Spaceflight environmental and psychological stressors can significantly disrupt one's ability to function effectively and efficiently, and the associated performance deficits can seriously jeopardize space missions. Mission success can be jeopardized either directly, from the potentially life threatening consequences of lapses in performance, or indirectly, by adding to the workload and stress of other crewmembers. The substantial likelihood and potentially serious consequences of neurobehavioral conditions during spaceflight, such as depression, helps explain why the Bioastronautics Roadmap Risk of human performance failure due to neurobehavioral problems is a high priority risk for all mission types (International Space Station (ISS), Moon, Mars). For depression, a variety of therapies are already available, including preventative measures, medications, and psychological consultations with ground-crews. However, current methods to decide whether a therapy needs to be used rely heavily on subjective self-report. The biological basis of mood disorders suggests that neural biomarkers may be able to provide a more objective method for assessing depression and potential performance deficits. The goal of this proposal was to identify neural biomarkers sensitive to, and specific for both detecting depression and assessment of depression severity. In this project, we identified multiple putative brain biomarkers of both the presence/absence of depression as well as of depression severity. These included both structural alterations in regional cerebral gray and white matter, as well as changes in brain function. This work strongly supports the feasibility of using brain measures to more objectively detect and assess depression. While these findings were promising, there is currently no reliable way to monitor brain state or function in spaceflight. Thus, the second important component of our project was development, evaluation, and validation of a novel and flight-capable neuroimaging technology: near-infrared neuromonitoring (NIN). We first developed a novel, noninvasive NINscan 2a device, and then sought to test it in suitable analog settings. A parabolic flight test demonstrated the device's performance in microgravity, and also identified differences in cerebral versus systemic hemodynamic response to changing gravitational fields. The NINscan 2a prototype was also tested during three separate treks to the peak of Mt. Kilimanjaro. These treks demonstrated (1) the system's robustness to remote and extreme environments, (2) its usability by non-experts, and (3) its sensitivity to brain tissue by identifying cerebral hemodynamic changes associated with both altitude and acute mountain sickness induced by hypoxia and hypobaria.
In a head-down tilt analog study, we further demonstrated that the NIN technology is only minimally affected by the headward fluid shifts associated with microgravity. Since the NINscan 2a prototype was found to be only modestly sensitive to the small signals associated with brain function, we therefore began development of a second and third new NINscan prototype (3a and TD). Both were designed for significantly improved sensitivity and flexibility. The most recent, NINscan TD, included a novel embedded microcontroller that could serve as the foundation for developing a whole-head NIN imaging instrument. In sum, we identified a number of putative brain-based biomarkers for more objectively detecting depression and assessing its severity. We simultaneously developed and tested novel prototype devices for brain monitoring, including multiple independent tests in analog environments, and demonstration of NIN sensitivity to cerebral hemodynamics. Jointly, these efforts substantially increase the readiness level of using brain monitoring technologies to more objectively assess in-flight depression and perform in-flight brain assessment in general.