Magnetogenetic stimulation inside MRI induces spontaneous and evoked changes in neural circuits activity in rats

Abstract

The ability to modulate specific neural circuits and simultaneously visualize and measure brain activity with MRI would greatly impact understanding brain function in health and disease. The combination of neurostimulation methods and MRI in animal models have already shown promise in elucidating fundamental mechanisms associated with brain activity. We developed an innovative magnetogenetics neurostimulation technology that can trigger neural activity through magnetic fields. Similar to other genetic-based neuromodulation methods, magnetogenetics offers cell-, area- and temporal-specific control of neural activity. However, the magnetogenetics protein (Electromagnetic Preceptive Gene (EPG)) are activated by non-invasive magnetic fields, providing a unique way to target neural circuits by the MRI gradients while simultaneously measure their effect on brain activity. EPG was expressed in rat's visual cortex and the amplitude of low-frequency fluctuation (fALFF), resting-state functional connectivity (FC), and sensory activation was measured using a 7T MRI. The results demonstrate that EPG-expressing rats had significantly higher signal fluctuations in the visual areas and stronger FC in sensory areas consistent with known anatomical visuosensory and visuomotor connections. This new technology complements the existing neurostimulation toolbox and provides a mean to study brain function in a minimally-invasive way which was not possible previously.

Keywords: EPG; connectivity; magnetogenetics; neuromodulation; neurostimulation; visual cortex.

Figure 1.. EPG expression in the visual cortex leads to increases in fractional amplitude of low frequency fluctuation (fALFF).

(A) Power spectra of the resting-state fMRI signals from selected brain regions show elevated signal fluctuations above 0.1Hz in the EPG (red) compared to the GFP (blue) group. Errorbar represents the standard error of mean (SEM). (B) Voxel-wise comparison of fALFF between the EPG and GFP groups (two-sample t-test, p < 0.05, FDR corrected). (C) Regional analysis of the fALFF demonstrated that EPG rats exhibit significantly larger fluctuations at the primary visual cortex (V1m) compared to control rats (Two-way ANOVA, F (1, 64) = 12.88, p = 0.0006). This increased spontaneous neural activity in the region that the EPG was expressed suggests that EPG could be activated by the magnetic field of the MRI. See supplementary Table S1 for abbreviations of brain regions.

Figure 2.. EPG expression in the visual cortex leads to increases in Functional Connectivity (FC) across cortical and subcortical areas.

(A) A seed ROI was placed in the V1m of the left hemisphere, where the EPG was expressed. In the GFP control group, FC was mostly in the visual cortex with certain connectivity with the medial prefrontal cortex (one-sample t-test, p<0.01 FDR corrected). In the EPG group, broadly increased FC can be seen over the whole brain. Between group comparison shows significantly higher connectivity between brain areas of EPG rats compared to controls (two-sample t-test, p < 0.05 FDR corrected). (B) Whole brain FC (two-sample t-test, p<0.001 uncorrected) shows extensively increased connectivity beyond the visual cortex. See supplementary Table S1 for abbreviations of brain regions.

Figure 3.. Evoked visual responses.

(A) ROI in the visual pathway and the thalamus. Two epochs of 20s visual stimulation were delivered, leading to activation in the visual pathway in the (B) GFP and (C) EPG groups (one-sample t-test, p < 0.01 FDR corrected). (D) The EPG group showed significant increased activation in the primary visual cortex (V1), hippocampus (HP) and ventral thalamus, and decreased activation in the striatum (STR), inferior colliculus (IC) and cerebellum, compared to control rats (two-sample t-test, p<0.05, FDR corrected). (E) Averaged signal time-courses from selected ROI. Error bar represents SEM and the gray bars indicate the stimulation periods.

Figure 4.. Evoked tactile responses.

Two epochs of 20s tactile stimulation were delivered to the forepaw of the rat, leading to significant activation in the somatosensory pathway in the (A) GFP and (B) EPG groups (one-sample t-test, p < 0.01 FDR corrected). (C) Between group comparison shows that the EPG group had increased activation in the Thalamus (TH) and in the anterior cingulate cortex, and decreased activation in the striatum (STR), compared to control rats (two-sample t-test, p<0.05, FDR corrected). (D) Averaged signal time-courses from selected ROI. Errorbar represents SEM and the gray bars indicate the stimulation periods.

Figure 5.. Immunohistology of EPG expression in the visual cortex.

10X magnification ((A), Scale bar = 300μm) and 20X magnification ((B), Scale bar = 200μm of EPG (labeled with green, anti-GFP) throughout the layers of the visual cortex in excitatory neurons (labeled with red, anti-CamKII) ((C), Scale bar=200μm.