The classic example of a Jacksonian release phenomenon is the increased stretch reflex observed in muscles affected by upper motor neuron damage. In hemiplegia similar stimuli, applied bilaterally, produce an increased muscular reaction on the affected side. It has been generally inferred that this represents an increase of synaptic excitability at the final common path, somehow resulting from the disturbance of impulses normally projected there from the rostral neuraxis.
In 1957 Buller1 proposed a new mechanism based on his study of five cases of early hemiplegia. He compared the maximal tendon jerk in each leg with the maximal electrically evoked response (H reflex) in the same muscles. It is significant that he considered the maximal H reflex to be not the largest evoked by any intensity, but rather the largest response "just short of that [intensity] necessary to produce direct stimulation of the motor fibers."
His reasoning was as
LANDAU WM, CLARE MH. Fusimotor Function: Part VI. H Reflex, Tendon Jerk, and Reinforcement in Hemiplegia. Arch Neurol. 1964;10(2):128–134. doi:10.1001/archneur.1964.00460140014003
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