Absolute refractory period of neurons involved in MFB self-stimulation

The refractory period of the directly stimulated neurons whose excitation elicits behavior can be measured by variation of the intra-pair interval of trains of stimulating pulse pairs. It is shown that at high frequencies of stimulation (e.g. 200 pulses/sec) the current threshold of the neurons directly excited in self-stimulation may be approached. Thus to measure the absolute refractory period of neurons, the electrical stimulation must be at least twice the threshold value. In Experiment 2, using twice threshold currents, the absolute refractory periods of the neurons involved in the continuation of medial forebrain bundle (MFB) self-stimulation were found to be in the range 0.8–1.1 msec in six rats. The measure may represent a priming effect of the stimulation. This value of the absolute refractory period of neurons excited in lateral and posterior hypothalamic self-stimulation corresponds to the value for the neurons through which the brainstem arousal system is excited (see preceding report), and provides further evidence that this brainstem neural system is involved in MFB self-stimulation.