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PubMed1999

Right prefrontal cortex and episodic memory retrieval: a functional MRI test of the monitoring hypothesis.

Though the right prefrontal cortex is often activated in neuroimaging studies of episodic memory retrieval, the functional significance of this activation remains unresolved. In this functional MRI study of 12 healthy volunteers, we tested the hypothesis that one role of the right prefrontal cortex is to monitor the information retrieved from episodic memory in order to make an appropriate response. The critical comparison was between two word recognition tasks that differed only in whether correct responses did or did not require reference to the spatiotemporal context of words presented during a previous study episode. Activation in a dorsal midlateral region of the right prefrontal cortex was associated with increased contextual monitoring demands, whereas a more ventral region of the right prefrontal cortex showed retrieval-related activation that was independent of task instructions. This functional dissociation of dorsal and ventral right prefrontal regions is discussed in relation to a theoretical framework for the control of episodic memory retrieval.

Adult↗
PubMed1999

Stress functional MRI: detection of ischemic heart disease and myocardial viability.

Breath-hold gradient-echo magnetic resonance imaging (MRI) in conjunction with pharmacologic dobutamine stress has become a practical tool to investigate patients with chest pain. The presence of high-grade coronary artery stenoses can be detected more accurately than with stress echocardiography. The main diagnostic advantage of MRI is in patients with suboptimal echocardiographic image quality. Depiction of left ventricular anatomy and function at rest and during low-dose dobutamine stress is also clinically useful for evaluating patients with severely impaired left ventricular function for the presence of residual myocardial viability. Recovery of regional and global left ventricular function can be accurately predicted by stress functional MRI. J. Magn. Reson Imaging 1999;10:667-675, 1999.

Cardiotonic Agents↗
PubMed2005

Resolution and reproducibility of BOLD and perfusion functional MRI at 3.0 Tesla.

Visual and somatosensory activation studies were performed on normal subjects to compare the spatial discrimination and reproducibility between functional MRI (fMRI) methods based on blood oxygen level-dependent (BOLD) and perfusion contrast. To allow simultaneous measurement of BOLD and perfusion contrast, a dedicated MRI acquisition technique was developed. Repeated experiments of sensory stimulation of single digits of the right hand showed an average variability of activation amplitude of 25% for BOLD data, and a significantly lower variability of 21% for perfusion data. No significant difference in the variability of the locus of activity was observed between the BOLD and perfusion data. In somatotopy experiments, digits II and V were subjected to passive sensory stimulation. Both the BOLD and perfusion data showed substantial overlap in the activation patterns from the two digits. In a retinotopy study, two stimuli were alternated to excite different patches of V1. Again there was substantial overlap between the activation patterns from both stimuli, although the perfusion performed somewhat better than the BOLD method. Particularly for the visual studies, the overlap in activation patterns was more than expected based on the fine-scale retinotopic mapping of cortical activity, suggesting that both BOLD and perfusion contrast mechanisms contribute substantially to the point-spread function (PSF).

Adult↗
PubMed1997

Sensorimotor cerebral activation during optokinetic nystagmus. A functional MRI study.

Self-motion or object motion can elicit optokinetic nystagmus (OKN), which is an integral part of dynamic spatial orientation. We used functional MR imaging during horizontal OKN to study cerebral activation patterns in sensory and ocular motor areas in 10 subjects. We found activation bilaterally in the primary visual cortex, the motion-sensitive areas in the occipitotemporal cortex (the middle temporal and medial superior temporal areas), and in areas known to control several types of saccades such as the precentral and posterior median frontal gyrus, the posterior parietal cortex, and the medial part of the superior frontal gyrus (frontal, parietal, and supplementary eye fields). Additionally, we observed cortical activation in the anterior and posterior parts of the insula and in the prefrontal cortex. Bilateral activation of subcortical structures such as the putamen, globus pallidus, caudate nucleus, and the thalamus traced the efferent pathways of OKN down to the brainstem. Functional MRI during OKN revealed a complex cerebral network of sensorimotor cortical and subcortical activation.

