, 5 66 



iiAMiiini ik ui i'in mi n i ir,\ 



XI I KOPHYSIOI.OOY III 



deficit of attention. These authors feel their results 

 indie. lie that barbiturate bursts and recruiting re- 

 sponses are more closely related to sleep spindles than 

 to alpha rhythm. In each of these three instances of 

 commonalit) in the burst pattern, there is not only a 

 tendency for induced sleep, but the point on the 

 human EEG and sleep-wakefulness continuum where 

 consciousness is greatly reduced or lost often corre- 

 sponds with this type of electrical activity. 



In general, behavioral studies before and after 

 lesions have so far contributed little to our under- 

 standing of the role of particular nuclei of the DTPS, 

 especially so far as attention and awareness are con- 

 cerned. This is due partly to the inability to make 

 precisely delimited lesions without affecting; other 

 systems, and partly to inadequate behavioral assess- 

 ment methods. Freudenberg et al. (81 ) observed some 

 distractibility in the monkey after unilateral destruc- 

 tion of the dorsomedial thalamic nucleus. Chow (47) 

 found no outstanding deficits in learning or be- 

 havior in the monkey after pulvinar and combined 

 pulvinar and dorsomedial nuclei lesions. In cats 

 Schreiner et al. (210) observed increased hostility and 

 aggressiveness following destruction of dorsomedial 

 nuclei, but Pechtel et al. (191) were less certain of this 

 in follow-up studies. Ingram (123), summarizing ex- 

 periments clone with Knott and others, reported that 

 bilateral destruction of dorsomedial thalamic nuclei 

 slows performance rate and retards learning in the 

 cat, but that lesions of the nucleus centromedian had 

 no such effects. The results of Brierley & Beck (39) in 

 the cat and monkey indicate that restlessness and 

 distractibility follow bilateral dorsomedial nuclei 

 lesions in the monkey, but thai bilateral lesions in the 

 nuclei composing the anterior complex have relativel) 

 little effect upon behavior, because of the role of these 

 nuclei in the recruiting response mechanism, and 

 because their stimulation often induces changes in 

 the level of consciousness, as well as electrocortical 

 . nous. il .mil behavioral arousal under some condi- 

 tions of Stimulation, and sleep under others, it ap- 

 pears that there is nrrd for further restricted lesion 

 tudies oi the mid line and intralaminar nuclei and 

 the nucleus ventralis anterioi relative to attention, 

 pen eptual discrimination .mil learning. 



< )l isen at ions ol behavior resulting from stimulation 

 nl the midbrain relic 11l.11 formation, medial intra 

 I. num. 11 thalamus, ventrolateral thalamus, dorso 

 medial 1l1.1l.nnus and rhinencephalon have been 

 made l>v Monnier ..V Tissol (177) in the rabbit. 

 1 ligh-frequency stimulation ol the reti< ular formation 

 produced the characteristic arousal and alerting 



sponses behaviorally and desynchronization electro- 

 cortieallv, but with synchronization in the rhinen- 

 cephalon which showed rhythmic 5 to 7 per sec. 

 waves during the conical activation. Both behavioral 

 and electrocortical arousal reactions could also be 

 produced with low-frequency stimuli of 4 per sec. in 

 the reticular formation, but with much longer latency, 

 occurring toward the end or even after stimulation. 

 This suggested to these authors a dual mesencephalic 

 reticular system lor arousal and alerting, one of short 

 latency and one of very long latency. Tissot & Mon- 

 nier (225) and Monnier et al. (176) have observed a 

 similar dichotomy from stimulation in the medial 

 thalamus, again with short and longer latency (6 to 

 12 msec, and 20 to ;jb' msec). They identify the 

 early response mechanism as ergotropic and related 

 to the reticular system because it is a quick-acting 

 system, with persistent response, which increases with 

 wakefulness and is enhanced by ergotropic alerting 

 drugs. The other slower response mechanism they 

 identity as trophotropic in type because it decreases 

 during arousal, is facilitated by tranquilizing drugs 

 and is identical with the thalamic recruiting system. 

 Mil roelectrode records from cortical neurons seem 

 to bear out their contention that these two svsiems 

 anchored in the medial intralaminar regions of the 

 DTPS are antagonistic and bear a somewhat recip- 

 rocal relation to one another. Tissot & Monnier (225) 

 believe that this reciprocal antagonism probaMv 

 plays an important role in the regulation of vigilance 

 and consciousness. 



Interaction oj ARAS, DTPS, STPS and Neocortex 



Although neuroanatomical and neurophysiologic.il 

 details are far from complete, the foregoing surve) 

 of neurophysiological experiments bearing on the 

 ARAS and DTPS seems to support certain generali- 

 zations concerning sleep, wakefulness, consciousness 

 and attention. The ARAS is ., system promoting wake- 

 fulness lis origins are in the reticular formation of 

 the lower brain stem, situated Strategically at the 

 i rossroads of afferent and efferent svsiems from which 

 it receives collaterals. Its upward extensions permit 



it, either directl) or indirectly, to influence the neo- 

 cortex in a diffuse manner, and in turn to be in- 

 fluenced by the neocortex through widespread corti- 

 c ifugal connections. 



When excited through its afferent collaterals or by 

 cortieiliig.il connections, it is capable of arousing a 

 sleeping animal or alerting a wakeful one. In so doing 

 il modifies the electrical aeliv itv of the cortex, shifting 



