My Brain Made Me Do It

A growing body of research has found that head injury can make people more prone to criminal behaviour…

- Linda Geddes

The tumour growing in the front of the schoolteacher’s brain was the size of an egg. It was the likely source of his recent headaches, balance problems, and difficulties writing and drawing. But these symptoms paled in comparison to the personality change that the tumour apparently brought about. Several months earlier, the man had been arrested after making sexual advances.

He knew his urges were unacceptable, yet claimed that his ‘pleasure principle’ overrode his restraint. He also insisted that his compulsion to act upon his sexual urges was new. It was certainly plausible, his doctors concluded. The tumour was growing in the right lobe of his orbitofrontal cortex, which is a brain area linked to social behaviour, judgment and impulse control. Once the tumour was removed, his deviant urges apparently disappeared, and his drawing, writing and balance improved. He successfully completed a Sexaholics Anoymous programme, and was allowed home. But the following year, a brain scan showed the tumour was regrowing. Once more, he underwent surgery to have it removed.

We often assume that people who commit atrocious acts are nothing like us; they were either born bad or became that way because of maltreatment during their own childhood. Increasingly though, brain injury – caused by a blow to the head, a stroke, or a tumour pressing on neighbouring brain tissue – is being recognised as another factor that can predispose to or trigger criminal behaviour. Sometimes these injuries bring about personality changes so obvious that they raise immediate alarm bells, but more often the personality change is subtler, and the brain injury goes undetected.