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PubMed1999

Temporal properties of the hemodynamic response in functional MRI.

Today, most studies of cognitive processes using functional magnetic resonance imaging (fMRI) adopt an event-related experimental design. Highly flexible stimulation settings require new statistical models where not only the activation amount, but also the time course of the measured hemodynamic response is analyzed. It is possible to obtain statistically valid descriptions of single hemodynamic responses from a robust nonlinear estimation procedure. Focus is placed on the temporal behaviour of the hemodynamic response: relative temporal order, changes induced by modification of the experimental context, and interindividual differences. Example analyses from recent fMRI studies underline the usefulness of this approach.

Adult↗
PubMed2006

Auditory cortical responses evoked by pure tones in healthy and sensorineural hearing loss subjects: functional MRI and magnetoencephalography.

BACKGROUND: Blood oxygen level dependent functional magnetic resonance imaging (fMRI) and magnetoencephalography are new techniques of brain functional imaging which can provide the information of excitation of neurons by measure the changes of hemodynamics and electrophysiological data of local brain tissue. The purpose of this study was to study functional brain areas evoked by pure tones in healthy and sensorineural hearing loss subjects with these techniques and to compare the differences between the two groups. METHODS: Thirty healthy and 30 sensorineural hearing loss subjects were included in this study. In fMRI, block-design paradigm was used. During the active epoch the participants listened to 1000 Hz, sound pressure level 140 dB pure tones at duration 500 ms, interstimulus interval 1000 ms, which presented continuously via a magnetic resonance-compatible audio system. None stimulus was executed in control epoch. In magnetoencephalography study, every subject received stimuli of 1000 Hz tone bursts delivered to the bilateral ear at duration 8 ms, interstimulus intervals 1000 ms. Sound pressure level in healthy subjects was 30 dB; in sensorineural hearing loss subjects was 20 dB above everyone's hearing threshold respectively. All subjects were examined with 306-channel whole-scalp neuromagnetometer. RESULTS: In fMRI, all subjects showed significant activations in bilateral Heschl's gyri, anterior pole of planum temporale, planum temporale, precentral gyri, postcentral gyri, supramarginal gyri, superior temporal gyri, inferior frontal gyri, occipital lobes and cerebellums. The healthy subjects had more intensive activation in bilateral Heschl's gyri, anterior pole of planum temporale, inferior frontal gyri, left superior temporal gyri and right planum temporale than the hearing loss subjects. But in precentral gyri, postcentral gyri and occipital lobes, the activation is more intensive in the hearing loss subjects. In magnetoencephalography study, both in the hearing loss and the healthy subjects, the most evident audio evoked fields activated by pure tone were N100m, which located precisely on the Heschl's gyrus. Compared with the hearing loss subjects, N100m of the healthy subjects was stronger and had longer latencies in right hemisphere. CONCLUSIONS: Under proper pure tone stimulus the activation of auditory cortex can be elicited both in the healthy and the sensorineural hearing loss subjects. Either at objective equivalent stimuli or at subjectively perceived equivalent stimuli, the auditory responses were more intensive in healthy subjects than hearing loss subjects. The tone stimuli were processed in a network in human brain and there was an intrinsic relation between the auditory and visual cortex. Blood oxygen level dependent fMRI and magnetoencephalography could reinforce each other.

Acoustic Stimulation↗
PubMed2002

Neuronavigation and functional MRI for surgery in patients with lesion in eloquent brain areas.

OBJECTIVE: Surgery in patients with lesions in eloquent areas is still a challenge for the neurosurgeon. The aim of surgical interventions should be the radical removal of the lesions with functional preservation. Functional brain imaging methods provide the preoperative demonstration of those brain areas and their relationship to pathologic structures. MATERIAL: Twenty-seven patients with pathologic lesions in or near eloquent regions were investigated with functional magnetic resonance imaging (fMRI). Nineteen patients were neurologically intact preoperatively, and presented only with headache and/or seizure. Eight patients had a minor neurological deficit. Twenty-five patients underwent surgery. Preoperatively a computed tomography (CT) scan or a magnetic resonance imaging procedure with five skin fiducials was performed. The data were transferred to the neuronavigation workstation. The tumour was lined out in colours, and reconstruction in a triplanar format as well as three-dimensionally was implemented. The information from the fMRI concerning the functional areas was transferred into the images manually to account for EPI distortions. Fifteen patients were operated on using the combination fMRI/neuronavigation. Diagnoses included eleven gliomas, two meningeomas, one metastasis and one cavernoma. RESULTS: In seven patients the tumour was removed completely, eight patients had residual tumour, demonstrated by early postoperative MRI. All patients with residual tumour had gliomas that involved functional areas. Postoperatively no patient had an additional neurological deficit. CONCLUSION: Functional MRI provides important additional information in patients with lesions in eloquent brain areas. In combination with neuronavigation this is a very helpful technique for surgical interventions on these patients to reduce morbidity. Nonetheless, there are still open questions concerning accuracy of display of the functional areas and integration into a neuronavigation system.

