neurophysiology: an integration 



1947 



few seconds of tetanus, the potential changes can last 

 for minutes, the metabolic and threshold alterations, 

 for hours, and synaptic transmissivity changes, for 

 days. There is now much evidence that many min- 

 utes must elapse between having a sensory experience 

 and establishing a permanent memory of it (61, 102, 

 171, 227, 237, 278, 279; Galambos & Morgan). 

 This period for fixation may well involve continued 

 reverberation of impulses in the appropriate neuron 

 nets; and with some hundred thousand repetitions 

 possible in the fixation time, a relatively enduring 

 trace is left, rather than a quickly reversible altera- 

 tion. 



A dynamic memory thus precedes a structural one; 

 and interruption of the dynamic process, by cold or 

 electroshock or anoxia, as well as its modification by 

 temperature (238) and drugs (236), give results which 

 fit well into such a neurophysiological interpretation. 

 The memory blank after an ictal seizure is likewise 

 explicable by mass discharge that precludes rever- 

 beration (see also Gloor). If the amygdala indeed 

 controls fixation (Gloor, 224), this mighl well I «• l>\ 

 altering cortical neuron potentials, and so thresholds 

 ana 1 the ease and duration of reverberation. Strych- 

 nine has been found to shorten fixation time (Krech, 

 personal communication), presumably by such an 

 action. Indeed, the lasting memory of emotionally 

 charged experiences ma\ depend on such enhanced 

 reverberation resulting from action ol die non- 

 specific s\stem to lower thresholds. A more detailed 

 model in terms of neuron sheets, and some behavioral 

 inferences from these considerations, will be presented 

 filer. Il deserves note now, however, thai functional 

 rather than spatial parameters mav be important in 

 Storing information (Neff). Different receptor ele- 

 ments activate different kinds of fibers and reach 

 central neurons that differ in properties as well as 

 position. Such physiological variables as kind of 

 substance released, shape of potential generated, time 

 constants, and the like may be of great importance. 



BRAIN AND BEHAVIOR SUGGESTIONS 



Guesses guide experimentation; nowhere are they 

 needed more than in relating the brain to behavior. 

 This section deals largely with such guesses. If they 

 stimulate only their experimental demolition, or in 

 other ways lead to better ones, they are justified. 



The Physiological X tut an Reserve 



Turn now from patterns of architecture that endure 

 in time back to those of activity which are evanescent. 



Much has already been presented on these, but 

 further attention must be directed to the number of 

 neurons active and to summation, irradiation, 

 reverberation and their consequences. The value of a 

 large population of neurons to a complex and varie- 

 gated behavior has been briefly considered. 



With fewer neurons available, fewer categories can 

 be established, fewer patterns laid down and the like. 

 Cortical ablations do not affect simple sensorv 

 thresholds or motor acts, these are cared for by more 

 ancient structures. [Even here, triploid salamanders, 

 with larger neurons than normal but only two thirds 

 as many, show an impoverished behavior, according to 

 Fankhauser ft til. (68).] But more complex and 

 discriminative behavior is lost as cortex is removed 

 patterned vision or patterned hearing (the tone 

 sequences, ABA versus BAH) goes with the projection 

 areas (Bartley, Galambos & Morgan, 21(1) and 

 conceptual analysis or the level of difficulty of a 

 problem that can be solved collapses with the re- 

 striction of cortical m;i«, just .is the skill of movement 

 decreases with less motor cortex available (Denny- 

 Brown 1. ( )nlv with the ureal richness of neurons in 

 his cortex can man stand away from the immediate 

 input suflieientlv to achieve import. mi generaliza- 

 tions, applv normative criteria, guide responses by 

 dist. ml goals, use abstractions and "bind time.' The 

 relatively slight behavioral defects so far found with 

 hemispherectomv may represent a real bilateral 

 duplication of function or, perhaps more likely, m.iv 

 resull from inadequate test-. Improvement in brain- 

 damaged children bv such an operation can be 

 attributed to elimination of conflicting abnormal 

 neuron activities. Whether the essential uncondition- 

 abilitv of spinal cord is due to inadequate neuron 

 supplv or to qualitative neuron differences is an open 

 question. Actually, enduring reflex alteration follow- 

 ing transiently altered input does occur in the lower 



cord (101 ; Brookhart). 



Anatomy, however, merely sets an upper limit; 

 the physiologically available neurons rather than the 

 anatomically existent ones must determine behavioral 

 capacity at anv time. This physiological neuron 

 reserve could be reduced from the anatomical 

 population in two ways; some neurons may not be 

 accessible to activation at that time, others ma\ 

 already be activated and fully engaged in routine 

 performance. The phvsiological reserve must increase 

 as neurons have their thresholds lowered, as bv 

 epinephrine or alerting impulses from the reticular 

 system, or by increased neural bombardment resulting 

 from continuing input with progressive summation 

 and irradiation, and ultimately reverberation, of 



