Contralateral Sensorimotor Cortex Activation Research Articles

Modulation of Cortical Interhemispheric Interactions by Motor Facilitation or Restraint

Cortical interhemispheric interactions in motor control are still poorly understood and it is important to clarify how these depend on inhibitory/facilitatory limb movements and motor expertise, as reflected by limb dominance. Here we addressed this problem using functional magnetic resonance imaging (fMRI) and a task involving dominant/nondominant limb mobilization in the presence/absence of contralateral limb restraint. In this way we could modulate excitation/deactivation of the contralateral hemisphere. Blocks of arm elevation were alternated with absent/present restraint of the contralateral limb in 17 participants. We found the expected activation of contralateral sensorimotor cortex and ipsilateral cerebellum during arm elevation. In addition, only the dominant arm elevation (hold period) was accompanied by deactivation of ipsilateral sensorimotor cortex, irrespective of presence/absence of contralateral restraint, although the latter increased deactivation. In contrast, the nondominant limb yielded absent deactivation and reduced area of contralateral activation upon restriction. Our results provide evidence for a difference in cortical communication during motor control (action facilitation/inhibition), depending on the “expertise” of the hemisphere that controls action (dominant versus nondominant). These results have relevant implications for the development of facilitation/inhibition strategies in neurorehabilitation, namely, in stroke, given that fMRI deactivations have recently been shown to reflect decreases in neural responses.

Neuro-Physiological Adaptations Associated with Cross-Education of Strength

Cross-education of strength is the increase in strength of the untrained contralateral limb after unilateral training of the opposite homologous limb. We investigated central and peripheral neural adaptations associated with cross-education of strength. Twenty-three right-handed females were randomized into a unilateral training group or an imagery group. A sub-sample of eight subjects (four training, four imagery) was assessed with functional magnetic resonance imaging (fMRI) for patterns of cortical activation during exercise. Strength training was 6 weeks of maximal isometric ulnar deviation of the right arm, four times per week. Peak torque, muscle thickness (ultrasound), agonist-antagonist electromyography (EMG), and fMRI were assessed before and after training. Strength training was highly effective for increasing strength in trained (45.3%; P < 0.01) and untrained (47.1%; P < 0.01) limbs. The imagery group showed no increase in strength for either arm. Muscle thickness increased only in the trained arm of the training group (8.4%; P < 0.001). After training, there was an enlarged region of activation in contralateral sensorimotor cortex and left temporal lobe during muscle contractions with the untrained left arm (P < 0.001). Training was associated with a significantly greater change in agonist muscle EMG pooled over both limbs, compared to the imagery group (P < 0.05). These results suggest that cross-education of strength may be partly controlled by adaptations within sensorimotor cortex, consistent with previous studies of motor learning. However, this research demonstrates the involvement of temporal lobe regions that subserve semantic memory for movement, which has not been previously studied in this context. We argue that temporal lobe regions might play a significant role in the cross-education of strength.

Differential effect of spinal cord injury and functional impairment on human brain activation.

Reorganization of human brain function after spinal cord injury (SCI) has been shown in electrophysiological studies. However, it is less clear how far changes of brain activation in SCI patients are influenced by the extent of SCI (neuronal lesion) or the consequent functional impairment. Positron emission tomography ([15O]-H2O-PET) was performed during an unilateral hand movement in SCI patients and healthy subjects. SCI patients with paraplegia and normal hand function were compared to tetraplegic patients with impaired hand movements. Intergroup comparison between paraplegic patients and healthy subjects showed an increased activation of contralateral sensorimotor cortex (SMC), contralateral thalamus, ipsilateral superior parietal lobe, and bilateral cerebellum. In contrast to this, tetraplegic patients with impaired upper limb function revealed only a significant activation of supplementary motor area (SMA). Correlational analysis in the tetraplegic patients showed that the strength of hand movement was related to the activation of contralateral SMC. However, the severity of upper limb sensorimotor deficit was related to a reduced activation of contralateral SMA and ipsilateral cerebellum. The findings suggest that in paraplegic patients with normal hand function the spinal neuronal lesion itself induces a reorganization of brain activation unrelated to upper limb function. Compared to this, in tetraplegic patients changes of brain activation are related to the impaired upper limb function. Therefore, in patients with SCI a differential impact of spinal lesion and functional impairment on brain activation can be shown. The effect of impaired afferent feedback and/or increased compensatory use of non-impaired limbs in SCI patients needs further evaluation.

Changes in motor cortex activation after recovery from spinal cord inflammation.

