236 Information Storage and Neural Control 



If this selection can be made, on what grounds is a resukant efferent 

 discharge determined? 



No one yet knows what the mechanism effecting these decisions 

 may be, but it has occurred to many that discriminations may be 

 made by the brain on a statistical basis, i.e., on the probability that 

 the afferent patterns are significantly different from those which 

 are currently taking place in the brain or which its past experience 

 has set its neurons to "expect" by a change in their cellular 

 function. 



This statistical viewpoint may be defined as the "probabilistic" 

 model in contrast to a "deterministic" one in which a given stimulus 

 elicits a stereotyped response irrespective of the likelihood of its 

 occurrence. 



The probabilistic approach recognizes the need for the brain to 

 assign iinportance to those signals which require effector action 

 and suggests that this assay of importance must be on a basis of the 

 probability of the signal not being a chance variation. With all 

 the on-going discharges of cerebral neurons that workers with 

 microelectrodes have so convincingly demonstrated, some pro- 

 cedure must surely take place before a 'meaningful' signal can be 

 selected from this incessant activity. 



No assessment of probability can be made without averaging. 

 Therefore, those who have begun to explore a statistical model for 

 coding in the nervous system have turned to techniques for averag- 

 ing neuroelectric activity over the passage of time as well as over 

 space as represented by neuronal aggregates. To aid in this task 

 many have adopted a prosthesis Just as the microanatomist has 

 adopted the microscope as a prosthesis to enrich his visual ability, 

 so has the neurophysiologist begun to use the computer as a pros- 

 thesis for his calculating ability. 



The statistical characteristics of spontaneously discharging 

 neurons must be known to the brain before it can react appropri- 

 ately to an unexpected, meaningful signal requiring action. One 

 might even speculate that the nonresponding but spontaneously 

 discharging neurons that so many observers have found with their 

 microelectrodes, are "comparison" generators and the responding 

 neurons "information" generators. If this were so, only when the 

 normally expected difference between the two categories of genera- 



