Book - Comparative Study of the Sensory Areas of the Human Cortex

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Cajal SR. Comparative Study of the Sensory Areas of the Human Cortex (1899)

1899 Human Sensory Cortex: 1. The Visual Cortex | 2. Layer of the Large Stellate Cells | 3. The Sensori-Motor Cortex | Figures | Cajal
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Comparative Study of the Sensory Areas of the Human Cortex

Santiago Ramón y Cajal
Santiago Ramón y Cajal

By Santiago Ramón y Cajal

1899


Comparative Study of the Sensory Areas of the Human Cortex

  1. LECTURE I. The Visual Cortex
  2. LECTURE II. Layer of the Large Stellate Cells
  3. LECTURE III. The Sensori-Motor Cortex

Introduction

In order to respond worthily to the gracious invitation with which Clark University has honored me, I ought to offer you, as was my original intention, a work of synthesis, a general summary of the present state of our knowledge of the minute anatomy of the nervous system. Unfortunately, the duties of my professorship, every day more pressing, have deprived me of the time necessary for the accomplishment of such a task, and have compelled me to moderate my ambition, and to limit it to presenting to you a modest analytical contribution to our knowledge of the microscopical structure of the sensory centres of the human cerebral cortex, a subject to which I have devoted the leisure of the past months.


This subject is so vast and so difficult that, in spite of my efforts and the time devoted to it, I have been able to clear up only a few points. Consequently, my contribution will be, to my utmost regret, a very incomplete one, treating, as it does, only the visual cortex as I have made it out in man and some of the higher mammals. I shall add, however, a few observations on the structure of other sensory regions.


This anatomical study of the sensory areas of the cortex, at the present state of our knowledge, presents points of special interest, since, as you well know, neurologists who have interested themselves in the histology of the brain are divided at present into two camps, the unicists and the pluralists.


The unicist doctrine, proclaimed by Meynert and reaffirmed quite recently by Golgi and KoUiker, supposes that all regions of the cortex possess essentially the same structure, functional diversity being due to diversity of origin of afferent or sensory nerves. This amounts to saying that cerebral specific energy of nerves is the necessary effect of the particular organization of each sense as well as of the special character of the stimuli received by the peripheral sensory surfaces, skin, retina, organ of Corti, etc. The pluralist doctrine, upheld recently by Flechsig, without rejecting the particular influence of connections with different nerves, maintains that diversities of function result also from the particular structure of each cortical area.


It is this latter opinion, as we shall presently see, that presents a closer agreement with the observed facts. In fact, my researches tend to prove that the topographical specialization of the brain depends not only on the quality of the stimuli analyzed and gathered up by the sensory mechanisms, but also on the structural adaptations which the corresponding cerebral areas undergo; since it is very natural to suppose, even if one were to form an a priori judgment, that the cortical areas connected with the spacial senses sight and touch, which form exact images of the exterior world with fixed relations of space and intensity, have by accommodation to the stimuli received an organization different from that existing in cortical areas attached to the chemical senses of taste or smell, and from that which is appropriate to the chronological sense hearing, which gives only relations of succession, free from every spacial quality.


We may add that if there exist in the human cerebral cortex, as Flechsig supposes, besides the sensori-motor centres, other regions, association centres, characterized by absence of direct sensory or motor connections, it seems very natural also to associate to these important regions of the brain, with which are connected the highest activities of psychic life, a special organization corresponding to their supremacy in the hierarchy of functions.


But we must not carry to an extreme the structural plurality of the brain. In fact, our researches show that while there are very remarkable differences of organization in certain cortical areas, these points of difference do not go so far as to make impossible the reduction of the cortical structure to a general plan. In reality, every convolution consists of two structural factors: one, which we may call a factor of a general order, since it is found over the whole cortex, is represented by the molecular layer and that of the small and large pyramids; the other, which we may call the special factor, particularly characteristic of the sensory areas, is represented by fibre plexuses formed by afferent nerve fibres and by the presence at the level of the 8o*caIled granular layer of certain cell types of peculiar form.


But, before proceeding to outline the general conclusions of an anatomico-physiological order, that result from all our researches taken together, permit me to present very briefly the facts of observation.



1899 Human Sensory Cortex: 1. The Visual Cortex | 2. Layer of the Large Stellate Cells | 3. The Sensori-Motor Cortex | Figures | Cajal


Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)



Cite this page: Hill, M.A. (2019, October 22) Embryology Book - Comparative Study of the Sensory Areas of the Human Cortex. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Comparative_Study_of_the_Sensory_Areas_of_the_Human_Cortex

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