On the character of central nervous processes.

Abstract

Upon what basis central nervous functions operate has been even more mysterious than the mechanism of nerve-fiber conduction. A large rôle is assignable to the synaptic junction, and to its changes in resistance. Attempts to show that memory and forgetting, favorable to analysis because of their duration and gradual change, are really due to the modification of materials in the cortex, have not been altogether convincing. The development and decay of speed in the execution of a simple action has been described (Robertson) with the aid of the formula of autocatalysis, but it can scarcely be held that this result demonstrates the autocatalytic transformation of a synaptic material concerned in central transmission.

The reflex immobility of certain arthropods, and particularly of the isopod Cylisticus convexus, is found to be of rhythmic duration. If suitably stimulated following spontaneous emergence from induced immobility, the isopod again becomes immobile, but for a longer time; the duration of later acts of immobility decreases. Continuously repeated tests of this sort show a periodic rise to a certain maximum duration. The amount of this maximum duration is determined chiefly by the temperature. At 6°, the maximum duration is 270 sec.; at 29°, 23 sec. The cycle of immobility is not the reflection of a general metabolic cycle, but is determined by a central nervous process initiated by the first stimulations of the series of trials.

The relation of temperature to the processes underlying the duration of reflex immobility involves comparing the durations at different temperatures but at corresponding stages of the cycle. Between 5° and 16° the maxima lie upon one exponential curve with respect to temperature; above 16°, and continuing to 30°, the maxima lie upon an interesting exponential curve of lesser slope.