Brain↗
PubMed1996

[Functional MRI of the pharynx in obstructive sleep apnea using rapid 2D FLASH sequences].

Functional imaging of the pharynx used to be the domain of cineradiography, CT and ultrafast CT. The development of modern MRI techniques led to new access to functional disorders of the pharynx. The aim of this study was to implement a new MRI technique to examine oropharyngeal obstructive mechanisms in patients with obstructive sleep apnea (OSA). Sixteen patients suffering from OSA and 6 healthy volunteers were examined on a 1.5 T whole-body imager ("Vision", Siemens, Erlangen Medical Engineering, Germany) using a circular polarized head coil. Imaging was performed with 2D flash sequences in midsagittal and axial planes. Patients and volunteers were asked to breathe normally through the nose and to simulate snoring and the Mueller maneuver during magnetic resonance imaging (MRI). Prior to MRI, all patients underwent an ear, nose and throat (ENT) examination, functional fiberoptic nasopharyngoscopy and polysomnography. A temporal resolution of 6 images/s and an in-plane resolution of 2.67 x 1.8 mm were achieved. The mobility of the tongue, soft palate and pharyngeal surface could be clearly delineated. The MRI findings correlated well with the clinical examinations. We propose ultrafast MRI as a reliable and non-invasive method of evaluating pharyngeal obstruction and their levels.

Adult↗
PubMed2004

Functional MRI study of verbal fluency in a patient with subcortical laminar heterotopia.

RATIONALE: Double cortex syndrome is a malformation in which there is a band of subcortical heterotopic grey matter separated from the cortex by white matter. The functional activity of the heterotopic neurons is unclear. PATIENT: A 13-year-old female was evaluated for seizures. The EEG showed bifrontal spike wave disturbance. Band heterotopia, in association with mild reduction of sulcation of the cerebral hemispheres, was found on MRI. Psychological assessment indicated the presence of variable cognitive abilities, with verbal IQ [82] generally better than nonverbal IQ [59], and specific difficulties in language comprehension and mathematics. METHOD: Functional MRI was used to localize the areas of language and motor activation. The language activation paradigm was a visual verb generation task with a visual fixation baseline. The motor paradigm consisted of alternating blocks of sequential finger tapping and rest. Coronal functional and anatomical images were obtained. RESULTS: The motor paradigm produced activation of the primary motor cortex, the band heterotopia and the supplementary motor cortex. The language paradigm produced activation of the left inferior frontal gyrus and left supplementary motor area, but not of the band heterotopia. CONCLUSIONS: The activation of heterotopic grey matter during a motor task demonstrates a hemodynamic association with motor activity and suggests that this tissue may be functional. Such association was not seen with the language task. We speculate that later maturing functions such as language are restricted in their development to the normal situated superficial cortex in our patient.

Adolescent↗
PubMed1993

Functional MRI of human brain activation at high spatial resolution.

Functional activation maps of the human visual cortex were obtained at a spatial resolution almost two orders of magnitude better than achievable by positron emission tomography and within measuring times of a few seconds. Transient alterations in the concentration of paramagnetic deoxyhemoglobin were conveniently detected at 2.0-T with use of RF-spoiled FLASH MRI sequences employing gradient echo times of 6 to 60 ms and voxel sizes of 2.5 to 39 microliters.

Adult↗
PubMed1993

Processing strategies for time-course data sets in functional MRI of the human brain.

