'954 



II VXDHi ink OF PIIYSIol i k_;y 



NEUROPHYSIOLOGY III 



spike to tli. it of sodium, and the whole activity- 

 recovery cycle to differential permeability changes. 

 Such a picture obviously demanded energy for 

 pumping ions and recharging die system, and various 

 relations have been seen between the delayed heat 

 .mil chemistry and die after-potentials; but no 

 inclusive model relating metabolic events to physio- 

 logical properties has been developed. (G. Ling, in an 

 extensive monograph on his fixed charge induction 

 hypothesis, soon ready for publication, does supply a 

 genera] model of this type.) 



With the need of enduring restitution processes 

 alter a brief action, the many cumulative changes 

 with repeated activity became understandable; but a 

 solid quantitative formulation is still lacking for 

 the progressive changes in after-potentials, in spike 

 height, in thresholds, in heat production and oxygen 

 consumption, and in other manifestations of equili- 

 bration. Over still longer times it has been established 

 that there is vigorous synthesis in the cell body and 

 ste.idv movement of substances from it down the 

 nerve fiber. The modulation of these processes — for 

 repair after cell damage, to meet the needs of activity, 

 and in relation to experience fixation and information 

 storage are mostly for the future. 



mi kon properties. For die entire neuron, as for its 

 fiber, the emerging facts and theories of neurophysi- 

 ology have uiven progressive emancipation from the 

 passive and inflexible telephone-exchange model of 

 central activity seen in the simple reflex. Neurons 

 proved spontaneously active, with rhythmic changes 

 in thresholds and potentials; they maintained so- 

 matic potentials along the dendritic-. ixonie axis, and 

 Steady potential fields, acting upon these, altered 

 thresholds, rhythms and, particularly, favored or 

 disrupted synchronous activity. These potentials, 

 and their rhythmic discharge, also depended on the 

 cell metabolism, rapidly being unfolded, and on a 

 trip mechanism, probably ionic, operated by the 

 energy flow. Qualitative differences in metabolism 



between cell i;roups, even between cell parts, and 



quantitative gradients along the neuraxis, a- well ,i, .1 

 mediol.iin.il organization, further led to differing 

 physiological .mil pharmacological behaviors of 

 various brain i egions. 



Besides these internal and external sir.idv 



influences, threshold was modulated hv incoming 

 nerve impulses, espe< iaily affecting the dendritic pole 

 i 'I thi 'ell. Eddy currents From various cell regions 

 converged upon the proximal axon segment and 

 Inllock where their total effeci vvas integrated to 



produce discharges of varying number and timing, 

 including none. The picture thus became clear of a 

 differentiation of cell regions, part for the storage of 



information, part for its transmission; and the concept 

 of the synaptic mechanism as a decision point, able to 

 integrate in a continuous or analogue manner the 

 varied stimuli excitatory and inhibitory, patterned 

 in time and space, present and past and so to 

 control the presence and pattern of efferent dis- 

 charges, gained precision. 



The junctional mechanism has also achieved 

 complexity and the attendant relaxing of input- 

 output linkage, a result of attention to the tv pes, 

 numbers or strength, and positions of synaptic 

 endings; the character of the receptor sites in the 

 postsynaptic membrane associated with these, the 

 probable existence of transmitter packets; and the 

 analysis of conditions of formation, release, spread 

 and action of such agents, as well as of the longer- 

 known eddy currents. 



xiikun groups. Further knowledge and insights 

 have developed as to the interrelations of these 

 neural units, as well as for the units themselves. The 

 model of a closed loop of neurons, supplementing a 

 linear sequence, proved most fruitful, as did the 

 simpler one of an avalancfiing net of interneurons. 

 These accounted for summation, irradiation and 

 reverberation, and foreshadowed the presence of 

 homeostatic negative feed-back controls. Such net- 

 works raise questions regarding the importance of 

 topology versus topography in the nervous system and 

 of the table of organization, describing the balance 

 between central and peripheral and between scries 

 and parallel flow of information and decisions. Re- 

 verberation (with inhibition!, and synchronization, 

 leads to models for the fixation of experience the 

 laying down of real patterns in real brain loci that 

 are congruent with a real outer world —and also lead 

 io hypotheses concerning personality traits. 



When the v.isi numbers of neurons in man's brain 

 are considered, the dichotomy between specific- neural 

 nets and generalized held effects lends to resolve into 

 probabilistic relations. Certainly, specific and diffuse 

 Synaptic systems exist and presumably are of prime 



importance, respectively, for conation and affect, for 



pattern and level of awareness, for sei and program, 



and for the Storage and handling Of experience. 

 Between and within these various systems exisi the 

 integrative mechanisms, including reciprocal inhi- 

 bition, .is they clo for simple spinal reflexes. But 

 beyond these fractionating factors, then- remain 



