THE PLANTAR REFLEX - RePub

FLEXION AND EXTENSION SYNERGIES
The Babinski sign as part of a flexor synergy
We have seen how Babinski (1896 a, 1898) regarded the abnormal
extensor movement of the toes as a disturbance of the normal synergy, in
which the roes flexed together with all other limb segments. This view was
at first genera!ly accepted, along with the diagnostic value of the sign.
Collier (1899) was no exception, and he even expanded the concept by
pointing out some other change in the flexor synergy of the leg, in addition
to reversal of toe movements and increased activity of other flexor
muscles, viz. late contraction of the musculus tensor fasciae latae. This
reflex was first described by Brissaud (1896) as the response which has the
lowest threshold on plantar stimulation, in patients and normal subjects
alike. Collier noted that it appeared much later in the sequence - i.e. at
higher stimulus intensities- in patients with pyramidal disease, but these
observations have not been confirmed.
However, van Gehuchren (1900 a,b), to some extent preceded by
Mingazzini (1899), was the first proponent of a different point of view
that was to receive increasing support over the years. In his opinion, the
normal plantar response did not change, but disappeared when the corticospinal
fibres were affected (just like the abdominal and cremasteric
reflexes). The normal reflex was replaced by reflex extension of the roes as
part of something basically different: an exaggerated medullary activity, a
defensive reflex analogous to the classic experiments on the decapitated
frog. These defensive movements might constitute a cutaneous reflex, but
strictly speaking not a plantar reflex, because in some cases they could be
evoked by stimulation of any part of the lower limb.
The fact that the receptive zone for reflex withdrawal of the leg,
including dorsiflexion of the hallux, extended beyond the sole of the foot,
although the reflex threshold was ususally at its lowest there, had also been
pointed out by Stri.impell (1899) and was later confirmed by many
others including Babinski himself (1900 b). Van Gehuchten's opinion that
the Babinski roe phenomenon was part of a primitive bur complex
medullary mechanism, whereas the normal response of the toes constituted
a separate reflex with a limited receptive field, was subsequently shared
by Schneider (1901) and Noica (1912). Finally, this was confirmed beyond
doubt by Marie and Foix (1910, 1912, 1913, 1915) and Walshe (1914); I
shall discuss these studies in some detail.
Marie and Foix (1910) added a further aspect to the Babinski sign by
showing that forceful flexion of the little toes could also evoke it, together
with retraction of the leg as a whole. It has been mentioned earlier (p. 19)
that this was already a time-honoured manoeuvre, practised by Brown-
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