Effect of hand position and feedback on cortico-spinal excitability during bilateral contractions.

When the right hand muscles are contracting, the left motor cortex is active.
This activity can be measured with transcranial magnetic stimulation (TMS) by
measuring the evoked response in the EMG (motor evoked potential, MEP). The MEP
amplitude will increase with increasing activity in the hand. A recent study
from our lab (Heetkamp et al., 2014; METc 2011-244) showed a similar or
increased MEP amplitude when the left hand also becomes active. These results
are in contrast with another study (Soteropoulos et al., 2011). Soteropoulos
showed that during bilateral contractions the MEP decreases. We have 3 possible
explanations for the difference.

There are 3 possible explanations for the differences. First: handposition;
Soteropoulos et al. (2011) used a pronated handposition (hand palm flat on the
table surface) during index finger abduction while during our experiment the
handposition was neutral (thumbs up). Second: feedback; Soteropoulos used a
feedback system with LED lights while we used a line for the force task on a
computerscreen. Because our feedback method is more precise, the task becomes
more difficult and could yield different results. Third: TMS machine;
Soteropoulos used a TMS machine with a mono-phasic pulse while we used a TMS
machine with a bi-phasic pulse. This could also be an explanation for the
different results.
In this study we want to determine whether 'handpostition', 'task complexity'
or 'TMS machine' could be the reason for the increase in MEP amplitude during a
bilateral contraction in our study.

This is an intervention study in which we determine the effect of hand position
and feedback method on the cortico-spinal excitability of the motor cortex
during bilateral contractions.

We want to include 5 subjects that perform a force production task with their
index fingers on different levels of their maximal force. During the task, we
stimulate the motor cortex using TMS to measure brainactivation. We repeat the
task 3 times under different conditions; feedback line and hand position
neutral; feedback LED and hand position neutral; feedback line and hand
position flat. After these 5 subjects we will perform an interim analysis on
subject level to determine the next step.
We will show the results after 5 subjects to the METc UMCG as well as the
desired next step. Depending on the results we will ask for an additional 5 or
10 subjects.
If there is no effect of hand position or feedback, we will measure the same 5
subjects performing the task but use a different TMS machine.
If there is an effect of feedback, we will include another 5 subjects that
perform the same task to make sure the difference is due to the feedback method.
If there is an effect of handpostition, we will include an additional 10
subjects that will perform the same task but with a more extensive protocol for
the TMS meaures. This will give an idea whether the origin of the inhibition is
in one hemisphere or between the two hemispheres.

The hand position and feedback method are varied between the force tasks. If
after 5 subjects we do not see a difference in hand position or feedback, we
will also vary the TMS machine between force tasks.

There are no known risks of (single pulse) TMS or electric nerve stimulation