Aga Khan University Nairobi

Brain-age models trained mostly on Global North data lose accuracy when applied to Nigerian adults. A population-specific Gaussian process regression model trained on clinical T1-weighted MRI from 309 Nigerian adults reached a mean absolute error of 9.82 years on a 47-participant held-out test set without age-bias correction; on the 44-participant head-to-head set it reached 10.24 years, against 10.52 years for PyBrainAge, 12.33 for SynthBA, 17.51 for ENIGMA-Brain Age and 7.87 for SPARROW. After correction it reached 6.39 years internally but 8.78 years on a separate Nigerian cohort, where every model's R2 was negative.

Brain-age models trained mostly on Global North data lose accuracy when applied to Nigerian adults. A population-specific Gaussian process regression model trained on clinical T1-weighted MRI from 309 Nigerian adults reached a mean absolute error of 9.82 years on a 47-participant held-out test set without age-bias correction; on the 44-participant head-to-head set it reached 10.24 years, against 10.52 years for PyBrainAge, 12.33 for SynthBA, 17.51 for ENIGMA-Brain Age and 7.87 for SPARROW. After correction it reached 6.39 years internally but 8.78 years on a separate Nigerian cohort, where every model's R2 was negative.