Abstract
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.
Highlights
Dynamic interaction with the outside world requires the translation of several modalities of sensory information into the appropriate motor output [1]
Directional parameters were demonstrated to be derived from visuospatial information, which is facilitated primarily by frontoparietal networks [12,17,18,19], how direction of movement is further used in the motor cortex for planning and execution of final motor commands remains to be elucidated
It was suggested that, in order to translate complex sensorimotor information into muscle activity patterns, in humans direction may be used as a unifying sensorimotor parameter encoded within M1 [32,33]. In addition to these human studies, the present study aimed to explore how direction of hand movement is incorporated in the representation of the manual effector system in M1 by employing functional magnetic resonance imaging (fMRI) and a centre-out step-tracking task [34]
Summary
Dynamic interaction with the outside world requires the translation of several modalities of sensory information into the appropriate motor output [1] It is not clear how the brain achieves this translation, the final motor commands are thought to be partly based on extrinsic parameters derived from a visuospatial framework [1,2,3,4]. In parallel, facilitated by parieto-occipital networks, proprioceptive information is integrated in the visually acquired image, resulting in a three-dimensional map serving as an egocentric visuospatial reference frame providing directional vectors for goaldirected movement [1,7,8,9,10,11,12,13,14] Based on this view, direction of movement is an important factor in translating complex multisensory information into parameters used for motor planning- and execution [15,16]. Directional parameters were demonstrated to be derived from visuospatial information, which is facilitated primarily by frontoparietal networks [12,17,18,19], how direction of movement is further used in the motor cortex for planning and execution of final motor commands remains to be elucidated
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