Wearing an eye patch alters grey matter in adult brains

Five days behind an eye patch

What happens inside an adult head when one eye is taped shut for five days? Researchers once thought that mature brains could not rewire themselves quickly. To test this, 21 healthy adults wore a patch over their right eye day and night for five days. This test is called monocular deprivation, which means blocking sight in one eye to see how the brain handles an unbalanced stream of signals.

Tracking shifts in brain tissue

Each volunteer had an MRI scan across five test visits. Scans took place before the patch went on, on days 1, 3, and 5 of wear, and seven days after removal. To map changes across the brain, researchers used voxel-based morphometry, a scan method that checks tissue amounts across tiny 3D points. They also used generalised estimating equations, a math tool that tracks repeated body readings in the same person over time. These methods matter because they let researchers measure physical brain reshaping without surgery.

The scans showed steady rises in grey matter volume, an estimate of the size and pack of nerve cell bodies and their links. These gains appeared across sight centres on both sides of the brain, including the calcarine, lateral occipital, and fusiform parts. Nearby sections of the cerebellum also expanded. This growth peaked between days 3 and 5. Even after strict checks to weed out chance findings, these time-based increases stayed strong in the occipital pole, fusiform, and calcarine zones.

When normal sight returns

Once normal two-eyed vision returned for seven days, the visual centres shifted again. Early checks hinted at a drop in grey matter within the left middle occipital gyrus, alongside a rise in the left hippocampus. This swift reset reflects homeostatic plasticity, the brain's drive to rebalance its setup when sensory input drops or surges.

Questions that remain

The study tested only 21 people and lacked an unpatched comparison group. Findings outside the main visual regions after recovery were also exploratory and need confirmation. In addition, the exact cell actions behind these large tissue shifts remain unknown.