ATTENTION, CONSCIOUSNESS, SLEEP AND WAKEFULNESS 



'577 



but with definite restrictions upon the span of con- 

 sciousness. In other words the threshold to slight 

 change in a restricted field of attention may be low- 

 ered, but the threshold of awareness for events outside 

 that field may be greatly elevated. This is the role of 

 selective attention for which we sought neurophysio- 

 logical mechanisms in the functioning of the ARAS 

 and DTPS. 



In excited emotion and in situations where strong 

 stimuli arc in abundance (sensory overload), there 

 are indications that the ARAS or DTPS may be 

 swamped or blocked so that awareness is either se- 

 verely restricted or is so broadened as to be useless. 

 Everyday experience attests to the confusion and the 

 unreliability of observations and testimony made 

 under stressful conditions. Higher-voltage last ac- 

 tivity usually characterizes this slate in contrast to 

 the lower-amplitude activation pattern of alert atten- 

 tiveness. 



Although sometimes viewed as a kind of epiphe- 

 nomenon, the EEG representing signs of changing 

 cortical activity seems to mirror changes going on in 

 subcortical mechanisms such as ARAS and D I PS. 

 In some respects and for some purposes this ma) be 

 more important to know than what one cortical unit 

 among to billion may be- doing, or low any small 

 sample of units may be responding, vet we need both 

 kinds of information. How docs die EEG reflect 

 changes in subcortical mechanisms? We have seen 

 how it changes from wakefulness t < > sleep and some "I 

 these changes we can account for in terms of ARAS 

 and DTPS activitv when modified l>\ stimulation, 

 lesions or drugs. Alpha waves ma\ be suppressed by 

 natural sensory stimulation or l>\ stimulation of the 

 reticular formation. In the course ol ulavition and 

 quiet alpha waves recede, spindle bursts and slow- 

 waves appear, consciousness is lost and sleep pervades. 

 Blocking the ARAS by lesion or barbiturates shifts 

 the REG pattern from one of activation or alpha 

 waves to one of sleep spindles, slow waves and somno- 

 lence. Sleep spindles have been removed in animal 

 preparations by anterior thalamic lesions, a fact sug- 

 gesting that the transient appearance of sleep spindles 

 during the shift from wakefulness to sleep may repre- 

 sent a shift in the dominance or control manifested 

 by certain thalamic nuclei. Stimulation of medial 

 and intralaminar nuclei of the thalamus by repetitive 

 low-frequency shocks produces recruiting waves in the 

 EEG which resemble the slow waves of sleep, and 

 slightly lower-frequency stimulation actually induces 

 sleep in chronic animal preparations. These are some 

 of the changes reflected in the EEG, and judicious use 



of it as an indicator will continue to help reveal the 

 effects of even more restricted experimental manipula- 

 tions of subcortical structures and mechanisms. 



As Adrian (5) so well pointed out, we have thought 

 of the cortex as a screen upon which patterns are 

 thrown by different sense organs, but there are even 

 broader problems of attention, perception, recognition 

 and so forth to contend with. The EEG, when further 

 elucidated by analysis of the subcortical mechanisms 

 whose activity it reflects and by microelectrode studies 

 of the substance from which its potentials arise, 111 a.) 



well be one of our more important tools in further in- 

 vestigation of higher mental processes 



We siill eld not know the precise source or origin 

 of the alpha waves, but thev are generally believed i<> 

 be summated dendritic potentials. What determines 



their time COnstanl and rhythm? Is there .1 cortical 



or subcortical pacemaker? We have- observed that 

 tin it time 1 onstant is different in young children and 

 adults, but so also is die latency and time constant of 

 evoked potentials, as Ellingson (711 lias shown. Are 

 these- differences clue to structure, chemical constitu- 

 tion, metabolism, niaiiiration.il changes, lack of de- 

 velopment and integration of specific and unspei ifi< 

 sensor) mechanisms, or to a combination of facti 

 I low do these characteristics affect the functions sub- 

 served? The approaches t<> these questions must neces- 

 sarily In- broad and mn-t include- phylogenetic, 

 ontogenetic and longitudinal approaches as well as 



the detailed experimental manipulations in aeule and 



chronic- animal preparations. In humans, except for 

 limited observations made during operative- pro- 

 cedures on the brain, we are mainly limited to external 

 measurements such as the- EEG, coupled with psycho 

 logical and behavioral assessments. B\ paralleling 

 these with appropriate animal experiments, certain 

 inferences and deductions may be made. 



EEG mi,/ Ey* Movement Studies oj Dreaming During Sleep 



Loomis et nl. (169) Blake- & Gerard (27) and Blake 

 it id. (28) have studied the EEG and general boelv 

 motility during sleep Movement of a part of the body 

 or of the whole body during sleep regularly lightens 

 the level nl sleep as indicated bv the EEG. A move- 

 ment during the- />' stage of sleep or drowsiness in- 

 evitably reinstates a short period of alpha waves, and 

 a major movement during the D stage of sleep has 

 frequently been observed to shift the EEG pattern 

 from delta waves to a C, B or even .1 stage momen- 

 tarily. Thus it appears that kinesthetic, proprioceptive 

 and tactual stimulation excites the ARAS, and it in 



