The objective of this study was to determine the relationship between descending motor pathway reorganization and abnormal coordination, defined as a reduced set of muscle coactivation patterns between shoulder and elbow muscles in hemiparetic chronic stroke subjects, using transcranial magnetic stimulation (TMS). Specifically, we wanted to 1) determine the relationship between the ipsilateral and contralateral projections to the paretic arm and strength, clinical impairment level, and degree of abnormal coordination; 2) determine an optimal paired pulse TMS interstimulus interval (ISI) to cause facilitation in both healthy and paretic distal and proximal upper limb muscles at rest; 3) quantify the relative strength of the contralateral and ipsilateral projections to distal and proximal upper limb muscles in the paretic arm using paired pulse TMS; 4) estimate the possible contribution of corticobulbospinal systems in the expression of abnormal coordination in the paretic limb using asymmetric tonic neck reflexes (ATNRs) and TMS. Our results indicate that the relative magnitude of the ipsilateral and contralateral responses in a paretic proximal limb muscle was correlated with the Fugl-Meyer score as well as with the degree abnormal coordination, but not with strength. In addition, we identified the ISIs of 25-40 ms as the optimal ISI. Using 30 ms ISI, we found that all the paretic muscles studied had a greater ipsilateral than contralateral input than in the control subjects, and that muscles involved in the pathological flexor synergy had significantly greater ipsilateral input than the muscles in the pathological extensor synergy. In addition, the onset of flexor synergy was delayed compared to extensor synergy muscles, suggesting a more indirect route to the flexor muscles. Interestingly, we only observed ATNR modulation of the ipsilateral and contralateral responses in the biceps and triceps. The results presented in this dissertation demonstrate the preferential input of the ipsilateral projections to the pathological flexor synergy muscles of the upper limb of stroke subjects. The delayed onset, and similarity of responses to those observed with reticular formation stimulation in the monkey suggest that a corticobulbospinal pathway may be upregulated following stroke and may be involved in the expression of abnormal coordination

Last modified

• 05/07/2018

Creator

• Susan Schwerin

DOI

• https://doi.org/10.21985/N2TX21

Subject

• Neuroscience Institute Graduate Program

Keyword

• reorganization
• muscle
• transcranial magnetic stimulation
• proximal
• cortex
• TMS

Date created

• 2006-12-07

Resource type

• Dissertation

Rights statement

• In Copyright