subjects' performance in two cognitive tasks known to be differentially mediated by the two cerebral hemispheres. In a first experiment (right-hemisphere task), subjects memorized object-location associations while being stimulated with cold water in the left ear or right ear or not at all (control group). In the second experiment (left-hemisphere task), subjects memorized a list of sequentially presented function words while being stimulated in the same manner as the subjects in the first experiment. A recall phase followed each encoding phase. In the first experiment, subjects who had been stimulated in the left ear recalled the object locations significantly faster than subjects who had been stimulated in the right ear and those in the control group. The second experiment yielded the reverse pattern: correct word recognition was faster for subjects who had been stimulated in the right ear than for subjects stimulated in the left ear and those of the control group. We suggest that unilateral caloric stimulation leads to a selective activation of contralateral cerebral structures and speeds up cognitive processes mediated by these structures. These results are discussed with respect to findings in neglect patients and functional-imaging studies in healthy subjects.

Adult↗
PubMed2001

Associations to smell are more pleasant than to sound.

To assess and compare the quantitive and qualitative aspects of verbal associations of olfaction and audition, we conducted two verbal category fluency tasks, one consisting of the generation of 'smelling' associations and the other of 'auditory' associations. The responses of the 40 subjects on these fluency tasks were rated as pleasant or unpleasant by themselves as well as by an independent group of 40 subjects. In addition, all 80 healthy, right-handed subjects rated their momentary emotional state on a visual analog scale. The mean number of words generated by the 40 subjects did not differ between the two tasks, and in both tasks pleasant associations were more frequent than unpleasant associations. However, for all subjects, the proportion of pleasant associations was significantly higher in the olfactory compared to the auditory fluency task. The finding of more pleasant associations in both tasks confirms previous reports, but the pronounced effect in the olfactory task suggests that odors may be more hedonically coded than other sensory modalities, i.e., audition. Although there is evidence that the majority of odors are initially perceived as unpleasant, when retrieved from memory, pleasant connotations seem to dominate. The possible mechanisms for this dissociation are discussed.

Adult↗
PubMed2001

Kleptomania in a patient with a right frontolimbic lesion.

OBJECTIVE: The authors report the case of a patient in whom kleptomania developed in the course of a right frontolimbic behavior syndrome after undergoing surgery. BACKGROUND: Kleptomania is a behavior abnormality that is classified as an impulse-control disorder; however, little is known about its organic correlates. METHOD: History included neurologic data, neuropsychological data, electroencephalographic data, and magnetic resonance images. RESULTS: Observation of kleptomania associated with a large sellar craniopharyngioma with right-sided extension suggests that the site of a lesion may be crucial for the development of an impulse-control disorder. CONCLUSIONS: The authors discuss kleptomania in the context of functional deficits associated with damage to orbitofrontal-subcortical circuits, and they suggest that kleptomania is a neuropsychiatric symptom that can be conceptualized as being an uncommon compulsive display of impulse dyscontrol.

Adult↗
PubMed2000

Beyond re-membering: phantom sensations of congenitally absent limbs.

Phantom limbs are traditionally conceptualized as the phenomenal persistence of a body part after deafferentation. Previous clinical observations of subjects with phantoms of congenitally absent limbs are not compatible with this view, but, in the absence of experimental work, the neural basis of such "aplasic phantoms" has remained enigmatic. In this paper, we report a series of behavioral, imaging, and neurophysiological experiments with a university-educated woman born without forearms and legs, who experiences vivid phantom sensations of all four limbs. Visuokinesthetic integration of tachistoscopically presented drawings of hands and feet indicated an intact somatic representation of these body parts. Functional magnetic resonance imaging of phantom hand movements showed no activation of primary sensorimotor areas, but of premotor and parietal cortex bilaterally. Movements of the existing upper arms produced activation expanding into the hand territories deprived of afferences and efferences. Transcranial magnetic stimulation of the sensorimotor cortex consistently elicited phantom sensations in the contralateral fingers and hand. In addition, premotor and parietal stimulation evoked similar phantom sensations, albeit in the absence of motor evoked potentials in the stump. These data indicate that body parts that have never been physically developed can be represented in sensory and motor cortical areas. Both genetic and epigenetic factors, such as the habitual observation of other people moving their limbs, may contribute to the conscious experience of aplasic phantoms.

