Motoneurone afterhyperpolarisation time-course following stroke.
OBJECTIVE
Our aim was to investigate any changes in the estimated time-course of the afterhyperpolarisation (AHP) in motoneurones innervating the tibialis anterior following stroke, with a secondary objective to compare the results from two different AHP estimation techniques.


METHODS
Motor units from tibialis anterior on the paretic and non-paretic sides of 15 subjects with chronic stroke were recorded using intramuscular electrodes during voluntary isometric contraction. Participants varied the motor unit firing rate from its lowest rate to approximately 10 Hz. The AHP duration was estimated using the interval death rate (IDR) and transition point methods.


RESULTS
The AHP decay time-constant was significantly different between sides (paretic: 41.7 ± 8.5 ms, non-paretic: 36.2 ± 6.4 ms). Additionally, the paretic AHP time-constant was significantly longer in participants with low motor recovery (45.9 ± 9.1 ms) than with high motor recovery (39.3 ± 10.0 ms) as measured by CMSA score. The AHP estimates from the two techniques were correlated (r=0.78).


CONCLUSIONS
The AHP time-course prolongation on the paretic side of people with chronic stroke is more pronounced in people with low motor recovery.


CONCLUSIONS
Changes in the motoneurone AHP time course post-stroke were related to muscle function and may play a role in the commonly-observed reduction of motor unit discharge rate during voluntary contractions following stroke.
Department of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada.
Tanya D
TD
Ivanova
Graduate Program in Health and Rehabilitation Sciences, University of Western Ontario, London, Ontario, Canada.
Svetlana
S
Knorr
Spinal Cord Research Centre, Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada.
Christopher W
CW
MacDonell
Department of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada.
Courtney L
CL
Pollock
Department of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address: jayne.garland@ubc.ca.
S Jayne
SJ
Garland
D000200:Action Potentials / Q000502:physiology; D000368:Aged; D004566:Electrodes; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020521:Stroke / Q000503:physiopathology*; D013997:Time Factors
Afterhyperpolarisation; Human; Stroke