Sinusoidal stimulation on afferent fibers modulates the firing pattern of downstream neurons in rat hippocampus

¹ The Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering and Instrument Science, Zhejiang University, Hangzhou, Zhejiang, 310027, P. R. China

^*Correspondence: fengzhouyan@zju.edu.cn (Zhou-Yan Feng)

J. Integr. Neurosci. 2020, 19(3), 413–420; https://doi.org/10.31083/j.jin.2020.03.207

Submitted: 4 July 2020 | Revised: 11 September 2020 | Accepted: 13 September 2020 | Published: 30 September 2020

This is an open access article under the CC BY-NC 4.0 license (https://creativecommons.org/licenses/by-nc/4.0/).

Abstract

Electrical stimulation in the brain is an emerging therapy for treating a wide range of neurological disorders. Although electrical pulses are commonly used in the clinic, other electrical waveforms such as sinusoidal-waves have been investigated to improve the therapeutic efficacy, to reduce the risk of tissue damage induced by stimulation, and to decrease the consumption of electrical energy. However, the effects of sinusoidal stimulation on neuronal activity are still unclear. In the present study, we investigated the neuronal responses to the stimulation of 50-Hz sinusoidal-waves applied on the afferent fibers of the neurons in the hippocampal CA1 region of Sprague-Dawley rat in vivo. Results show that the stimulation increased the firing rate of both pyramidal neurons and interneurons in the downstream region of stimulation. Also, the stimulation eliminated the original theta rhythms (2-5 Hz) in the single-unit activity of the two types of neurons and entrained these neurons to fire at the stimulation rhythm. These results provide new clues for the mechanisms of brain stimulation to suppress the pathological rhythms in the neuronal activity, and for the application of sinusoidal waveforms in brain stimulation therapy.

Keywords

Deep brain stimulation

sinusoidal stimulation

unit spike

firing pattern

theta rhythm

hippocampus

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Fig. 1.

Increase of neuronal firing by 50-Hz sinusoidal stimulations.(A) Schematic diagram of the stimulation electrode (SE) at Schaffer collaterals and the recording electrode (RE) in the CA1 region. (B) A typical recording of neuronal responses to a 1-min 50-Hz sinusoidal stimulation with raw recording (0.3-5000 Hz), LFP around the theta frequency (1-10 Hz), and MUA (500-5000 Hz). The shadow denotes the stimulation period. The red curves denote the sinusoidal waveforms applied at the Schaffer collaterals. Note that the sinusoidal artifacts in the raw recordings are out of phase with the sinusoidal waveforms from the inner pole of the bipolar SE because the location of the recording site in the pyramidal layer was near the outer pole level of the SE. (C) Comparisons of the firing rates of pyramidal neurons and interneurons between the baseline recordings of pre-stimulation and the recordings during stimulation. ${}^{**}$ P $<$ 0.01, paired t-test.

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