Image processing strategies for functional magnetic resonance imaging (FMRI) data sets acquired using a gradient-recalled echo-planar imaging sequence are considered. The analysis is carried out using the mathematics of vector spaces. Data sets consisting of N sequential images of the same slice of brain tissue are analyzed in the time-domain and also, after Fourier transformation, in the frequency domain. A technique for thresholding is introduced that uses the shape of the response in a pixel compared with the shape of a reference waveform as the decision criterion. A method is presented to eliminate drifts in data that arise from subject movement. The methods are applied to experimental FMRI data from the motor-cortex and compared with more conventional image-subtraction methods. Several finger motion paradigms are considered in the context of the various image processing strategies. The most effective method for image processing involves thresholding by shape as characterized by the correlation coefficient of the data with respect to a reference waveform followed by formation of a cross-correlation image. Emphasis is placed not only on image formation, but also on the use of signal processing techniques to characterize the temporal response of the brain to the paradigm.

Brain↗
PubMed2006

Altered baseline brain activity in children with ADHD revealed by resting-state functional MRI.

In children with attention deficit hyperactivity disorder (ADHD), functional neuroimaging studies have revealed abnormalities in various brain regions, including prefrontal-striatal circuit, cerebellum, and brainstem. In the current study, we used a new marker of functional magnetic resonance imaging (fMRI), amplitude of low-frequency (0.01-0.08Hz) fluctuation (ALFF) to investigate the baseline brain function of this disorder. Thirteen boys with ADHD (13.0+/-1.4 years) were examined by resting-state fMRI and compared with age-matched controls. As a result, we found that patients with ADHD had decreased ALFF in the right inferior frontal cortex, [corrected] and bilateral cerebellum and the vermis as well as increased ALFF in the right anterior cingulated cortex, left sensorimotor cortex, and bilateral brainstem. This resting-state fMRI study suggests that the changed spontaneous neuronal activity of these regions may be implicated in the underlying pathophysiology in children with ADHD.

Adolescent↗
PubMed2006

A comparison of functional MRI and magnetoencephalography for receptive language mapping.

We compared functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) for the mapping of receptive language function. Participants performed the same language task in the two different imaging environments. MEG activation profiles showed prominent bilateral activity in superior temporal gyrus and left-lateralized activity in middle temporal gyrus. fMRI activation profiles revealed bilateral activity in prefrontal, superior temporal, middle temporal, and visual areas. Laterality quotients derived from the two modalities showed poor agreement between the two methods for commonly active regions of interest. Locations of peak activity also varied considerably within participants between the two methods.

Adult↗
PubMed2005

Spontaneous dissociation during functional MRI experiments.

It is assumed that the procedures of functional magnetic resonance imaging (fMRI) are able to provoke significant dissociative responses. Trait and state dissociation of 32 healthy subjects undergoing fMRI have been recorded. At least one-third of the subjects showed dissociative responses of very large effect size (d=4.10). The contributing causal factors for that dissociative response could not yet identified clearly. Considering the impact of dissociation on mental functions, we recommend controlling subjects undergoing fMRI studies for dissociative responses. Further studies on the actual phenomenological experience of subjects undergoing fMRI procedures are warranted.

Adult↗
PubMed2005

The effect of working memory performance on functional MRI in schizophrenia.

INTRODUCTION: Studies of prefrontal cortical (PFC) function in schizophrenia have been inconsistent, with studies showing both increased and decreased PFC activation compared to healthy controls. Discrepant findings may be due to task performance effects or demographic differences between samples. We report functional magnetic resonance imaging (fMRI) data comparing subjects with schizophrenia and healthy controls performing a 2-back working memory (WM) task, addressing the effects of task performance. METHODS: Twenty-two controls and 14 patients with DSM-IV schizophrenia, scanned on a Siemens 1.5 T scanner, performed a visual letter 2-back task and control task (CPT-X) during fMRI. Data were analyzed using Statistical Parametric Mapping (SPM)-99. RESULTS: After statistical adjustment for performance differences, persons with schizophrenia showed significantly greater activation than controls in the right medial frontal gyrus and left inferior parietal lobule/medial temporal gyrus region (BA 39/40), and a trend toward greater activation in the left ventrolateral PFC. This pattern was also observed in demographically matched subgroups of participants. CONCLUSIONS: Data are consistent with findings reported in recent studies showing increased PFC and parietal activation in schizophrenia when the effects of reduced WM task performance in patients with schizophrenia are addressed. Further studies are needed to clarify the pathophysiological basis of WM load sensitivity in schizophrenia and its relationship to genes.

