Rapid-presentation event-related functional MRI (ER-fMRI) allows neuroimaging methods based on hemodynamics to employ behavioral task paradigms typical of cognitive settings. However, the sluggishness of the hemodynam...
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Rapid-presentation event-related functional MRI (ER-fMRI) allows neuroimaging methods based on hemodynamics to employ behavioral task paradigms typical of cognitive settings. However, the sluggishness of the hemodynamic response and its variance provide constraints on how ER-fMRI can be applied. In a series of two studies, estimates of the hemodynamic response in or near the primary visual and motor cortices were compared across various paradigms and sampling procedures to determine the limits of ER-fMRI procedures and, more generally, to describe the behavior of the hemodynamic response, The temporal profile of the hemodynamic response was estimated across overlapping events by solving a set of linear equations within the general linear model. No assumptions about the shape were made in solving the equations. Following estimation of the temporal profile, the amplitude and timing were modeled using a gamma function. Results indicated that (1) within a region, for a given subject, estimation of the hemodynamic response is extremely stable for both amplitude (r(2) = 0.98) and time to peak (r(2) = 0.95), from one series of measurements to the next, and slightly less stable for estimation of time to onset (r(2) = 0.60). (2) As the trial presentation rate changed (from those spaced 20 s apart to temporally overlapping trials), the hemodynamic response amplitude showed a small, but significant, decrease. Trial onsets spaced (on average) 5 s apart showed a 17-25% reduction in amplitude compared to those spaced 20 s apart. Power analysis indicated that the increased number of trials at fast rates outweighs this decrease in amplitude if statistically reliable response detection is the goal. (3) Knowledge of the amplitude and timing of the hemodynamic response in one region failed to predict those properties in another region, even for within-subject comparisons. (4) Across subjects, the amplitude of the response showed no significant correlation with timing of the response,
The etiology of spasmodic dysphonia (SD) is still unknown. In the present study, cortical function of a 59-year-old male patient with adductor type SD was examined during phonation with positron emission tomography (P...
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The etiology of spasmodic dysphonia (SD) is still unknown. In the present study, cortical function of a 59-year-old male patient with adductor type SD was examined during phonation with positron emission tomography (PET). Magnetic resonance imaging showed no organic abnormality in the brain. However, PET showed remarkable activities during phonation in the left motor cortex, Broca's area, the cerebellum, and the auditory cortices, whereas the supplementary motor area (SMA) was not activated. The SMA is known to function for motor planning and programming and is usually activated in normal phonation. Several previous reports have shown that the damage of the SMA caused a severe disturbance of voluntary vocalization, In the present case, it was suggested that the functional deficit of the SMA might be related to SD. (Am J Otolaryngol 2001;22:219-222. Copyright (C) 2001 by W.B. Saunders Company).
Using (H2O)-O-15 positron emission tomography in 6 healthy volunteers, we found that self-initiated and externally cued blinking activated the right primary motor cortex and supplementary motor area (SMA). The left do...
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Using (H2O)-O-15 positron emission tomography in 6 healthy volunteers, we found that self-initiated and externally cued blinking activated the right primary motor cortex and supplementary motor area (SMA). The left dorsolateral prefrontal cortex (DLPFC) and the rostral SMA showed greater activation during the self-initiated task compared to the externally cued task. This study confirms the hypothesis of right hemispheric lateralization of volitional blinking derived from observations in stroke patients. Furthermore, it underscores the role of DLPFC and rostral SMA in self-initiated movements, which has been found in similar experiments with hand movements.
Using functional magnetic resonance imaging (fMRI), we measured regional blood flow to examine which motor areas of the human cerebral cortex are preferentially involved in an auditory conditional motor behavior. As a...
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Using functional magnetic resonance imaging (fMRI), we measured regional blood flow to examine which motor areas of the human cerebral cortex are preferentially involved in an auditory conditional motor behavior. As a conditional motor task, randomly selected 330 or 660 Hz tones were presented to the subjects every 1.0 s. The low and high tones indicated that the subjects should initiate three successive opposition movements by tapping together the right thumb and index finger or the right thumb and little finger, respectively. As a control task, the same subjects were asked to alternate the two opposition movements, in response to randomly selected tones that were presented at the same frequencies. Between the two tasks, MRI images were also scanned in the resting state while the tones were presented in the same way. Comparing the images during each of the two tasks with images during the resting state, it was observed that several frontal motor areas, including the primary motor cortex, dorsal premotor cortex (PMd), supplementary motor area (SMA), and pre-SMA, were activated. However, preferential activation during the conditional motor task was observed only in the PMd and pre-SMA of the subjects' left (contralateral) frontal cortex. The PMd has been thought to play an important role in transforming conditional as well as spatial visual cues into corresponding motor responses, but our results suggest that the PMd along with the pre-SMA are the sites where more general and extensive sensorimotor integration takes place.
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