Adult↗
PubMed2000

Processing of spatial locations: hemispace effects during encoding but not recall.

Traditionally, functional differences in the visual modality between the two hemispheres are investigated by tachistoscopic procedures. In these experiments, the stimuli reach the contralateral hemisphere first, and results are commonly interpreted on the basis of neuroanatomical access models. However, numerous studies demonstrated that the hemispace where the stimulus is perceived also plays a critical role in producing laterality effects ("hemispace effects"). In the present experiment, subjects were instructed to memorize the relative spatial positions of six figures horizontally aligned on a presentation board. The presentation board was located either to the left, to the right or in front of the subjects (left, right and central learning positions). During a recall phase, each figure was presented in the center of a computer screen and subjects were required to indicate by keypress whether a figure had been located in the left or right half of the presentation board. As in the learning phase, the computer screen was located to the left, the right or in front of the subjects (left, right and central recall positions). We found that the positions of the figures initially memorized in the left hemispace were recalled faster than figures initially memorized in the right hemispace. Hemispatial position during recall had no effect on performance. These results are discussed with respect to hemispheric specialization and theories of hemispace effects.

Adult↗
PubMed2000

Face-elicited ERPs and affective attitude: brain electric microstate and tomography analyses.

OBJECTIVES: Although behavioral studies have demonstrated that normative affective traits modulate the processing of facial and emotionally charged stimuli, direct electrophysiological evidence for this modulation is still lacking. METHODS: Event-related potential (ERP) data associated with personal, traitlike approach- or withdrawal-related attitude (assessed post-recording and 14 months later) were investigated in 18 subjects during task-free (i.e. unrequested, spontaneous) emotional evaluation of faces. Temporal and spatial aspects of 27 channel ERP were analyzed with microstate analysis and low resolution electromagnetic tomography (LORETA), a new method to compute 3 dimensional cortical current density implemented in the Talairach brain atlas. RESULTS: Microstate analysis showed group differences 132-196 and 196-272 ms poststimulus, with right-shifted electric gravity centers for subjects with negative affective attitude. During these (over subjects reliably identifiable) personality-modulated, face-elicited microstates, LORETA revealed activation of bilateral occipito-temporal regions, reportedly associated with facial configuration extraction processes. Negative compared to positive affective attitude showed higher activity right temporal; positive compared to negative attitude showed higher activity left temporo-parieto-occipital. CONCLUSIONS: These temporal and spatial aspects suggest that the subject groups differed in brain activity at early, automatic, stimulus-related face processing steps when structural face encoding (configuration extraction) occurs. In sum, the brain functional microstates associated with affect-related personality features modulate brain mechanisms during face processing already at early information processing stages.

Adult↗
PubMed1999

Qualitative hemispheric differences in semantic category matching.

A unilateral category matching task with words as stimuli was employed to investigate semantic processing in the right and left hemispheres (RH, LH). An overall right visual field (RVF)/LH dominance was observed and performances were better than chance, also in the left visual field (LVF)/RH. A qualitative analysis of reaction times with individual differences multidimensional scaling (INDSCAL) revealed that LVF/RH INDSCAL solutions were significantly more differentiated in structure than RVF/LH solutions in terms of number and size of dimensions. These findings support a depth of activation hypothesis of hemispheric processing, with the LH rapidly and focally and the RH slowly and diffusely activating the semantic network.

Adult↗
PubMed1999

Rapid emotional face processing in the human right and left brain hemispheres: an ERP study.

