Tendon reflex asymmetry by voluntary mental effort in healthy subjects
J. Stam, H. D. Speelman and H. van Crevel
Department of Neurology, University of Amsterdam, the Netherlands.
The effect of voluntary mental influences on the tendon reflexes was
examined in healthy subjects. The patellar reflexes were evoked by a method
comparable with the clinical examination, and the reflexes were recorded by
surface electrodes. Eighteen subjects were instructed to increase and then
decrease the right patellar reflex by mental effort, without contracting
any muscles. Most subjects increased the reflex in both conditions.
Subsequently, ten subjects were instructed to increase the right patellar
reflex and decrease the left by mental effort. Measurement showed reflex
asymmetry in seven subjects consistent with the instruction. The experiment
was repeated in another 20 subjects with symmetric reflexes at rest. Ten of
these subjects were, after random assignment, instructed to increase either
the right or the left knee jerk. All subjects (and an additional 15
asymmetric control subjects) were examined by a neurologist without
knowledge of the instruction. Three of the ten instructed subjects were
correctly judged to be asymmetric, but the agreement between instruction
and neurologic judgment was not statistically significant. Mentally induced
reflex asymmetry is possible, and may be clinically relevant in some cases.
