Is movement or muscle coded in the motor cortex? Implications for motor rehabilitation

Motor Imagery (MI) is a cognitive process, in which an individual performs a
goal directed movement without any actual (overt) movement (Decety, 1996). It
is known that MI results in similar brain activation patterns as overt
movement, and it is therefore thought to be a potential tool for relearning
difficult movements (Decety, 1996). Previous research has proven MI training to
have a beneficial effect in increasing skilled motor performances in healthy
subjects as well as in diseased patients, for example in stroke patients (Braun
et al, 2006; Sharma et al., 2006; Simmons et al., 2008). Thus, MI is a relevant
tool as part of motor rehabilitation, further it is easy to perform and the
training can be carried out at home.
Nonetheless, no attention has been paid to the position of the patient during
imagery so far. From experiments in which subjects actually perform muscle
movements, it is known that the motor cortex codes the activity of the movement
direction rather than the active muscle ensemble (Post et al., 2009). If this
also holds for MI, this would imply that patients have to sit in a position
that encourages movement performance.
The objective of this project is to investigate whether the posture of the
patient is important for the efficacy of motor imagery. We assume that a
stronger corticospinal activity would result in a better motor imagery.

The corticospinal spinal tract is an important descending pathway for control
of hand muscles (Lemon, 2008). About 50 years ago, direct connections between
the primary motor cortex and the motoneurons were discovered, but it is still a
matter of debate what is actually coded in the motor cortex: the active muscle
ensemble needed to perform the task, or rather the movement direction? And are
the muscles specified at a *lower* organizational level (e.g. spinal cord)?
If the motor cortex codes for movement direction, this would have direct
effects on the requirements of an efficient motor rehabilitation program. In
the present proposal, we want to address this question by investigating
differences in the corticospinal excitability during motor imagery with the
target ("active") hand in different positions.

The corticospinal excitability during hand tasks can easily be assessed by TMS
of the motor cortex . If the muscle is the primary parameter to be coded, we
don*t expect changes in corticospinal excitability by altering the resting hand
position. However, if movement direction is the important parameter we would
expect to observe differences for different hand positions
In addition, it is known that during overt movement not only the excitability
of the target motor cortex (the *classical*contralateral motor cortex) is
modulated but also that of the non-target motor cortex. Thus, when you change
the position of the non-target hand, we expect that it will also modulate the
excitability of the target motor cortex. Therefore we want to change the
position of both target and non-target hand during the experiment.

Ojective: Is the excitability of the corticospinal tract during motor imagery
modulated by the position of the target and the non-target hand?

The study is an intervention study in which we evaluate the effect of a change
in hand position on the excitability of the motor pathway (corticospinal tract)
during motor imagery.

Subjects are asked to complete two questionnaires at home before the
experiment.

change of hand position

no risks known of single pulse trancranila magnetic stimulation or electrical
nerve stimulation