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Abstract

Introduction. Performing fMRI and electrophysiological measurements simultaneously offer a better understanding of the hemodynamic response function due to the high temporal and spatial resolution of the combination of these methods. In 2020 we introduced a monolithically integrated NMR chip on a needle for local in vivo measurements (Handwerker et al., 2020). As the NMR needle achieved a similar spatiotemporal resolution as electrophysiology while offering the specificity and versatility of NMR, an electrophysiology setup has been developed to detect multi-unit activity (MUA) as well as local field potential (LFP) simultaneously to the NMR needle measurements, potentially closing the gap between these complementary modalities. Methods. The electrophysiological electrode was based on carbon monofilament, causing low susceptibility distortions in a 14 Tesla MR scanner close to the NMR needle. Furthermore, it was electroplated with PEDOT:pTS to be able to record MUA additional to LFP activity (Chuapoco et al., 2019). In order to prevent SNR loss, the non-magnetic, custom-made preamplifier was placed inside the magnet close to the recording electrode. We used a custom-designed galvanically separated main amplifier. We added several shielding applications to work under high magnetic-field conditions and to minimize interferences between the transmission pulse of the NMR needle and the microelectrode inside the tissue. (Image 1) Results. The electrophysiological electrode including magnetic field proof electronics was designed and constructed to detect stimulus-evoked neuronal signals with simultaneous NMR needle recordings. First experiments outside the magnet have shown its ability to detect multi-unit activity. Conclusion. This combined experimental setup will allow capturing localized BOLD activity within distinct cortical layers. It will enable to observe neurovascular coupling directly at high temporal and spatial resolution. We aim to detect the hemodynamic response of different non-evoked neuronal activities at distinct locations with this.