Bauhaus-Universität Weimar

Studies in the physiology of the nervous system, XXII: On the phenomenon of facilitation, 1: Its occurence in reactions induced by stimulation of the "motor" cortex of the cerebrum in monkeys
Brown, T. Graham
Studies in the Physiology of the Nervous System 
actions which demonstrate primary flexion. In the case of the repeated 
stimulation of cortical points which yield primary flexion a reversal to 
primary extension is less common a phenomenon. 
It is more usual for the series of flexion reactions to continue without 
reversal to extension. This fact makes the examination of the serial 
stimulation of flexion-yielding points a more useful one for our purpose 
than that of extension-yielding points. But a result of the repeated 
stimulation of flexion-points not infrequently seen is the production of an 
epileptiform discharge—the so-called “cortical epilepsy.” 
In the examination of the effects of repeated stimulation of flexion- 
points we may proceed first to those cases in which the stimulus used gives 
a positive reaction at its first application—submaximal stimuli. The 
experimental conditions may be varied either by altering the strength of 
the stimuli made use of in successive series of stimulations, or by altering 
the intervals of time which elapse between the individual members of the 
series of stimuli in such successive series. 
In the first place, the general appearance of the reactions in a typical 
record may be examined. 
Where the stimulus used is a comparatively strong one, the first few 
reactions in a series may exhibit successive augmentations in the extent of 
the muscular response. A maximum is thereafter attained. In these 
earlier reactions of the series the act of contraction as studied in the flexor- 
muscle shews a comparatively rapid movement. When the reaction is of 
maximum extent a plateau is attained even within the short period— 
1 second—of stimulation, and that plateau is held for the remainder of the 
short period. At the withdrawal of the stimulus there follows a relaxation 
phase which shews a rapid movement, so that the level of rest may be 
attained before the end of the short interval—e.g. I second—which is 
allowed to elapse before the next period of stimulation commences. 
When such comparatively strong stimuli are used an epileptiform dis¬ 
charge may not rarely make its appearance at or about the point in the 
record at which the reactions become of maximum extent. When this is 
the case there may first appear a few “ clonic ” movements in the periods 
between stimuli. Then the movement of relaxation after stimulation 
becomes of small extent. The curve registered by the flexor shews that 
the muscle enters into a period of prolonged contraction, which gradually 
diminishes in extent below the level of maximum contraction. During 
this the repeated stimulations of the cortical point appear to have little or 
no effect. The presence of the “ epileptic ” discharge seems, at any rate in 
some cases, not merely to mask the effects of stimulation, but to suppress 
them. With the diminution of the epileptiform discharge the effects of 
stimulation again become evident, but they may be of less extent than 
before (fig. 4, record a). The character of the reaction is then found to 
have changed. The movement of contraction is a very rapid one, the 
period of relaxation comparatively slow. Thereafter the cortical reactions


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