CONSCIOUSNESS 201 



to Stimulation, as is sometimes done, because an imcon- 

 scious man can in some measure do this, as exhibited 

 by reflex action, and so can a calculating machine to 

 which we have no reason to attribute any measure of 

 consciousness in the biological sense. 



Stanley Cobb, the neurologist, defines consciousness as 

 'awareness of environment and of self/ But this defini- 

 tion is not wholly satisfactory because it fails to tell us 

 how to obtain objective evidence of this awareness. Is 

 a bird, singing in the dawn, a conscious creature? Or a 

 fish, darting among the Hghts and shadows of the sea- 

 weed? Or an octopus, half -concealed in a rocky crevice, 

 waiting for its prey? 



It is well to defer attempting to answer these ques- 

 tions until we have found an objective definition of con- 

 sciousness, a definition which we must seek in the broad 

 perspectives of biology. 



We may begin with man. As observed subjectively in 

 omrselves, consciousness is variable in intensity, complex- 

 ity, and duration. It comes and goes as between waking 

 hours and sleep; it presents a distorted and fragmentary 

 pattern in dreams and hallucinations; and, even in the 

 waking state when it is normally continuous, it varies 

 greatly in acuteness, reaching its peak in moments of 

 excitement or intense attention when we are most 'wide 

 awake.' 



Abundant evidence in man as well as in other mam- 

 mals indicates that consciousness depends on a state of 

 continuous excitation of the cortex, and possibly requires 

 for its presence a repetitive series of nerve impulses im- 

 pinging on the cortex from lower centers. Loss of con- 

 sciousness is sometimes associated with sharply circum- 

 scribed lesions in the brain stem, but these anatomical 

 areas cannot be conceived to be 'centers of conscious- 

 ness'; they are, rather, bottlenecks through which ex- 

 citatory impulses between the brain stem and the cortex 

 must pass in order to maintain the reverberating circuits. 



