September 27, 2022

Are brain scans telling the truth?

Functional magnetic resonance image scans have been used as lie detectors which have been used in murder trials as well as testing whether conservatives are psychopaths or liberals are more broad-minded. Yet recent studies suggest that the scans are only giving insight into a very small part of the brain.

Functional magnetic resonance image scans have been used as lie detectors which have been used in murder trials as well as testing whether conservatives are psychopaths or liberals are more broad-minded. Yet recent studies suggest that the scans are only giving insight into a very small part of the brain.

Most research with fMRI scans have very small sample sizes. The very useful blog Neuroskeptic reviews two recent articles which had very large sample sizes. The author says:

“Both studies found that pretty much the whole brain ‘lit up’ when people are doing simple tasks. In one case it was seeing videos of people’s faces, in the other it was deciding whether stimuli on the screen were letters or numbers.

“With all that data, the authors could detect effects too small to be noticed in most fMRI experiments, and it turned out that pretty much everywhere was activated. The signal was stronger in some areas than others, but it wasn’t limited to particular ‘blobs’.

“So conventional fMRI experiments may just be showing us the tip of the iceberg of brain activity. In a small study, only the strongest activations pass the statistical threshold to show up as blobs, but that doesn’t mean the rest of the brain is inactive. It just means it’s less active. The idea that only small parts of the brain are ‘involved’ in any particular task may be a statistical artefact.”

Will this spark a debate over the usefulness of brain imagining? Back in 2009, a controversial paper, “Voodoo Correlations in Social Neuroscience” claimed that much of the data from fMRI scans was junk. Perhaps we are about to see another wave of scepticism. 

Michael Cook
fMRI
neuroscience