In the course of experiments in which the cerebral cortex of the monkey is stimulated, it is peculiarly noticeable that the activity of the cortex varies from time to time. That such variation should occur is by no means strange, in view of the difficulty of maintaining a constant depth of narcosis. But there are other variations which seemingly are not conditioned by variation of depth of narcosis. Thus it not rarely happens that, when the depth of narcosis is certainly a constant one, the motor cortex becomes suddenly inexcitable. This occurs, for instance, after a cortical discharge, which is followed by “ epileptic ” after-discharge. But it also occurs without any apparent preceding cause. Thus suddenly the cortical excitability becomes abolished—at any rate, to practicable strengths of stimulation. This sudden loss of cortical excitability is a phenomenon of interest. It is accompanied by two marked states. Of these, the first is an anæmia of the cortex ; the second is a maintained postural contraction of certain of the muscles of the limbs. The anæmia seems to occur over the whole of the small area of cortex—pre-central and post-central—usually exposed in these experiments. It causes a sudden change in appearance from the “raw ham” look of the cortex when it is in the most favourable condition for electrical stimulation to a pale “ dead ” look. The cortex blanches; it may be surmised that it faints.
Exploring the effects of synchronous pharyngeal electrical stimulation with swallowing carbonated water on cortical excitability in the human pharyngeal motor system