492 



HANDBOOK OF PHYSIOLOGY 



NEITROPHVSIOLOGY I 



pain on the affected side which no longer requires a 

 discrete external stimulus for its appearance. The 

 unpleasant sensations, often worse than those after 

 the operation of mesencephalic tractotomy a) are 

 diffuse and peculiarly disagreeable, h} come on only 

 after a latent period of i or more sec, c) are localized 

 with gross errors, (f) may appear only at a high 

 threshold and i) persist after the stimulus is removed. 

 It is not yet known whether permanent hemianal- 

 gesia is produced by a sutliciently massi\e lesion to 

 destroy all of the presently described thalamic nu- 

 clei of termination of somatic and visceral afferent 

 pathways. From many of the published descriptions 

 one cannot l)e certain that even the whole nucleus 

 ventralis posterior has been destroyed. Walker's 

 careful report illustrates preservation of some of 

 the nucleus ventralis posterolateralis in his patient 

 (279, p. 81). Nor do we know if a complete lesion 

 would preclude the appearance of the frightful con- 

 tralateral dysesthesias and pain of the thalamic 

 syndrome. Now that many more nuclei of termina- 

 tion for spinothalamic fibers have been found in 

 man by Bowsher it .seems even more likely that the 

 thalamic lesions recorded to date leave intact por- 

 tions of the pain pathways. Their relation to the 

 distortion of pain sensation remains to be elucidated. 



CEREBR.AL HE.MISPHERES 



The parts of the cerebrum known to be concerned 

 with pain have been established by a variety of con- 

 trived and spontaneous irritations and destructions. 



Stinndatidn 



Foerster (77, pp. 141 to 144), one of the early 

 workers to explore extensively in man the responses 

 to electrical stimulation of the cerebral cortex, found 

 the usual response from the postcentral gyrus or 

 superior parietal lobule to consist of contralateral 

 paresthesias, occasionally so strong as to be painful. 

 The sensations were referred to a comparativelv 

 small area of the body on stimulus to the postcentral 

 gyrus, whereas from the less excitable superior 

 parietal lobule a response when obtained was re- 

 ferred "more or less to the entire half of the body." 

 Although the majority of the responses are referred 

 to or near the body surface, visceral pain is also 

 represented in the postcentral gyrus. 'Cardiac pain' 

 and severe abdominal pain have been reported when 

 areas for the upper and lower trunk respectively 



were stimulated (78, p. 363). The response inay be 

 complex, especiallv when a lesion affects the stimu- 

 lated area. As a part of one such long complicated 

 response to stimulation of the postcentral gvrus, 

 Krause and Schum (78, p. 363) provoked frightful 

 pain referred ipsilaterally to an upper liinb. 



Penfield and his associates have given us the most 

 complete maps of cerebral localization based on the 

 technique of cortical stimulation. Penfield & Boldrey 

 (210) found that such stimulus of the cerebral surface 

 rarely causes frank pain, in fact in only 1 i out of 462 

 responses. But nearly half of the reports were of 

 'tinglins;' or 'electricity,' which at least raises the 

 question of activity in pain pathways. The great 

 majority of the points on the superolateral surface of 

 the hemisphere from which a stimulus elicited sensa- 

 tion are in the postcentral gyrus, but many are in 

 the precentral gyrus, and a few lie anterior or pos- 

 terior to these two gyri. Penfield & Boldrey obtained 

 no ipsilateral .sensory responses but the reference was 

 at times bilateral for the face, tongue and eyes. 

 Bilateral pressure sensations encircling the torso 

 were noted by Foerster. 



In the subcortical white matter the limited ex- 

 plorations thus far carried out have yielded to 

 Hecaen et al. (124) an area in the parietal lobe deep 

 to the gyrus cinguli in which weak electrical stimuli 

 provoked violent localized lightning-like pain. 



Patients with severe pain elsewhere in the body, 

 upon cortical stimulation, seem especially prone to 

 feel pain often akin to the clinical complaint. Thus 

 Horrax (129) elicited pain upon strong electrical 

 stimulation of the postcentral gyrus in three of four 

 patients suffering from painful states. Erickson et al. 

 (74) recorded similar results in three of five patients 

 afflicted with either a painful phantom limb or the 

 syndrome of thalamic pain. Both patients with pain 

 probleins described by White & Sweet (296, pp. 334 

 to 337 and p. 413) had pain upon stimulation of the 

 postcentral gyrus, and in one case even more severe 

 pain occurred upon stimulation of the precentral 

 gyrus. This patient's spontaneous pain in each 

 phantom finger was stopped dramatically as the 

 appropriate area of the postcentral gyrus was in- 

 jected subpially with procaine. Lewin & Phillips 

 (169) reproduced preoperative pain — either a part 

 of an epileptic seizure or a painful phantom — upon 

 stimulation of the postcentral gvrus in three of three 

 patients and secured relief by removal of this area 

 of the cortex. 



Cortical and subcortical lesions have also pro- 

 vided irritative foci giving rise to pain, a) as an aura 



