Changing cortical excitability with low-frequency magnetic stimulation.
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Humans↗
Biomedical subjects
R J Seitz
Publications and source records attributed to R J Seitz.
A neural correlate of syntactic encoding during speech production.
Spoken language is one of the most compact and structured ways to convey information. The linguistic ability to structure individual words into larger sentence units permits speakers to express a nearly unlimited range of meanings. This ability is rooted in speakers' knowledge of syntax and in the corresponding process of syntactic encoding. Syntactic encoding is highly automatized, operates largely outside of conscious awareness, and overlaps closely in time with several other processes of language production. With the use of positron emission tomography we investigated the cortical activations during spoken language production that are related to the syntactic encoding process. In the paradigm of restrictive scene description, utterances varying in complexity of syntactic encoding were elicited. Results provided evidence that the left Rolandic operculum, caudally adjacent to Broca's area, is involved in both sentence-level and local (phrase-level) syntactic encoding during speaking.
Adult↗
Syntactic processing in left prefrontal cortex is independent of lexical meaning.
In language comprehension a syntactic representation is built up even when the input is semantically uninterpretable. We report data on brain activation during syntactic processing, from an experiment on the detection of grammatical errors in meaningless sentences. The experimental paradigm was such that the syntactic processing was distinguished from other cognitive and linguistic functions. The data reveal that in syntactic error detection an area of the left dorsolateral prefrontal cortex, adjacent to Broca's area, is specifically involved in the syntactic processing aspects, whereas other prefrontal areas subserve general error detection processes.
Adult↗
[Reversible multifocal encephalopathy in fulminant eclampsia].
Fulminant eclampsia characterised by the onset of focal neurological signs and convulsions is a rare complication of normal pregnancy in the third trimenon. We report on eight women (22-35 years old) with fulminant eclampsia who were admitted to our hospital due to seizures and central pareses. The patients presented with multifocal lesions involving grey and white matter preferentially of the occipital lobes, as evidenced by neuroimaging. Transcranial Doppler sonography revealed increased cerebral blood flow velocities. Treatment consisted of antihypertensive and anticonvulsive medication and operative termination of pregnancy. The patients normalised within 14 days. Our data show that fulminant eclampsia can induce a severe multifocal encephalopathy that can be reversible when treatment and termination of pregnancy are initiated immediately.
Acute Disease↗
Cerebral networks in sensorimotor disturbances.
Increasing evidence suggests that the human brain employs multiple, interconnected brain areas for information processing and control of behavior, including the performance of laboratory tasks. Brain diseases are expected to affect these networks directly by interference and indirectly as a consequence of deficit compensation. Covariance analyses applied to functional brain imaging data open the opportunity to study neural networks and their disease-related changes in the human brain. Here, we review our analytic approach based on principal component analysis (PCA) to address such questions. We will discuss its methodological foundations and applications in patients with sensorimotor disorders. We will show that PCA in combination with, both, hypothesis-driven testing and correlation statistics provides a powerful tool for elucidating disease-related abnormalities and postlesional reorganization of neural networks in the human brain.
Adult↗
Activation of frontoparietal cortices during memorized triple-step sequences of saccadic eye movements: an fMRI study.
To determine the cortical areas controlling memory-guided sequences of saccadic eye movements, we performed functional magnetic resonance imaging (fMRI) in six healthy adults. Subjects had to perform a memorized sequence of three saccades in darkness, after a triple-step stimulus of successively flashed laser targets. To assess the differential contribution of saccadic subfunctions, we applied several control conditions, such as central fixation with or without triple-step visual stimulation, self-paced saccades in darkness, visually guided saccades and single memory-guided saccades. Triple-step saccades strongly activated the regions of the frontal eye fields, the adjacent ventral premotor cortex, the supplementary eye fields, the anterior cingulate cortex and several posterior parietal foci in the superior parietal lobule, the precuneus, and the middle and posterior portion of the intraparietal sulcus, the probable location of the human parietal eye field. Comparison with the control conditions showed that the right intraparietal sulcus and parts of the frontal and supplementary eye fields are more involved in the execution of triple-step saccades than in the other saccade tasks. In accordance with evidence from clinical lesion studies, we propose that the supplementary eye field essentially controls the triggering of memorized saccadic sequences, whereas activation near the middle portion of the right intraparietal sulcus appears to reflect the necessary spatial computations, including the use of extraretinal information (efference copy) about a saccadic eye displacement for updating the spatial representation of the second or third target of the triple-step sequence.
Adult↗
Neural correlates of religious experience.
