Vagus Nerve Stimulation Selectively Diverts Brain Fluid Flow in Rat Study

Noninvasive electrical stimulation of the vagus nerve alters cerebrospinal fluid transport along specific cranial pathways in rats rather than triggering a uniform increase throughout the brain, according to a study published in Fluids and Barriers of the CNS. The investigation, conducted in Sprague-Dawley rats, revealed that transcutaneous auricular vagus nerve stimulation selectively enhanced fluid outflow along the olfactory bulb route while dampening movement along the optic nerve pathway.

Cerebrospinal fluid circulation through the subarachnoid space is essential for clearing metabolic waste from the brain. While dynamic contrast-enhanced magnetic resonance imaging has advanced the mapping of these pathways using chemical tracers, tracer-dependent techniques remain constrained by their reliance on specific injection sites and limited repeatability. Intravoxel incoherent motion magnetic resonance imaging offers a complementary, noninvasive alternative that enables repeatable evaluations of fluid dynamics and provides distinct biophysical measurements of fluid motion.

To examine how auricular stimulation influences intracranial fluid transport, the researchers engineered customized magnetic resonance-compatible electrodes fitted directly into the imaging cradle. All imaging sessions were performed while the animals were maintained under isoflurane anesthesia.

The experimental protocol combined two distinct imaging approaches to capture different characteristics of fluid transport. Intravoxel incoherent motion imaging evaluated within-subject differences between baseline and post-stimulation states by measuring initial signal decay at low b-values, quantified as D star. Dynamic contrast-enhanced imaging assessed group-wise differences between active stimulation and sham control cohorts by tracking the arrival time, initial slope, and area under the signal curve.

Statistical evaluation of the intravoxel incoherent motion data revealed significant shifts in D star magnitude across several intracranial pathways following nerve stimulation. Measurable changes occurred in the subarachnoid space along the cisterna magna, the perivascular space surrounding the circle of Willis, the subarachnoid space adjacent to the olfactory bulb, and the subarachnoid space neighboring the dural venous sinus. Across these regions, the stimulation-associated alterations in the initial slope measured by contrast-enhanced imaging correlated strongly with the shifts in D star magnitude, yielding a linear correlation coefficient of r = 0.958 with a significance level of p < 0.01.

The dual-modality measurements demonstrated diverging functional responses between separate cranial outflow tracts. Compared with the sham intervention, active stimulation produced statistically significant differences in both the area under the curve and arrival times between the olfactory bulb and optic nerve pathways, with p < 0.05 for both measures. These coordinated changes indicated that stimulation accelerated fluid outflow toward the olfactory bulb while simultaneously suppressing transport along the optic nerve pathway.

The authors concluded that the contrasting modulation observed across the olfactory bulb and optic nerve pathways indicates that transcutaneous auricular vagus nerve stimulation acts on discrete anatomical routes rather than universally enhancing intracranial fluid clearance. The team noted that integrated analytical frameworks combining noninvasive motion metrics with contrast kinetics are necessary to characterize the complex dynamics governing cerebrospinal fluid transport during neuromodulatory interventions.

Subject of Research: Neuromodulation of rat cerebrospinal fluid transport pathways using MRI

Article Title: Integrated IVIM- and DCE-MRI analysis reveals differential modulation of CSF transport along olfactory bulb and optic nerve pathways by taVNS

Article References: Jin, S., Kim, W., Tessema, A. W., Carré, F. Y., Chung, G., Kim, S. K., & Cho, H. (2026). Integrated IVIM- and DCE-MRI analysis reveals differential modulation of CSF transport along olfactory bulb and optic nerve pathways by taVNS. Fluids and Barriers of the CNS. https://doi.org/10.1186/s12987-026-00868-5

Image Credits: AI Generated

DOI: 10.1186/s12987-026-00868-5

Keywords: cerebrospinal fluid, vagus nerve stimulation, magnetic resonance imaging, intravoxel incoherent motion, dynamic contrast-enhanced MRI, olfactory bulb, optic nerve, Sprague-Dawley rats, Integrated, IVIM-, DCE-MRI, analysis