Microgravity effects on the human brain and behavior: Dysfunction and adaptive plasticity

Abstract

Emerging plans for travel to Mars and other deep space destinations make it critical for us to understand how spaceflight affects the human brain and behavior. Research over the past decade has demonstrated two co-occurring patterns of spaceflight effects on the brain and behavior: dysfunction and adaptive plasticity. Evidence indicates the spaceflight environment induces adverse effects on the brain, including intracranial fluid shifts, gray matter changes, and white matter declines. Past work also suggests that the spaceflight environment induces adaptive neural effects such as sensory reweighting and neural compensation. Here, we introduce a new conceptual framework to synthesize spaceflight effects on the brain, Spaceflight Perturbation Adaptation Coupled with Dysfunction (SPACeD). We review the literature implicating neurobehavioral dysfunction and adaptation in response to spaceflight and microgravity analogues, and we consider pre-, during-, and post-flight factors that may interact with these processes. We draw several instructive parallels with the aging literature which also suggests co-occurring neurobehavioral dysfunction and adaptive processes. We close with recommendations for future spaceflight research, including: 1) increased efforts to distinguish between dysfunctional versus adaptive effects by testing brain-behavioral correlations, and 2) greater focus on tracking recovery time courses.

Keywords: Adaptation; Compensation; Head-down-tilt bed rest; Plasticity; Spaceflight.

Fig. 1.. Overview of spaceflight effects on the brain.

Different stages (pre-flight, in-flight, and post-flight) associated with spaceflight are depicted as a primary organizing principle of the framework. The gray bars represent ongoing positive and negative factors hypothesized to play a causal role in brain and behavioral changes corresponding with each stage. The gradients depicted in the “Responses” represent magnitude of impact (e.g., structural brain changes increase during flight and subsequently recover). Mission duration is shown in black during the in-flight period. Effects of spaceflight durations spanning greater than one year are currently unknown. Each stage corresponds to a section of Tables 1-3, which provides a detailed summary of evidence to date associated with each of these effects. For example, studies pertaining to the effects of stressors and resilience on the pre-flight state (first column in Fig. 1) are highlighted in Section 1 of Table 1.