DETERMINATION OF NEURAL CONNECTIONS
203
showing the myotypic modulation, briefly touched upon in Section ΙΙ,Β.
In similar experiments, Weiss (1941, 1950) found that the stretch of a
given muscle in a supernumerary limb grafted into the brachial region
was followed by contraction of the muscle as well as contraction of the
synonymous muscle in the normal limb. He called this phenomenon
"proprioceptive specificity" and gave it an interpretation similar to
myotypic modulation: namely, that each muscle stamped on its afferent
fibers a specific discriminative mark which ensured selective connections
with appropriate motoneurons.
Probably the most beautiful experiment ever made for the demonstration of acquired specificity is the misdirected wiping reflex upon rotation
of the skin in frogs (Miner, 1951). When nocuous stimuli are applied
to its back, a frog wipes the back with the hind leg; the movement is
correctly directed to the place of stimulation. It wipes with the foreleg
to remove nocuous stimuli from the belly. Miner cut out a strip of
trunk skin in tadpoles extending transversely from the middorsal to the
midventral line and of the width of about 3^ dermatomes. She severed
every original nerve connection, rotated the skin 180°, and replaced it
so that the dorsal skin was on the belly and the belly skin covered the
back. After metamorphosis, the frog wiped with the foreleg on the belly
when stimuli were applied to the back, and with the hindleg on the
back when the belly was stimulated. The result was interpreted as meaning that there are refined local differentiations within the covering skin,
and a local sign specificity is stamped upon the sensory neurons in
consequence of the formation of their integumentary connections. The
central processes of these "stamped" neurons selectively terminate on
central neurons with corresponding specifications. Many similar experiments were made to show that "limb-specific" reflexes could be elicited
from grafted limbs and "cornea-specific" reflexes from extra eyes as a
consequence of the induction of specificity by the corresponding periphery
via the peripheral contact.
In the following sections, "corneal specificity" and "limb specificity"
will be surveyed in detail. Since a thorough electrophysiological analysis
of rotated wiping reflexes from rotated skin is currently in progress in
Dr. WalFs laboratory, it would be premature to speculate in advance
of the results. The discussion of "proprioceptive specificity" is postponed for a forthcoming paper mentioned already in relation with the
myotypic modulation.
A. Corneal Specificity
An eye withdrawal (corneal reflex) is present in amphibia after metamorphosis. This consists of retraction of the bulb with consecutive lid
203
showing the myotypic modulation, briefly touched upon in Section ΙΙ,Β.
In similar experiments, Weiss (1941, 1950) found that the stretch of a
given muscle in a supernumerary limb grafted into the brachial region
was followed by contraction of the muscle as well as contraction of the
synonymous muscle in the normal limb. He called this phenomenon
"proprioceptive specificity" and gave it an interpretation similar to
myotypic modulation: namely, that each muscle stamped on its afferent
fibers a specific discriminative mark which ensured selective connections
with appropriate motoneurons.
Probably the most beautiful experiment ever made for the demonstration of acquired specificity is the misdirected wiping reflex upon rotation
of the skin in frogs (Miner, 1951). When nocuous stimuli are applied
to its back, a frog wipes the back with the hind leg; the movement is
correctly directed to the place of stimulation. It wipes with the foreleg
to remove nocuous stimuli from the belly. Miner cut out a strip of
trunk skin in tadpoles extending transversely from the middorsal to the
midventral line and of the width of about 3^ dermatomes. She severed
every original nerve connection, rotated the skin 180°, and replaced it
so that the dorsal skin was on the belly and the belly skin covered the
back. After metamorphosis, the frog wiped with the foreleg on the belly
when stimuli were applied to the back, and with the hindleg on the
back when the belly was stimulated. The result was interpreted as meaning that there are refined local differentiations within the covering skin,
and a local sign specificity is stamped upon the sensory neurons in
consequence of the formation of their integumentary connections. The
central processes of these "stamped" neurons selectively terminate on
central neurons with corresponding specifications. Many similar experiments were made to show that "limb-specific" reflexes could be elicited
from grafted limbs and "cornea-specific" reflexes from extra eyes as a
consequence of the induction of specificity by the corresponding periphery
via the peripheral contact.
In the following sections, "corneal specificity" and "limb specificity"
will be surveyed in detail. Since a thorough electrophysiological analysis
of rotated wiping reflexes from rotated skin is currently in progress in
Dr. WalFs laboratory, it would be premature to speculate in advance
of the results. The discussion of "proprioceptive specificity" is postponed for a forthcoming paper mentioned already in relation with the
myotypic modulation.
A. Corneal Specificity
An eye withdrawal (corneal reflex) is present in amphibia after metamorphosis. This consists of retraction of the bulb with consecutive lid