Some knowledge of the brain

Nowadays, we are often shown coloured brain images from MRI scans, with the explanation that this allows us to detect which areas of the brain are more or less active at a given moment (which would justify these areas being responsible for a given action).

But apart from the fact that we know that the networks are interconnected and therefore spread across several areas of the brain, the reality is not nearly as precise. The coloured areas in functional magnetic resonance imaging (fMRI) do not directly represent brain activity, but rather neuronal correlates and oxygen requirements, the interpretation of which can be subject to error. The colours seen in an fMRI image (red, orange, yellow) do not indicate the intensity of activation, but the probability that an area is involved in a given task.

fMRI is a neuroimaging technique that measures brain activity by observing changes in cerebral blood flow. It detects regions of the brain that consume more energy. However, fMRI has limited temporal resolution: at best, it provides one image per second (or every 500 milliseconds under optimal conditions). This means that fMRI cannot capture the rapid dynamics of neuronal activity.

This means that the signals can be affected by thoughts unrelated to the task in hand, which can distort the results. For example, you're supposed to be concentrating on reading a book and you have a flash of memory, such as the memory of a dish you like.

It is therefore important to note that fMRI provides an indirect measure of brain activity, and that its interpretation requires a degree of caution.