The commonsense view of religious experience is that it is a preconceptual, immediate affective event. Work in philosophy and psychology, however, suggest that religious experience is an attributional cognitive phenomenon. Here the neural correlates of a religious experience are investigated using functional neuroimaging. During religious recitation, self-identified religious subjects activated a frontal-parietal circuit, composed of the dorsolateral prefrontal, dorsomedial frontal and medial parietal cortex. Prior studies indicate that these areas play a profound role in sustaining reflexive evaluation of thought. Thus, religious experience may be a cognitive process which, nonetheless, feels immediate.
Adult↗
Tactile apraxia: unimodal apractic disorder of tactile object exploration associated with parietal lobe lesions.
Tactile apraxia is characterized by an isolated disturbance of hand movements for use of and interaction with an object (transitive movements) in the presence of preserved intransitive movements (movements without use of an object, for example repetitive movements or gestures). It is, however, still unclear whether motor and sensory abnormalities represent causal or associated features of tactile apraxia. To address this question, quantitative kinematic recordings of exploratory finger movements (transitive movements) and rapid alternating finger movements (intransitive movements) were studied in 20 healthy volunteers and 22 patients with focal lesions of the parietal, anterofrontal and motor cortex. The most severe deficits of manual object exploration were found in patients with parietal lesions, using the hand contralateral to the lesion. Patients with lesions of the anterior parietal lobe who exhibited prominent sensory deficits and astereognosia showed a decrease in frequency and regularity of exploratory finger movements and a marked increase in exploration space. Patients with posterior parietal lesions exhibiting severe astereognosia, apraxia and deficits in dexterity had a greater decrease in frequency and regularity of manipulative movements, but a less pronounced increase of exploration space than the patients with anterior parietal lesions. Although the patients with parietal lobe lesions could generate rapid alternating finger movements, the regularity of these movements was also impaired. In comparison, patients with frontal lobe lesions exhibited impaired contralesional manipulatory and rapid alternating finger movements but no sensory abnormalities or astereognosia. We conclude that tactile apraxia represents a deficit in the programming of exploratory finger movements mediated by the parietal lobe. The comparison with lesions of other regions participating in the cortical network for tactile exploration reveals that apraxia of exploratory movements in parietal lobe lesions represents a disturbance distinct from elementary motor or sensory abnormalities, but closely related to stereognostic functioning.
Adolescent↗
Recovery of motor functions following hemiparetic stroke: a clinical and magnetic resonance-morphometric study.
Predictors for the degree of clinical recovery after stroke are still poorly defined. In this study we tried to assess the predictive value of clinical data and of lesion size for motor recovery after ischemic stroke. In 52 hemiparetic patients we monitored the course of clinical recovery by a dedicated score of sensorimotor hand function after their first stroke. The course of the lesion size was measured in proton density magnetic resonance images. Three groups of patients were identified. Patients with moderate initial motor deficit recovered almost completely within 9 days (17/17, group 1). From the patients with severe initial motor deficit, about equal numbers recovered (16/35, group 2) or remained severely impaired during the entire observation period of more than 6 months (19/35, group 3). There was no correlation between changes of lesion size and motor deficit. Logistic regression of probability of good clinical outcome on initial lesion size, initial motor score and subcortical versus cortical location of lesion showed that only the initial motor score was predictive (p = 0.006). A relative improvement of the initial motor score of about 20% in the first 4 weeks after stroke appeared to be a relevant cut point for good outcome. The data indicate that patients with mild initial motor deficits recover well, whereas severely affected patients may differ in outcome. Since lesion size was not correlated with outcome the amount of spared residual function appeared as major determinant for the capacity for motor recovery.
Activities of Daily Living↗
Action observation activates premotor and parietal areas in a somatotopic manner: an fMRI study.
Functional magnetic resonance imaging (fMRI) was used to localize brain areas that were active during the observation of actions made by another individual. Object- and non-object-related actions made with different effectors (mouth, hand and foot) were presented. Observation of both object- and non-object-related actions determined a somatotopically organized activation of premotor cortex. The somatotopic pattern was similar to that of the classical motor cortex homunculus. During the observation of object-related actions, an activation, also somatotopically organized, was additionally found in the posterior parietal lobe. Thus, when individuals observe an action, an internal replica of that action is automatically generated in their premotor cortex. In the case of object-related actions, a further object-related analysis is performed in the parietal lobe, as if the subjects were indeed using those objects. These results bring the previous concept of an action observation/execution matching system (mirror system) into a broader perspective: this system is not restricted to the ventral premotor cortex, but involves several somatotopically organized motor circuits.