Adult↗
PubMed2000

A silent event-related functional MRI technique for brain activation studies without interference of scanner acoustic noise.

A new data acquisition method for silent, event-related functional MRI in which scanner acoustic noise does not interfere with brain activation is introduced and evaluated in an auditory tonotopic mapping experiment. This method takes into account the hemodynamic-response characteristics of the brain during activation, associated with both task performance and scanner noise. A data acquisition scheme was designed to collect task-induced brain activation signals without interference of scanner noise on stimulus delivery or on the measured response. The advantages of the technique were demonstrated in a tonotopic mapping experiment of human auditory cortex. Tonotopic maps obtained by the technique in normal subjects showed distinct spatial shifts of the activation foci in the lateral part of Heschl's gyrus with changing stimulus frequency, whereas no systematic shift was shown in a conventional event-related experiment using the same stimulation paradigm. Signal change in the activation foci with the new technique was 54% larger than with the conventional technique, suggesting an increased dynamic range of the signal change associated with task-induced brain activation under silent conditions.

Acoustic Stimulation↗
PubMed1996

Functional MRI and the study of OCD: from symptom provocation to cognitive-behavioral probes of cortico-striatal systems and the amygdala.

Functional magnetic resonance imaging (fMRI) first appeared in 1991. Since that time there has been a burgeoning use of the technology by psychiatric researchers and neuroscientists. Our group first used fMRI to study obessive compulsive disorder (OCD) with a symptom provocation paradigm and then moved to the use of circuitry-specific cognitive-behavioral probes. The techniques we utilized for the symptom provocation study remain valid today, but have been supplemented by a wide array of new tools. Functional MRI continues to be a rapidly developing technology which could become the gold standard for neuroimaging research in psychiatry. With this in mind, this paper focuses on the past, present, and future applications of fMRI to one model illness, namely OCD. We examine the strengths and limitations of our initial OCD symptom provocation study and then evaluate the use of fMRI with cognitive-behavioral probes of cortico-striatal circuitry and limbic (amygdala) circuitry. We conclude with a brief summary of foreseeable developments which will influence the implementation of fMRI for psychiatric neuroscience in general.

Arousal↗
PubMed2003

Quantitative NumART2* mapping in functional MRI studies at 1.5 T.

Quantitative mapping of the effective transverse relaxation time, T2* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART2* (Numerical Algorithm for Real time T2*). Comparisons between NumART2* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T2* value, relative changes in T2* remained unaffected. Statistical analysis of the T2* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART2* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART2* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T2* maps.

Algorithms↗
PubMed2006

Functional MRI of memory in the hippocampus: Laterality indices may be more meaningful if calculated from whole voxel distributions.

Lateralization of memory by functional MRI (fMRI) may be helpful for surgical planning related to the medial temporal lobe (MTL). Most fMRI memory studies have calculated lateralization indices (LI) in the MTL from suprathreshold voxels only, but the selection of threshold remains highly arbitrary. We hypothesized that LIs could be reliably extracted from the distribution of voxels encompassing all positive T statistical values, each weighted by their own statistical significance. We also hypothesized that patient LIs that are two or more standard deviations (SD) away from the control group mean LI may be more clinically relevant than LIs that are not compared to control group. Thirteen healthy subjects had memory fMRI, and five epilepsy patients had both fMRI and the intracarotid amobarbital procedure (IAP). The fMRI task consisted of encoding patterns, scenes, and words. We found that normal subjects' LIs extracted from whole weighted statistical distributions tended to lateralize to the left for words, to the right for patterns, and intermediately for scenes, consistent with previous research. Weighted LIs were less variable than those calculated from suprathreshold voxels only. Using this approach, all patients had fMRI memory lateralizations consistent with IAP results. The weighted LIs provided a more clear-cut distinction of patients from the normal group (in terms of SDs from the group mean) than the suprathreshold voxel count approach. Our results suggest that using weighted distributions can be a useful strategy for assessing memory lateralization by fMRI in the MTL.

