[show abstract][hide abstract] ABSTRACT: The basal ganglia comprise a crucial circuit involved in force production and force selection, but the specific role of each nucleus to the production of force pulses and the selection of pulses of different force amplitudes remains unknown. We conducted an fMRI study in which participants produced force using a precision grip while (a) holding a steady-state force, (b) performing a series of force pulses with similar amplitude, and (c) selecting force pulses of different amplitude. Region of interest analyses were conducted in the basal ganglia and frontal cortex to compare percent signal change during force pulse versus steady-state force production and compare force amplitude selection to force production when selection of force amplitude was not present. There were three novel findings in the basal ganglia. First, the caudate nucleus increased activation during the selection of different force amplitudes when compared to producing a series of similar force pulses. Second, GPi, STN, and posterior putamen increased activation during the production of similar force amplitudes when compared to holding a steady-state force, and maintained similar activation during the production of different force amplitudes in which force selection was required. Third, GPe and anterior putamen had increased activation during the production of similar force pulses and further increased activation during the selection of different force pulses. These findings suggest that anterior basal ganglia nuclei are involved in selecting the amplitude of force contractions and posterior basal ganglia nuclei regulate basic aspects of dynamic force pulse production.
[show abstract][hide abstract] ABSTRACT: The mesial premotor cortex (pre-supplementary motor area and supplementary motor area proper), lateral premotor cortex (dorsal premotor cortex and ventral premotor cortex), and primary sensorimotor cortex (primary motor cortex and primary somatosensory cortex) have been identified as key cortical areas for sensorimotor function. However, the three-dimensional (3-D) anatomic boundaries between these regions remain unclear. In order to clarify the locations and boundaries for these six sensorimotor regions, we surveyed 126 articles describing pre-supplementary motor area, supplementary motor area proper, dorsal premotor cortex, ventral premotor cortex, primary motor cortex, and primary somatosensory cortex. Using strict inclusion criteria, we recorded the reported normalized stereotaxic coordinates (Talairach and Tournoux or MNI) from each experiment. We then computed the probability distributions describing the likelihood of activation, and characterized the shape, extent, and area of each sensorimotor region in 3-D. Additionally, we evaluated the nature of the overlap between the six sensorimotor regions. Using the findings from this meta-analysis, along with suggestions and guidelines of previous researchers, we developed the Human Motor Area Template (HMAT) that can be used for ROI analysis. HMAT is available through e-mail from the corresponding author.
[show abstract][hide abstract] ABSTRACT: The cerebellum, parietal cortex, and premotor cortex are integral to visuomotor processing. The parameters of visual information that modulate their role in visuomotor control are less clear. From motor psychophysics, the relation between the frequency of visual feedback and force variability has been identified as nonlinear. Thus we hypothesized that visual feedback frequency will differentially modulate the neural activation in the cerebellum, parietal cortex, and premotor cortex related to visuomotor processing. We used functional magnetic resonance imaging at 3 Tesla to examine visually guided grip force control under frequent and infrequent visual feedback conditions. Control conditions with intermittent visual feedback alone and a control force condition without visual feedback were examined. As expected, force variability was reduced in the frequent compared with the infrequent condition. Three novel findings were identified. First, infrequent (0.4 Hz) visual feedback did not result in visuomotor activation in lateral cerebellum (lobule VI/Crus I), whereas frequent (25 Hz) intermittent visual feedback did. This is in contrast to the anterior intermediate cerebellum (lobule V/VI), which was consistently active across all force conditions compared with rest. Second, confirming previous observations, the parietal and premotor cortices were active during grip force with frequent visual feedback. The novel finding was that the parietal and premotor cortex were also active during grip force with infrequent visual feedback. Third, right inferior parietal lobule, dorsal premotor cortex, and ventral premotor cortex had greater activation in the frequent compared with the infrequent grip force condition. These findings demonstrate that the frequency of visual information reduces motor error and differentially modulates the neural activation related to visuomotor processing in the cerebellum, parietal cortex, and premotor cortex.
Journal of Neurophysiology 03/2006; 95(2):922-31. · 3.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: The basal ganglia, motor cortex, and cerebellum have been implicated as a circuit that codes for movement velocity. Since movement velocity covaries with the magnitude of force exerted and previous studies have shown that similar regions scale in activation for velocity and force, the scaling of neuronal activity with movement velocity could be due to the force exerted. The present study implemented a parametric functional magnetic resonance imaging (fMRI) design to determine which brain regions directly scale with the rate of change of force production, independent of the magnitude of force exerted. Nine healthy adults produced force with their right middle finger and thumb at 25% of their maximal voluntary contraction across four conditions: (1) fast pulse, (2) fast hold, (3) medium hold, and (4) slow hold. There were three primary findings: (i) the activation volume in multiple regions increased with the duration of the force contraction, (ii) only the activation volume in the bilateral internal globus pallidus and left subthalamic nucleus parametrically scaled with the rate of change of force production, and (iii) there was an inverse relation between the activation volume in the subthalamic nucleus and internal globus pallidus with the rate of change of force production. The current findings are the first to have used neuroimaging techniques in humans to segregate the functional anatomy of the internal globus pallidus from external globus pallidus, distinguish functional activation in the globus pallidus from the putamen, and demonstrate task-dependent scaling in the subthalamic nucleus and internal globus pallidus. We conclude that fast, ballistic force production is preprogrammed, requiring a small metabolic demand from the basal ganglia. In contrast, movements that require the internal regulation of the rate of change of force are associated with increased metabolic demand from the subthalamic nucleus and internal segment of the globus pallidus.
[show abstract][hide abstract] ABSTRACT: Glover postulates that the inferior parietal lobule (IPL), along with the frontal lobes and basal ganglia, mediates planning, while the superior parietal lobule (SPL), coupled with motor processes in the cerebellum, regulates the control process. We demonstrate that the control process extends beyond the cerebellum and SPL into regions hypothesized to represent planning.
[show abstract][hide abstract] ABSTRACT: Anticipatory postural adjustments (APAs) in standing subjects were studied using different motor actions. We tested the hypothesis that a direct relation between the forthcoming perturbation and motor action is needed to trigger robust anticipatory postural adjustments. The same postural perturbation of a standard load release was induced by either a shoulder abduction, utilizing a motor action with a direct relation, or a biting or blowing action that had an indirect relation with the forthcoming perturbation. Electromyogram activity of trunk and leg muscles as well as the displacement of the center of pressure was recorded. Reduced APAs were observed in experimental trials using motor actions with an indirect relation to a perturbation as compared to the control series with perturbations induced by shoulder abduction. These results suggest that a direct relation between motor action and expected perturbation is important in the generation of anticipatory postural adjustments.