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H \M)BOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



that the intralaminar systems of the thalamus and 



the reticular formation of the brain stem and the 

 nonspecific projection systems satisfy the definition. 

 Penficld (194) points out that the "'stream of con- 

 sciousness" as well as "man's experiential record" or 

 memorv involves the temporal lobe where direct 

 electric. il stimulation in conscious man evokes flash- 

 back memories. The hippocampus or a more central 

 portion of the centrencephalic system may be the 

 actual storehouse, but these bear sufficiently close 

 functional relationship to the temporal lobes so that 

 the latter constitute the effective points of activation 

 of such memories and experiences. Penfield (192) 

 adds that not only do sensory impulses arriving at 

 the cortex descend to central integrating centers 

 where "highesl level" final integration is presumed to 

 take place but in their final form are impressed upon 

 the premotor cortex for outflow to effectors. However, 

 he believes that there is an alternative pathway for 

 directional voluntary impulses via subcortical motor 

 centers. 



Sperry (220) has put forth an interesting point of 

 view indicating that "all brain excitation has ulti- 

 matclv one end, to aid in the regulation of motor 

 coordination. Its patterning throughout is determined 

 on this principle. It follows that efforts to discover 

 the neural correlates of consciousness will be more 

 successful when directed on this basis than when 

 guided by arbitrary correlations with psychic ex- 

 perience, stimulus patterns, or outside reality, or by 

 analogies with various types of thinking machines." 

 He would approach the problem of perception, 

 thinking and even consciousness by attempting to 

 understand motor integration and adjustment. He 

 believes that we have been preoccupied with "sensor) 

 avenues to the stuck of mental processes" and these 

 "will need to be supplemented by increased attention 

 to the motor patterns, and especially to what can be 

 inferred from these regarding the nature of the asso- 

 ciative and sensor) functions." 



viiisii'ix \\n mi ml Jouvel (135) has investi- 

 gated in in. in at the time of operation the effect of 

 1 li . tive visual a 1 ten 1 ion and the intrusion of distract- 

 ing stimuli Hi other modalities upon the surface EEG 

 over the occipital cortex and the subcortical responses 

 m the optic radiations He has found that repeau-d 

 single flashes of lighl produce .1 marked augmentation 

 ol the responses in the optic radiations when the 

 mbjei 1 was asked to attend to and count the flashes 

 The surfaci EEG hows an increase in rapid low- 

 volt igi H n\ it) at the start ol the pei iod oi attention 



and then a decrease. When stimuli of a distracting 

 nature are introduced to other sense modalities than 

 vision, there is a reduction of the subcortical visual 

 responses almost to total disappearance. This would 

 indicate interaction and suppression among the 

 alternative sense modes competing for the field of 

 attention. Olfactory, auditory and nociceptive stimuli 

 were very effective in producing this suppression, 

 but tactile stimulation from objects placed in the 

 hands seemed less effective. Mental calculation and 

 problem solving also caused reductions in the mag- 

 nitude of the optic radiation responses. In a patient 

 with damage in the brain stem of 6-mo. duration 

 who had in addition to other neurological indications 

 difficulty in maintaining vigilance, it was found that 

 nociceptive stimuli did not affect the visual responses. 

 Jouvet feels that the subcortical reduction of response 

 observed at the time of attention to another sense 

 mode calls for a distinction between the neural mecha- 

 nisms put in play at the time of the arrest reaction 

 (EEG arousal) and those exhibited at the time of 

 attention. He states that his results confirm those 

 already obtained by others (100, 106) in animals and 

 previously mentioned in this chapter. However, he 

 is uncertain whether the inhibition he has demon- 

 strated is at the level of the lateral geniculate body 

 or the retina, since both have been shown to be 

 affected negatively by reticular stimulation, as well 

 as positively. He did not find habituation of the 

 subcortical visual responses to light flashes presented 

 once a second over a period of several minutes. 



Oswald (1881 has studied the human EEG under a 

 variety of experimental circumstances relative to 

 vigilance and habituation. During intent listening to 

 brief tones of near-threshold intensity to which the 

 subject was to respond bv pressing a kev , two tenden- 

 cies were found, one, for sleep and alertness to alter- 

 nate regularly and rapidly at the rate of the signals, 

 and two, a slower downward drift toward sleep to 

 the point of failure to respond. The tones were 

 presented at intervals of IO, 5 or ;j sec. during sessions 

 lasting 1 -, to 30 min. First there was ,1 blocking "I 

 alpha to each tone with return for a few seconds 

 between tones. Later this tendency was reversed 

 with alpha hlockage appearing between tones and 

 alpha bursts being triggered bv the tones. The ques- 

 tion arises of course as to whether this is merely a 

 shift from vigilance to a drows) state, with reversed 

 tendencies for the response, or whether this is a 

 unique reaction of the reticular system to repeated 

 near-threshold stimuli representing a form of habitua- 

 tion. Similar alternations of sleep signs and alertness 



