The effect of longitudinal magnetic resonance imaging on the quality of neurophysiological recordings using implanted micro- wire electrodes

Introduction. Valuable insights can be gained by combining both invasive and non-invasive schemes for analyzing and activating the central nervous system.. For example, combining fMRI and intracortical recording has yielded important information about metabolic mechanisms that are highly correlated with recorded neural activity[1]. Similarly, combining fMRI with electrical microstimulation has improved understanding on the extent of neural activation [1, 2]. An important step towards combining these technologies is an evaluation of safety and compatibility. Induced currents and associated tissue heating and damage, especially at electrode tips[3], are a major concern. Studies wherein neural tissue is sensed both by the implanted electrodes and MRI are challenging because sensing requires viability of the neural tissue in close proximity to the electrodes. Such requirements are inherently more stringent using, for example, microelectrode arrays recording extracellular multiunit activity (EMUA) since the sensing zone is limited to a couple of hundreds of microns from the metallic electrode tip [4,5]. It is also necessary that the electrodes are MRI-compatible while maintaining a high quality of neural recordings. Previous work presented by Santiesteban et al., [6] addressed important issues related to shortterm compatibility of silicon microelectrodes. In order to extend the work of Santiesteban et al. the project described here provides a quantitative assessment of the longitudinal stability and quality of EMUA, comparing animals that have undergone extensive MRI scanning vs. control animals that were not scanned.