Adult↗
A neural basis for general intelligence.
Universal positive correlations between different cognitive tests motivate the concept of "general intelligence" or Spearman's g. Here the neural basis for g is investigated by means of positron emission tomography. Spatial, verbal, and perceptuo-motor tasks with high-g involvement are compared with matched low-g control tasks. In contrast to the common view that g reflects a broad sample of major cognitive functions, high-g tasks do not show diffuse recruitment of multiple brain regions. Instead they are associated with selective recruitment of lateral frontal cortex in one or both hemispheres. Despite very different task content in the three high-g-low-g contrasts, lateral frontal recruitment is markedly similar in each case. Many previous experiments have shown these same frontal regions to be recruited by a broad range of different cognitive demands. The results suggest that "general intelligence" derives from a specific frontal system important in the control of diverse forms of behavior.
Adult↗
Potential time course of human immunodeficiency virus type 1-associated minor motor deficits: electrophysiologic and positron emission tomography findings.
BACKGROUND: We tested whether metabolic abnormalities in the prefrontal-striatal circuitry as demonstrated by positron emission tomography (PET) were present in patients seropositive for human immunodeficiency virus type 1 (HIV-1) with HIV-1-associated minor motor deficits as demonstrated by quantitative motor testing. PATIENTS: We examined 19 HIV-1-positive patients, covering the range from normal results of quantitative motor testing to clearly pathologic psychomotor slowing indicative of HIV-1-associated minor motor deficits. None fulfilled the clinical criteria for HIV-1-associated dementia. Results were compared with those of 15 healthy volunteers. METHODS: All subjects underwent clinical examination, routine magnetic resonance (MR) imaging, and electrophysiologic motor testing at the time of PET. RESULTS: Seven HIV-1-positive patients showed significant hypermetabolism in the basal ganglia. Nine patients showed a significant frontomesial hypometabolism. CONCLUSIONS: The data of our cross-sectional study strongly suggest a characteristic time course in the development of HIV-1-associated minor motor deficits. Hypermetabolism in the basal ganglia is associated initially with normal motor performance. Moderate motor slowing appears at a later stage when basal ganglia hypermetabolism drops toward hypometabolism. More severe functional deficits and highly pathologic motor slowing become manifest when hypometabolism is most widespread in the basal ganglia. This stage leads to dementia.
Adult↗
Visual hallucinations in recovery from cortical blindness: imaging correlates.
OBJECTIVE: To investigate the cerebral metabolic and functional patterns during recovery from cortical blindness. DESIGN: Follow-up study with serial clinical, metabolic, and functional imaging and visual evoked potentials. CASE PRESENTATION: A 24-year-old woman suffered from cortical blindness after cardiac arrest and recovered over a 6-month period. During recovery, she experienced complex visual hallucinations that could be initiated by visual imagery. RESULTS: Initially, the regional cerebral metabolic rate of glucose was severely reduced in the visual and parieto-occipital cortex bilaterally but recovered almost completely. Visual hallucinations led to significant increases of the regional cerebral blood flow in the initially severely hypometabolic parieto-occipital and temporo-lateral cortex. CONCLUSIONS: Recovery of vision was related to normalization of the postlesionally dysfunctional cortex. Visual hallucinations appeared as the clinical correlate of the electrophysiological hyperexcitability of the recovering partially damaged visual cortex.
Adult↗
Broca's region subserves imagery of motion: a combined cytoarchitectonic and fMRI study.
Broca's region in the dominant cerebral hemisphere is known to mediate the production of language but also contributes to comprehension. Here, we report the differential participation of Broca's region in imagery of motion in humans. Healthy volunteers were studied with functional magnetic resonance imaging (fMRI) while they imagined movement trajectories following different instructions. Imagery of right-hand finger movements induced a cortical activation pattern including dorsal and ventral portions of the premotor cortex, frontal medial wall areas, and cortical areas lining the intraparietal sulcus in both cerebral hemispheres. Imagery of movement observation and of a moving target specifically activated the opercular portion of the inferior frontal cortex. A left-hemispheric dominance was found for egocentric movements and a right-hemispheric dominance for movement characteristics in space. To precisely localize these inferior frontal activations, the fMRI data were coregistered with cytoarchitectonic maps of Broca's areas 44 and 45 in a common reference space. It was found that the activation areas in the opercular portion of the inferior frontal cortex were localized to area 44 of Broca's region. These activations of area 44 can be interpreted to possibly demonstrate the location of the human analogue to the so-called mirror neurones found in inferior frontal cortex of nonhuman primates. We suggest that area 44 mediates higher-order forelimb movement control resembling the neuronal mechanisms subserving speech.