Adult↗
PubMed2003

Brain activation patterns during a selective attention test-a functional MRI study in healthy volunteers and patients with schizophrenia.

Functional magnetic resonance imaging was used to compare cortical activation patterns in healthy volunteers with those in patients with schizophrenia during a modified verbal Stroop task. Healthy subjects (n=13) and patients with schizophrenia (n=13) on stable antipsychotic treatment, matched on demographic variables, were included. Patients were preselected on the basis of good performance on a selective attention test. Patients with schizophrenia showed a significantly increased pattern of activation in the left and right inferior frontal cortex and the anterior cingulate cortex. A significant negative correlation between activation of the left prefrontal cortex and accuracy in the modified Stroop test was observed for healthy controls but not schizophrenia patients. Although both groups recruited the prefrontal cortex during the modified Stroop task, for the schizophrenia patients this activation was bilateral, whereas for the controls this activation was primarily in the left hemisphere, suggesting that patients with schizophrenia recruited more prefrontal regions to perform the task with the same accuracy as healthy controls. Our findings of increased activity across multiple areas of the brain, including dorsolateral frontal cortex and anterior cingulate, in patients with schizophrenia who perform relatively well on a task of selective attention give further evidence that task performance may be a confounding factor in the interpretation of neuroimaging results.

Adult↗
PubMed2001

Temporal spatial differences observed by functional MRI and human intraoperative optical imaging.

Pre-operative functional magnetic resonance imaging (fMRI), cortical evoked potentials (EPs) and intraoperative optical imaging of intrinsic signals (iOIS) were employed to relate the temporal-spatial characteristics of sensorimotor responses in human brain. Peripheral somasthetic stimulation (2 s) was provided either by a 110 Hz finger vibrator or transcutaneous median nerve stimulation in eight patients undergoing neurosurgical procedures. Each technique provided unique spatial patterns and temporal response profiles. EPs and iOIS activities were observed over the surface of pre- and post-central gyri (at the level of the superior genu) with very similar spatial distributions. In contrast, fMRI spatial distributions depended upon the model used for statistical correlation analysis. Using a monophasic response model, fMRI primarily localized within the central sulcus and did not demonstrate large signal changes over the pre- and post-central gyri (areas with iOIS/EP activity). However, as initial negative responses were incorporated into the response model, fMRI progressively localized closer to the iOIS and somatosensory EP maps. Temporally, responses to single stimuli differed between the fMRI and iOIS techniques. Using a monophasic model for fMRI analysis, the total fMRI response was delayed by 2--3 s relative to iOIS. As initial negative responses were incorporated in the analysis, the fMRI time course developed temporal characteristics similar to iOIS. Ultimately, when fMRI time courses were examined over pixels co-localizing with iOIS activation (without using statistical correlation analysis), the fMRI temporal profile included an initial decrease in signal (an initial dip) that closely resembled the time course of iOIS response. This is the first study to experimentally co-localize (temporally and spatially) iOIS and fMRI signals in human subjects. The spatial/temporal differences in this study likely reflect the capillary versus venous contributions of iOIS and fMRI, respectively. The temporal/spatial co-localization of the iOIS signal and the fMRI initial dip suggests the initial fMRI dip and the iOIS signal may result from similar physiologic events.

Algorithms↗
PubMed2002

Functional MRI in human motor control studies and clinical applications.

Functional magnetic resonance imaging (fMRI) has been a useful tool for the noninvasive mapping of brain function associated with various motor and cognitive tasks. Because fMRI is based on the blood oxygenation level dependent (BOLD) effect, it does not directly record neural activity. With the fMRI technique, distinguishing BOLD signals created by cortical projection neurons from those created by intracortical neurons appears to be difficult. Two major experimental designs are used in fMRI studies: block designs and event-related designs. Block-designed fMRI presupposes the steady state of regional cerebral blood flow and has been applied to examinations of brain activation caused by tasks requiring sustained or repetitive movements. By contrast, the more recently developed event-related fMRI with time resolution of a few seconds allows the mapping of brain activation associated with a single movement according to the transient aspects of the hemodynamic response. Increasing evidence suggests that multiple motor areas are engaged in a networked manner to execute various motor acts. In order to understand functional brain maps, it is important that one understands sequential and parallel organizations of anatomical connections between multiple motor areas. In fMRI studies of complex motor tasks, elementary parameters such as movement length, force, velocity, acceleration and frequency should be controlled, because inconsistency in those parameters may alter the extent and intensity of motor cortical activation, confounding interpretation of the findings obtained. In addition to initiation of movements, termination of movements plays an important role in the successful achievement of complex movements. Brain areas exclusively related to the termination of movements have been, for the first time, uncovered with an event-related fMRI technique. We propose the application of fMRI to the elucidation of the pathophysiology of movement disorders, particularly dystonia, which exhibits involuntary co-contraction of agonist and antagonist muscles and manifests abnormal posture or slow repetition of movements.

