Basic neuroscience teaches us how individual brain cells communicate with each other, like neighbours chatting over the garden fence. This is a vital part of brain function. Increasingly however neuroscientists are zooming out and studying the information processing that happens within and between neural networks across the entire brain, more akin to the complex flow of digital information constantly pulsing around the globe.
This has led them to realise the importance of what they call “brain entropy” – intense complexity and irregular variability in brain activity from one moment to the next, also marked by greater long-distance correlations in neural activity. Greater entropy, up to a point, is indicative of more information processing capacity, as opposed to low entropy – characterised by orderliness and repetition – which is seen when we are in a deep sleep or coma.
A new study in Scientific Reports is the first to examine whether and how ingesting a psychostimulant – in this case caffeine – affects brain entropy. The results show caffeine causes a widespread increase in cerebral entropy. This dose of neural anarchy is probably welcome, especially considered in light of another new paper, in PLOS One, which finds greater brain entropy correlates with higher verbal IQ and reasoning ability.
For the caffeine study, Da Chang at Hangzhou Normal University in China and other researchers scanned the brains of 60 participants – 30 men and women – at baseline, and also after they ingested a 200mg caffeine pill (roughly approximate to two cups of coffee). It was a “resting-state” scan meaning that the participants simply lay in the scanner doing nothing. For both scans, Chang’s team analysed changing neural activity levels from one moment to the next, and looked for correlations in activity across and within brain regions to calculate brain entropy. They also measured changes in cerebral blood flow across the brain.
The scans showed that caffeine increased brain entropy across nearly the entire cerebral cortex, but especially in “lateral prefrontal cortex, the DMN [default mode network, involving in day-dreaming and self-reflection], visual cortex, and motor network”, which the researchers linked to caffeine’s known beneficial effects on “attention, vigilance, and action/motion function.” There was little correlation locally between increased entropy and cerebral blood flow (which was reduced by caffeine), suggesting the effects of the caffeine were via influences on neuronal function, rather than due to vascular changes.
“Increased resting brain entropy indicates increased resting brain activity irregularity or complexity, suggesting an increase of information processing capacity in the resting brain,” the researchers said.
Meanwhile, a separate group led by Glenn Saxe at New York University’s School of Medicine used the same methods as Chang’s team to measure brain entropy in 900 healthy participants, who also completed measures of their verbal intelligence and reasoning ability outside of the scanner. The New York researchers defined brain entropy as “a measure of the brain’s overall flexibility or readiness to encounter unpredictable stimuli” and they found that it correlated with intelligence.
Specifically, superior vocabulary performance was associated with greater resting-state entropy in the left inferior frontal lobe, while superior reasoning ability was associated with greater entropy in that same region, but also in bilateral prefrontal areas.
Saxe and his colleagues said that “entropy in this context provides an indicator of the brain’s general readiness to process unpredictable stimuli from the environment” – a brain with greater entropy may in effect be better able to model and predict the outcomes of a complex, chaotic world. The researchers added, though, that they had not measured “the active use of brain states during a particular task”. Indeed, follow up research is now needed to see how brain entropy varies during performance of specific mental challenges, and how caffeine and other substances might affect entropy during such tasks.
In contrast to the entropy–intelligence association, participants’ age and years of education did not correlate with their IQ test scores. “These results suggest that entropy is a reliable predictor of intelligence, and provides unique information not captured by developmental status and educational status alone,” the researchers said.
The new findings add to past research measuring neural entropy that’s shown entropy is reduced in adults diagnosed with ADHD, for example, and in people addicted to cocaine. However, the story is not as simple as more entropy is good, less is bad. For instance, patients diagnosed with schizophrenia have greater neural entropy than healthy controls, perhaps indicative of “an underlying dysregulation of more complex functional networks”.
It will be interesting to see how the research on neural entropy develops in the future. For now, it is enough to marvel that as you enjoy your morning coffee, you are increasing the entropy throughout your brain – the bitter tonic is not merely waking you up, but apparently also boosting your brain’s useful anarchy, its complexity and information processing capacity.