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At least 1,477 records · Page 82Linked to original sources
PubMed1993

Functional brain mapping by blood oxygenation level-dependent contrast magnetic resonance imaging. A comparison of signal characteristics with a biophysical model.

It recently has been demonstrated that magnetic resonance imaging can be used to map changes in brain hemodynamics produced by human mental operations. One method under development relies on blood oxygenation level-dependent (BOLD) contrast: a change in the signal strength of brain water protons produced by the paramagnetic effects of venous blood deoxyhemoglobin. Here we discuss the basic quantitative features of the observed BOLD-based signal changes, including the signal amplitude and its magnetic field dependence and dynamic effects such as a pronounced oscillatory pattern that is induced in the signal from primary visual cortex during photic stimulation experiments. The observed features are compared with the results of Monte Carlo simulations of water proton intravoxel phase dispersion produced by local field gradients generated by paramagnetic deoxyhemoglobin in nearby venous blood vessels. The simulations suggest that the effect of water molecule diffusion is strong for the case of blood capillaries, but, for larger venous blood vessels, water diffusion is not an important determinant of deoxyhemoglobin-induced signal dephasing. We provide an expression for the apparent in-plane relaxation rate constant (R2*) in terms of the main magnetic field strength, the degree of the oxygenation of the venous blood, the venous blood volume fraction in the tissue, and the size of the blood vessel.

Biophysical Phenomena↗
PubMed2000

Functional brain areas used for the lifting of objects using a precision grip: a PET study.

Positron emission tomography (PET) was performed in 10 normal volunteers to investigate regional cortical and subcortical activation induced by the lifting of an object repetitively using a precision grip between the index finger and thumb. Data were obtained for three object weights (4, 200 and 600 g) and a resting condition. Grip and lift forces on a similar object and the activity of selected muscles in the hand, arm and shoulder were also recorded in separate lifting trials. A comparison between all movement conditions and the resting condition revealed significant activation of the primary motor (M1), primary sensory (S1), dorso-caudal premotor (PM), caudal supplementary motor (SMA) and cingulate motor (CMA) cortices contralateral to the hand used. On the ipsilateral side, activation of the M1, caudal SMA and inferior parietal cortex (BA 40) was also found. In the subcortical areas, the bilateral hemispheres and right vermis of the cerebellum, left basal ganglia and thalamus were activated. Behavioral adaptation to a heavier object weight was revealed in a nearly proportional increase of both grip and lift forces, prolonged force application period and a higher level of hand and arm muscle activities. An increase in the rCBF associated with these changes was noted in several cortical and subcortical areas. However, consistent object weight-dependent activation was observed only in the M1/S1 contralateral to the hand used.

Adult↗
PubMed1996

Form-specific priming and functional brain asymmetries in perceptual identification.

Word form representations in intact cerebral hemispheres were studied by a lateralized perceptual identification priming task. During the study phase, word forms were primed by displaying words visually in uppercase or lowercase letters. During the test phase, perceptual identification of non-studied baseline words and studied words (presented in same or different lettercase as studied) was tested by displaying targets in the left or right visual field. Experiment 1 showed that the hemispheric pattern of priming effects was dependent on the lettercase at test. For uppercase test items, only the left visual field/right hemisphere was sentitive to study-test changes in lettercase, replicating an earlier result obtained in word-stem completion (Marsolek, Kosslyn and Squire, 1992). However, lowercase test items did not reveal any asymmetries in the form-dependent priming component indicating that in some conditions form-specific representations are computed in the left hemisphere also. No asymmetries were found in the abstract, form-independent component of priming. Experiment 2 revealed that use of explicit memory in the perceptual identification task eliminated the form-specific priming effects and suggested that the results of Experiment 1 were uncontaminated by explicit memory.

Adult↗
PubMed2003

Abnormalities of brain function during a nonverbal theory of mind task in schizophrenia.

Theory of mind (ToM), the specific ability to attribute thoughts and feelings to oneself and others is generally impaired in schizophrenia. Previous studies demonstrated a deficit of the attribution of intentions to others among patients having formal thought disorder. During nonverbal tasks, such a function requires both the visual perception of human figures and the understanding of their intentions. These processes are considered to involve the superior temporal sulcus and the medial prefrontal cortex, respectively. Are the functional patterns of activation associated with those processes abnormal in schizophrenia? Seven schizophrenic patients on medication performed a nonverbal attribution of intentions task as well as two matched physical logic tasks, with and without human figures, while H2O15 PET-scanning was performed. Data from the patients were compared to those of eight healthy controls matched for verbal IQ and sex. The experimental design allowed dissociating the effect of the perception of human figures from that of the attribution of intentions. During attribution of intentions, significant activations in the right prefrontal cortex were detected in the control subjects. Those activations were not found in the schizophrenic group. However, in both groups, the perception of human figure elicited bilateral activation of the occipitotemporal regions and of the posterior part of the superior temporal sulcus. Schizophrenic patients performing a nonverbal attribution of intentions task have an abnormal cerebral activity.

