知覚運動領野の投射—知覚核を中心として

Projections from the Sensory Motor Cortex to the Sensory Nuclei in Cats

I．緒言

　近年，猫の知覚運動領野からの投射について，Glees法，Nauta法などの銀染による研究がいくつか発表されている。知覚運動領野から視床への投射についてはAuer^2），秋葉^1），岸^9）の研究がある。Auerは知覚運動領野の前部とGyrusproreusからの投射，秋葉はS字状回と冠状回よりの投射の差，岸は知覚運動領野の全体を損傷したときの投射についてNauta法で研究している。本実験ではS字状回と冠状回を小さな部位にわけて，それぞれの領域から視床への投射を観察し，この所見を後索核，三叉神経知覚核，脊髄路核および脊髄への投射所見と比較検討した。

Small lesions were produced in the sensory motor cortex of one side in 5 cats and bilateral-ly (in different areas of two sides) in 14 cats,using suction.The brains and spinal cords were studied 7-10 days afterward,using the Nauta-Gygax method.

We have incidently observed that the poste-rior ventral thalamic nucleus is divided into three clear subdivisions by fiber bundles which are usually quite distinct.These fiber bundles have apparently not been previously described,and are important in defining accurately the projections from the cortical areas.These fiber bundles divide the nucleus into antero-lateral,intermediate and postero-medial parts (see fig. 3).

The results of the study of prolections aresummarized as follows.

1) Projections from the sigmoid and coronal gyri to the thalamus were ipsilateral except for those to the inferior part of the lateral central nucleus and to the nucleus centrum medianum.The latter projections were mostly ipsilateral,with a very small number of cont-ralateral fibers.Projections to the trigeminal nuclei,posterior funicular nuclei and spinal cord were predominantly contralateral.Ipsilate-ral projection fibers to the main sensory trige-minal nucleus and to the oral part of the spi-nal trigeminal nucleus were few,but definite.Very few,if any,fibers were found to project ipsilaterally to the interposed and caudal parts of the spinal trigeminal nucleus.

2) The motor facial area,located in the anterior corner of the coronal gyrus and of the lateral part of the anterior sigmoid gyrus,sent projections to the medial part of the late-ral ventral thalamic nucleus and to the reticu-lar formation just medial to the trigeminalnucleus.From the intermediate and posterior parts of the coronal gyrus,only a few fibers of this distribution (e.g.motor facial) were observed.

The motor arm area,located in the lateral part of the anterior sigmoid gyrus and the antero-lateral part of the posterior sigmoid gyrus,sent fibers to the ventro-lateral part of the lateral ventral thalamic nucleus and to the intermediate zone of the upper segments of the spinal cord.

Projections to the intermediate zone of the lower spinal cord were observed in two cases (out of 5),in which the lesion in the medial part of the anterior sigmoid gyrus also injured the cortex deep in the cruciate sulcus.This finding was interpreted as showing the motor leg area is not located on the free surface of the sigmoid gyrus.

3) From the cortical sensory leg area,the medial part of the posterior sigmoid gyrus,projection fibers were demonstrated to the an-tero-lateral division of the posterior ventral thalamic nucleus,to the gracile nucleus and to the central part of the posterior horn of the lower spinal cord.

From the sensory arm area,the lateral part of the posterior sigmoid gyrus,there were projections to the intermediate division of the posterior ventral thalamic nucleus,to the cuneate nucleusand to the central part of the posterior horn of the upper spinal cord.

From the sensory facial area,the coronal gyrus,fibers were found to project to the po-stero-medial division of the posterior ventral thalamic nucleus and to the trigeminal nucleus.Further,these findings confirm the conclusions of Mountcastle and of Woolsey that there is clear somatotopic localization in cortex, in posterior ventral thalamic nucleus and in the trigeminal and posterior funicular nuclei.

4) From the antero-medial part of the po-sterior sigmoid gyrus,there were massive pro-jections to the gracile nucleus.From the post-ero-medial part they were sparse.

From the lateral part of the posterior sig-moid gyrus,there were projections to the dor-sal and central parts of the cuneate nucleus and to the central part of its hilus.

From the medial and postero-lateral parts of the posterior sigmoid gyrus, degenerating fibers were found in the medial part of the cuneate nucleus and its hilus.

From the posterior part of the coronal gyr-us,a very few fibers projected to the ventro-lateral part of the cuneate nucleus and to the lateral part of its hilus.

5) The intermediate part of the coronal gyrus sent fibers to the maxillo-mandibular region of the posterior ventral thalamic nuc-leus,to the ventro-medial parts of the main sensory and of the oral and interposed parts of the spinal trigeminal nuclei.The posterior part of the coronal gyrus was found to project to the frontal and occipital regions of the posterior ventral thalamic nucleus,and to the ventro-lateral parts of the trigeminal nuclei,except for the caudal portion of the spinal trigeminal nucleus.

6) If the lesion extended into the gyrus proreus,projection fibers could be followed through the loose fiber bundles in the lateral ventral thalamic nucleus to the dorsal medial thalamic nucleus.

7) Following lesions in the posterior sig-moid gyrus or in the posterior part of the coronal gyrus,degenerating fibers were observed in the posterior lateral nucleus of the thalamus.

8) The inferior part of the lateral central nucleus and the nucleus centrum medianum received fibers from all parts of the sensory motor cortex.