Adult↗
PubMed2003

Dynamic changes in the cerebral metabolic rate of O2 and oxygen extraction ratio in event-related functional MRI.

Dynamic changes in the cerebral metabolic rate of oxygen (CMRO(2)) and oxygen extraction ratio (OER) in an event-related functional MRI (ER-fMRI) were measured in this study. Six subjects participated in this study at a magnetic field of 1.9 T. Cerebral blood flow (CBF) and blood oxygenation level-dependent (BOLD) changes were acquired during the brief visual stimulation, and the corresponding changes in CMRO(2) and OER were then determined. The results showed that the maximum relative changes in CMRO(2) and OER were about 10.36 +/- 0.85 and -6.54 +/- 0.55%, respectively, while the maximum changes in CBF and BOLD were approximately 17.35 +/- 1.37 and 1.03 +/- 0.06%, respectively. The CBF, CMRO(2), and OER changes reach their maximum approximately 1 s earlier than the BOLD signal change (4.15 +/- 0.21, 4.16 +/- 0.21, and 4.17 +/- 0.21 s vs 5.12 +/- 0.24 s after stimulation, P < 0.05).

Arousal↗
PubMedDate not supplied

Taste and smell phantoms revealed by brain functional MRI (fMRI).

PURPOSE: Our goal was to demonstrate the appearance of phantom tastes and smells (phantageusia and phantosmia, respectively) by use of functional MRI (fMRI) of the brain and to demonstrate the efficacy of drug treatment that inhibited both the subjective presence of these phantoms and the fMRI brain activation initiated by these phantoms. METHOD: Multislice FLASH MR or echo planar MR brain scans were obtained in two patients with phantageusia and phantosmia in response to memory of two tastants (salt and sweet); memory of two odors (banana and peppermint); actual smell of amyl acetate, menthone, and pyridine; and memory of phantom tastes and smells before and after treatment with thioridazine and haloperidol. Activation images were derived using correlation analysis, and ratios of brain area activated to total brain area were obtained. RESULTS: Prior to treatment, both patients experienced persistent birhinal and global oral obnoxious tastes and smells in the absence of any external stimulus. The fMRI response to memory of phantoms was activation in sensory-specific brain regions for taste and smell, respectively. fMRI activation was greater than for memory of any tastant or odorant or for actual smell of any odor. After treatment with thioridazine or haloperidol, which successfully inhibited each phantom in each patient, fMRI response to phantom memory was significantly inhibited and was significantly lower than for memory of any tastant or odorant or actual smell of any odorant. CONCLUSION: These results demonstrate that (a) phantom taste and smell can be revealed by fMRI brain activation, (b) brain activation in response to taste and smell phantoms is localized in sensory-specific brain regions for taste and smell, respectively, (c) brain activation in response to memory of each phantom initiated the greatest degree of activation we had previously measured, and (d) treatment with thioridazine or haloperidol inhibited both the presence of each phantom and its associated fMRI brain activation. This is the first study in which phantom tastes and smells have been demonstrated by an objective technique and treatment that inhibited the phantoms was characterized by objective inhibition of fMRI activation. These two patients represent a relatively common group that may be classified as having primary phantageusia and phantosmia distinct from those with phantoms or auras secondary to neurological, migrainous, psychiatric, or other causes.

Brain Mapping↗
PubMed2003

Morphological and carbogen-based functional MRI of a chemically induced liver tumor model in mice.

