Paradoxical modulation of tendon tap reflex during voluntary contraction in Parkinson's disease.
OBJECTIVE
Inadequate supraspinal modulation of spinal motor control mechanisms such as alpha-gamma coactivation is supposed to cause difficulty in maintaining proper voluntary contraction in Parkinson's disease (PD).


METHODS
Subjects were 42 patients with PD and 20 normal volunteers. Soleus H-reflex and tendon tap reflex (T-reflex) were recorded. The maximal reflexes (H(max) and T(max)) at rest were recorded first. Next, the stimulus intensities were fixed to obtain a reflex size of around 25% of M(max) at rest for both H- and T-reflexes, and the reflexes were recorded at rest, during tonic plantarflexion (TPF), and at the onset of plantarflexion.


RESULTS
H(max) at rest was 55% and T(max) 30% in normal subjects, while they were 36 and 31%, respectively, in PD. The size ratio of T(max) and H(max) at rest in PD was larger than normal. In PD, the size of H-reflex increased with TPF as in normal subjects, but T-reflex decreased. These changes in T-reflex were correlated with the grade of rigidity, bradykinesia, and time for 10 m gait. H-reflex had no such correlations.


CONCLUSIONS
T-reflex was abnormally modulated in PD especially during tonic contraction.


CONCLUSIONS
Inappropriate supraspinal modulation of the spinal reflex pathways disturbs motor performance in PD.
Morita
Hiroshi
H
The Third Department of Medicine, Shinshu University School of Medicine, Asahi 3-1-1, Matsumoto 390-8621, Japan. hmorita@hsp.md.shinshu-u.ac.jp
Shindo
Masaomi
M
Ikeda
Shu-Ichi
S
D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D010300:Parkinson Disease / Q000503:physiopathology*; D012026:Reflex, Stretch / Q000502:physiology*