216
GEORGE SZÉKELY
organization and the related function of nerve centers, a greater number
of more convincing examples can be brought forward, the idea may,
perhaps, be substituted for the selective connections theory.
V. A Final Remark
In seeking new paths in the study of neurogenesis, this paper cannot
avoid exaggerations. The data merely show that the old theories are
incapable of explaining recent findings ; as yet the data do not suggest a
convincing new theory. There are, very probably, many more factors
than we can think of at present in the background of organized nervous
function. Beside the morphological characteristics, there are various
physiological properties of neurons, such as fast and slow adaptation,
different sensitivity to various frequencies, and the relative ease or
difficulty in initiating and maintaining repetitive discharges in different
units. Their role may be instrumental in the "analyzing" mechanisms of
some centers. It might be worth considering the initial neighborhood of
certain neuroblasts in the medullary tube; their early interconnections
can assure selective connectivity between neurons migrating greater or
smaller distances away from each other in the later stages of development. There may be innumerable chemical and mechanical factors that
may influence the rate and manner of the development of cell processes,
etc. It is also likely that different mechanisms may be at work in different parts of the nervous system.
A certain amount of nervous activity is based on anatomically welldefined reflex arcs and on the function of specific ascending and descending pathways. It is obvious that their organization is effected by
selective connections, and their development may be studied in terms of
neuronal specificity. Since this is the most investigated and best known
part of the nervous system, we are inclined to regard the whole nervous
system as such. It is almost sure, however, that the above-mentioned
neural mechanisms and probably the greater part of nervous activity
belong to complex structures, within which the pathway of impulses can
be described only statistically. The inadequacy of an approach to these
structures in terms of selective connections is obvious. There are already
efforts to study the organization of such structures with histological
(Scheibel and Scheibel, 1958; Sholl, 1956; Szentâgothai, 1963, 1964) and
electrophysiological (Bishop, 1956; Bullock, 1959; Melzack and Wall,
1962) methods and with the aid of electronic (Harmon, 1964) and mathematical models (Beurle, 1956; Pitts and McCulloch, 1947; Uttley.
1962). It is hoped that this paper may contribute to these efforts from a
developmental point of view.
GEORGE SZÉKELY
organization and the related function of nerve centers, a greater number
of more convincing examples can be brought forward, the idea may,
perhaps, be substituted for the selective connections theory.
V. A Final Remark
In seeking new paths in the study of neurogenesis, this paper cannot
avoid exaggerations. The data merely show that the old theories are
incapable of explaining recent findings ; as yet the data do not suggest a
convincing new theory. There are, very probably, many more factors
than we can think of at present in the background of organized nervous
function. Beside the morphological characteristics, there are various
physiological properties of neurons, such as fast and slow adaptation,
different sensitivity to various frequencies, and the relative ease or
difficulty in initiating and maintaining repetitive discharges in different
units. Their role may be instrumental in the "analyzing" mechanisms of
some centers. It might be worth considering the initial neighborhood of
certain neuroblasts in the medullary tube; their early interconnections
can assure selective connectivity between neurons migrating greater or
smaller distances away from each other in the later stages of development. There may be innumerable chemical and mechanical factors that
may influence the rate and manner of the development of cell processes,
etc. It is also likely that different mechanisms may be at work in different parts of the nervous system.
A certain amount of nervous activity is based on anatomically welldefined reflex arcs and on the function of specific ascending and descending pathways. It is obvious that their organization is effected by
selective connections, and their development may be studied in terms of
neuronal specificity. Since this is the most investigated and best known
part of the nervous system, we are inclined to regard the whole nervous
system as such. It is almost sure, however, that the above-mentioned
neural mechanisms and probably the greater part of nervous activity
belong to complex structures, within which the pathway of impulses can
be described only statistically. The inadequacy of an approach to these
structures in terms of selective connections is obvious. There are already
efforts to study the organization of such structures with histological
(Scheibel and Scheibel, 1958; Sholl, 1956; Szentâgothai, 1963, 1964) and
electrophysiological (Bishop, 1956; Bullock, 1959; Melzack and Wall,
1962) methods and with the aid of electronic (Harmon, 1964) and mathematical models (Beurle, 1956; Pitts and McCulloch, 1947; Uttley.
1962). It is hoped that this paper may contribute to these efforts from a
developmental point of view.