A multifocal mouse liver tumor model chemically induced with 5,9-dimethyl-7H-dibenzo[c,g]carbazole was investigated by respiratory-triggered morphological and functional MRI (fMRI) at 4.7 Tesla. The model is characterized by the presence of two tumor types: hypovascular cholangioma and vascularized hepatocellular carcinoma (HCC). Growth curves measured by 3D-MRI showed limited growth of cholangiomas and rapid growth of HCCs after a latency of about 25 weeks. Functional imaging based on T(2) (*)-weighted fast gradient-echo MRI and carbogen breathing was optimized for liver imaging in mice. A response to carbogen was observed in HCCs but not in cholangiomas. Transversal analysis (50 HCCs) of signal change upon carbogen revealed four different types of response patterns: 1) signal increase upon carbogen administration (74%); 2) small or insignificant signal change (10%), 3) transient signal decrease and delayed increase (8%), and 4) signal decrease (8%). Longitudinal follow-up of a subgroup (N = 17) showed that an initially observed type 1 response, attesting to the presence of a functional vasculature, remained stable for at least 3 weeks in 14 HCCs. A switch from a type 1 response to another response type may be useful for demonstrating, in a noninvasive manner, a disturbance of tumor vasculature induced by anti-vascular or anti-angiogenic therapy.

Animals↗
PubMed2001

Functional MRI evidence of cortical reorganization in upper-limb stroke hemiplegia treated with constraint-induced movement therapy.

OBJECTIVE: The purpose of this pilot study was to test constraint-induced movement therapy for chronic upper-limb stroke hemiparesis and to investigate the neural correlates of recovery with functional magnetic resonance imaging (MRI) in two subjects. Both subjects had been discharged from traditional therapy because no further improvement was anticipated. DESIGN: Constraint-induced movement therapy consisted of 6 hr of daily upper-limb training for 2 wk; a restrictive mitt was worn on the nonparetic limb during waking hours. Functional MRI was performed on a 1.5-T MRI with echo-planar imaging; at the same time, the subjects attempted sequential finger-tapping. RESULTS: Compared with baseline, performance time improved an average of 24% immediately after training and also continued to improve up to 33% 3 mo after training. Lift, grip strength, and Motor Activity Log scores likewise improved. Initially, on functional MRI, subject 1 activated scattered regions in the ipsilateral posterior parietal and occipital cortices. Subject 2 showed almost no areas of significant activation. After training, subject 1 showed activity bordering the lesion, bilateral activation in the association motor cortices, and ipsilateral activation in the primary motor cortex. Subject 2 showed activation near the lesion site. CONCLUSION: Constraint-induced movement therapy produced significant functional improvement and resulted in plasticity as demonstrated by functional MRI.

Exercise Therapy↗
PubMed2004

Mapping of verbal working memory in nonfluent Chinese-English bilinguals with functional MRI.

Existing cognitive and neural imaging studies have suggested a frontoparietal network of multiple, cooperative components for verbal working memory (WM). We used functional MRI to investigate whether this neural network is also involved in the processing of second language by nonfluent bilinguals. Twelve (five males, seven females) native Chinese speakers who had limited English proficiency were scanned while performing working memory tasks in Chinese and English. They were asked to make judgment continuously whether the word presented on the screen was semantically related to (i.e., the semantic tasks) another word presented two words earlier. On a different task (i.e., the phonological tasks), they were asked to make judgment whether the target word rhymed with the other word. A naming and judgment task in each language was adopted to control for the visual process, initial lexical process, and motor responses. Behavioral data showed that subjects performed better at tasks in their native language (Chinese, L1) than in English (L2). Imaging results showed that all working memory tasks in both L1 and L2 elicited a very similar pattern of left-hemisphere-dominated activation in the dorsolateral prefrontal cortex, pars opercularis region, pars triangularis region, precentral cortex, and parietal lobule. Consistent with the behavioral data, the volume of activation in the left opercularis region, left parietal lobule, and right precentral region was greater for L2 than for L1. These results suggest that working memory in L1 and L2 is mediated by a unitary neural system (i.e., frontoparietal region), which is capable of recruiting surrounding cortical resources to meet the increased computational demand caused by low L2 proficiency.

