Previous work demonstrated a reduction in cerebrovascular reactivity (CVR) to carbon dioxide in multiple sclerosis patients¹. Preserved CVR is an essential component of neurovascular coupling (NVC)². Using a more physiologically appropriate stimulus to elicit a neuronal response, in conjunction with blood flow measurements, could yield a biomarker for assessing NVC alterations in disease states. We propose a method for empirically assessing neurovascular coupling and its repeatability in the human visual cortex. This method uses magnetoencephalography (MEG) to assess neuronal activation and associate it with cerebral flood flow (CBF) changes measured using fMRI techniques.Healthy volunteers underwent 2 MEG and 2 MRI scans. A checkerboard was generated in Matlab at 5 Michelson contrast levels (6.25%, 12.5%, 25%, 50% and 100%). Checks were displayed at 1 cycle per degree (cpd) reversing at 2Hz. The stimulating field was 16° of visual angle. Each contrast was displayed for 30 seconds and repeated 4 times; 30 second rest periods of 0% contrast were interleaved 8 times with active contrast blocks. Task duration was 14 minutes. Contrasts were displayed pseudorandomly in both MEG and MRI for each participant, but contrast order was maintained between scan sessions for each subject. MEG recordings were performed using a CTF-Omega 275-channel radial gradiometer system sampled at 1200Hz. MRI measures were acquired using a GE HDx scanner with eight channel receive only head RF coil. Simultaneous ASL-weighted and BOLD imaging data was collected using a PASL, quantitative imaging of perfusion using a single subtraction (PICORE QUIPSS II)³ imaging sequence with a dual-echo gradient echo readout and spiral k-space acquisition (TE1 = 3ms, TE2 = 29ms, TR = 2.2s, 64x64, 12 slices, TI1 = 700ms, TI2 = 1600ms). By using a dual echo sequence we were able to simultaneously acquire ASL-weighted (for CBF quantification purposes), and BOLD contrast images. MEG data were cut into 250ms epochs. A SAM beamformer was used to determine source field information. Evoked fields were extracted and averaged over contrasts for each subject. The amplitude of the major positive component (P100) of evoked responses and gamma oscillatory power were used as the neuronal measure. Prior to analysis data was preprocessed, checking for movement. Subjects with excessive motion were excluded from analysis. Excessive motion was defined as movement >20mm. A power law function was used to examine neuronal and blood flow responses with respect to stimulus contrast as well as describing the relationship between neuronal responses and blood flow measurements. This was expressed as: y = Kxⁿ where y = BOLD, CBF, VEF or gamma power and x = checkerboard contrast when investigating contrast responses (eq 1). When defining NVC y = BOLD or CBF, and x = gamma power or VEF amplitude (eq 2). Intra-class correlation, ICC (3,1), was performed on the exponent (n) of these relationships from both time points to assess stability of the neurovascular coupling relationship.6 male, 9 females were recruited in total (M_age ± SEM=22.7±0.7 years, 10.6±2.7 days between MEG scans and 12.4±2.7 days between MRI scans). 4 subjects were excluded for excessive motion. Coupling between neuronal measures, and their associated blood flow responses are shown in figure 1. Exponents describing the relationship between each modality and stimulus contrast were assessed for their similarity using ICC (3,1) and plotted to visualise the correlation between the exponents (n) from session 1 and session 2 (figure 2). BOLD and CBF measures both showed significantly positive ICC values, indicating a high stability of the response between sessions. Of the neuronal measures, only gamma power displayed a significantly positive correlation between timepoints; VEF amplitude did not (figure 2E). NVC stability was determined using a power law function fitted to blood flow responses against neuronal measures (eq 2). Figure 3 shows the significant, positive ICC values with gamma power-based NVC measures, whereas VEF-based NVC measures were not temporally stable, as indicated by the low, non-significant ICC values. Coupling between MEG and fMRI measures has been well documented⁴. Here we have demonstrated P100 VEF amplitude-based measures of NVC to be temporally unstable and therefore unsuitable for studying NVC. However, a significant, temporally stable relationship between gamma power and blood flow measures was found. This novel method for measuring NVC shows promise for further use as a biomarker in disease states and exploring the relationship between neuronal activity and blood flow.