Brain Mapping↗
PubMed1996

Functional MRI of the activated human visual cortex.

We explored the possibility of performing functional magnetic resonance imaging of visual evoked response in the primary visual cortex with a clinical MRI imager of 1.5 tesla. Gradient echo pulse sequence was chosen to acquire the functional image and binocular flash visual stimulation by light-proof goggles containing light emitting diodes was used as the source of cerebral activation. Data processing was performed utilizing direct subtraction for averaged images, correlation coefficient, statistical parametric mapping and matched filter. Of those methods, correlation coefficient and statistic parametric mapping proved to be the methods of choice in our study.

Brain Mapping↗
PubMed1999

Determination of drug-induced changes in functional MRI signal using a pharmacokinetic model.

As the applications of functional magnetic resonance imaging (fMRI) expand, there is a need for the development of new strategies for data extraction and analysis that do not require the presentation of stimuli in a repeated on/off pattern. A description and evaluation of a method and computer algorithm for the detection and analysis of brain activation patterns following acute drug administration using fMRI are presented. A waveform analysis protocol (WAP) input function has been developed that is based upon the single-dose pharmacokinetics of a drug of interest. As a result of this analysis, regional brain activation can be characterized by its localization and intensity of activation, onset of action, time to peak effect, and duration of action. A global statistical test for significant drug effects based upon the probability of a voxel being activated by a saline vehicle injection is applied to grouped data on a voxel by voxel basis. Representative data are presented using nicotine as a prototypical agent. Using this method, statistically significant drug-induced brain activation has been identified in several key cortical and subcortical brain regions.

Adult↗
PubMed2004

Spatiotemporal wavelet analysis for functional MRI.

Characterizing the spatiotemporal behavior of the BOLD signal in functional Magnetic Resonance Imaging (fMRI) is a central issue in understanding brain function. While the nature of functional activation clusters is fundamentally heterogeneous, many current analysis approaches use spatially invariant models that can degrade anatomic boundaries and distort the underlying spatiotemporal signal. Furthermore, few analysis approaches use true spatiotemporal continuity in their statistical formulations. To address these issues, we present a novel spatiotemporal wavelet procedure that uses a stimulus-convolved hemodynamic signal plus correlated noise model. The wavelet fits, computed by spatially constrained maximum-likelihood estimation, provide efficient multiscale representations of heterogeneous brain structures and give well-identified, parsimonious spatial activation estimates that are modulated by the temporal fMRI dynamics. In a study of both simulated data and actual fMRI memory task experiments, our new method gave lower mean-squared error and seemed to result in more localized fMRI activation maps compared to models using standard wavelet or smoothing techniques. Our spatiotemporal wavelet framework suggests a useful tool for the analysis of fMRI studies.

Algorithms↗
PubMed2006

Language lateralization in unmedicated patients during an acute episode of schizophrenia: a functional MRI study.

In a previous fMRI study of high-functioning outpatients with remitted schizophrenia, we found that healthy subjects and schizophrenia patients showed similar patterns of activation during a verbal fluency task. However, the activation in controls was primarily in Broca's area on the left, while it was more bilateral for schizophrenia patients, implicating a reduced language lateralization in schizophrenia patients. The same fMRI procedure was used in this subsequent study to investigate unmedicated patients during an acute episode of schizophrenia. Schizophrenia patients showed reduced language lateralization in the frontal cortex, because of a more bilateral activation of Broca's area compared with a primarily left hemisphere activation in healthy controls. Furthermore decreased lateralization was correlated to the severity of hallucinations. Although patients with schizophrenia showed a significantly reduced performance on the verbal fluency task when compared with healthy subjects, we were not able to find evidence of decreased language-related activity in the left hemisphere. These results suggest that decreased language lateralization is also evident in unmedicated patients experiencing an acute episode of schizophrenia.

Acute Disease↗