neurophysiology: an integration 



! 949 



the ease of summation of incoming stimuli and the 

 kinds of stimulus patterns to which the neuron is 

 exposed; the degree of accommodation; the duration 

 and character of refractory periods; the magnitude 

 of posttetanic changes; and the like. Similarly, for 

 interaction patterns of neurons such variables come 

 to mind as: the strength and form of steady potential 

 fields; the strength of synchronizing mechanisms 

 and the ease of desynchronizing neurons; the power 

 of feed-back controls at junctions; the ease of setting 

 up reverberating chains and loops; the ease of altering 

 the number and arrangement of neurons in such an 

 assembly or in a still larger table of organization; the 

 ease of irradiation through neural nets and masses; 

 the speed and firmness of fixation and the amount of 

 reverberation needed to produce it, and the like. 

 And at both levels there could be important differ- 

 ences in the statistical range and pattern from one 

 individual to another, as in timing and duration of 

 discharge from cell to cell. 



Some intriguing guesses can be made relating 

 personality attributes to physiological properties. 

 (Walter's EEG parameters — abundance, versatility, 

 etc. — and their relation to individual performance 

 constitute an approach of this sort. ) Defective fixation, 

 for example, seems to underly presbyophrenia, the 

 failure of aging brains to hold recent memories. Too 

 easy fixation would lead to great and detailed memory 

 storage, but with little flexibility in handling this 

 information beyond recalling it the usual quiz kid 

 type. Defective synchronization would make for 

 distractibility, and excessive locking of neurons would 

 give a narrowed attention and a 'tubular personality. 5 

 [It is interesting in this connection that airplane 

 pilots tend to give 'tuning fork' EEC J records, as 

 reported by Williams (295) and Kennard (personal 

 communication).] Excessively stable thresholds, simi- 

 larly, would lead to rigid personalities, the petty 

 official type; excessive threshold fluctuation would 

 be associated with a flight of ideas. High fluctuation, 

 but not quite so high, should favor imagination and 

 creativity. As mentioned, the specific neuroactive 

 and psychoactive agents presumably act upon such 

 physiological parameters even more than upon 

 anatomical loci. All, in turn, depend upon molecular 

 and metabolic properties — as the convulsion prone- 

 ness of mice with low brain ATP ( 1 ) or the poor 

 learning of rats with low cholinesterase (162, 254; 

 see, however, 42). When these have been explored, 

 a comparison with the behavioral effects of these 

 agents will show the extent to which such guesses as 



the above are sound [see Korev & Nurnberger 

 (.6:)]. 



Reverberation 



Convergence and divergence of nerve paths and 

 impulses is the rule. In autonomic chains, one presyn- 

 aptic fiber can activate nearly 40 postsynaptic ones 

 (Hillarp). In the central system, precise figures are 

 difficult to come by, yet there is clear evidence of 

 both arrangements (Lloyd)— just as many enzymes 

 may make a gene and many genes, an enzyme. If 

 inhibitory feed-back loops did not prevent, incoming 

 messages would probably -explode' up the neuraxis 

 (Bartley), as in tri^er-point pains, and normally 

 there is a considerable amount of avalanchiny, for 

 impulses from single receptors are picked up along 

 the afferent path with sjross electrodes (121) and are 

 widely picked up, as on the motor side, with micro- 

 electrodes (Patton & Amassian). Yet the summation 

 resulting from convergence is also essential — witness 

 the increasing number of optic nerve fillers that must 

 l.e excited to enable activity to reach further and 

 further into the nervous system (Bartley). The 

 sequence that results from convergence— spatial and 

 temporal is summation, irradiation, reverberation 

 and fixation. 



I he balance of positive and negative control has 

 been touched on in several connections, since both 

 phenomena may be involved in most neural proc- 

 esses Activation of additional neurons can involve 

 removal of inhibition as well as addition of excitation. 

 The following treatment is mainly in terms of sum- 

 mation, which probably dominates in immediate 

 stress situations. Inhibition (or the subsidence of 

 general irradiation and so of facilitating interneuron 

 bombardment) is perhaps most important in long- 

 range learning phenomena. 



INNOVATIVE BEHAVIOR. Experience establishes ap- 

 propriate stimulus-response relations and the neces- 

 sary open channels in the nervous system to mediate 

 these. During the learning process, activity irradiates 

 widely, even to the autonomic svstem (Halsted); 

 many irrelevant motor actions accompanv the 

 relevant one (as the child grimacing and moving its 

 tongue while its hand laboriously makes earlv letters), 

 tension and attention are high (Paillard) and manv 

 neurons in the cortex and deeper structures are active 

 (2, 20, 147). With learning and the establishment of 

 specific skilled responses, the irrelevant movements 

 drop out, muscle tension falls (Halstecli, and manv 