Adult↗
PubMed2001

Functional brain imaging based on ERD/ERS.

Sensory, cognitive and motor processing can result in changes of the ongoing EEG in form of an event-related desynchronization (ERD) or event-related synchronization (ERS). Both phenomena are time-locked but not phase-locked to the event and they are highly frequency-band specific. The ERD is interpreted as a correlate of an activated cortical area with increased excitability and the ERS in the alpha and lower beta bands can be interpreted, at least under certain circumstances, as a correlate of a deactivated cortical area. Spatial mapping of ERD/ERS can be used to study the dynamics of cortical activation patterns. Examples from a movement task are reported.

Alpha Rhythm↗
PubMed1997

5-HT brain function in affective disorder: d,l-fenfluramine-induced hormone release and clinical outcome in long-term lithium/carbamazepine prophylaxis.

Prolactin (PRL) and Cortisol (CORT) responses to d,l-fenfluramine (FEN) challenge (60 mg) were examined in patients with affective disorders on two occasions under euthymic conditions: drug-free before admission to prophylactic treatment and after about 9 months of medication with lithium or carbamazepine. Response to treatment was assessed by a complex algorithm using continuous ratings in outpatient clinic over a period of 2 years. In general, treatment resulted in a delayed and diminished CORT release (n.s.); subgroup analysis revealed an attenuated CORT response (P < 0.05) in responders, whereas nonresponders showed no change in CORT secretion pattern except an enhanced CORT baseline value (P < 0.05). Cross-sectional comparison of responders with nonresponders under medication yielded a trend for greater CORT stimulation in nonresponders. This result was not affected by FEN/NorFEN or lithium/carbamazepine serum levels, baseline CORT values, age, sex, diagnostic distribution, number of appointments to the outpatient clinic or duration of medication at the time of FEN test session. Before onset of prophylactic medication responders and nonresponders could not be discriminated significantly regarding stimulated hormone release, probably due to the small sample size (n = 17). CORT response to FEN was increased in drugfree unipolar patients compared to bipolar (P < 0.05) and to schizoaffective patients (P < 0.1). In accordance with its well-documented presynaptic 5-HT-agonistic action lithium medication resulted in a significantly greater increase in CORT release than carbamazepine (P < 0.05). Evaluation of PRL stimulation showed patterns of secretion quite similar to those of CORT, without reaching statistical significance in most cases. Perhaps due to methodological differences in assessing treatment response, these data do not confirm former results, which supposed an enhanced 5-HT net activity in long-term prophylactic lithium treatment. Because of high interindividual variances of hormone parameters, the FEN-test procedure is not a useful tool for the prediction of therapeutical outcome in terms of clinical routine use. Relations of stimulated hormone response as a marker of central serotoninergic activity and clinical outcome are discussed.

Adult↗
PubMed2000

Functional brain imaging and pharmacotherapy in social phobia: single photon emission computed tomography before and after treatment with the selective serotonin reuptake inhibitor citalopram.

1. Despite increased understanding of the prevalence and pharmacotherapy of social phobia (or social anxiety disorder), the neurobiology of the disorder is little understood. 2. Little data exists on the effect of pharmacotherapeutic intervention on regional cerebral blood flow (rCBF) in this disorder. Patients (n=15) who met DSM-IV diagnostic criteria for social phobia were subjected to single photon emission computed tomography (SPECT) with technetium-99m hexamethylpropylene amine oxime (Tc-99m HMPAO) before and after an eight-week trial of pharmacotherapy with the selective serotonin reuptake inhibitor (SSRI) citalopram. 3. Pharmacotherapy led to significantly reduced activity in the anterior and lateral part of the left temporal cortex; the anterior, lateral and posterior part of the left mid frontal cortex; and the left cingulum. 4. Despite the small sample size, medication non-responders (n=6) had higher activity at baseline in the anterior and lateral part of the left temporal cortex and the lateral part of the left mid frontal regions compared with responders (n=9). These data from this exploratory study are consistent with work suggesting that the anxiety disorders share certain mediating neurocircuitry, although activity in other brain regions may differ. 5. Further research is necessary to determine the neurobiological underpinnings of social phobia.

Adult↗
PubMed1986

Functional brain imaging with I123-amphetamine. First experience in the Netherlands.

