TOUCH AND KINESTHESIS 



421 



fields is puzzling since all synaptic regions of the 

 lemniscal system including the postcentral cortex are 

 in fact organized topically quite precisely. 



Electrophysiological evidence indicates that repeti- 

 tive electrical stimulation of the sensoriinotor cortex 

 may depress the postsynaptic response which is 

 evoked in the following regions: a) in the trigeminal 

 nucleus by stimulation of the infraorbital nerves (i 25); 

 b') in the posterior column nuclei by stimulation of the 

 posterior columns (217); and (r) in the anterolateral 

 column by stimulation of the contralateral dorsal 

 roots (112). A destruction of the midbrain reticular 

 formation (presumably the destruction of the mid- 

 brain tegmentum), on the other hand, was observed 

 to enhance the postsynaptic response in the trigeminal 

 nucleus when the infraorbital nerve was stimulated 

 (126). In harmony with the latter observation King 

 et al. (137) observed recentK' that responses recorded 

 in the internal capsule to stimulation of the peripheral 

 nerve displayed a reduced amplitude but also a de- 

 crease of the latent period when an EEG arousal was 

 induced by repetitive electrical stimulation of the 

 sciatic nerve, of the midbrain reticular formation or 

 of the centrum medianum and n. centralis lateralis. 



How to interpret these findings may be left an open 

 question since, except for the work of King el al. (137), 

 no quantitative data have been thus far offered to 

 substantiate an effect which manifests itself bv influ- 

 encing the test response only quantitatively. It is, 

 however, doubtful that the effects produced bv stimu- 

 lation of the sensorimotor area could have been 

 mediated by the pathways proposed by the Norwegian 

 workers since, if this were so, one could have expected 

 indiscriminate effects from stimulation of anv cortical 

 region in either hemisphere, which apparentk did 

 not occur. 



Activation of Brain Stem Reluiilar Formation by 

 Sensory Somatic Discharges 



In 1949, Moruzzi & Magoun (179) reported that 

 electrical stimulation of the medial portions of the 

 medulla, of the pontine and midbrain tegmentum, 

 and of the dorsal hypothalamus and subthalainus 

 produces generalized changes in the EEG which 

 appear identical with those which result when the 

 animal is aroused from sleep or alerted to attention. 

 They suggested, therefore, that the central core of 

 the brain stem represents an ascending activating 

 system, the activity of the system being essential for 

 wakefulness, the depression of this activity producing 

 normal sleep or somnolence. A great deal of effort 



has been expended in recent years, particularly by 

 the research group of Magoun, by the group of 

 Moruzzi in Italy and by Bremer and his colleagues, to 

 substantiate this concept — which was suggested by the 

 early work of Bremer (30, 31) — and to determine the 

 functional organization of the reticular ascending 

 system and the sources of its inflow. 



Just to what extent and in which sense one can 

 consider the reticular activating system as a functional 

 unit (it is certainly not a unit morphologically) is at 

 present still conjectural. Basic as this question may be 

 for considerations of sensations in general, we shall not 

 discuss it further since the present status of the prob- 

 lem is presented in detail in Chapter XLII of this 

 work. However, we shall consider briefly the evidence 

 regarding the activation of the brain stem by somatic 

 sensory afferents since the available evidence suggests, 

 we ijelieve, a departure from conclusions usually 

 reached on this subject. 



Little is known about actisation of brain-stem 

 groupings by natural tactile stimuli. One may pre- 

 sume, however, that activity aroused by electrical 

 stimulation of a nerve (it was usually the sciatic nerve 

 which was stimulated) reflects, at least partially, 

 activity aroused by tactile stimulation as well. 



In a series of papers the C^alifornia workers (72-74, 

 229, 230) concluded that, in addition to the medial 

 lemniscal system, there exists in the brainstem a 

 medially located, multisynaptic path, conducting 

 centripetally, which is fed by collaterals arising from 

 virtualh the entire length of the medial lemniscus. 

 They felt that this medial system must be composed 

 of a multisynaptic chain of neurons since in compari- 

 son with the potentials in the lemniscal system those 

 evoked in the reticular formation displayed much 

 longer latencies and longer recovery time and were 

 more sensitive to anesthetics. It is likely that the 

 California workers understand by the medial lemnis- 

 cal system, not only the system which we have defined 

 under that term but also the spinothalamic tract. 

 Nevertheless, all their data pertaining to the classical 

 pathways seem to refer to the medial lemniscal system, 

 as we understand it, and there is little doubt that 

 collaterals of the classical medial lemniscal pathway 

 are believed to activate the reticular ascending system. 



While it is, of course, possible that the reticular 

 potentials are indeed of medial lemniscal origin, it 

 appears more likely that they are evoked, at least 

 predominantly, through activation of the antero- 

 lateral columns in the spinal cord rather than of the 

 medial lemniscus. There are several reasons for this 

 belief. First of all there is little anatomical evidence 



