We’re all at it, all the time. Yet thinking, or how we should think about thought, is surprisingly hard to pin down. When I did a vox pop, for instance, a couple of friends described thoughts as “wispy things”. Another saw them as sparklers, fizzing with chaotic flashes but containing a central light source that is controllable.
All of which is decidedly unscientific. But then even the experts aren’t so sure about what thoughts are, and what we can surmise from the latest neuroimaging studies suggests we may never truly pin down how they manifest in the brain.
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“The short answer is that ” says , a philosopher at Monash University in Australia and author of Thought: A very short introduction. Even so, it is useful to consider two aspects of thought, he says: their content and their nature.
‘s definition does exactly that. “Thought is a mental state, or series of mental states, that has some kind of content to it, with some personal attitudes towards the content – like an attitude of remembering or believing or imagining,” says Christoff, who runs the Cognitive Neuroscience of Thought Laboratory at the University of British Columbia in Canada.
First, let’s consider content. Thinking isn’t the same as perceiving or sensing: all involve holding something before one’s mind, so to speak, but thoughts are distinct in that they are independent of any stimulus produced by the thing being thought about.
In terms of how they arise, Christoff identifies three streams that feed into our consciousness to instigate thoughts: exteroceptive (from the outside world), interoceptive (from your organs and internal physiological environment) and conceptive (a term she uses to describe input that “wells up” from the subconscious in the form of , including mind wandering or daydreaming, as opposed to intentional thought such as reasoning and problem-solving).
Five kinds of thought
Within content, there is form. There are five main kinds of thought, according to at the University of Nevada, Las Vegas, who invented “thought sampling”, in which volunteers record their current inner experience when prompted randomly by a beeper. This process reveals that a thought can be verbal, visual, emotional, founded in bodily sensations or unsymbolised (none of the above, yet still distinct) – or a mixture of these. There is enormous variation between individuals in terms of how they think, says Hurlburt, even if many of us fail to recognise this.
As for the nature of thought, or what thoughts look like in the brain, Christoff uses functional magnetic resonance imaging to explore this. “For sure there are neural correlates,” she says. Some of the brain activity simply reflects the kind of thought being had – for example, a visual thought will show activation in the visual cortex.
More surprising is : about 3 seconds beforehand, there is activity in parts of the default mode network, which generally fires up when your brain is idling, and also in brain regions associated with memory. The latter have unusually diverse connections, which might help explain why spontaneous thoughts are so eclectic and arbitrary.
Neuroimaging can give us a general idea of what someone is thinking, then. But Christoff doesn’t believe it will ever accurately interpret the subjective experience of thinking and thus make it possible to read people’s minds – something that has been touted as a goal for the brain-computer interfaces being pursued by Elon Musk’s Neuralink, among other companies. “The mind emerges out of a physical substrate, the brain, and the relationship of emergence is not deterministic,” she says.
