The primary motor cortex (M1) plays a major role in the control of movements. Monkeys are able to control a prosthetic arm by modulating the neuronal activity of M1 without any overt movements. However, the neural mechanisms of learning such ability (abstract skill learning) has remained unexplored so far. In their study, Koralek and his colleagues from Berkeley investigated this learning process in rodents. They show that abstract skill learning follows a similar time course to physical skill learning (involving movements of the limbs). In addition, they also demonstrate the importance of corticostriatal pathways for this process.
How reward affects motor behavior has been the focus of the motor control field for decades. For instance, it has been shown that monkeys make faster saccades towards rewarded target than non-rewarded ones (Takikawa et al. 2002). It has been suggested that the higher velocity of the saccades, which is linked to a decrease in movement time, was due to temporal discount of reward (Shadmehr et al. 2010). Namely, if movement time to get to the target is larger, the target is less rewarding. In a paper published recently in the Journal of Neuroscience, Joshua and Lisberger (2012) investigated the effect of reward on smooth pursuit eye movements. Smooth pursuit consists in a smooth motion of the eyes that is triggered by the motion of a target in the environment. During smooth pursuit initiation, the eyes smoothly accelerate until eye velocity matches target velocity.
At the Society for Neuroscience meeting in Washington last year, I came across a really interesting study by the team of Eric Wassermann (NINDS/NIH).
In a couple of papers, the authors demonstrate that expected reward does modulate the activity in the primary motor cortex. Their technique was rather simple but intelligent. They simulate a slot machine on a computer screen in front of the subjects. If the first two symbols matched, there was a 50% chance that the third symbol would match too. By delivering a double pulse TMS in between the second and third symbols appearance, they were able to capture the influence of the reward function on the primary motor cortex activity. How this reward signal depends on dopamine will be the topic of their next paper.
Kapogiannis D, Campion P, Grafman J, Wassermann EM
Reward-related activity in the human motor cortex - European Journal of Neuroscience 27 1836-1842 2008
written by Jean-Jacques Orban de Xivry
Scientist in the motor control field.