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DISCUSSION<br />
Effector of Babinski sign<br />
Recording from the extensor hallucis longus and brevis during mechanical<br />
stimulation of the sole has made it clear that the Babinski sign is<br />
mediated by the extensor hallucis longus. Activity in the extensor hallucis<br />
brevis is not essential, and it is also found in normal subjects. As we saw<br />
earlier, a similar conclusion was expressed by Landau and Clare (1959), but<br />
contradicted by Grimby (1963 a) on the basis of experiments involving<br />
electrical stimulation of the plantar surface. The results of the present<br />
study re-emphasize the principle - almost a truism - that the effector of<br />
any motor phenomenon can' be determined with confidence only when the<br />
phenomenon is actually taking place, in this case when the great toe is<br />
going up after conventional mechanical stimulation.<br />
The role of the extensor hallucis longus as mediator of the Babinski sign<br />
would have been at least probable from simpler observations than<br />
electromyographic recording, had it not become a matter of controversy.<br />
First, when a Babinski sign appears, the tendon of the extensor hallucis<br />
longus can be seen or at least felt to contract on the dorsum of the foot and<br />
hallux (figure 7). Secondly, it is hard to attribute the vigorous upward<br />
FIGURE 7. Babinski sign -note the protrusion of the EHL tendon.<br />
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