TES-fMRI in rats

Using single-unit recordings is more effective for studying specific and localized aspects of neuronal assemblies in particular areas of interest, rather than assessing brain-wide activity. When using Transcranial Electrical Stimulation (TES), the electric fields are stronger near the stimulation electrode, but they decrease rapidly with depth. However, modeling studies suggest that deep areas, such as the brainstem, can also be affected due to the effects of cerebrospinal fluid and the less explored inhomogeneities in brain tissue.

Integrating TES with MR imaging techniques allows researchers not only to study how stimulation affects targeted brain regions but also to understand its impact on anatomical and functional connectivity. TES-fMRI can offer crucial insights into the most effective ways, locations, and timing for stimulation.

Applying results from rodent studies to human applications is challenging because our brains differ in size (number of neurons and connections) and the presence of gyri (folds) in humans. Moreover, animal studies usually involve placing stimulation electrodes beneath the skin and applying much higher electric fields compared to humans. To bridge this gap between rodents and humans, I combined neurostimulation with MRI. MRI is a safe tool that works for both species and provides information about the brain’s structure and functions.

In this project, I developed an MRI compatible and artifact-free stimulation setup to deliver electrical stimulation in rats. To avoid metal-induced artifacts during MRI scans, a deuterium-filled (5% NaCl) compartment, invisible in proton MR, and a watertight pocket system were used for the stimulation electrodes.