Can brains bounce back? Recovering addicts turn to science to map the effects of meth

Cohen Irwin is part of a group of former addicts in New Zealand working with researchers to trace signs of healing in the brains of those who stop smoking

Every few months, Cohen Coey" Irwin lies on his back and lets the walls close in. Lights move overhead, scanning over the tattoos covering his cheeks. He lies suspended, his head encased by a padded helmet, ears blocked, as his body is shunted into a tunnel. The noise begins: a rhythmic crashing, loud as a jackhammer. For the next hour, an enormous magnet will produce finely detailed images of Irwin's brain.

Irwin has spent much of his adult life addicted to smoking methamphetamine - or P, as the drug is known in New Zealand. He knows its effects intimately: the euphoria, the paranoia, the explosive violence, the energy, the tics that run through his neck and lips. Stepping outside the MRI machine, however, he can get a fresh view for the first time - looking in from the outside at what the drug has done to his internal organs.