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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



the sensory pathways appear to be represented en- 

 tirely in tlie homologies of the intralaminar nuclei 

 of the thalamus and the elaborate corpus striatum. 

 So far as is known, the cerebral cortex of the avian 

 brain receives no ascending pathways directly from 

 the thalamus. Clark concludes that if the instinctive 

 aspects of willed ljeha\ior are mediated at the higher 

 functional levels of the brain by the intralaminar 

 nuclei and the corpus striatum, it may be assumed 

 that the equivalent .system in mammals, and even in 

 man himself, may perform comparaljle functions. 

 Subtle changes in the ability to perform willed 

 responses have been seen following striatal lesions 

 in the monkey (4). 



We have discussed here the problems of willed 

 movements without specific reference to the brain- 

 mind relationship. Little can be said at tiiis stage 

 concerning the functions of the mind in relation to 

 the microcosm of the individual cell. Eccles (137) 

 has accepted Sherrington's view that mind is not a 

 form of energy and has developed hypotheses as to 

 how nonenergy mind can act on matter at the 

 cellular level, ascribing to certain minute "influences' 

 a capacity to act upon a synaptic junction and modify 

 behavior. This point of view has been criticized by 

 Lashley (255) on the grounds that the use of the un- 

 certainty principle of Heisenberg in this connection is 

 invalid and quite irrelevant to the cjuestion of causal 

 determination. 



An interesting and probably highly significant 

 finding in relation to willed movements has Ijeen 

 oljtained by Kupalov. In a review by this author 

 (242), an account is given of the estal.ilishment and 

 elaboration of a shaking conditioned reflex in a dog. 

 The conditioned response recjuired much training 

 with the dog assisting the initiation of the response by 

 scratciiing the skin with the paw or rolling on the 

 floor. In subsequent trials, the dog Ijegan to perform 

 the movement to the conditioning stimulus with 

 great alacrity. "In view of the way the dog shook, it 

 seemed that movement was con\erted into a volun- 

 tary act." 



Studies of Conditioned Motor Performance 



The technique of conditioned reflexes has been 

 applied in this field, first, to the study of sensorimotor 

 interaction, and more recently with a view to pro- 

 viding, by a combination with electrophysiological 

 techniques, a neurophysiological correlate of higher 

 processes such as learning. These studies are con- 



sidered in C:hapter LXI by Galambos & Morgan 

 in this work. 



It has been demonstrated that conditioning photic 

 stimuli may induce Clementi's photic epilepsy more 

 readily than unconditioned stimuli of the same 

 modality (293). The results obtained b\- Russian 

 authors in this field demonstrate the occurrence of 

 changes in electrical activity of Ijoth sensory and 

 motor cortex during the establishment of an avoidance 

 respon.se, as summarized in a review by Rusinov & 

 Raiiinovich (388). Modification of the electrical 

 activity in subcortical structures also occurred under 

 these conditions. There remains, however, the funda- 

 mental difliculty of reaching conclusions from these 

 data about the basic processes underlying the altera- 

 tions in the recorded wa\'es. The view expressed by 

 some of the Russian authors in this area is too briefly 

 reported in the review cited to permit comparison of 

 their interpretation of the data with the knowledge 

 of the mechanisms upon which neuronal firing appears 

 to depend (138). It is unlikely that background 

 activity, recorded with gro.ss electrodes, reflects 

 changes at the unit level, at least under most con- 

 ditions. 



Nevertheless, by the use of microelectrodes in 

 conjunction with conditioning experiments, it has 

 been possible to secure a more intimate view of 

 integrative processes related to motor activity in 

 diff'erent cortical areas. The pattern of firing of single 

 neurons has been studied in the motor and sensory 

 cortex of the monkey during the performance of a 

 conditioned motor response in an avoidance situation. 

 In the experiments of Jasper et al. (221) the units 

 recorded within the arm area of the motor cortex, 

 contralateral to the limb performing the avoidance 

 act, have shown varied patterns of activity, as shown 

 in figure 6. While acceleration of firing can precede 

 and outlast the movement in some units, about a 

 third of the units studied showed no change in firing 

 patterns throughout this period. This occurred both 

 lor conditioned responses as well as during movement 

 performed spontaneously In the animal. When the 

 conditioning stimulus is present, the firinc; of other 

 units can Ije arrested until the end of the conditioning 

 signal. In still other units, a brief burst can appear 

 at the onset of the conditioning stimulus without 

 further participation of this unit in the response. 



Under similar conditions, records from the sensory 

 arm area ha\c shown that the firing rate, which is 

 usuallv increased, changes more commonly with 



