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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



remain partial throughout their whole duration or 

 which may become generalized only after a certain 

 time. 



EXPERIMENTAL PARTIAL EPILEPSY' OF CORTICAL (iSO- 



cortical) ORIGIN, o) Local application of strychnine. 

 When strychnine or another convulsant is applied to 

 the isocortex, it provokes clinical and electrical mani- 

 festations reminiscent of certain seizures of partial 

 epilepsy in man. Only those clinical manifestations 

 which involve discharges provoked in the motor, and 

 notably the somatomotor, areas have been studied 

 [(15) and numerous more recent authors], probably 

 because they are the only ones which can be demon- 

 strated in the anesthetized animal under the special 

 experimental conditions required. 



In the classical 'cortical strychnine clonus' of Bag- 

 lioni & Magnini (15), convulsions appear in the 

 contralateral musculature a few seconds after the ap- 

 plication of strychnine. They are at first confined to 

 the parts corresponding to the cortical region treated 

 but they later spread to other muscular groups on that 

 side of the body. Contrary to the generalized epilep- 

 sies already discussed, the impulses for these clonic 

 movements are undouljtedly transmitted from the 

 somatomotor cortex to the spinal motor neurons by 

 way of the pyramidal tracts. This conclusion arises 

 out of the following experimental results: /) convul- 

 sive discharges can be recorded from pyramidal fibers 

 synchronously with the clonic twitches (2); 2) both 

 the movements and the pyramidal discharges con- 

 tinue when the brain stem is interrupted at midbrain 

 levels, leaving only the pes pedunculi intact (196). 



If the cutaneous zones corresponding to the strych- 

 ninized region are stimulated, these convulsions ap- 

 pear sooner and are intensified and rapidly general- 

 ized. This "reflex' reinforcement of the cortical epi- 

 leptic process was discovered by Amantea (8) in 1921 ; 

 it is lost when the strychninized cortical focus is 

 destroyed. 



The EEG manifestations of the local application of 

 strychnine consist of a bioelectric oscillation of great 

 magnitude (more than a millivolt), known as the 

 "strychnine spike', which is repeated at more or less 

 regular intervals. This spike does not remain localized 

 to the spot on which the strychnine is applied but 

 spreads like a drop of oil to the whole of the cor- 

 responding area (for example to the whole of the 

 somatomotor area). It is also propagated at a distance 

 to the homologous structures of the opposite hemi- 

 sphere and to the allied subcortical structures (for 

 example to the \entrolateral nucleus of the thala- 



mus when the strychnine is applied to the somato- 

 motor region). The strychnine spike however can 

 develop to its fullest and continue to be repeated even 

 though it is not accompanied by these phenomena of 

 propagation. Indeed, neuronal isolation of a cortical 

 area (that is to say, its separation from neighboring 

 cortical areas and from subcortical centers) does not 

 prevent the appearance of strychnine spikes on local 

 application. 



The strychnine discharge has been very fully in- 

 vestigated by workers in basic neurophysiology [see 

 bibliographies (143, 146)] because it is so easily pro- 

 voked and so easily repeated. From these studies, and 

 particularly those of Jung (117) and Moruzzi (146) 

 one ma\' draw the following conclusions. /) The 

 strychnine spike results from a process of hyper- 

 synchrony, that is from the simultaneous discharge of 

 the great majority of the neurons in the strychninized 

 area, a hypersynchrony which probably is due to 

 ephaptic (extrasynaptic) interactions between the 

 different elements which are put into play by elec- 

 tric currents conducted through the intercellular 

 spaces. 2) Recorded with macroelectrodes, the 

 strychnine spike only shows its slow triphasic (posi- 

 tive, negative, positive) envelope, which corresponds 

 no doubt to slow potentials and to an electrotonic 

 spread and decremental conduction in the dendritic 

 plexuses. With microelectrode recording, however, 

 one observes in addition a burst of very rapid spikes 

 (400 to 1 ,000 cps) which begins with the first positive 

 phase and ends with the second negatise pha.se. It is 

 this burst of rapid spikes, which is transmitted along 

 the axons of the pyramidal cells (i) to the spinal 

 motor neurons, which provokes the muscular twitch. 



i) Localized electrical stimulation. The electroenceph- 

 alographic effect of a single Isrief electric shock is 

 seen as a \ariation of the local potential which differs 

 little from the strychnine spike except that it is di- 

 phasic, at first negative and then positive. Using 

 intracellular microelectrodes, Buser & Albe-Fessard 

 (24) were aisle to record this slow variation of po- 

 tential at actual neuronal level. In addition the micro- 

 electrodes record the burst of brief spikes (less than a 

 millisecond) at high frequency (up to 1,000 cps) which 

 accompanies the strychnine discharge and which is 

 propagated along the length of the axons. (The.se 

 spikes are oljviouslv positive in the interior of the 

 neurons and negative in their neighborhood.) 



A series of electrical shocks results in repetition of 

 the above phenomena so long as the frecjuency of 

 stimuli is not too rapid. Above a certain frequency, 

 the discharge appears only at the end of stimulation 



