840 Comparative Animal Physiology 



contralateral occipital cortex (area striata in rats).-^*^ Areas responding to tac- 

 tile stimulation are not confined to the postcentral gyrus but also extend some- 

 what anteriorly. The sensory areas correspond in size to the more important 

 parts of the sensory pattern, as the mouth parts in rabbits, claws and dorsal and 

 lateral forelimb in cats, face in dog, hands and face in monkey.^ Auditory areas 

 show sharp projection from regions of the cochlea, hence of sound frequency, 

 in monkeys,'^*' less of point-to-point projection in cats, and probably still less 

 in rats/'' 



The motor area is best known from direct stimulation. Cortical stimula- 

 tion usually elicits responses not of single muscles but rather of groups of 

 muscles, exciting some and inhibiting their antagonists, the delineation of 

 cortical areas corresponding to discrete movements rather than to individual 

 muscles. The motor points which on stimulation yield discrete movements in 

 higher primates lie in the precentral gyrus (area 4), with areas for feet and 

 legs dorsally, then, progressing downward, for body, arms, neck, face, tongue. 

 Corresponding sensorv points lie opposite on the postcentral gyrus (Fig. 

 312). 



Ahead of the motor cortex lies the premotor area (area 6), which effects 

 movement by way of the motor area. Also anterior to the motor area are re- 

 gions with specific regulatory functions, such as pupillary constriction, eye 

 movements, and respiration. Overlapping these and the motor and premotor 

 areas are regions concerned with autonomic regulation, cardiovascular and 

 gastrointestinal control, sweating, salivation, etc. The extreme rostral por- 

 tion of the cortex, the frontal areas (prefrontal of many authors), are "as- 

 sociation" regions, and stimulation here elicits no motor response. Removal 

 of these regions, of frontal lobotomy, as practiced in certain neuropsychiatric 

 patients, has little postural effect but results in a distinct "intellectual deficit" 

 in respect to insight and foresight, and reduces the responses to emotional 

 tension and the "worry tendency. "^^^ 



Areas which are "silent" with respect to electrical stimulation also occur 

 in other lobes, parietal and temporal. Aphasia of various types results from 

 ablations in several regions. Hence, although intelligence in primates has 

 been interfered with most by prefrontal lesions, strict association function is 

 widely distributed in the cortex with recent evidence emphasizing the impor- 

 tance of the temporal lobes. 



Quadrupedal vertebrates (also to some extent arthropods) display placing 

 reactions of their legs which are initiated by tactile, visual, or proprioceptive 

 stimuli. Also when their feet are dragged laterally against a plane surface 

 they show a hopping reaction. In cats, dogs, and monkeys hopping reac- 

 tions are lost when the contralateral sensori-motor cortex is removed and are 

 retained when all but these gyri are ablated. In the rat, placing reactions 

 are controlled by a larger area, approximately one third of the cortex, and 

 hopping may be subcortical. In the opossum, placing reactions are controlled 

 by the contralateral excitable cortex, as in higher mammals.*'^ In the alli- 

 gator and lizard, proprioceptive placing remains when all of the brain ahead 

 of the mesencephalon is removed, but placing fails contralaterally after re- 

 moval of a lateral half of the midbrain (not tectum alone). •*^' ^^ These re- 

 actions illustrate different degrees of dependence on the forebrain, and de- 

 grees of localization within the cerebral cortex. In man, the only subcortical 



