Excitability of the Motor Cortex Ipsilateral to the Moving Body Side Depends on Spatio-Temporal Task Complexity and Hemispheric Specialization

Unilateral movements are mainly controlled by the contralateral hemisphere, even though the primary motor cortex ipsilateral (M1ipsi) to the moving body side can undergo task-related changes of activity as well. Here we used transcranial magnetic stimulation (TMS) to investigate whether representations of the wrist flexor (FCR) and extensor (ECR) in M1ipsi would be modulated when unilateral rhythmical wrist movements were executed in isolation or in the context of a simple or difficult hand-foot coordination pattern, and whether this modulation would differ for the left versus right hemisphere. We found that M1ipsi facilitation of the resting ECR and FCR mirrored the activation of the moving wrist such that facilitation was higher when the homologous muscle was activated during the cyclical movement. We showed that this ipsilateral facilitation increased significantly when the wrist movements were performed in the context of demanding hand-foot coordination tasks whereas foot movements alone influenced the hand representation of M1ipsi only slightly. Our data revealed a clear hemispheric asymmetry such that MEP responses were significantly larger when elicited in the left M1ipsi than in the right. In experiment 2, we tested whether the modulations of M1ipsi facilitation, caused by performing different coordination tasks with the left versus right body sides, could be explained by changes in short intracortical inhibition (SICI). We found that SICI was increasingly reduced for a complex coordination pattern as compared to rest, but only in the right M1ipsi. We argue that our results might reflect the stronger involvement of the left versus right hemisphere in performing demanding motor tasks

Direction of Movement Is Encoded in the Human Primary Motor Cortex

The present study investigated how direction of hand movement, which is a well-described parameter in cerebral organization of motor control, is incorporated in the somatotopic representation of the manual effector system in the human primary motor cortex (M1). Using functional magnetic resonance imaging (fMRI) and a manual step-tracking task we found that activation patterns related to movement in different directions were spatially disjoint within the representation area of the hand on M1. Foci of activation related to specific movement directions were segregated within the M1 hand area; activation related to direction 0° (right) was located most laterally/superficially, whereas directions 180° (left) and 270° (down) elicited activation more medially within the hand area. Activation related to direction 90° was located between the other directions. Moreover, by investigating differences between activations related to movement along the horizontal (0°+180°) and vertical (90°+270°) axis, we found that activation related to the horizontal axis was located more anterolaterally/dorsally in M1 than for the vertical axis, supporting that activations related to individual movement directions are direction- and not muscle related. Our results of spatially segregated direction-related activations in M1 are in accordance with findings of recent fMRI studies on neural encoding of direction in human M1. Our results thus provide further evidence for a direct link between direction as an organizational principle in sensorimotor transformation and movement execution coded by effector representations in M1

Motor recovery and cortical reorganization after constraint-induced movement therapy in stroke patients: a preliminary study.

Constraint-induced movement therapy (CIMT) is a physical rehabilitation regime that has been previously shown to improve motor function in chronic hemiparetic stroke patients. However, the neural mechanisms supporting rehabilitation-induced motor recovery are poorly understood. The goal of this study was to assess motor cortical reorganization after CIMT using functional magnetic resonance imaging (fMRI). In a repeated-measures design, 4 incompletely recovered chronic stroke patients treated with CIMT underwent motor function testing and fMRI. Five age-matched normal subjects were also imaged. A laterality index (LI) was determined from the fMRI data, reflecting the distribution of activation in motor cortices contralateral compared with ipsilateral to the moving hand. Pre-intervention fMRI showed a lower LI during affected hand movement of stroke patients (LI = 0.23+/-0.07) compared to controls (LI unaffected patient hand = 0.65+/-0.10; LI dominant normal hand = 0.65+/-0.11; LI nondominant normal hand = 0.69+/-0.11; P < 0.05) due to trends toward increased ipsilateral motor cortical activation. Motor function testing showed that patients made significant gains in functional use of the stroke-affected upper extremity (detected by the Motor Activity Log) and significant reductions in motor impairment (detected by the Fugl-Meyer Stroke Scale and the Wolf Motor Function Test) immediately after CIMT, and these effects persisted at 6-month follow-up. The behavioral effects of CIMT were associated with a trend toward a reduced LI from pre-intervention to immediately post-intervention (LI = -0.01+/-0.06, P = 0.077) and 6 months post-intervention (LI = -0.03+/-0.15). Stroke-affected hand movement was not accompanied by mirror movements during fMRI, and electromyographic measures of mirror recruitment under simulated fMRI conditions were not correlated with LI values. These data provide preliminary evidence that gains in motor function produced by CIMT in chronic stroke patients may be associated with a shift in laterality of motor cortical activation toward the undamaged hemisphere

Cervical dystonia : abnormal cerebral activation patterns related to preparation and execution of hand movement

