Functional organization of human motor cortex: directional selectivity for movement

Area of Science:

• Neuroscience
• Motor Control
• Brain Imaging

Background:

• Neurons in the hand area of the primary motor cortex (M1) in monkeys are directionally tuned to hand movements.
• Evidence suggests these neurons are clustered by preferred movement direction.
• This organizational principle has not been clearly demonstrated in human M1.

Purpose of the Study:

• To investigate the presence and nature of directional organization in the human primary motor cortex (M1).
• To determine if M1 neurons in humans are clustered according to preferred movement direction, similar to findings in monkeys.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure brain activity.
• Participants performed a reaching task using a joystick to move a cursor to different targets.
• Analysis focused on the sensitivity of voxel signals to movement direction and pattern correlations.

Main Results:

• The fMRI signal in individual voxels was sensitive to the direction of hand movement.
• Direction-specific adaptation was observed in the fMRI signal.
• The correlation between voxel response patterns varied with the angular distance between movement directions.

Conclusions:

• The findings suggest that neurons in the human M1 are organized in clusters based on preferred movement direction.
• This clustered organization is necessary to explain the observed directional selectivity at the voxel level.
• Estimated cluster size suggests a diameter on the order of a few hundred micrometers.