Adult↗
PubMed2000

Nonlinear regression of functional MRI data: an item recognition task study.

A classical item-recognition task was used to examine human verbal working memory in an event-related functional MRI (fMRI) study. A highly flexible experimental design incorporated a broad variation of memory load and delay time. This design allows for only three or four repetitions per stimulus condition. In a first step, linear regression analysis was applied to locate functional activation in the fMRI data. As a second step, the time course of the hemodynamic response (HR) was analyzed using nonlinear regression, which served to quantify the dependency between HR shape properties and stimulation conditions in several regions-of-interest. On the basis of this study, a closer description of the frontoparietal network involved in verbal working memory was possible.

Adult↗
PubMed2006

Corticospinal tract compression by hematoma in a patient with intracerebral hemorrhage: a diffusion tensor tractography and functional MRI study.

The purpose of this study was to demonstrate corticospinal tract compression that was due to a hematoma by using diffusion tensor tractography (DTT) and functional MRI (fMRI) in a patient with an intracerebral hemorrhage (ICH). A 23-year-old right-handed woman presented with severe paralysis of her right extremities at the onset of a spontaneous ICH. Over the first three days from onset, the motor function of the affected upper and lower extremities rapidly recovered to the extent that she was able to overcome applied resistance to the affected limbs, and her limbs regained normal function 3 weeks after onset. The tract of the right hemisphere originated from the primary sensori-motor cortex (SM1) and it passed through the known corticospinal tract pathway. However, the tract of the left hemisphere was similar to that of the right hemisphere except that it was displaced to the antero-medial side by the hematoma at the cerebral peduncle. Only the contralateral SM1 area centered on the precentral knob was activated during affected (right) or unaffected (left) hand movements, respectively. In conclusion, fMRI and DTT demonstrated a corticospinal tract compression due to hematoma in this patient. We conclude that the combined use of these two modalities appears to improve the accuracy of investigating the state of the corticospinal tract.

Adult↗
PubMedDate not supplied

Fuzzy clustering of gradient-echo functional MRI in the human visual cortex. Part II: quantification.

Fuzzy cluster analysis (FCA) is a new exploratory method for analyzing fMRI data. Using simulated functional MRI (fMRI) data, the performance of FCA, as implemented in the software package Evident, was tested and a quantitative comparison with correlation analysis is presented. Furthermore, the fMRI model fit allows separation and quantification of flow and blood oxygen level dependent (BOLD) contributions in the human visual cortex. In gradient-recalled echo fMRI at 1.5 T (TR = 60 ms, TE = 42 ms, radiofrequency excitation flip angle [theta] = 10 degrees-60 degrees) total signal enhancement in the human visual cortex, ie, flow-enhanced BOLD plus inflow contributions, on average varies from 5% to 10% in or close to the visual cortex (average cerebral blood volume [CBV] = 4%) and from 100% to 20% in areas containing medium-sized vessels (ie, average CBV = 12% per voxel), respectively. Inflow enhancement, however, is restricted to intravascular space (= CBV) and increases with increasing radiofrequency (RF) flip angle, whereas BOLD contributions may be obtained from a region up to three times larger and, applying an unspoiled gradient-echo (GRE) sequence, also show a flip angle dependency with a minimum at approximately 30 degrees. This result suggests that a localized hemodynamic response from the microvasculature at 1.5 T may be extracted via fuzzy clustering. In summary, fuzzy clustering of fMRI data, as realized in the Evident software, is a robust and efficient method to (a) separate functional brain activation from noise or other sources resulting in time-dependent signal changes as proven by simulated fMRI data analysis and in vivo data from the visual cortex, and (b) allows separation of different levels of activation even if the temporal pattern is indistinguishable. Combining fuzzy cluster separation of brain activation with appropriate model calculations allows quantification of flow and (flow-enhanced) BOLD contributions in areas with different vascularization.

