49 8 TEXT-BOOK OF PHYSIOLOGY. 



A knowledge of the situation of these areas, the order of their 

 development, the effects that arise from their stimulation or follow 

 their destruction, are matters of the highest importance in the study 

 of cerebral activity and indispensable to the physician in the localiza- 

 tion of lesions which manifest themselves in perversions or abolition 

 of sensations and in convulsive seizures or paralyses. 



The Sensor Areas. The sensor areas which should theoret- 

 ically be present in the cortex are primarily those which receive 

 and translate into conscious sensations nerve impulses, developed by 

 changes going on in the body itself; and secondarily those which 

 receive and translate into conscious sensations the nerve impulses 

 developed in the special sense-organs by the impact of the external 

 or objective world. In the former areas, are received the nerve im- 

 pulses that come from the skin, mucous membranes, muscles, viscera, 

 etc., and give rise to cutaneous, muscle, and visceral sensations. In 

 the latter are received the nerve impulses that come from the sense- 

 organs and give rise to tactile, gustatory, olfactory, auditory, and 

 visual sensations. A number of such sense areas may be predicated : 

 e. g., areas of cutaneous and muscle sensibility, of gustatory, oljactory, 

 auditory, and visual sensibility. 



The Motor Areas. The motor areas which should theoretically 

 be present in the cortex are those which in consequence of the dis- 

 charge of nerve impulses excite contraction of special groups of 

 muscles and which, from their coordinate and purposive character, 

 are conventionally termed volitional. Five such general motor areas 

 may be predicated: e. g., one for the muscles of the head and eyes, 

 one for the muscles of the face and associated organs, and areas for 

 the muscles of the arm, leg, and trunk. They are usually designated 

 as head and eye, face, arm, leg, and trunk motor areas. 



The existence and anatomic location of these areas in the cortex 

 of animals have been determined by the employment of two methods 

 of experimentation: viz., stimulation and destruction or extirpation; 

 the first by means of the rapidly repeated induced electric currents, 

 the second by the electric cautery and the knife. If the stimulation 

 or excitation of any given area is followed by contraction and its 

 destruction by paralysis of muscles, it is assumed that the area is 

 motor in function is a center of motion. If the stimulation of a 

 given area is attended by phenomena which indicate that the 

 animal is experiencing sensation, and its destruction by a loss of 

 this capability or the loss of a special sense, it is assumed that the 

 area is sensor in function is an area of special sense. The animals 

 generally employed for experiments of this character are dogs and 

 monkeys, though other animals have frequently been employed by 

 different investigators. Of all animals, the monkey is the most fre- 

 quently selected, as the configuration of the brain in its general out- 