Imaging work has begun to elucidate the spatial organization of emotions; the temporal organization, however, remains unclear. Adaptive behavior relies on rapid monitoring of potentially salient cues (typically with high emotional value) in the environment. To clarify the timing and speed of emotional processing in the two human brain hemispheres, event-related potentials (ERPs) were recorded during hemifield presentation of face images. ERPs were separately computed for disliked and liked faces, as individually assessed by postrecording affective ratings. After stimulation of either hemisphere, personal affective judgements of face images significantly modulated ERP responses at early stages, 80-116 ms after right hemisphere and 104-160 ms after left hemisphere stimulation. This is the first electrophysiological evidence for valence-dependent, automatic, i.e. pre-attentive emotional processing in humans.

Adult↗
PubMed1999

Affective attitudes to face images associated with intracerebral EEG source location before face viewing.

We investigated whether different, personality-related affective attitudes are associated with different brain electric field (EEG) sources before any emotional challenge (stimulus exposure). A 27-channel EEG was recorded in 15 subjects during eyes-closed resting. After recording, subjects rated 32 images of human faces for affective appeal. The subjects in the first (i.e., most negative) and fourth (i.e., most positive) quartile of general affective attitude were further analyzed. The EEG data (mean=25+/-4. 8 s/subject) were subjected to frequency-domain model dipole source analysis (FFT-Dipole-Approximation), resulting in 3-dimensional intracerebral source locations and strengths for the delta-theta, alpha, and beta EEG frequency band, and for the full range (1.5-30 Hz) band. Subjects with negative attitude (compared to those with positive attitude) showed the following source locations: more inferior for all frequency bands, more anterior for the delta-theta band, more posterior and more right for the alpha, beta and 1.5-30 Hz bands. One year later, the subjects were asked to rate the face images again. The rating scores for the same face images were highly correlated for all subjects, and original and retest affective mean attitude was highly correlated across subjects. The present results show that subjects with different affective attitudes to face images had different active, cerebral, neural populations in a task-free condition prior to viewing the images. We conclude that the brain functional state which implements affective attitude towards face images as a personality feature exists without elicitors, as a continuously present, dynamic feature of brain functioning.

Adult↗
PubMed1999

Hallucinatory experiences in extreme-altitude climbers.

OBJECTIVE: This study attempted a systematic investigation of incidence, type, and circumstances of anomalous perceptual experiences in a highly specialized group of healthy subjects, extreme-altitude climbers. BACKGROUND: There is anecdotal evidence for a high incidence of anomalous perceptual experiences during mountain climbing at high altitudes. METHOD: In a structured interview, we asked eight world-class climbers, each of whom has reached altitudes above 8500 m without supplementary oxygen, about hallucinatory experiences during mountain climbing at various altitudes. A comprehensive neuropsychological, electroencephalographic, and magnetic resonance imaging evaluation was performed within a week of the interview (8). RESULTS: All but one subject reported somesthetic illusions (distortions of body scheme) as well as visual and auditory pseudohallucinations (in this order of frequency of occurrence). A disproportionately large number of experiences above 6000 m as compared to below 6000 m were reported (relative to the total time spent at these different altitudes). Solo climbing and (in the case of somesthetic illusions) life-threatening danger were identified as probable triggers for anomalous perceptual experiences. No relationship between the number of reported experiences and neuropsychological impairment was found. Abnormalities in electroencephalographic (3 climbers) and magnetic resonance imaging (2 climbers) findings were likewise unrelated to the frequency of reported hallucinatory experiences. CONCLUSIONS: The results confirm earlier anecdotal evidence for a considerable incidence of hallucinatory experiences during climbing at high altitudes. Apart from hypoxia, social deprivation and acute stress seem to play a role in the genesis of these experiences.

Adult↗
PubMed1999

Persistent Klüver-Bucy syndrome after bilateral thalamic infarction.

