An intra-neural microstimulation system for ultra-high field magnetic resonance imaging and magnetoencephalography
Journal of Neuroscience Methods
h i g h l i g h t s • We propose an intra-neural microstimulation system for 7 T fMRI and MEG. • This custom-built system removes issues with existing equipment. • It provides efficient work-flow and improved participant comfort and safety. • Stimulating single mechanoreceptors evokes activity in 7 T fMRI and MEG. • Responses to unitary stimulation are shown for the first time in MEG. Low-noise amplifier Nerve stimulation Magnetoencephalography Functional magnetic resonance imaging Ultra-high
... gnetic field Human Microneurography Tactile Touch Low-threshold mechanoreceptor a b s t r a c t Background: Intra-neural microstimulation (INMS) is a technique that allows the precise delivery of low-current electrical pulses into human peripheral nerves. Single unit INMS can be used to stimulate individual afferent nerve fibres during microneurography. Combining this with neuroimaging allows the unique monitoring of central nervous system activation in response to unitary, controlled tactile input, with functional magnetic resonance imaging (fMRI) providing exquisite spatial localisation of brain activity and magnetoencephalography (MEG) high temporal resolution. New method: INMS systems suitable for use within electrophysiology laboratories have been available for many years. We describe an INMS system specifically designed to provide compatibility with both ultra-high field (7 T) fMRI and MEG. Numerous technical and safety issues are addressed. The system is fully analogue, allowing for arbitrary frequency and amplitude INMS stimulation. Results: Unitary recordings obtained within both the MRI and MEG screened-room environments are comparable with those obtained in 'clean' electrophysiology recording environments. Single unit INMS (current <7 A, 200 s pulses) of individual mechanoreceptive afferents produces appropriate and robust responses during fMRI and MEG. Comparison with existing method(s): This custom-built MRI-and MEG-compatible stimulator overcomes issues with existing INMS approaches; it allows well-controlled switching between recording and stimulus mode, prevents electrical shocks because of long cable lengths, permits unlimited patterns of stimulation, and provides a system with improved work-flow and participant comfort. Conclusions: We demonstrate that the requirements for an INMS-integrated system, which can be used with both fMRI and MEG imaging systems, have been fully met.