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HANDBOOK III- I'HYSloIOGY " NEUROPHYSIOLOGY III 



|6)]; indeed, even in long axons the question of a 

 slight decrement has recently been reopened ( 1 88). 



Further development yielded the older integrating 

 structures of the reticular formation, hypothalamus 



and rhinencephalon, using express conduction paths, 

 yet in a somewhat primitive fashion. Here are the 

 diffuse systems, including cells with short processes, 

 multiple synapses, wide connections, high chemical 



sensitivity, slow adaption and prolonged potenli.il 

 changes. These act widely and relatively [hut not 

 entirely, as shown by John & Killam (151)] non- 

 specifically, serving a protopathic type of affective 

 experience and mainly setting the conditions in which 

 the discrete systems operate. The newest cortex and 

 its associated lemniscus tracts and way stations, the 

 discrete systems, are concerned primarily with con- 

 tent rather than set and serve an epicritic type of 

 patterned and discriminating conative experience. 

 Vet, even here, in the cell sheets of the neocortex, 

 held eflects and mass action are important; the 

 integration contributed by steady potential fields 

 and the differentiation contributed by ordered 

 nerve impulses arc both needed for full function. 



Diffuse systems, with their rich intcrneurons, able 

 to put cell masses under barrage with repeated and 

 recurrent showers of impulses (187), largely control 

 the background excitation level. The old finding of 

 Llovd (185) that a 7 msec, delay between arrival of a 

 pyramidal fiber volley and discharge of an anterior 

 horn cell is shortened 10-fold on repetition, when the 

 local Lnterneuron pool has become active, is much 

 to the point. Main examples are currently in atten- 

 tion: the gamma fiber discharges which give the 

 motor set for alpha fiber action (Eldred) and which 

 come from vestibule, reticulum and cerebellum 

 (( iernandt) ; the auditory , visual and other modulators 

 of receptor threshold and sensory inflow (Livingston, 

 French); the associated feedback from receptors 

 which also contributes to 'set' (Adrian, Galambos & 



Morgan, Rose \- Momili aslle ) , the modification ol 



cortical responses bv manipulation of the reticular 

 formation (French) or amygdala, or by thalamic 

 impulses (Chang, 50); the similar modification of 

 cortical stead) potentials (10); the influence of 

 nonspecific impulses to the < ortex in conditioning the 

 perception induced In specific ones (.Nell), the 

 interaction ol spa tfii and nonspei ifu impulses al 



ingle cortical neurons (153); the excessive suffering 

 from pain where discrete paths are inactive (101), 



uffering which is relieved by leucotomy and other 



that, .11 leasl in some cases, cut into 



diffuse system paths 5 et); even the control of 



alertness level, from sleep to vigilance, by inhibitory 

 and facilitatory portions of the reticular formation 

 (Jasper, Chang). The amygdala facilitates the hy- 

 pothalamus and may be involved in the increased 

 pituitary-adrenal response that accompanies psy- 

 chological distress (iyt>), activity of the amygdala 

 increases emotional behavior in response to mild 

 stimuli, including rage attacks and psychotic-like 

 behavior (Gloor), but it inhibits cortical responses 

 and ease of conditioning (Galambos & Morgan) and 

 produces slow and perseverative thought (Gloor). 

 Recent work (152) shows that correct learned re- 

 sponses to flicker are associated with matching po- 

 tential frequencies in the reticular formation and 

 cortex, interpreted as congruence between past learn- 

 ing and current perceptual display. 



The cortical "unit' (Chang, Patton & Amassian) is 

 affected differently by incoming diffuse and discrete 

 fibers (Chang, Jasper). The former act mainly on 

 superficial layers but can depolarize apical dendrites 

 of deep pyramids as well, giving a surface negativity. 

 This negativity builds up locally on repetition which 

 suggests that the 'recruitment' response is more a 

 summation on the same elements than the addition 

 of new ones, as the term implies. Discharge, as well as 

 EEG waves which spindle or dome, is increased 

 by virtue of lowered thresholds, thus making the 

 discrete afierents more effective. The diffuse system 

 is not without structure and can alter the spread of 

 activity in the cortex along different paths (Jasper; 

 compare with Pribram). That the diffuse svstein 1n.1v 

 also fire motor neurons is suggested bv the retention 

 of facial movements associated with strong emotion 

 in patients unable to perform voluntary movements 

 with the facial muscles, h also bears thought that a 

 clear reciprocal inhibition (see later) operates be- 

 tween attending to content and to mood, as also 

 between different contents and different moods. 



All the old brain centers interconnect (Gloor) 

 and interact with the new ones a veritable metabolic 

 pool of message flow with vast opportunities for 

 feedback and lor circular causation, Here, indeed, is 

 'organized Complexity,' and the two great svsienis 

 function smoothl) together as do, in Mail, can's 

 phrase, a horse and rider. The diffuse svstem mainly 

 serves drive, affect, alertness, attention the sub- 

 stratum on which perception and action are carried. 



I he discrete svstem deals more with the specific 



patterns ol organism-environmeni transactions, with 

 percepts and ideas, with learned manipulation 



especially with using symbols, as in language. The 



television picture comes through only when sweep 