Single Photon Emission Computed Tomography (SPECT) has been used in the last five years as a method for cerebral bloodflow imaging, especially in cerebral infarction. In this study the first experiences in the Netherlands are presented. In 57.6% of our patients lesions, defined by SPECT were larger than those found by CT. This was not only seen in patients with cerebral infarction but also in hematoma. In 33.3% the size of the lesions were comparable. In 10 out of 14 patients with a solitary lesion in one hemisphere a decreased perfusion was seen in the contralateral cerebellar hemisphere. This phenomenon is called crossed cerebellar diaschisis. One patient with probably Alzheimer disease, showing a specific flow pattern, is discussed.

Aged↗
PubMed2001

Brain function in a patient with torture related post-traumatic stress disorder before and after fluoxetine treatment: a positron emission tomography provocation study.

We report positron emission tomographic measurements of regional cerebral blood flow (rCBF) in a male patient with war and torture related post-traumatic stress disorder (PTSD) during symptom provocation. The subject was exposed to war related sounds before and after treatment with a selective serotonin reuptake inhibitor (SSRI; Fluoxetine; Fontex((R))). Therapy reduced PTSD symptoms, provoked anxiety and heart rate. Before treatment trauma reminders resulted in decreased rCBF in the insula, prefrontal, and inferior frontal cortices. Increased activity was evident in the cerebellum, precuneus and supplementary motor cortex. This was normalized after SSRI administration. Prefrontal and cingulate rCBF correlated with heart rate. Hence, the anxiolytic effect of SSRI for PTSD could be mediated by prefrontal and paralimbic cortices. Data suggest that SSRI treatment normalize provocation induced rCBF alterations in areas involved in memory, emotion, attention and motor-control.

Anxiety↗
PubMed2003

Anatomical and functional brain variables associated with clozapine response in treatment-resistant schizophrenia.

Clozapine alleviates the symptoms of a significant proportion of treatment-resistant schizophrenic patients. Previous studies suggest that the response to clozapine may be associated with prefrontal and temporal anatomy as well as with prefrontal, basal ganglia and thalamic metabolism. A sample of 25 treatment-resistant (TR) schizophrenic patients underwent magnetic resonance imaging (MRI) and 18F-deoxyglucose positron emission tomography (PET) before and after treatment with clozapine. We investigated the association between changes in positive, disorganized, and negative schizophrenic syndromes with clozapine treatment and a set of cerebral variables that included total intracranial volume (ICV); hippocampal, dorsolateral prefrontal (DLPF) and temporal gray-matter volume and metabolism; and metabolic activity of the thalamus, pallidum/putamen, and caudate head. Improvement in positive symptoms with clozapine was directly related to temporal gray-matter volume, whereas improvement of disorganization symptoms was inversely related to ICV and hippocampal volume. Patients with high baseline DLPF cortical volume and metabolic activity were more likely to experience improvement in their negative symptoms. We conclude that clinical improvement with clozapine may be related with the anatomy and metabolic activity of specific brain areas, with the structural integrity of the DLPF and temporal regions showing the maximum predictive capacity.

Adult↗
PubMed1998

Brain function in spider phobia.

Measurements of regional cerebral blood flow (rCBF) were performed in 16 women suffering from spider phobia. The non-invasive 133Xe inhalation method, giving information about the blood flow of superficial areas, was used. The subjects were studied under three conditions: during resting, when exposed to a videotape showing nature scenery, and finally when watching a video with living spiders. During the rCBF measurements the subjects' behaviour was registered systematically and respiration, blood pressure, Pco2, and heart rate were monitored. Eight subjects who showed and reported severe panic during the spider exposure had marked rCBF decreases in frontal areas, especially in the right hemisphere. The remaining eight subjects displayed a more efficient control of their emotions and became frightened, but not panic-stricken, during the spider exposure. These showed a consistent rCBF increase in the right frontal area compared to neutral stimulation. Thus, results revealed significant functional changes in the frontal cortex in subjects with spider phobia during phobogenic exposure. It seems likely that these frontal changes are related to the experience and control of phobic anxiety.

Adult↗
PubMedDate not supplied

Neural substrate of nicotine addiction as defined by functional brain maps of gene expression.

The distributed neural networks involved in the intravenous self-administration of nicotine and cocaine, and in a model of relapse of nicotine-taking after abstinence, were compared in Wistar rats. Post-mortem brain maps of c-fos-related antigens expression showed specific activation in prefrontal cortex, anterior cingulate and nucleus accumbens for both drugs, but of the anterior cingulate cortex only during relapse, suggesting that a subset of the neural network involved in drug self-administration is activated during relapse.

Animals↗