FACILITATION AND DIFFICILITATION EFFECTED BY NERVE IMPULSES IN PERIPHERAL FIBERS

Abstract

The facilitation effected by the constituent spikes of a series was estimated by measuring the voltage required to block anodally a given number of the successive spikes and referring this value to the voltage required to block the 1st spike of the series. Thus measured, the facilitating action at such an artificial synapse increases, though at a decreasing rate, with the number of the successive spikes through at least 20, and with the frequency through a range wider than 10 to 200 per sec. If during continuous bombardment of a block along a fiber with spikes, one of them succeeds in passing, all succeeding spikes of the continuous tetanus will pass, due presumably to the persistence in the postblock fiber of a supernormality which raises excitability more than it is lowered during the spontaneous excitability changes, and by fatigue. When a block is thus overcome a temporary interruption of the tetanus (0.5-0.6 sec. is the optimum pause) may reestablish the block, which then is not removed by the indefinite continuance of the tetanus. This is designated difficilitation. Interrupting the tetanus during the difficilitation for a few secs. ordinarily stops the difficilitation. Similar phenomena are demonstrable at the site of stimulation of a fiber with induction shocks, and evidently both facilitation and difficilitation result from the electrical action of the preblock fiber on the postblock fiber. Difficilitation and the "extinction" of Dusser de Barenne and McCulloch may be identical phenomena.