OBJECTIVE: To describe a patient who exhibited a partial Klüver-Bucy syndrome after small bilateral ischemic lesions in the thalami. BACKGROUND: Previously reported patients with Klüver-Bucy syndrome had very large, mostly bilateral lesions in the limbic system and could not provide sufficient information about its anatomo-functional correlate. METHOD: Behavioral assessments and clinical examinations, including magnetic resonance imaging and positron emission tomography, were conducted. RESULTS: The patient was severely amnestic, distractible, hyperoral, and affectively dyscontrolled, and she behaved socially inappropriately. Magnetic resonance imaging showed bilateral infarctions in the territories of both thalamoperforating arteries, and positron emission tomography revealed bilaterally decreased fluorodeoxyglucose uptake in the anterior parts of the ventral thalami and, to a lesser extent, in the fronto-temporal cortices. CONCLUSIONS: This behavioral syndrome has not yet been reported with isolated diencephalic lesions, but it has been observed after bilateral temporal lobe lesions. The authors conjecture that this syndrome resulted from a disruption of the pathways connecting the dorsomedial thalami with the prefrontal cortices and with other limbic areas, systems essential for memory and the regulation of impulses and emotions.

Aged↗
PubMed1998

Faces and emotions: brain electric field sources during covert emotional processing.

Covert brain activity related to task-free, spontaneous (i.e. unrequested), emotional evaluation of human face images was analysed in 27-channel averaged event-related potential (ERP) map series recorded from 18 healthy subjects while observing random sequences of face images without further instructions. After recording, subjects self-rated each face image on a scale from "liked" to "disliked". These ratings were used to dichotomize the face images into the affective evaluation categories of "liked" and "disliked" for each subject and the subjects into the affective attitudes of "philanthropists" and "misanthropists" (depending on their mean rating across images). Event-related map series were averaged for "liked" and "disliked" face images and for "philanthropists" and "misanthropists". The spatial configuration (landscape) of the electric field maps was assessed numerically by the electric gravity center, a conservative estimate of the mean location of all intracerebral, active, electric sources. Differences in electric gravity center location indicate activity of different neuronal populations. The electric gravity center locations of all event-related maps were averaged over the entire stimulus-on time (450 ms). The mean electric gravity center for disliked faces was located (significant across subjects) more to the right and somewhat more posterior than for liked faces. Similar differences were found between the mean electric gravity centers of misanthropists (more right and posterior) and philanthropists. Our neurophysiological findings are in line with neuropsychological findings, revealing visual emotional processing to depend on affective evaluation category and affective attitude, and extending the conclusions to a paradigm without directed task.

Adult↗
PubMed1997

The anterior and posterior selective temporal lobe amobarbital tests: angiographic, clinical, electroencephalographic, PET, SPECT findings, and memory performance.

The techniques, results, and problems of three types of selective temporal lobe (TL) amobarbital procedures (balloon technique with temporary occlusion of the internal carotid artery distal to the origin of the anterior choroidal artery (acha) [n = 19]; selective anterior catheterization of the acha [n = 20]; and selective catheterization of the peduncular P2-segment of the posterior cerebral artery [n = 5]) are described in a group of 40 patients with medically refractory complex partial seizures of mesial TL origin. Selective amobarbital tests were carried out before surgery to predict the memory deficit after an intended selective amygdalohippocampectomy. The effects of selective anaesthetization of TL were correlated with clinical data, pattern and duration of amobarbital induced EEG changes, and performance on verbal and nonverbal memory tasks measured during the test. In 4 patients the effect of selective amobarbital injection on regional and global metabolism was studied with 18F-FDG-PET, with the PET tracer being injected intravenously immediately after amobarbital. More recently in 2 patients the vascular territory perfused by amobarbital in the acha test was studied with SPECT using 99m Tc ECD injected immediately prior to the amobarbital into the acha. Whereas the PET studies showed a rather widespread and bilateral amobarbital-induced decrease of metabolism, the SPECT studies confirmed the selective distribution of the tracer in the vascular territory of the acha, i.e., in amygdala and hippocampus. The comparison of selective TL amobarbital test performance with postoperative neuropsychological performance showed that the predictive value of this test is rather good for the postoperative verbal memory but underestimates postoperative nonverbal ("figural") memory performance.

Adult↗