CONSCIOUSNESS 219 



the exclusive seat of any particular cortical function. In 

 a qualified sense, however, there is a greater degree of 

 cortical localization in man than in the ape, and more in 

 the ape than in the white rat. The neurosurgeon has 

 thoroughly explored the cortex by means of electrical 

 stimulation or other methods during operations on the 

 brain, and has thus identified numerous areas which are 

 more or less specifically involved either in sensory or 

 motor activity, and which are functionally related to spe- 

 cific parts of the body. This localization is, however, in 

 great part a matter of functional pattern rather than of 

 anatomy, as is shown by the extent to which it changes 

 during the growth of the individual. If one were to out- 

 line on the head of a very young infant the areas con- 

 cerned with each subdivision of the body, the resulting 

 homunculus would consist of a great suctorial mouth 

 and tongue and a big nose almost entirely surrounded 

 by the two hands— because these are the parts of the 

 body with which it is importandy concerned throughout 

 its early fife. Only with the passage of some months do 

 the hand and mouth areas shrink as the eyes, ears, and 

 feet come to occupy attention, and only later do the 

 shoulders, toes, arms, and thighs, and lastly the back, 

 acquire significance. Furthermore, the very young in- 

 fant quahtatively resembles the ape and rat, in that lo- 

 calization is not very important for fimction, and wide- 

 spread substitution is possible. But with the growth of 

 the brain, which increases in size fourfold between birth 

 and adulthood, localization becomes more marked and 

 increasingly important, so that in an older adult the 

 destruction of a small area in one hemisphere may have 

 severe and permanent consequences for function on the 

 opposite side of the body. 



Of all the areas in the cortex that have puzzled neuro- 

 physiologists and neurosmrgeons, the most intriguing are 

 the so-called 'silent areas,' which, on stimulation, evoke 

 neither sensory nor motor response. The frontal lobes in 

 man consist, in large part, of such silent areas. It is in 



