An fMRI Study on Supra-Spinal Contributions to Upper and Lower Limb Motor Control

The differences in the neural mechanisms contributing to upper and lower extremity movement have not been fully elucidated, and this might be a factor that leads to the ineffectiveness of rehabilitation techniques for most stroke survivors. It is unclear whether therapies designed for upper extremities should also be used for the lower extremities, and vice versa. In this study, fMRI was used to examine the supraspinal control of UE and LE movement in both neurologically intact individuals and people with post-stroke hemiparesis. We compared the location, volume, and intensity of brain activity associated with upper and lower extremity pedaling and unilateral flexion/extension of the hand and ankle. We hypothesized that if the supraspinal control strategies were the same for upper and lower extremities, then the pattern of brain activity would be the same across upper and lower limb movement. Alternatively, if the strategies were not the same, then brain activation would differ for each task. We found movement related brain activity in three cortical regions (S1, M1, and Brodmann Area 6) among healthy subjects. The location of activity complied with the somatotopic order in the sensorimotor cortex, but upper extremity produced greater activities during both pedaling and flexion/extension movement compared to the lower extremities. These observations suggested that the general brain activation strategies were similar between upper and lower extremities, while the involvement of cortical structures was more substantial for upper than lower limb movements. The four stroke subjects showed activity in the same regions as compared to the healthy group, yet the volume, intensity and symmetry of activation varied across the subjects and motor tasks. These observations suggested that there were multiple strategies for cortical reorganization after stroke and the controlling strategies for the effectors differed

Neural Coding of Movement Direction in the Healthy Human Brain

Neurophysiological studies in monkeys show that activity of neurons in primary cortex (M1), pre-motor cortex (PMC), and cerebellum varies systematically with the direction of reaching movements. These neurons exhibit preferred direction tuning, where the level of neural activity is highest when movements are made in the preferred direction (PD), and gets progressively lower as movements are made at increasing degrees of offset from the PD. Using a functional magnetic resonance imaging adaptation (fMRI-A) paradigm, we show that PD coding does exist in regions of the human motor system that are homologous to those observed in non-human primates. Consistent with predictions of the PD model, we show adaptation (i.e., a lower level) of the blood oxygen level dependent (BOLD) time-course signal in M1, PMC, SMA, and cerebellum when consecutive wrist movements were made in the same direction (0° offset) relative to movements offset by 90° or 180°. The BOLD signal in dorsolateral prefrontal cortex adapted equally in all movement offset conditions, mitigating against the possibility that the present results are the consequence of differential task complexity or attention to action in each movement offset condition

The use of current steering during subthalamic deep brain stimulation to alleviate upper limb symptoms of Parkinson\u27s disease

Subthalamic (STN) deep brain stimulation (DBS) is an established treatment to alleviate the appendicular motor symptoms of Parkinson\u27s Disease (PD). Current steering during DBS allows the unequal fractionation of current between two electrodes on the lead, resulting in a non-spherical electrical field. It is hypothesized that the way the electrical field is shaped will affect a patient’s upper limb symptom alleviation. Seven PD patients who underwent bilateral STN-DBS were tested over four weeks post-operation. 16 current fractionation settings were tested each week at an amplitude that increased weekly. Optimal setting was defined as the setting that provided the best symptom improvement based on kinematic data detected by a motion capture system and the Unified Parkinson\u27s Disease Rating Scale. Results assessing right and left upper limb symptoms gave 14 optimal settings in seven patients, of which eight settings employed current steering either unilaterally or bilaterally, and six settings employed bilateral monopolar stimulation. Thus, the use of current steering was patient-dependent and limb-dependent; factors contributing to this finding include differences in lead placement, symptom heterogeneity, and possible differences in STN functionality

Effector-invariant movement encoding in the human motor system

Ipsilateral motor areas of cerebral cortex are active during arm movements and even reliably predict movement direction. Is coding similar during ipsilateral and contralateral movements? If so, is it in extrinsic (world-centered) or intrinsic (joint-configuration) coordinates? We addressed these questions by examining the similarity of multivoxel fMRI patterns in visuomotor cortical regions during unilateral reaching movements with both arms. The results of three complementary analyses revealed that fMRI response patterns were similar across right and left arm movements to identical targets (extrinsic coordinates) in visual cortices, and across movements with equivalent joint-angles (intrinsic coordinates) in motor cortices. We interpret this as evidence for the existence of distributed neural populations in multiple motor system areas that encode ipsilateral and contralateral movements in a similar manner: according to their intrinsic/joint coordinates