FUNCTIONS OF THE CEREBRAL HEMISPHERES 443 



According to Meyer and Barbour, the anterior part of the corpus striatum 

 plays an important part in the regulation of body temperature. In the 

 experiments a metal tube, closed at one end, was introduced through 

 the brain so as to lie in or on the corpus striatum. Through this tube water 

 at any temperature could be passed. It was found that cooling the water 

 gave rise to shivering and increased heat production in the body with a rise 

 of body temperature, while warming the water had the reverse effect. They 

 are therefore inclined to regard this part of the nervous system as representing 

 the chief thermo-taxic mechanism of the body. 



THE LOCALISATION OF SENSORY FUNCTIONS IN THE CORTEX 



It was pointed out by Ferrier that movements might be obtained on 

 electrical excitation of regions of the cortex cerebri other than those we have 

 described as motor. Thus excitation of the superior temporal convolution 

 on the right side causes the animal to turn its head and eyes to the left and to 

 prick up its ears. In the same way stimulation of the right occipital lobe 

 causes movement of both eyes and head to the left side. These portions 

 of the brain cannot be regarded as having a direct relationship to the motor 

 mechanisms involved in the above movements, since their ablation leads to 

 no defect of movement but does, in many cases, lead to defect of sensation. 

 Thus excision of the right occipital lobe in the monkey, though leaving the 

 eye movements intact, causes a loss of power to discern objects lying to the 

 left of the middle line. The obvious explanation therefore of the movements 

 obtained on excitation of this portion of the cortex is that they are due to 

 the revival or arousing of sensory impressions, that these portions of the 

 cortex represent the cortical receiving-stations for the impulses from 

 definite sense-organs, and that the movements obtained are simply those 

 which are normally associated with a corresponding sensory excitation. 



This conclusion is borne out by the fact that to excite movement it requires 

 a greater strength of stimulus when applied to the sensory areas than is 

 necessary if the stimulus be applied to the Rolandic area. Moreover Schafer 

 has shown that the latent period which intervenes between the stimulus and 

 the resulting movement is considerably longer when the stimulus is applied 

 to the sensory centre than when it is applied to the motor centre, suggesting 

 that more neurons are interpolated between the point of stimulus and the 

 discharging motor neuron in the first case than in the latter. Thus in one 

 experiment the latent period between the stimulus and the resulting move- 

 ment of the eyes amounted to 0'2 sec. when the frontal lobes were stimulated 

 and 0'4 sec. when the occipital lobes were stimulated. Finally the anatomi- 

 cal investigation of the course of the fibres in the white matter of the cerebral 

 hemispheres points to a concentration of sensory fibres from different sense- 

 organs towards certain regions of the cortex. The diagrams (Fig. 230 

 and 231) show those portions of the brain to which the endings of the sensory 

 tracts of the central nervous system are directed. 



From the purely anatomical standpoint we may designate as ' sensory 

 areas ' of the cortex : 



