neurophysiology: an integration 



!9 2 5 



It broadens the perspective to realize that inter- 

 viewing an individual in a group in order to under- 

 stand the group's behavior, or leading from a neuron 

 cluster to understand that of a brain, or polarizing a 

 neuron through an impaling electrode to modify its re- 

 sponses are all maneuvers of essentially the same type. 



entering the organism. The living organism is 

 interesting in terms of its behavior. The higher the 

 organism, the more rich and variable its repertoire of 

 actions and the more cues to action does it discrimi- 

 nate in its environment. Psychology has dealt pri- 

 marily with the whole organism as a 'black box' 

 giving responses to stimuli, able to receive, process 

 and utilize information. The properties of the box, 

 the throughput, were inferred from the relation of 

 output to input; and certain molar relationships were 

 established. The vast studies of sensory physiology 

 and physiological psychology have dealt with the 

 mechanical or chemical transducers which transmute 

 or encode patterns of light and taste, chemically, and 

 of sound and touch, mechanically, into patterns oi 

 inflowing messages in bundles of nerve fibers; the \ast 

 studies of motor and neurosecretory physiology have 

 been concerned with the converse decoding or trans- 

 mutation of outflowing patterns of nerve messages 

 into mechanical and chemical patterns of perform- 

 ance. The discovery of action potentials, and the 

 development of instrumental and manipulative 

 techniques that made il possible to tap the nerve 

 impulses to and from the central nervous system, 

 enabled investigators to enter the organismic black 

 box and study directly the input and output of tin- 

 central nervous system. 



Such fractionation of the total problem also made 

 it possible to locus investigation in other ways. In one 

 direction, with input and output of the single trans- 

 ducer directly observable progressively down to the 

 level of the individual unit, progress was rapid in 

 obtaining the transform function and the physico- 

 chemical mechanisms of the various receptors and 

 effectors. In another, the entire body could be exam- 

 ined directly as an environment of the nervous 

 system — stimuli from the body initiating afferent 

 messages and efferent messages acting upon it, and 

 negative feed-back loops from the nervous system 

 controlling the receptors and the effectors, largely by 

 regulating their sensitivity and modulating" their 

 output. In this case it also proved important, to a far 

 greater extent than for the external environment, to 

 recognize that the messages are not exclusively nerve 

 impulses bul include as well specific substances, 

 hormones or humors, which may act on or be pro- 



duced by the nervous system at any station of the 

 input, throughput or output sequence. Thus, metab- 

 olism may lower oxygen or raise carbon dioxide in 

 the blood to carotid chemoreceptors or to medullarv 

 neurons; catechol amines may be liberated from 

 brain-stem structures or from adrenal medulla (von 

 Euler) ; a rise in plasma osmotic pressure may release 

 antidiuretic hormones from the hypothalamus; 

 the hypothalamus controls the anterior pituitary, 

 even to the extent of differential sex maturation 

 (Harris) ; food or hormones or temperature specifically 

 alter activity of appropriate neuron groups (Strom, 

 Stellar); and so on. 



entering THE brain. The initial problem of stimulus 

 and response of the organism now reappeared in the 

 refined but similar form of input and output to the 

 central nervous system. The same basic procedure, 

 of entering the inner black box, again produced great 

 rewards. By following incoming messages with probe 

 electrodes for evoked potentials, and by initiating 

 impulses with electrical or chemical stimuli, or block- 

 ing them with anatomical lesions or chemical or 

 polarization depressions, the functional connections 

 and transform functions of brain regions and nuclei, 

 down to the single neurons, are being explored in- 

 tensively. Here the problem in one sense is much 

 simpler because (except for the chemical mess.^es 

 and possible decrementing impulses) the inputs and 

 outputs at some distance are all basically similar 

 nerve impulses; but this very uniformity throws the 

 weight of specificity on variations in pattern rather 

 than in kind of signal and so raises the problem of 

 coding and decoding in its purest form. This will be 

 considered later. 



interacting units. The synaptic system (which 

 includes [lie specialized pre- and postjunctional 

 components .is well as the actual area of contact, and 

 even the interaction of several of these at, say, an 

 axon hillock) is thus a decision point to which infor- 

 mation converges and from which instructions emerge. 

 Here, individually and collectively, the output is a 

 nonlinear and variable function of the input, being 

 determined not only by the total contemporary input, 

 but also by past activations, by current physiological 

 state (a resultant of the chemical and electrical 

 field in which it lies and the chronology of its more 

 recent activities l and by such unanalyzed micro- 

 events as result in spontaneous rhythms or irregular 

 threshold fluctuations. It is no accident that in 

 neural evolution the rapid and accurate conduction 

 in an unbroken nerve fiber has been so little used to 



