Every Tuesday and Thursday morning for a year and a half, Russell Poldrack, a psychologist at Stanford University in US, took MRI scans of his brain for 10 minutes.
Poldrack also fasted and drew blood on Tuesdays, which was analysed to draw connections between brain function and gene expression.
This step also showed definitive - and surprising - evidence of just how the brain reorganises itself when it is low on coffee.
Such an influence had never been observed before. In particular, the connection between the somatosensory motor network and the systems responsible for higher vision grew significantly tighter without caffeine.
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"That was totally unexpected, but it shows that being caffeinated radically changes the connectivity of your brain," Poldrack said.
"We don't really know if it's better or worse, but it's interesting that these are relatively low-level areas. It may well be that I'm more fatigued on those days, and that drives the brain into this state that's focused on integrating those basic processes more," he said.
These messages are communicated over more than a dozen networks, sets of functional areas of the brain that preferentially talk to one another.
There are multiple networks for vision, a somatosensory/motor network, and there are others that are attributed to attention or task management. Collectively, these are known as the connectome.
Previously produced connectome maps have consisted of snapshots of individual brains, averaged together to identify general networks between different functional areas of the brain.
"Easily the biggest factor we found in terms of affecting my brain connectivity was whether I had had breakfast and caffeine or not," Poldrack said.
The study was published in the journal Nature Communications.