When the body enters microgravity, fluid that normally drains downward toward the legs instead pools toward the head. A landmark 2017 study in the New England Journal of Medicine found that long-duration spaceflight pushes the brain upward within the skull, narrows the central sulcus, and shrinks the space occupied by cerebral spinal fluid. The longer the astronaut is in orbit, the more pronounced the changes become.
More recent work — including a 2026 BBC investigation and research from the Shenzhou-21 mission — has pushed the question further: can microgravity alter cognition, mood, or even consciousness? Some studies suggest the physiological shifts may mimic the way psychedelic substances change brain signalling, though the exact chain from fluid movement to perception remains uncertain.
The practical challenge is that these changes have not been engineered away. Astronauts who return from months in space sometimes report blurred vision, headaches, and balance problems — collectively described as the Spaceflight-Associated Neuro-ocular Syndrome (SANS). For future lunar bases and crewed Mars missions, where return to Earth is not an option for months or years, understanding and mitigating these effects is a medical requirement, not a curiosity.
Potential solutions being explored include artificial gravity on short rotating arms, targeted brain-stimulation protocols, and exercise regimes designed to keep fluid moving. None of them are yet a complete fix, but they frame a research agenda that space agencies cannot ignore as missions grow longer.
Knowledge takeaway: long-duration microgravity shifts the brain upward, narrows the central sulcus and reduces cerebrospinal fluid space; the changes intensify with time in orbit and underpin vision, balance and cognitive concerns that lunar and Mars missions must solve before launch.