A larger brain protects against disability in multiple sclerosis according to a recent report by Sumowski and colleagues. The brain reserve hypothesis states that people with larger brain growth during development are better able to withstand aging or neurological disease. Maximal lifetime brain growth which is estimated by measuring intracranial volume, is genetically determined and is fixed during adolescence. “Greater maximal lifetime brain growth is thought to produce more robust neural networks, additional plasticity and, consequently, higher brain reserve.”
Over the five year study period, multiple sclerosis physical disability worsened more in patients with smaller brains. Previous work has shown that brain reserve does indeed protect against cognitive impairment. The findings extend the brain reserve hypothesis to physical function, and could be beneficial for treatment decisions and trial design.

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Sumowski JF, Rocca MA, Leavitt VM, Meani A, Mesaros S, Drulovic J, Preziosa P, Habeck CG, Filippi M: Brain reserve against physical disability progression over 5 years in multiple sclerosis. Neurology [Epub ahead of print, April 27, 2016; pii: 10.1212/WNL.0000000000002702.]
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http://www.ncbi.nlm.nih.gov/pubmed/27164681