1482 



IIVNDBOOK OF PHYSIOLOGY 



M.I KOI'IIYSIOI.OGY III 



'photic driving 1 pattern. Analogous results arc re- 

 ported in Type I learning as well as in sensory- 

 sensory learning (70, 210, 248). 



On<- ol the earliest studies of cortical evoked po- 

 tentials as influenced by learning is the work of 

 Livanov & Poliakov (140) on the rabbit. Shocks to 

 the leg (US), paired with light flashes, led in time to 

 leu flexion (CR) upon presentation of the light alone 

 it Si. Both light and shock occurred at 3 per sec. 

 During the learning process a 3 per sec. rhythm 

 appeared first in 'certain' cortical regions, later in 

 the whole of it; when the CR was fully developed 

 3 per sec rhythms of large amplitude tended to be 

 present during the CS and to be absent at other times. 

 I [owever, every motor response, whether spontaneous 

 or provoked by painful or other stimuli, was now 

 accompanied by the ; per see. rhythm. The authors 

 suggest from this that "the process of formation of 

 the conditioned reflex defense reaction in response to 

 the rhythmic stimulus is developed on the basis of 

 .1 system of rhythms reflecting periodical changes 

 in the excitability of the motor centers of the cortex" 

 (see also 80, H'",, 190). 



Tin- brain wave CR pattern evoked by the CS 

 approximates the frequency of the photic stimulus 

 IS beiter and better as conditioning proceeds, and 

 the CR appeals progressively earlier in time (165). 

 It is limited to the occipital leads, is unstable as 

 compared to the alpha block CR, and it quickly 

 extinguishes (165). This CR appears not only at the 

 cortical level but also in thalamic and mesencephalic 

 his where it is reported to lie large and stable 



lip evoked response to sound also undergoes in- 

 teresting changes. lis magnitude has been shown to 

 \.n\ somewhat from one stimulus to the next in the 

 untrained animal, but a Type 1 conditioning proo 

 dure Stabilizes such responses at large amplitude in 

 the auditor) region (l>7, llo). looked responses also 

 appeal in ical areas not previously involved and 



the Complexity of all of them increases, with those 



features that follow the click by 30 to 100 msec. 



econdary' responses) being particularly influenced. 



Artemyev & Bezladnova (10) undertook in cats 

 "to follow the dynamic changes in the nervous 

 processes ol die cerebral hemispheres arising oul oi 

 the development ol conditioned rellex links." A I ke- 

 tone, 60 db above die human threshold and lasting 

 ei constituted the CS, with shocks to the hind 

 leg as die l s llo EEG onsel response to die tone 

 was recorded on .1 cathode raj oscillograph. Electro- 

 myograms oi die leg muscle showed thai to of 12 



cats developed the CR ("defensive conditioned re- 

 flexes'). In all animals a positive correlation is re- 

 ported between the CR and the occurrence of EEG 

 change in the auditory area as follows. "Where the 

 percentage of occurrence of the electrical reaction in 

 the cerebral cortex is low, the conditioned reflex is 

 absent," and "in the course of forming the conditioned 

 reflex in the auditory projection area with sound 

 stimuli, the primary electrical reaction occurs in a 

 markedly greater number of cases than before and 

 at the beginning of the combinations." Fluctuation in 

 magnitude of the EEG response was seen during the 

 conditioning process and during extinction. The re- 

 sponse disappeared in sleep and with simultaneous 

 "strong stimulation of other analyzer systems." The 

 findings are discussed as follows: "if the animal is 

 passive to the stimulus the level of excitability of the 

 neurons of the cortex is lowered and the primary 

 electrical reaction is decreased in amplitude and 

 disappears. When the ineffective stimulus is linked 

 with another which is biologically important to the 

 animals, the excitability of the nervous elements 

 increases, of which we can judge by the more frequent 

 occurrence of the primary electrical reaction." 



Confirmation of these observations has in the main 

 been reported by others (e.g. 67, 1 ml. Since, however, 

 similar results have also been obtained at the level 

 of the cochlear nucleus (by, 90, 91, 1 10, 142), the 

 changes seen at the auditory cortex may merely 

 reflect events that occur at subcortical levels. 



New /'.'/<< in, ,1/ II fives 



Among the least understood of die central correlates 

 of die CR are die "new potentials 1 thai have been 

 reported to be associated with the conditioning 

 process. Many published records show high- or low- 

 frequency events not characteristic of the normal 

 record; these either appear during the alpha block 

 or, when alpha is present, constitute distortions of the 

 base line These new events bear no relation to the 



stimulus frequency as is true of the evoked potentials 

 jus) discussed. 



In man they may be beta (20 to 30 per set I, 

 kappa llo per see I (()), or dicta (5 per seel waves. 

 Motokawa & llu/iinori (ili<|i, Motokawa (if>8) and 

 lw.1111.1 (loll consider the high amplitude waves at 

 3 to 5 per sec. ('excitation potentials'] to indicate 

 increased activity of die area in which they appear, 

 this presumably being a necessary precursor of the 

 cortical events in conditioning. Popov ( 190), however, 

 has shown the occurrence of such waves in the parietal 



