A hemispheric asymmetry in the functional activation of the human motor cortex during contralateral (C) and ipsilateral (I) finger movements, especially in right-handed subjects, was documented with nuclear magnetic resonance imaging at high field strength (4 tesla). Whereas the right motor cortex was activated mostly during contralateral finger movements in both right-handed (C/I mean area of activation = 36.8) and left-handed (C/I = 29.9) subjects, the left motor cortex was activated substantially during ipsilateral movements in left-handed subjects (C/I = 5.4) and even more so in right-handed subjects (C/I = 1.3).

The relations of ongoing single-cell activity in the arm area of the motor cortex and area 5 to parameters of evolving arm movements in two-dimensional (2D) space were investigated. A multiple linear regression model was used in which the ongoing impulse activity of cells at time t + tau was expressed as a function of the (X, Y) components of the target direction and of position, velocity, and acceleration of the hand at time t, where tau was a time shift (-200 to +200 msec). Analysis was done on 290 cells in the motor cortex and 207 cells in area 5. The time shift at which the highest coefficient of determination (R2) was observed was determined and the statistical significance of the model tested. The median R2 was 0.581 and 0.530 for motor cortex and area 5, respectively. The median shift at which the highest R2 was observed was -90 and +30 msec for motor cortex and area 5, respectively. For most cells statistically significant relations were observed to all four parameters tested; most prominent were the relations to target direction and least prominent those to acceleration.

Reward and punishment are potent modulators of associative learning in instrumental and classical conditioning. However, the effect of reward and punishment on procedural learning is not known. The striatum is known to be an important locus of reward-related neural signals and part of the neural substrate of procedural learning. Here, using an implicit motor learning task, we show that reward leads to enhancement of learning in human subjects, whereas punishment is associated only with improvement in motor performance. Furthermore, these behavioral effects have distinct neural substrates with the learning effect of reward being mediated through the dorsal striatum and the performance effect of punishment through the insula. Our results suggest that reward and punishment engage separate motivational systems with distinctive behavioral effects and neural substrates.

Handedness is the clearest example of behavioral lateralization in humans. It is not known whether the obvious asymmetry manifested by hand preference is associated with similar asymmetry in brain activation during movement. We examined the functional activation in cortical motor areas during movement of the dominant and nondominant hand in groups of right-handed and left-handed subjects and found that use of the dominant hand was associated with a greater volume of activation in the contralateral motor cortex. Furthermore, there was a separate relation between the degree of handedness and the extent of functional lateralization in the motor cortex. The patterns of functional activation associated with the direction and degree of handedness suggest that these aspects are independent and are coded separately in the brain.