INTRODUCTION AND OBJECTIVE: The main goal of the current study was to assess changes in O2Hb signals for both brain and bladder during natural filling in efforts to establish a four-quadrant grid to enhance categorization of Overactive Bladder (OAB) subtypes. Functional near infrared spectroscopy (fNIRS) was used to assess pre-frontal cortex (PFC) neuroexcitation and standard bladder NIRS (bNIRS) was used to assess bladder hemodynamics. METHODS: Both OAB (ICIq-OAB urgency question ≥2) and healthy control participants completed two natural filling cycles. fNIRS data for the PFC (Brite,Artinis) and bNIRS data for the bladder (Portalite, Artinis) were simultaneously recorded. Average O2Hb signals were recorded during a period of high sensation defined as the time from patient-reported ‘first desire to void’ to bladder capacity. The early (1st half) and late (2nd half) of this period were analyzed and compared for both the PFC and bladder. To compare bladder and brain O2Hb, relative change in bladder O2Hb was plotted against relative change in bladder O2Hb. Data were compared with Fisher’s Exact tests or t-tests. RESULTS: Twenty-seven participants were recruited and 22 completed the study with sufficient data (OAB: n=12, normal controls: n=10). The OAB group was significantly older and with higher BMI (ptextless0.05). Groups had comparable race and baseline fluid intake. Groups are compared in Figure 1. In the normal quadrant (top right: high bladder and brain O2Hb) there were 9/10 normal (90%) and 2/12 OAB (17%), ptextless0.05. The remainder of the OAB participants clustered in the Bladder-Based OAB quadrant (top left: low bladder O2Hb and high brain O2Hb) with 4/12 (33%), Brain-Based OAB quadrant (bottom left: high bladder O2Hb and low brain O2Hb) with 2/10 (33%), and Both quadrant (bottom right: low bladder and brain O2Hb) with 2/10 (17%). CONCLUSIONS: Combined Brain and Bladder fNIRS during natural filling represents a non-invasive and more objective technique that can potentially be used to categorize OAB subgroups. The grid enables a visual method to determine if OAB pathophysiology is a brain problem, a bladder problem, or a combined organ problem. Further research is required to validate this combined fNIRS and bNIRS subtyping approach.