neurophysiology: an integration 



1941 



cord section. In contrast, situations demanding the 

 maximum amount of experience and choice, in- 

 volving multiple alternate input and output patterns, 

 may be lost with even small lesions in the highest 

 structures — as in the aphasias. Nevertheless, our 

 quantitative knowledge of the actual flow of traffic 

 through the complicated channel network is minimal; 

 the extent to which one route can substitute for 

 another in an emergency, what type of traffic has 

 priority on the boulevards (like passenger cars) and 

 what type takes the byways are questions for the 

 future. 



loops. The significance of feed-back loops also has 

 already been mentioned. At this level such questions 

 as the following present: what factors determine the 

 number of synaptic breaks in the direct path; the 

 number and kind of modulating connections that play 

 upon each of these way stations; the secondary paths 

 that issue from each way station to modulate still 

 other primary and secondary paths in the nervous 

 system; the intensity and dominance order of these 

 various flows of messages. Many of these are described 

 in detail throughout the Handbook (Livingston, Whit- 

 teridge, Jasper, Gloor, Paillard, Bartlcv, Brookhart, 

 Rose & Mountcastle, etc.), but the ordering or inte- 

 grating questions have certainly not been answered; 

 mostly we are not yet even asking them. Scrvomccha- 

 nistic studies at the peripheral level made by Stark 

 and Baker (269, 270) and Clynes (44) are a good 

 start. 



specific and general. A final dichotomy has been 

 adumbrated ever since the terms reason and emotion 

 became meaningful, and much recent research bears 

 out the existence of two basically different neural 

 systems related to these. A distinction between diffuse, 

 affect-tinged, unlearned experiences, on the one 

 hand, and particularized, rational and learned ones, 

 on the other, was attempted in the protopathic- 

 epicritic distinction of Head and Holmes (happily 

 exhumed by Rose & Mountcastle, also discussed by 

 MacLean). A similar separation was seen in fiber 

 types, especially those serving quick and slow pain 

 recognized by the St. Louis group (but challenged l>\ 

 Sweet), and was met clinically in the phenomena 

 related to causalgia (101, 184). 



Clinical and experimental studies first opposed 

 the hypothalamus to higher centers. Later the differ- 

 ent structures and functions of the old and the new 

 cortex became clear, with the former (whether called 

 the limbic s\ stem or some other name) associated 



with the emotional components of behavior. Still 

 later, the extensive reticular system was recognized 

 in its various portions as biochemically distinctive, 

 and as controlling, througli diffuse systems, the level of 

 cortical activity and the degree of alertness or even of 

 consciousness. It is useful to discriminate the level or 

 intensity or set of consciousness from the content or 

 patterns within it. The former is closely related to the 

 medial diffuse systems and to such chemicals as the 

 indole and catechol amines; the latter to engrams 

 laid down by experience, presumably mainly in the 

 cortical sheets. 



The opposed aspects of neural organization, mass 

 or molar on the one hand and particulate or micro 

 on the other, appear in all phases of structure and 

 function. Pavlov (and Lashley) has been pitted 

 against Sherrington, the gestaltists against the 

 behaviorists, adherents to field mechanisms against 

 those favoring synaptic ones, diffuse against discrete 

 in neural svsiems and behavioral patterns. Both are, 

 of course, present and useful. 



As the nervous system, during individual develop- 

 ment, passes from massive to differentiated reflex 

 responses (4;,, [42), so, during evolution, it has 

 probably followed a like course. Coclenteratcs possess 

 a neuropil-like nervous svstem, witli generalized 

 nonpol.it svnapses and with massive responses of the 

 whole organism prominent in their behavior. Such 

 undifferentiated structures, perhaps able to transmit 

 symmetrically, are seen in the neuropil of the old 

 central graj masses of the brain stem and in the short 

 axon connecting paths and feltworks; and the cor- 

 responding responses are met in the mass reflexes of 

 the spinal animal and the ietal discharges of the 

 intact one, and to some extent in the intense pseudo- 

 affective responses of diencephalic and other "basal' 

 preparations. 



LTpon raw mass properties were early superposed a 

 differentiation of units. Neurons became structurally 

 and chemically specialized, and developed different 

 sets of physiological properties, considered elsewhere, 

 which favored particular roles in the integrated 

 functioning of the nervous svstem. Larger cells with 

 longer processes and faster all-or-none conduction 

 supplemented the smaller, shorter and slower units; 

 and discrete action spikes become relatively more 

 important compared to fields and gradients, to 

 steady clectrotonic potentials and to chemicals. The 

 high speed quantized messages of axons may be a 

 specialization from conduction by decrementing 

 electrotonic spread which evolved earlier and per- 

 il, ips still dominates in gray masses [e.g. Bullock 



