Anna stares at the computer screen and considers her options. In front of her are two shapes - a flower and a stripy diamond. If she picks the right one she will be rewarded with banana milkshake, but the wrong choice will briefly switch the lights off in her Perspex box. She opts for the diamond and is plunged into darkness.
During the next nine minutes Anna makes the same mistake over and over again. The neuroscientists who designed this experiment are testing how good Anna is at learning new rules. Over the last few weeks she has learned that the diamond was her ticket to a tasty, sugary drink, but this is the first test in which the rules have been reversed. Most of the subjects adapt quickly. But Anna is different.
In March she was subjected to precision brain surgery in which researchers destroyed a small area of her brain. To the untrained eye this has not affected her behaviour at all; she moves, eats and socialises normally. But the experiments are showing that the specific brain region knocked out is crucial for subtle behavioural abilities.