336 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



those of clinical petit mal which are well known to be 

 precipitated by sensory stimulation, especially those 

 that are unexpected or repeated, for example the 

 intermittent photic stimulation at 1 5 flickers per sec. 

 used by Walter et al. (193). 



The possibility of producing myoclonus at will, in 

 either animals or man, by the combination of camphor 

 and touch, or of pentylenetetrazol and photic stiinu- 

 lation enabled Muskens and later Gastaut to stud\ 

 its mechanism and describe the followina; character- 

 istics. 



a) Myoclonic jerks occur, as do the convulsions of 

 grand mal, even in the rhombencephalic animal. 

 (Similarly, bilateral myoclonic jerks, either sponta- 

 neous or provoked by noise or touch, are character- 

 istically seen in pontine anencephalics.) 



i) The multiple spike and wave of myoclonus, far 

 from being limited to the rolandic cortex or even to 

 the whole of the cortex, is recorded in all the grey 

 matter of the brain, right into the mesencephalon. 



f) In myoclonus provoked by sensory stimulation, 

 the electrical discharge appears in the mesencephalic 

 formation and the thalamus before Ijeing projected 

 to the cortex. 



cf) A discharge with the same cerebral distribution 

 and in every other way comparable to myoclonic 

 multiple spikes is provoked by electrical stimulation 

 of the anterior part of the thalamic nuclei in the mid- 

 line. 



i) The clinical and electrical phenomena of 

 myoclonus, as in the case of grand mal, may be en- 

 tirely independent in their time relationships; thus 

 multiple spikes and waves may occur without jerks 

 and vice versa. 



With reference to propagation of the discharge, it 

 has been shown that photic stimulation in an animal 

 given pentylenetetrazol provokes, quite apart from 

 the specific geniculostriate response, a discharge in the 

 reticular formation of the brain stem together with 

 an ascending thalamocortical discharge and a de- 

 scending reticulocerebellar and reticulospinal dis- 

 charge (55, 65, 68). The existence of reticulospinal 

 irradiation is also implicated in the work of De Hass 

 et al. (37) who showed that clonic responses evoked 

 by afferent stimulation persist in the decorticate cat 

 given pentylenetetrazol. Muskens (149) in 1926 

 already had a presentiment of this kind of irradiation 

 when he related the sensoclonic phenomenon to "an 

 influx produced in a reflex way in the region of the 

 reticular substance in the pons and medulla." 



Thalamocortical and reticulocortical irradiation, 

 observed bv Gastaut & Hunter (66) and confirmed 



by Hunter & Ingvar (loi), was further demonstrated 

 in an indirect way by the results of De Hass et al. 

 (37). They showed that the presence of the specific 

 .sensory cortex was not necessary for obtaining an 

 irradiated frontal response to photic or auditory 

 stimulation in the cat after pentylenetetrazol ad- 

 ministration; this obviou.sly excludes the hvpothesis 

 of purely corticocortical conduction. Reticulocortical 

 propagation was also demonstrated \i\ Jasper et al. 

 (108) who showed electrographically a) that the 

 postdi-scharges from the visual cortex do not irradiate 

 to other cortical regions by corticocortical pathways 

 and certainly not to the frontocentral region where the 

 multiple spikes, irradiated under the effect of photic 

 stimulation, are recorded; and b') that a parastriate 

 postdischarge projects directly to the intralaminar 

 nuclei which project in turn to the frontal cortex. 

 It seems therefore that the concept of the subcortical 

 origin of petit mal iif nnoclonic type is well founded. 



PETIT M.AL OF '.ABSENCE' TYPE. This is the onh' varietv 

 of generalized epilepsy which has not been satisfacto- 

 rily reproduced experimentally. The various measures 

 causing generalized cerel^ral disturbance, which so 

 effectively reproduce grand mal and myoclonus, have 

 never provoked in the nonanesthetized animal tran- 

 sient loss of 'consciousness' comparable to the 

 'absence' of petit mal. 



It is very easy to induce brief loss of consciousness 

 \)\ means of focal cerebral disturbances and particu- 

 larly by limited electrical stimulation of many differ- 

 ent structures with indwelling electrodes (thalamus, 

 hypothalamus, sul^thalamus, the basal and limbic 

 rhinencephalon, etc.). Loss of consciousness in these 

 cases, however, is accompanied by an 'arrest' and 

 'orientation' reaction with postural readjustment and 

 various types of gesture, which are much more sug- 

 gestive of psychomotor attacks than the 'ab.sence' of 

 petit mal. One must therefore conclude that, despite 

 the attempts of various authors and notably of Hunter 

 & Jasper (102), of Kaada (i 19) and of Ingvar (103), 

 petit mal 'absence' has not yet been definitely re- 

 produced in animals. The same holds true of man 

 according to Gastaut & Roger (77). 



On the other hand the bilateral synchronous 3 cps 

 spike-and-wave discharge has been reproduced in 

 animals under special conditions. All the authors, 

 having injected pentylenetetrazol or other con- 

 vulsants systemically in the anesthetized and cranioto- 

 mized animal, have provoked at will long-lasting, 

 self-perpetuating discharges of spike and wave which 

 are generalized, bilateral, synchronous and symmeiri- 



