Source of Hand Weakness After Stroke

The incidence of stroke-induced hemiparesis among veterans is likely to rise as this
population ages. Post-stroke hemiparesis is often marked by persistent hand impairment,
which adversely affects both a person's ability to work and his/her quality of life. We
believe that impairment is primarily due to neural, rather than biomechanical, factors. At
the muscle level, these factors relate either to the inability to activate muscles (i.e.,
low muscle activation) or to activate them appropriately (i.e., abnormal muscle
co-activation). Currently it is unclear as to which one is largely responsible for weakness
in the hand as the net mechanical effect, e.g., reduced fingertip force production, could be
the same. Determination of voluntary muscle force generation could help to explain deficits
in fingertip force production in specific directions, as well as to customize treatment
approaches in which force generation ability of some muscles is decreased and others
increased. The goal of this work is to explain the source of neurally-mediated weakness at
the fingertip following hemiparetic stroke, and to design and experimentally test
rehabilitation interventions that attempt to offset this weakness.

Inclusion Criteria:

- clinical diagnosis of stroke;

- stroke occurred no less than 6 months prior to study;

- must have had only 1 stroke;

- must demonstrate severe hand impairment;

- must have no substantial evidence of motor and sensory deficits in non-paretic limb;

- must have no history or clinical signs of neurologic diseases other than stroke;

- must have no cognitive dysfunction that precludes comprehension of experimental
tasks;

- must be able to give informed consent

Exclusion Criteria:

- taking medication that can increase the risk of lidocaine toxicity such as cimetidine
(ulcer treatment drug), phenytoin (anticonvulsant drug), nadolol (drug for treatment
of headache, hypertension, chest pain);

- taking anticoagulant medication, i.e., aspirin, coumadin;

- has a low platelet count or a bleeding disease