Adult↗
Control of action as mediated by the human frontal lobe.
Conscious control of action involves the voluntary initiation and the continuous adjustment of motor activity. Neuroimaging data provide evidence that the plan for a movement is developed with respect to the behavioral context in prefrontal cortex, while the synergies of a motor program are coded by premotor cortex and the specific movement parameters by the motor cortex. It is suggested that the initiational aspects of conscious motor activity are implemented in a medial system of information flow and the integrative aspects in a lateral system of the human frontal lobe.
Adult↗
Focal cortical dysplasia of the temporal lobe with late-onset partial epilepsy: serial quantitative MRI.
We describe serial studies of focal cortical dysplasia causing temporal lobe seizures and progressive aphasia in a 54-year-old woman. Initially, MRI volumetry of the temporal lobes showed significant left cortical thickening corresponding to an elevated amino-acid uptake in the left temporoparietal and inferior frontal cortex on SPECT using 3-[123I]iodo-alpha-methyl-L-tyrosine (IMT). After 1 year there was severe shrinkage of the left temporal lobe, possibly the result of recurrent complex partial seizures.
Aphasia↗
Temporal lobe epilepsy with sensory aura: interictal glucose hypometabolism.
Patients with mesial temporal lobe epilepsy (mTLE) exhibit marked depressions of the regional cerebral glucose metabolism (rCMRGlu) in the mesiotemporal region. We hypothesised that patients with temporal lobe epilepsy (TLE) who have a bilateral somatosensory or acoustic ( = temporolateral/SII-) aura can be differentiated from mTLE by rCMRGlu depressions primarily involving temporo-perisylvian locations. We therefore used this ictal semiology as a clinical criterion to define a subgroup of such patients and measured the rCMRGlu in 16 patients with TLE as evident from interictal and ictal EEG-video monitoring. Clinically, they presented with medically refractory complex partial seizures and were subjected to presurgical evaluation. The pattern of the interictal rCMRGlu in the TLE patients was different from that observed in patients with mTLE and showed significant depressions ipsilateral to the epileptic focus in mesial temporal and lateral temporal regions but spared the thalamus. The neocortical metabolic depressions were spatially more extended in right than in left TLE patients. Magnetic resonance images (MRI) were either normal (n = 5) or revealed unilateral or bilateral hippocampal atrophy/sclerosis (n = 7), or temporal or extratemporal focal cortical dysplasia (n = 4). The selected TLE patients presented here comprise a heterogeneous group showing most pronounced metabolic depressions in the lateral temporal cortex. Thus, our data suggest that non-invasive metabolic imaging can assist in identifying the neocortical symptomatogenic zone in putative temporo-perisylvian lobe epilepsy.
Abdomen↗
Diffusion- and perfusion-weighted MRI: influence of severe carotid artery stenosis on the DWI/PWI mismatch in acute stroke.
BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) have been used increasingly in recent years to evaluate acute stroke in the emergency setting. In the present study, we compared DWI and PWI findings in acute stroke patients with and without severe extracranial internal carotid artery (ICA) disease. METHODS: Twenty-seven patients with nonlacunar ischemic stroke were selected for this analysis. DWI, PWI, and conventional MRI were performed in all patients within 24 hours of symptom onset and after 1 week. To exclude patients with partial or complete reperfusion, we included only patients with a PWI deficit larger than the DWI lesion. Severe ICA disease (>70% stenosis) was present unilaterally in 9 and bilaterally in 2 patients. Acute DWI lesion volume, the size of the acute PWI/DWI mismatch, and final infarct size (on T2-weighted images) were determined. RESULTS: The PWI/DWI mismatch was significantly larger in patients with severe ICA disease than in patients without extracranial carotid stenosis, both when time-to-peak and mean transit time maps (P<0.01) were used to calculate the mismatch. Quantitative analysis of the time-to-peak delay in the mismatch indicated that a relatively smaller fraction of the total mismatch was critically ischemic in patients with carotid stenosis than in those without. Average lesion volume increased less in the stenosis group (P=0.14), despite the larger PWI/DWI mismatch, and final infarct size was smaller in the stenosis group (P<0.05). In the 2 patients with bilateral ICA disease, variable hemodynamic involvement of the contralateral hemisphere was found in addition to the ipsilateral PWI deficit. CONCLUSIONS: In most acute stroke patients with severe ICA stenosis, a considerably smaller fraction of the total PWI/DWI mismatch is at risk than in patients without carotid disease.
Acute Disease↗