Dr. Walter Koroshetz, deputy director of the National Institute of Neurological Disorders and Stroke, says that these days doctors will perform scans on patients with prior brain tumors every couple of months to check for early evidence of regrowth.

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The results were spectacular - in one instance 14mm of nerve regrowth was produced.

BBC: Nerve growth success

It suggests that doctors must have determined there was no evidence on brain scans that Kennedy is suffering from an obvious regrowth of the brain tumor, called a glioblastoma, that caused his first seizure last May.

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Other research has shown that lens injury can promote nerve regrowth in these sorts of injury.

BBC: Nerve growth success

Dr James Fawcett, from the Cambridge Centre for Brain Repair, says that any successful attempt to produce nerve regrowth in humans would probably depend on a combination of treatments, both aimed at breaking down scar tissue and encouraging nerves to sprout.

BBC: Nerve growth success

One question: Why would regrowth in the hippocampus reverse depression, when the ailment also affects many other areas of the brain?

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