Journalists adore research that allows them to write stories along the lines of “scientists have tracked down the brain’s love HQ” or “researchers have located the brain’s god spot”. It is very satisfying to imagine that we can divide the brain into neat components with distinct functions like the parts of a car engine. We dream that one day, neuroscientists will be able to lift the bonnet (or the hood if it’s an American brain), point and say “here’s the valve that causes schizophrenia – we can readjust that with this chemical spanner. Here’s the tank that causes OCD when it overflows – we can drain that by turning this tap here. Over there are the spark plugs that we clean up to cure depression …”
Unfortunately the brain is a lot messier and more wonderful than your average motor engine, which is why we’re still standing over it scratching our heads trying to figure out how on earth it all works. It’s a tangle of connections, with myriad networks of components involved in creating thoughts, consciousness, sensations and emotions.
So it is with a mixture of excitement and wariness that I approach a study by researchers at Beijing Normal University in China that seems to point to a particular part of the brain that switches mindfulness on and off. It’s called the thalamus (shown in red on the animated gif), a pair of bulbous structures that sit at the top of the brainstem (yellow) on the midline of the brain. The thalamus plays a pivotal role as the brain’s switchboard, relaying information from all the senses apart from smell to the cerebral cortex, which is the thinking, conscious part of the brain.
It also helps to direct our focus of attention, which is telling because the thalamus is part of the default mode network, an interconnected collection of regions associated with mind-wandering. If you slide someone into a brain scanner and tell them to simply lie there and do nothing in particular, this is the brain network that fires up as their mind starts to wander and they ponder things like where they’re going to go for lunch – is the canteen serving vegetarian lasagne today? Did Mollie remember her dentist appointment this morning? What are those scientists in the other room up to? They’re certainly taking their time.
It’s not all trivia of course. The default mode network is essential for creativity, planning ahead and making sense of the past. When we’re focused on performing a cognitively demanding task, however, whether it’s mental arithmetic, reading or changing the spark plugs in an engine, the network goes quiet. It also quietens down when people meditate, otherwise known as practising mindfulness.
There’s much more to mindfulness than formal meditation, of course. Mindfulness is an everyday psychological trait like introversion and extroversion, optimism and pessimism, that varies from person to person. It can be defined loosely as “living in the moment”, paying attention to what your senses are telling you is happening right here and now. Research suggests that greater mindfulness is associated with mental stability, whereas mind-wandering is associated with mental illnesses such as depression, OCD and schizophrenia. But the good news is that your level of mindfulness is not fixed – it can be nurtured through regular meditation.
What the cognitive neuroscientists in China seem to have discovered is that the thalamus acts as a kind of switch that toggles brain activity between the mind-wandering mode that is mediated by the default mode network, and the focused-attention mode of mindfulness. They asked 245 college students to fill out a psychological questionnaire called the Mindful Attention Awareness Scale, which is a reliable measure of “trait mindfulness”. They then imaged the students’ brains in an MRI scanner after instructing them to close their eyes and relax. In other words they were looking at the “resting state” of their brains (which is a bit of a misnomer since the brain uses almost as much energy when it’s not focused on a particular task as when it’s left to its own devices).
The researchers were interested in the functional connectivity of the different components of the default mode network, which is neurospeak for how closely correlated their activity was. They analysed every possible pairing of the different components and put a figure on how tightly coordinated they seemed to be.
One pair of components stood out from all the other pairs: the thalamus and the posterior cingulate cortex (part of the cerebral cortex). Among students who had a low mindfulness score, there was a strong connection between these two components, but among those with high trait mindfulness there was a weak connection. Further analysis revealed that it was activity in the thalamus that played the critical role in determining whether a particular student had a mindful personality or was prone to mind-wandering. To use the switch metaphor, for those who scored poorly on mindfulness the thalamus seemed to be stuck in the “on” position.
The researchers conclude that the thalamus may be “a switch between mind-wandering and mindfulness”. This makes sense because it sits at the intersection of two competing networks in the brain: one that promotes mind-wandering (the default mode network) and another that promotes attention and wakefulness, known as the ascending reticular activating system (ARAS).
So the thalamus may be a bit like a politician who is known to be highly influential because she sits on two important, rival committees. That’s not to say that the other components of the two networks aren’t also important players in mindfulness (the posterior cingulate cortex, for example, may be closely involved when we get “caught up” in our thoughts and emotions), but this study suggests that in future we should pay more attention to this curious pair of bulbous structures at the top of the brainstem.
What may happen when people practise mindfulness is that, over time, this weakens the connection between their thalamus and the rest of the default mode network, and perhaps strengthens its connection with the ARAS. Their trait mindfulness score would climb as a result and they might just become more mentally robust and less prone to depression and other mental illnesses. That really would be brain plasticity in action.
Image: the thalamus via Wikimedia Commons