Some electrical measurements of cortical elements and neuronal responses to direct stimulation with particular reference to input resistance

Abstract

Electrical properties of the cerebral cortical elements were examined by passing current through intracellular micropipette electrodes. It was found that the threshold strength for direct excitation of neurons was 0.20–0.40 × 10 −9 amp. Upon supramaximum strength of stimulation, the neurons discharged at high frequencies up to 500/sec; the frequency of discharges rapidly reduced and in 40–110 msec became fairly constant at 45–200/sec. The response to direct excitation was followed by hyperpolarization; however, if the excitation was immediately preceded by a prolonged passage of negative current, hyperpolarization tended to be replaced by depolarization and spike discharges. Further, during the period of hyperpolarization the input resistance of the neuron was markedly reduced. Resting membrane potentials of cortical neurons were found to be 59.92 ± 7.45 mv; of the inexcitable elements, presumably glial cells, 70.08 ± 8.62 mv. Of the neurons, the resistance was 9.17 ± 2.68 × 10 6 ohms; capacitance, 0.69 ± 0.35 × 10 −9 farads; and time constant, 5.69 ± 1.34 × 10 −3 sec. Of the inexcitable elements, the resistance was in the order of 2.40 × 10 6 ohms; capacitance, 1.36 × 10 −9 farads; and time constant, 2.83 × 10 −3 sec.