Cervical dystonia (CD) is a movement disorder characterized by sustained involuntary muscular contractions which cause repetitive twisting movements and abnormal postures of the head. CD is primarily a brain disorder. Several studies show that CD patients have abnormal brain activity not only during movement execution but also movement preparation. An important area for movement preparation is the parietal cortex where sensory information is integrated in the movement preparation plan. In CD, this parietal cortex seems to function abnormally since extra sensory information (by touching the chin or cheek) can temporarily reduce dystonia. This thesis investigated execution and preparation of movement in CD and healthy controls by letting the subjects perform and imagine a flexion/ extension movement in a normal, non-dystonic hand. Imagination of movement activates specific brain areas which are related to preparation of movement. Both tasks showed lower parietal cortex activity in CD compared to healthy controls. Induced impairment of the parietal cortex by transcranial magnetic stimulation (TMS) in healthy controls showed specific brain activation changes that were similar to brain activation patterns in CD patients without TMS. Parietal cortex TMS in CD reduced the already low activity even further and increased activity in other brain regions. These results confirm that the parietal cortex is impaired in CD. This functional impairment seems to be compensated by other brain regions during movement in normal, non-dystonic body parts. However, the electromyography study in this thesis showed that full compensation is not reached, although visually the movement looked normal. Execution of a flexion/ extension movement of a normal, non-dystonic hand in CD patients demonstrated lower muscle strength during wrist flexion and longer muscle activation during wrist extension. Nevertheless, in CD other factors besides impaired compensation mechanisms may be in play to undermine the neck movements in CD patients in such a way that it becomes dystonic.

More than skin deep: body representation beyond primary somatosensory cortex

The neural circuits underlying initial sensory processing of somatic information are relatively well understood. In contrast, the processes that go beyond primary somatosensation to create more abstract representations related to the body are less clear. In this review, we focus on two classes of higher-order processing beyond somatosensation. Somatoperception refers to the process of perceiving the body itself, and particularly of ensuring somatic perceptual constancy. We review three key elements of somatoperception: (a) remapping information from the body surface into an egocentric reference frame (b) exteroceptive perception of objects in the external world through their contact with the body and (c) interoceptive percepts about the nature and state of the body itself. Somatorepresentation, in contrast, refers to the essentially cognitive process of constructing semantic knowledge and attitudes about the body, including: (d) lexical-semantic knowledge about bodies generally and one’s own body specifically, (e) configural knowledge about the structure of bodies, (f) emotions and attitudes directed towards one’s own body, and (g) the link between physical body and psychological self. We review a wide range of neuropsychological, neuroimaging and neurophysiological data to explore the dissociation between these different aspects of higher somatosensory function

Therapeutic Instrumental Music Performance to Improve Upper Extremity Function in Patients with Paresis and Apraxia after Stroke

Therapeutic Instrumental Music Performance (TIMP) has been shown to improve upper extremity (UE) functions in stroke survivors. While numerous studies have examined stroke-induced paresis, research on stroke-related comorbid disorders remains limited, with relatively little consideration being given to the consequences of stroke. Ideomotor apraxia (IMA) is one such common post-stroke consequence that may hinder the purposeful UE action and movements necessary for the performance of daily living tasks. This study investigated the therapeutic potential of TIMP intervention to improve UE functions in post-stroke patients suffering concurrently from paresis and IMA. Seven left-hemisphere stroke patients with IMA participated in 9 individual 1-hour TIMP interventions over a period of 3 weeks. During each intervention, participants engaged in gross and fine motor exercises that primarily utilized drum and keyboard playing. All outcome measures were assessed at baseline, pretest, posttest and a follow-up test 3 weeks post-intervention. Clinical measures included the UE section of the Fugl-Meyer Assessment (FMA), Wolf Motor Function Test (WMFT), Box and Block Test (BBT), strength, ADL/IADL, and hand domains of the Stroke Impact Scale (SIS). The Apraxia Screen of TULIA (AST) was used to assess apraxic impairments. While therapeutic benefits varied, all UE functional levels of the participants demonstrated post-intervention improvements in gross and fine motor skills (FMA, WMFT, BBT) as well as perceived ADL skills (SIS). Moreover, such positive gains persisted for 3 weeks after the intervention. Participants continued to experience persistent IMA across the study timeline. The results of this study indicated that patients with post-stroke IMA were able to reap benefits from the TIMP intervention, as evidenced by improvement in their UE functions and perceived ADL skills despite the persistence of IMA. The findings of the study support the perception of TIMP intervention’s emerging efficacy in individuals suffering from post-stroke paresis and IMA, providing new information, implications and applications for both for researchers and clinicians. Rigorous future research is recommended to spur the development of efficacious and innovative rehabilitation interventions aimed at optimizing patient quality of care