Evaluating functional MRI procedures for assessing hemispheric language dominance in neurosurgical patients.

Two methods of quantifying hemispheric language dominance (HLD) in neurosurgical patients are compared: (1) an average magnitudes (AM) method, which is a calculation of the average signal intensity variation in regions of interest for each patient that were predefined in a group analysis for each task, and (2) a lateralization indices (LI) method, which is based on the number of activated pixels in regions of interest predefined in each individual patient. Four language tasks [a living/nonliving (LNL) judgment, word stem completion (WSC), semantic associate (SA) and a phonological associate (PA) task] were compared with "gold standard" measures such as the Wada test or electrocortical stimulation. Results showed that the LI method was more accurate (73% agreement with gold standard methods) than the AM method (only 40% agreement) across tasks and subjects. Furthermore, by varying the threshold used for determining laterality, the ability of functional magnetic resonance imaging (fMRI) to predict HLD was influenced for the AM method, whereas the LI method was relatively unaffected by changing the threshold. Using the LI method, the SA task was the most accurate for quantifying HLD (100% agreement with gold standard methods) with respect to the other three language tasks (80% accuracy for WSC, 65% for the LNL and 63% for phonological task). Depending on the method and the task, fMRI may be a promising tool for assessing HLD in neurosurgical patients.

Functional MRI reveals an interhemispheric dissociation of frontal and temporal language regions in a patient with focal epilepsy.

We report the case of a patient with frontal lobe epilepsy in whom the Wada test failed to lateralize representation of language (fluent speech was observed after amobarbital injection on both the right and left side). Functional magnetic resonance imaging (fMRI) during a lexical processing task revealed an atypical organization of language represented by an interhemispheric dissociation of language regions with a right frontal dominance and a left temporal dominance. Consistent with the fMRI results, the patient's ability to name pictures was not reliably impaired by electrocortical stimulation (ECS) of left frontal cortex. The findings from Wada, fMRI, and ECS were confirmed by a lack of language impairment after left frontal lobectomy for seizures. This case illustrates that fMRI can precisely map cortical language networks in epileptic patients and that fMRI may be used to help interpret laterality results provided by the Wada procedure.

Central processing of rectal pain: a functional MR imaging study.

BACKGROUND AND PURPOSE: Although the central processing of somatic pain has been dealt with in numerous brain imaging studies, the neural correlates of visceral pain have received much more limited attention. Our goal was to assess the feasibility of detecting brain activation patterns induced by rectal pain by means of functional MR imaging. We hypothesized that the cerebral processing of rectal pain would exhibit strong similarities with the central processing of somatic pain. METHODS: Functional MR imaging data were obtained from eight healthy subjects. A block paradigm was applied. Rectal pain was induced by inflating a latex balloon catheter that had been inserted into the rectum. Functional responses were established by means of cross-correlation analysis. RESULTS: Activation was detected within the anterior cingulate gyrus, the prefrontal cortex, the insular cortex, the sensory-motor cortex, the inferior parietal lobule, the posterior cingulate gyrus, and the visual cortex. CONCLUSION: Functional MR imaging of visceral pain is feasible in healthy subjects. The activation patterns observed in this study support the hypothesis that the cerebral processing of visceral pain involves multiple components, similar to the central processing of somatic pain. Our results constitute a first step toward the identification of possible aberrations in the activation patterns of patients suffering from visceral hypersensitivity.

fMRI assessment of hemispheric language dominance using a simple inner speech paradigm.

Hemispheric language dominance (HLD) has been determined by means of functional MRI (fMRI) using a simple, inner speech, word fluency paradigm. During the task periods, subjects perform mental imagery of visual scenes and generate silently the nouns of all objects visualized. During the control periods, subjects attend to the scanner noise. Activated areas have been identified by means of cross-correlation analysis. HLD indices have been determined by comparing the number of activated pixels detected in both hemispheres within predefined cortical areas (Brodmann areas 6, 9, 10, 39, 40 and 44-47). The paradigm has been assessed on 10 healthy, right-handed volunteers. A volume 35 mm thick, centered on the inferior frontal gyrus, was imaged. A conventional GRE MR sequence was used on a 1.5 T clinical MR scanner. HLD indices were compared with those determined for overt speech. Robust fMRI responses were obtained. HLD indices indicated left hemispheric language dominance for all subjects examined. They correlated well with those obtained for overt speech (R(2) = 0.93, regression coefficient = 0.998, with p < 10(-4)). Thus, an inner speech paradigm based on visual imagery is well adapted for assessment of HLD by means of fMRI.