Adult↗
PubMedDate not supplied

Rapid imaging of olfaction by functional MRI (fMRI): identification of presence and type of hyposmia.

PURPOSE: Our goal was to develop a rapid, simple, near-real-time method of functional MRI (fMRI) to measure brain activation in response to olfactory stimuli, to use it to identify patients with smell loss (hyposmia), and to differentiate their types of hyposmia. METHOD: fMRI was obtained in 16 patients with Type I hyposmia (who could detect but not recognize odors), 5 patients with Type II hyposmia (who could both detect and recognize odors, albeit with less than normal acuity), and 2 volunteers with normal olfactory acuity by use of a rapid echo planar imaging technique in which one coronal brain section from the anterior cortical region was studied and a single olfactory stimulus was used. Actual scanning time performed by a variation of methods previously published required 26 s. Three patients with Type I hyposmia were treated with theophylline 250-500 mg for 4-6 months and were studied before and after treatment. RESULTS: Brain activation in response to olfactory stimuli was demonstrated using a new, rapid, and simple fMRI technique. Patients with Type I hyposmia had less activation than patients with Type II hyposmia. Both patient groups had less activation than normal volunteers. Activation in patients with Type I hyposmia was essentially absent from regions of the middle frontal, orbitofrontal, and temporal cortex and was totally absent in regions of inferior frontal, insular, and cingulate cortex. Activation in patients with Type II hyposmia was greatest in the middle frontal cortex and the orbitofrontal cortex bilaterally and was present in regions of inferior frontal, temporal, and cingulate cortex. Each patient with Type I hyposmia treated with theophylline had improved smell function to Type II hyposmia and after treatment demonstrated activation in inferior frontal and cingulate cortex bilaterally, whereas before treatment, no activation in these regions was apparent. CONCLUSION: We describe a simple, rapid technique that can be used in a practical clinical setting to identify patients with hyposmia and to differentiate patients with different types of olfactory loss. These studies confirm the presence and classification of patients with Type I and Type II hyposmia. Results of this study suggest that regions of the frontal cortex may act to guide or direct olfactory signals to other brain areas such as temporal and cingulate regions. Although these latter regions are involved with olfactory recognition, their role in olfactory memory, olfactory meaning, and attention needs to be considered.

Adolescent↗
PubMed2004

Functional MRI near vascular anomalies: comparison of cavernoma and arteriovenous malformation.

BACKGROUND AND PURPOSE: Mapping of eloquent cortex using blood-oxygen-level-dependent (BOLD) contrast functional MRI (fMRI) has rapidly gained acceptance as part of the evaluation of patients being considered for neurosurgical interventions. The BOLD signal measures local susceptibility in the blood, which can change during periods of increased neuronal activation as a result of alteration in blood flow and cerebral oxygen utilisation. Vascular anomalies could influence the BOLD signal via their effects on both blood flow and susceptibility. METHODS: In the present study we have compared the fMRI signal associated with functional activation near arteriovenous malformations and cavernomas in a group of patients referred for pre-surgical mapping of eloquent cortex. RESULTS: The magnitude of the BOLD signal was not different for the cavernoma group and the AVM group (mean percentage signal change 6.3% vs. 5.5%). For subjects with cavernoma, there was an increase in cavernoma volume on the functional images compared to T1-weighted anatomical images (mean 570%), and a BOLD signal was only detected outside the enlarged cavernoma. CONCLUSION: The findings show that susceptibility effects associated with cavernoma, most likely due to hemosiderin deposition, can result in an apparent increase in the separation between the BOLD signal and the cavernoma itself. This could lead to falsely high levels of surgical confidence during neurosurgical resection. Differential patterns of blood flow associated with cavernoma and AVM do not appear to significantly affect the BOLD signal magnitude.

Adolescent↗