How Can Models from InJormatio7i Theory be Used in Neurophysiology? 237 



tor activity was exceeded by a statistically significant amount 

 would the incoming" signal be meaningful. 



To analyze the myriad complexities of the brain's function by 

 nonstatistical description of unit discharges is too gigantic a task 

 to be conceived, but exploration in terms of probability theory is 

 both practical and rational. 



In characterizing nervous activity, therefore, one would not 

 attempt the precise definition that arithmetic demands but would 

 seek the statistical characteristics of the phenomena that appear 

 to be relevant. The margin of safety that the brain has for appropri- 

 ate reaction is thus much greater than a deterministic, arithmetic- 

 ally precise operation would impose. Chaos would result from the 

 least slip-up of the latter, whereas only a major divergence from 

 the mean would disturb a system working on a probabilistic basis. 

 The rigidity of arithmetic is not for the brain, and a search for a 

 deterministic code based on arithmetical precision is surely doomed 

 to disappointment. 



Turning now to the scanty data which are all that today's neuro- 

 physiologist has as yet. In terms of actual data culled from the brain 

 I propose to mention only two categories here: 



1 ) The averaging, over time, of intervals between unit discharges 

 in the brain; 



2) The averaging, over time and space, of activity in neuronal 

 aggregates. 



An example of averaging units over time, the first category, is 

 the work of Mountcastle (8) in which he has been designing experi- 

 ments to test the hypothesis that an intracortical mechanism 

 exists which integrates frequency over short periods of time and 

 responds only when intervals of sufficient brevity occur. These 

 experiments have revealed a striking change in pulse-interval 

 distribution in circumstances that give support to this hypothesis. 



This investigation is alluded to so briefly at this time because 

 it is being quoted solely as an example of the first category of 

 statistical approach, i.e., averaging over time only. But the central 

 nervous system must have some mechanism for dealing with 

 multiple complex inflow, and it would seem more profitable to 

 expand this approach to the second category of study that I men- 



