Modulation of Multiunit Spike Activity by Transcranial AC Stimulation (tACS) in the Rat Cerebellar Cortex

Abstract

Transcranial electrical stimulation (tES) techniques have garnered significant interest due to their non-invasiveness and potential to offer a treatment option in a wide variety of brain disorders. Among several modulation techniques, transcranial alternating current stimulation (tACS) is favored for its ability to entrain the neural oscillations. The cerebellum is one of the targeted sites because of its involvement in motor and cognitive functions. However, animal studies are lacking in the literature looking into the mechanism of action in cerebellar tACS. In this study, we used a rat model and monitored the activity of the cerebellar cortex, which sculpts the cerebellar output by adjusting the firing rate and timing of the neurons in the deep cerebellar nuclei (DCN). For neural recording, a tungsten electrode was inserted into the cerebellar cortex through a craniotomy hole located over the right paramedian lobule (PML). A helical Ag/AgCl wire electrode was placed atop the skull near the caudal edge to inject a 1 Hz biphasic sinusoidal current. Our results showed that the multiunit activity (MUA) of the cerebellar cortex was strongly modulated by tACS. The negative phase of the electric current enhanced the neural firing rate while the positive phase suppressed the activity. Furthermore, the spike rate showed modulation by the instantaneous strength of the injected current within the sinusoidal cycle. This warrants research to further look into the mechanism of tACS acting on the cerebellar cortex at the cellular level.

Figure 1.

Recording and stimulation electrode placements. The helical Ag/AgCl stimulation electrode was positioned on the right caudal edge of the skull and the recording electrode was inserted into the PML cortex of the cerebellum. The inset shows the PML area on the lateral cerebellum.

Figure 2.

Multiunit spike recording (from Trial 5). The red sinusoidal signal represents the injected current as a function of time. Upper row shows a small episode of the recorded signal on a larger time scale.

Figure 3.

Raster plot of all 5 recordings (Trial 1–2) from rat1 (Trial 3–5) from rat2. The top row exemplifies the shape of the applied current and rows below show the spike timings in each recording.

Figure 4.

Firing rates during the baseline activity and during the positive and negative phases of the AC stimulus. Errorbars are the standard deviation.