How Can Models Jrom Information Theory he Used in Neurophysiology)? 231 



Let us look first at the difference between energy-based concepts 

 and information-based concepts. All down the ages the nerves have 

 been recognized as message-carriers and as late as the last century 

 the most distinguished physiologist of the time, Johannes Miiller, 

 was using the term "nerve energy.'' "We are," he wrote, "com- 

 pelled to ascribe, with Aristotle, peculiar energies to each nerve, 

 energies which are vital qualities of the nerve." Even the later 19th 

 century neurophysiology, dominated by Du Bois Reymond, was 

 primarily focussed on the concept of the conservation of energy. 



You will remember that it was because of his adherence to 

 energy concepts that Sherrington (10) found himself unable to 

 envisage a physiological basis for mental processes. In Man on His 

 Nature he wrote: 



"No attributes of 'energy' seem findable in the process of mind. 

 That absence hampers explanation of the tie between cerebral and 

 mental." 



He goes on to write of the brain being "a physiological entity held 

 together by energy-relations" and expresses his despair of being 

 able to correlate such a physiological entity with a mental experi- 

 ence. "The two for all I can do," he wrote "remain refractorily 

 apart. They seem to me disparate; not mutually convertible; un- 

 translatable the one into the other." 



Coming to our own times, we have seen a great deal of investiga- 

 tive effort go into a search for energy correlates of brain function. 

 An example is the search for a metabolic change underlying the 

 sleep state. Anesthesiology is another field in which one finds many 

 studies centering around alterations of brain metabolism as the 

 major factor of importance in the changing levels of consciousness. 



It is only with recent years that we find attention being diverted 

 from the question "What is the level of activity in the brain as a 

 whole?" to "Which system within the brain is now dominantly 

 active?" The latter question contains the implication that it is a 

 re-routing of nerve impulses, a change in the informational coupling 

 rather than in the general metabolic level of the brain's activity 

 that may yield the clue to functional changes. In order to effect a 

 coupling of parts within the nervous system there does not have 

 to be a great interchange of energy— only the infinitesimal transfer 

 concomitant with the passage of the nerve impulse. 



