The effects of age and somatosensory electrical stimulation on motor learning

Old adults have difficulty in learning new motor tasks. In clinical studies of
stroke and dystonia patients somatosensory electrical stimulation (SES) has
been used as a promising method to augment motor learning. In this study we
examine the effects of age and SES on motor learning in healthy young and old
adults. Understanding the mechanism of why and how age impairs motor learning
is important for neurorehabilitation settings because many individuals who
suffer from a unilateral trauma (e.g. stroke) are over age 65. Based on
previous data almost exclusively in patients, we hypothesize that 1) aging
impairs the ability to acquire and retain complex motor skills, 2) SES augments
motor learning but this augmentation decreases with age, and 3) changes in the
excitability of specific motor cortical circuits contribute to the learning
effect and the learning augmentation caused by the SES.

The primary objective is to determine the effects of age and SES on motor
learning using a motor practice (MP) task. The secondary objective is to
determine if the effects of age and SES on the changes in motor cortical and
corticospinal excitability during the motor learning process.

We will use a single-blind MP intervention with or without SES. There are four
groups: MP only, MP+SES, SES only and a Control group. A pre-, post- and
follow-up test will be conducted.

One session of non-invasive MP with the right wrist flexors and extensors for
35 minutes. The MP+SES group receives SES at 10 Hz trains of 5 pulses of 1ms
during the practice, the MP group only performs the practice and the SES group
only receives the stimulation. Furthermore, there is a control group that does
not perform the MP and does not get the SES. This group only performs the pre-,
post-test and follow-up test. In between the measurements, the participants in
this control group rest when sitting in the same set-up as the participants in
the other three groups. They see the trials on the screen, but do not perform
the movement.

Participants will visit the Center for Human Movement Sciences once. The
duration of the session is approximately 2 h. TMS may cause slight discomfort
lasting less than a second on the scalp near the coil. It may also cause some
twitching of the muscles, the face and jaw, which may be unpleasant and
surprising but not painful. SES will be below motor threshold, and can be more
surprising than painful. It can cause some momentary burning and tingling
sensation. The SES can cause momentary sensation of discomfort when determining
the Mmax. There are no known long-term risks of SES or magnetic brain
stimulation.