As the reverence with which Swedish zoologist Carl Linnaeus is held symbolises, classification is central to human psychology. Now, new research coming from the lab of Earl Miller at the Massachusetts Institute of Technology’s Picower Institute for Learning and Memory sheds light on how mysterious “brainwaves” may help us to understand the way the brain puts things into categories.
Brainwaves, also known as neural oscillations, are the rhythmic electrical activation of large groups of neurons. These oscillations are labelled according to the frequency with which they occur, and different frequencies are loosely correlated with certain kinds of cognitive function.
The alpha brainwave, for example, was first discovered by the Hans Berger, the German psychiatrist who invented the electroencephalograph (EEG) in 1924. It operates in the frequency range of 7.5 to12.5 hertz and is associated with mindful relaxation.
There are many others and, for the most part, science has yet to truly understand them. Nonetheless, the team from Miller’s lab has noted some fascinating correlations between gamma and beta waves and classification.
“Categorisation is a fundamental cognitive mechanism,” says Miller. “It’s the way the brain learns to generalise. If your brain didn’t have this ability, you’d be overwhelmed by details of the sensory world. Every time you experienced something, if it was in different lighting or at a different angle, your brain would treat it as a brand new thing.”
The new research, published in the journal Neuron, and led by Andreas Wutz and Roman Loomis, sought to investigate the connection between different types of classification with brainwaves and the different locations from which they emanate.
The scientists measured the brainwaves of animals as they completed different kinds of classification tasks and noticed something remarkable: when the test subjects were putting together objects that looked similar, such as apples, their brains exhibited strong gamma waves at the front of the prefrontal cortex.
This part of the brain is strongly associated with decision-making and complex cognition, among other things. When they were putting together objects that were more abstractly related, such as a screwdriver and a drill, there was a peak of beta waves in the back of prefrontal cortex. Different parts of the brain, then, seem to be associated with different kinds of classification.
The power of these waves also seemed to peak when the animal subjects were making correct category judgments and could often be detected before the judgment itself was made.
If these findings hold true in humans, say the researchers, then they could help in understanding aspects of some autism spectrum disorders, which are often associated with impaired ability to classify objects.
Stephen Fleischfresser is a lecturer at the University of Melbourne's Trinity College and holds a PhD in the History and Philosophy of Science.
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