184
GEORGE SZÉKELY
The other problem is whether the genetic apparatus is capable of
transferring the necessary amount of information to specify every neuroblast according to its prospective participation in various reflex arcs.
On the basis of our present knowledge about the role of the deoxyribonucleic acid-ribonucleic acid system in the storage and transfer of
genetic information, there would be no difficulty in imagining devices
for the synthesis of an almost infinite number of proteins out of the
twenty amino acids, on the one hand, but, on the other hand, the number
of possible connections among several million nerve cells constitute an
almost infinite figure. It is also doubtful whether such minute differences
in the protein structure of the membrane or of other part of the perikaryon could sufficiently distinguish the nerve cells from each other.
There is, moreover, a serious difficulty in the application of the idea
of neuronal specificity to nervous activities—a difficulty which has
already been considered by Sperry in his early papers. In discussing the
possible synaptic formation within the trigeminal nucleus following different cross-union of the branches of the trigeminal nerve, Sperry and
Miner (1949) wrote: "Although this interpretation [i.e., the neuronal
specificity] is the simplest we can see at present, a number of difficulties
in its application will become apparent: First any such schema of
selective central connections must allow for considerable plasticity in
function and even for complete reversal of the responses. . . . Secondly
. . . Establishment of both excitatory and inhibitory linkages on an
interneuronal affinity basis introduces obvious complication for the
hypothesis." This is exactly the difficulty arising from our own observations on the results of sensory heteroregeneration (Székely, 1959a,b;
Székely and Szentâgothai, 1962), which clearly suggest that the mechanism of plasticity and even rudimentary (re) learning and conditioning
phenomena are involved. In a system of specific connections, secured
once and for all by attraction or repulsion of specific biochemical or
antigen-antibody character, no room is left for these mechanisms and
phenomena. In short, with the neuronal specificity theory a switchboard-like character had to be attributed to the nervous system in
general.
This review by no means denies the importance of specific matchings
—whatever their underlying mechanisms may be—in the establishment
of neuronal connections. There are data strongly suggesting that refined
specificities may govern the modes and loci of contacts established between different kinds of neurons in various centers. Mechanisms for the
establishment of specific connections between different sets of neurons
undoubtedly exist; the only question raised here is that this specificity
could be extended and generalized so far as to encompass all possible
GEORGE SZÉKELY
The other problem is whether the genetic apparatus is capable of
transferring the necessary amount of information to specify every neuroblast according to its prospective participation in various reflex arcs.
On the basis of our present knowledge about the role of the deoxyribonucleic acid-ribonucleic acid system in the storage and transfer of
genetic information, there would be no difficulty in imagining devices
for the synthesis of an almost infinite number of proteins out of the
twenty amino acids, on the one hand, but, on the other hand, the number
of possible connections among several million nerve cells constitute an
almost infinite figure. It is also doubtful whether such minute differences
in the protein structure of the membrane or of other part of the perikaryon could sufficiently distinguish the nerve cells from each other.
There is, moreover, a serious difficulty in the application of the idea
of neuronal specificity to nervous activities—a difficulty which has
already been considered by Sperry in his early papers. In discussing the
possible synaptic formation within the trigeminal nucleus following different cross-union of the branches of the trigeminal nerve, Sperry and
Miner (1949) wrote: "Although this interpretation [i.e., the neuronal
specificity] is the simplest we can see at present, a number of difficulties
in its application will become apparent: First any such schema of
selective central connections must allow for considerable plasticity in
function and even for complete reversal of the responses. . . . Secondly
. . . Establishment of both excitatory and inhibitory linkages on an
interneuronal affinity basis introduces obvious complication for the
hypothesis." This is exactly the difficulty arising from our own observations on the results of sensory heteroregeneration (Székely, 1959a,b;
Székely and Szentâgothai, 1962), which clearly suggest that the mechanism of plasticity and even rudimentary (re) learning and conditioning
phenomena are involved. In a system of specific connections, secured
once and for all by attraction or repulsion of specific biochemical or
antigen-antibody character, no room is left for these mechanisms and
phenomena. In short, with the neuronal specificity theory a switchboard-like character had to be attributed to the nervous system in
general.
This review by no means denies the importance of specific matchings
—whatever their underlying mechanisms may be—in the establishment
of neuronal connections. There are data strongly suggesting that refined
specificities may govern the modes and loci of contacts established between different kinds of neurons in various centers. Mechanisms for the
establishment of specific connections between different sets of neurons
undoubtedly exist; the only question raised here is that this specificity
could be extended and generalized so far as to encompass all possible