Brain-machine-interfaceI requires a set of neurons to change their activity in order to control a cursor on a screen or a robotic arm. Neural activity from the primary motor cortex or the parietal reach region (PRR) is mapped to cursor or robotic arm movements through a decoder. Monkeys can learn to modulate their neural activity to become efficient at that task. In this paper (Hwang et al. 2013), Hwang and colleagues demonstrate that the mod.ulation of neural activity during learning is shaped by the existing neural structure.
Some kids are very efficient crawler. One can therefore wonder why these kids ever start walking. This question is central to the motor control field: what motivates people to change or adapt their behavior if they are already successful?
So, one of my last paper is out in JNP. It talks about how predictive smooth pursuit eye movements are affected in frontotemporal lobar degeneration (left brain) but not in Alzheimer's disease (right brain). Have a look at it and feel free to comment it below.
Usually, motor memories are created in the lab by perturbing the trajectory of the hand (e.g. force field perturbation Shadmerh and Mussa-Ivaldi, 1994) or the trajectory of the cursor (e.g. visuomotor rotation Krakauer et al. 2005). Initially, these perturbations lead to large errors that are reduced over the course of trials through learning. This learning depends on an error-dependent process (as discussed in Smith et al. 2006) that takes into account the error on one trial in order to update the motor commands for the next movements. Unfortunately, the resulting motor memories quickly fade away once the perturbation disappears. This forgetting of motor memories has been a major obstacle for the translation of motor learning paradigms to rehabilitation therapies because the beneficial effects of motor training do not last long. In a new paper, Shmuelof and colleagues present a novel technique that makes motor memories resistant to forgetting and opens up new avenues for the translation of motor learning paradigms to rehabilitation.
Writing is a very common skill but becomes difficult for disabled persons. Even when the limbs are not able to move anymore, the eyes still can. Therefore a method that could enable voluntary smooth pursuit eye movements and transform them into words would reestablish communication in severely disabled persons.
Until now, no one had succeeded in eliciting reliable smooth-pursuit eye movements in humans without a moving target on the screen. Smooth-pursuit eye movements in the absence of a target was only possible for short periods of time in anticipation of target motion onset (Barnes 2008) or during transient blanking of a moving target (Orban de Xivry et al.2008) but these movements cannot be voluntarily controlled. An article by Lorenceau (2012) precisely describes such an experiment.
Reorganization of motor networks
Anodal transcranial direct current stimulation (tDCS) of the dominant hemisphere improves learning and retention of a new skill performed with the dominant hand (e.g. Reis et al. 2009). These effects have been demonstrated several times in young healthy subjects for different learning tasks. In stroke patients, both anodal tDCS of the ipsilesional hemisphere (Hummel et al. 2005) and cathodal stimulation of the contralesional hemisphere improve motor functions of the paretic hand (Fregni et al. 2005). These tDCS protocols are balancing the activities of motor areas of both hemispheres by increasing activity in the ipsilesional hemisphere and decreasing activity in the contralesional hemisphere (Stagg et al.2012) and affect how the brain is reorganized after stroke (picture, Grefkes et al. 2011)
The question here is, if cathodal tDCS of the contralesional (unaffected) hemisphere is able to improve motor function of the paretic hand, can this protocol also improve motor learning in these patients?
Immobilization of an arm to favor the use of the other arm is a major component of Constrained-Induced Therapy (CIT). In stroke patients, this therapy improves the motor function of the affected hand. However, the neurological effect of this therapy has not been studied in non-patients populations.
In a recent paper published in the journal Neurology, Swiss scientists took advantage of arm immobilization after arm injury as a proxy for constrained-induced therapy in non-stroke patients. They investigated the effect of limb immobilization on brain structure, especially on gray and white matter plasticity.
or Memory interference at the single neuron level
Could Roger Federer be a world champion at tennis and table tennis at the same time? A new study suggests that it depends on the motor cortex neurons encoding those skills. If the same neurons are involved in tennis and table tennis, then the two tasks will interfere one with the other. If different sets of neurons are used, then Roger Federer could become a tennis table champion while maintaining his tennis ranking.
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.