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

Melodic Accent as an Emergent Property of Tonal Motion

In a previous continuation tapping study (Ammirante, Thompson, & Russo, in press), each tap triggered a discrete tone in a sequence randomly varying in pitch height and contour. Although participants were instructed to ignore the tones, pitch distance and pitch contour influenced intertap interval (ITI) and tap velocity (TV). The current study replicated these findings with original melodies. Results were interpreted as an effect of apparent tonal motion, with deviation in ITI and TV mirroring implied tonal acceleration. Due to overlapping perceptual and motor representations, participants may have failed to disambiguate acceleration implied by tonal motion from the acceleration of their finger trajectory. Dissociative effects of pitch distance on ITI and pitch contour on TV implied that pitch distance influences the initial finger extension while pitch contour influences later finger flexion. Acceleration in ITI and TV were also both correlated with melodic accent strength values from perceptual data (Thomassen, 1982), suggesting that perception and production of melodic accent emerge from shared action associations

Functional dominance of finger flexion over extension, expressed in left parietal activation

Sensory stimuli may elicit a widely distributed parietal-premotor circuitry underlying task-related movements such as grasping. These stimuli include the visual presentation of an object to be grasped, as well as the observation of grasping performed by others. In this study, we used functional Magnetic Resonance Imaging (fMRI) to test whether the performance of simple finger flexion, contrasted to extension, might similarly activate higher-order circuitry associated with grasping. Statistical Parametric Mapping (SPM) showed that flexion, compared to extension, was related with significant activation of the left posterior parietal cortex and posterior insula, bilaterally. This pattern supported our hypothesis that simple finger flexion has a specific relation with circuitry involved in preparing manual tasks. Although the two motor conditions showed major overlap in the primary motor cortex, increased flexion-related activation at the precentral motor-premotor junction further supported its association with higher-order motor control

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.