I 4811 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



rats (34, 57, 150, 231) and monkeys (106) with such 

 lesions tend to make more perseverative errors and 

 anticipatory errors than normal animals or animals 

 with more posterior lesions. This impairment is 

 probably closely related to the deficit seen in the 

 delaved reaction. 



Summm v 



Since psychologists have not seen fit to agree on 

 any single set of procedures to be employed in studies 

 of conditioning and learning, many different learning 

 tasks more than iliere is room to describe here — 

 have been devised for the study of the effects of 

 ablations. Furthermore, different experimenters often 

 do not make the same lesions even when they intend 

 to do so. As a result, ablations may produce impair- 

 ment on some tasks and not on others, and experi- 

 ments do not always agree with each other because 

 of minor differences in procedure. 



Despite these and related problems, certain facts 

 seem clear. When the habit requires a sensory capacity 

 (e.g. form vision ) abolished by the ablation, no amount 

 of retraining ever effaces the deficit produced, as 

 might be cxpciied. On the whole, however, cortical 

 ablations have little or no effect on classical CR's; 

 animals learn these just as easily after injury as be- 

 fore and retain them after lesions are made. But it 

 differential CR's arc called for (or if the learning 

 task involves instrumental responses), retention is 

 often impaired, thus, typically, removal of the pri- 

 mary sensor) area relevant to the habit causes a par- 

 tial or complete memory loss, but the animal re- 

 learns in a reasonable number of trials. II a number 

 ol sensorv modalities are concerned, as in maze 

 learning, then one sees .1 mass-action effeel a cor- 

 relation between amount of deficit and size of the 

 cortical lesion. And, finally, lesions that include all 

 primary and association areas oi one modality may 

 cause considerable, lasting impairment. 



The posterior assoi iation areas ly ing in the parietal- 



ipital-temporal sector are proving to have con- 



siderable importance, particularly in discrimination 



learning, Certain parts Ol the temporal pole seem 

 1 pecially implicated. The frontal areas are clearly 



involved in learning where the ordering ol responses 

 in time is .1 critical feature. When learning involves 

 the cortex oi one side only, the corpus callosum 

 plainly participates in its transfer n> the opposite 



side, al least foi some h.il.ils. 



EEC CORRELATES 



Promptly after Berber's rediscovery of the brain 

 waves, serious attempts were made to put these 

 electrical events to work in uncovering the neural 

 events of learning and conditioning. In the following 

 description of these efforts it must be taken for 

 granted that the reader is familiar with certain 

 general propositions about brain waves, neurophysi- 

 ology and neuroanatomy. The reader may wish to 

 consult Chapter XI by Walter of this Handbook in 

 which autogenous brain waves are discussed. 



The search for electrical brain events reliably 

 related to learning began with the discovery that 

 exposing the eyes to light leads to the disappearance 

 of alpha waves. It was soon found (54, 143) that 

 simply pairing a sound (CS) with the light (US) led 

 rather promptly to disappearance of the alpha waxes 

 in response to the sound alone. Thus there started 

 some 20 years ago a new and potentiallv fruitful era 

 of research that is currently in full swing. 



The Alpha Block CR 



The cortex of most animals generates a more or 

 less continuous series of waves in the region of 5 to 20 

 per sec. The exact frequency range varies with the 

 species studied, and for man the figure 9 to 11 is 

 ordinarily given as normal. For convenience these all 

 can be called alpha waves. Experiments in which 

 their disappearance is conditioned to a stimulus 

 typically proceed as follows. 



The scalp EEG is recorded from the subject at 

 rest and in the dark. From time to time a light is 

 turned on and off; the alpha waves disappear as long 

 as illumination continues. From time to time also a 

 sound is turned on; at first this stimulus, like the 

 visual stimulus, temporarily blocks alpha activity, 

 but eventually it does not do so, an example ol 

 habituation (70, p. i<>; 165). Finally the stimuli are 

 paired, with sound (CS) preceding light (US) In .1 

 brief interval. Shortly there. liter the alpha rhythm 

 disappears as soon as the sound conies on and the 

 alpha block Ck has been established. 



Where no motor response is employed, the term 

 sensory-sensory conditioning is applied to these EEG 

 studies. The blocked ('desynchronized,' 'arrested,' 

 llallened'l EEC J response is, in addition, a common 

 event in I v pe I and fype II conditioning procedures. 



Morrell & Jasper ( 165) contribute .1 recent example 

 of the so-called sensory-sensory experiment. Tones 

 paired with light produced conditioned alpha block 



