COVER STORY
The other you Six things your brain can do when your back is turned
T
HINK you know what’s going on in your mind? You must be kidding. Much of our mental life happens in the unconscious: a place that Freud famously considered to be a cesspit of our most basic animalistic desires. This is a view that modern neuroscientists definitely don’t share, but they do agree with Freud on one thing – that our brains have an uncanny knack for working stuff out, with no need for conscious involvement. So how do the thoughts you don’t know you’re having run your life? Is it possible to bring those murky machinations to the surface for closer inspection? New Scientist investigates.
30 | NewScientist | 1 October 2016
1 THINK WHILE YOU SLEEP Simon Makin
Some people swear that if they want to wake up at 6 am, they just bang their head on the pillow six times before going to sleep. Crazy? Maybe not. A study from 1999 shows that it all comes down to some nifty unconscious processing. For three nights, a team at the University of Lubeck in Germany put 15 volunteers to bed at midnight. The team either told the participants they would wake them at 9 am and did, or told them they would wake them at 9 am, but actually woke them at 6 am, or said they would wake them at 6 am and did. This last group had a measurable rise in the stress hormone adrenocorticotropin from 4.30 am, peaking around 6 am. People woken unexpectedly at 6 am had no such spike. The unconscious mind, the researchers concluded, can not only keep track of time while we sleep but also set a biological alarm to jump-start the waking process. The pillow ritual might help set that alarm. The sleeping brain can also process language. In a 2014 study, Sid Kouider of the École Normale Supérieure in Paris and his colleagues trained volunteers to push a button with their left or right hand to indicate whether they heard the name of an animal or object as they fell asleep. The team
monitored the brain’s electrical activity during training and when the people heard the same words when asleep. Even when asleep, activity continued in the brain’s motor regions, indicating that the sleepers were preparing to push the correct button. The people could also correctly categorise new words, first heard after they had dropped off, showing that they were genuinely analysing the meaning of the words while asleep. It’s an ability that makes good evolutionary sense, says Kouider. “If you stop monitoring your environment, you become very vulnerable during sleep… It makes sense that you don’t simply shut down, but continue tracking in a kind of standby mode.” This might explain why some sounds, like our names, wake us more easily than others. This protective monitoring may not last all night, however. A study published this year found that while language processing continues in REM sleep for words heard just before bed, once in deep sleep all responses disappear as the brain goes “offline” to allow the day’s memories to be processed. “Your cognition about things in the environment declines progressively towards deep sleep,” Kouider says. “Sleep is not all-or-none in terms of cognition, it’s all-or-none in terms of consciousness.”