Diseases of the spinal cord are associated with reactive changes in cerebral cortex organization. Many studies in this area have examined spinal cord conditions not associated with recovery, making it difficult to consider the value of these cortical events in the restoration of neurological function. We studied patients with myelitis, a syndrome of transient spinal cord inflammation, in order to probe cortical changes that might contribute to recovery after disease of the spinal cord. Seven patients, each of whom showed improvement in hand motor function after a diagnosis of myelitis involving cervical spinal cord, were clinically evaluated then studied with functional MRI. During right and left index finger tapping, activation volumes were assessed in three cortical motor regions within each hemisphere. Results were compared with findings in nine control subjects. Compared to the control group, myelitis patients had larger activation volumes within contralateral sensorimotor as well as contralateral premotor cortex. The degree of daily hand use showed a significant correlation with the volume of activation in contralateral sensorimotor cortex. Recovery from myelitis is associated with an enlarged activation volume in contralateral motor cortices. This change in motor cortex function is related to behavioral experience, and thus may contribute to motor improvement. The expanded activation in motor cortex, seen with several forms of spinal cord insult may have maximal utility when corticospinal tract axons are preserved.

随意運動と脳機能の画像化 機能的ＭＲＩを中心に健常者および脳血管障害患者での知見について

Functional imaging of the brain is of great value in investigating the mechanisms of motor control and reorganization of motor function after brain damage. Functional magnetic resonance imaging (fMRI) is one of the newer imaging techniques developed. The image contrast of fMRI is generated mainly by regional changes in levels of deoxy-hemoglobin associated with activated neural function. In contrast to positron emission tomography (PET), fMRI allows the study of single subjects without radiation risk and produces images with higher spatial resolution. Moreover, it can be conducted repeatedly. Brain activation observed in studies using fMRI and other techniques such as PET and single photon emission computed tomography depends on various attributes of motor tasks including the rate of performance; the body parts involved; the muscle force exerted; the amplitude during the motor tasks; the method for pacing (externally cued or self-paced) or starting the motions; and the complexity of the task. All of these attributes must be considered to reliably evaluate the results of functional imaging. Although SMC (sensorimotor cortex) activation is generally lateralized, some functional imaging studies showed the activation in ipsilateral SMC with movement of a unilateral hand. This was most pronounced in left hand motion of right-handers and depended on the task complexity. In contrast to the ipsilateral cortical activation, investigators have not yet reached a consensus on the asymmetry in contralateral SMC activation between right- and left-hand motions. The underlying mechanisms of the recovery of motor function following stroke are poorly understood. Some studies with fMRI have investigated the functional reorganization and showed that paretic hand movement produced extended activation in the ipsilateral sensorimotor cortex. This result indicated that the preexisting uncrossed motor pathway might be one of the important components of motor recovery after stroke. Other cortical areas such as the inferior parietal lobe and secondary motor areas have also been suggested to be involved in motor recovery. One study demonstrated that the peri-infarct area played a role in the reorganization of the cortical motor map.

Exploring the temporal nature of hemodynamic responses of cortical motor areas using functional MRI.

To use functional MRI (fMRI) to study grouped patterns of cerebral activation and the course of hemodynamic responses during performance of two activation tasks (paradigms) using a hand-held joystick to perform movements in a repetitively fixed direction and movements in freely selected random directions. Evidence from lesion, electrophysiologic, and functional imaging studies implicates prefrontal and mesial frontal cortex in motor preparation and primary motor cortex in motor execution. fMRI can be used to study cerebral activation and has practical advantages over other methods of functional neuroimaging. We acquired 100 multislice T2*-weighted data sets from five healthy volunteers during performance of each paradigm using conventional fMRI. For each paradigm, rest and movement epochs were alternated every 30 seconds. After coregistration and spatial normalization, we combined the data for group studies. We used statistical parametric mapping to compare the early (first 15 seconds) components of the movement epochs with rest as well as the late (last 15 seconds) components of the movement epochs with rest. During the early phase of both paradigms, significant activation was present in rostral and caudal mesial premotor cortex. Right prefrontal cortex was significantly activated during the early component of freely selected joystick movements. Activation of rostral supplementary motor area was maintained during the late component of freely selected movements but decreased during repetitively fixed movements. In contrast, significant activation in contralateral sensorimotor cortex was maintained during both early and late components of both paradigms. fMRI can detect cortical activation. The temporal resolution of fMRI also allows adaptation of blood oxygenation level-dependent (BOLD) contrast signal to be detected in association cortex. However, the level of BOLD contrast signal in primary motor cortex remained significantly elevated throughout task performance.