16 



Survey of Neurobiology 



a systematic study of the topography of 

 representation in different parts of the 

 brain in relation to the orientation of bodily 

 parts. No explanation would appear 

 necessary for such gross arrangements as 

 having the legs innervated by the caudal 

 end of the spinal cord and the arms by 

 the cranial end, or even that the trunk 

 muscles are represented in groups of neu- 

 rons placed medially in the spinal gray 

 matter and the limb musculature largely 

 laterally. But how far can such correla- 

 tions be carried, and what would be the 

 predictive value of such work? In the 

 motor area of the cerebrum of lower mam- 

 mals (for example the goat) the hind limbs 

 are represented posteriorly and the fore- 

 legs more anteriorly, and the head and 

 face even more anteriorly though the fa- 

 cial representation spreads laterally. In 

 higher mammals, with the development 

 of the frontal association areas anteriorly 

 and medially, the motor area is pivoted 

 laterally leaving the area for hind legs 

 medial in position. In the motor area of 

 the cat the foreleg representation shows 

 finer topographic orientation. Stimuli ap- 

 plied anteriorly in this area result in pro- 

 traction of the limb, and stimuli applied 

 more posteriorly result in retraction. 



In the auditory area there is an order- 

 liness in representation of octaves along 

 the cortex, with change from high to low 

 pitch being represented progressing pos- 

 teriorly. In the visual cortex and in the 

 geniculate bodies a topographic orderli- 

 ness prevails. In the cerebellum response 

 to cortical stimulation shows a topographi- 

 cal representation of a double sort. The 

 head moves toward the side stimulated 

 while the stimulus is in progress but toward 

 the opposite side in rebound when the 

 stimulus ceases. If stimulated in the mid- 

 line the direction of head movement dur- 

 ing stimulation is downward and forward 

 when the stimulus is anterior to the pri- 

 mary fissure, and upward and backward 

 when the stimulus is posterior to this fis- 

 sure; and in each case the opposite move- 

 ment occurs in rebound just following stim- 

 ulation. Removals of approximate halves 

 of the cerebellum, dividing it along sag- 



ittal or transverse planes, is followed by a 

 sustained tendency to "fall" in the direc- 

 tion in which the intact animal would have 

 moved during stimulation of the part left 

 intact. Explanation of such topographic 

 relationships might go far toward explain- 

 ing the way in which the nervous system 

 functions. 



Evidence exists of similar topographic 

 patterns of representation in the deeper 

 structures of the cerebrum as basal gan- 

 glia and thalamus. But what is the situa- 

 tion within the olfactory and gustatory 

 cortex and the cortex concerned with 

 speech, or even that devoted to the phe- 

 nomena of higher integration of memories 

 and experience which is loosely referred 

 to as thinking? The observations of Pen- 

 field that electrical stimuli to the temporal 

 cortex of man can repeatedly elicit con- 

 scious recognition of a complicated series 

 of incidents appearing to the patient like 

 the events in a dream raise interesting ques- 

 tions, as he points out in the "Anatomy of 

 Memory." Details of topographical rep- 

 resentation along these lines appear to need 

 correlation with Lashley's experiments in- 

 dicating lack of specificity of cortical rep- 

 resentation of function. Further detailed 

 analysis of the relationship of cortical areas 

 related to speech in patients with aphasia 

 is needed. 



THE PATHWAYS 



Aside from the facts that might be 

 gleaned from blunt dissection of major 

 bundles of white matter in the brain, almost 

 every pathway that is named or described 

 needs further investigation if it is to be 

 completely known. We are here reminded 

 again of the need for adequate terminology 

 to be applied after accurate knowledge is 

 available of the origin, course, and term- 

 ination of tracts. Within recent years there 

 has occurred an example of complete rever- 

 sal in the direction described for a fiber 

 bundle. As the result of experiments, the 

 Hansons converted the strio-nigral bundle 

 to a nigro-striatal one. 



Comparative studies on pathways as well 

 as more intensive study of tracts in an in- 

 dividual species are needed. For example, 

 in the descriptions of afferent cerebellar 



