Part 3: Can I Know What’s on Your Mind?

In this third installment concerning military technology, we are going to look at functional magnetic resonance imaging (fMRI). Magnetic resonance imaging is one of the most popular diagnostic tools because it is non-invasive and safe. MRI can be used to determine if a bone is broken or if a tumor is present because it detects differences in tissue density. Various forms of MRI, such as functional MRI or real-time MRI are used to investigate specific parts of the body or specific activities. Functional magnetic resonance imaging analyzes brain activity. The military is interested in using fMRI as a more accurate lie detector than the typical polygraph.

Polygraph tests usually measure changes in physiology that are thought to be associated with lying. For example, it is assumed that a person’s heart rate, breathing rate, and sweat production will likely increase if the person is lying. The lie detector will measure when these factors change compared to a baseline. However, polygraph tests are controversial because they can result in false-positives or can be faked so that the person’s physiology does not appreciably change when he is lying. Therefore a more accurate lie detector is needed. Since fMRI provides information on what part of the brain is active, the theory is that it would serve as a more accurate lie detector.

But does fMRI really show us what someone is thinking? When a particular area of the brain becomes active, it consumes more oxygen. The body responds by sending oxygenated blood to the part of the brain that is actively consuming oxygen. FMRI measures this blood flow. This is the observed phenomenon. The assumption is that this correlates to a particular thought pattern. Furthermore, many of these assumptions are based on the idea that there are regions of the brain where certain functions take place (such as the memory part of the brain, or the decision-making part of the brain), which is also a controversial. Scientists who use fMRI for lie detection assume that a lie is neurologically more complicated than the truth, so if someone is telling a lie, his fMRI scan will show a more complicated pattern.

Importantly, while fMRI may be advertised as being more precise or definitive, it is still a qualitative measurement, just like the polygraph. As National Academy of Science magazine, In Focus, suggests, “But brain scans encounter the same problem as polygraphs: no physiological indicator, or neural activity pattern, exists that has a one-to-one correspondence with mental state.” Furthermore, because of how fMRI acquires a signal, there is approximately a 6-second delay between the brain signal and the image display, meaning that the actual part of the brain that becomes active in response to a stimulus is still only an estimate.  Researchers have been working on improvements in the time lag. For example, they have looked at heart activity using “real-time MRI.” However, neurological activity is very fast, and blood flow is relatively slower, so there may be a fundamental issue with relating blood flow with certain neurological activity.

Tennison and Moreno discuss in their article on military technology the ethics of using brain scanning technology for lie detection. They focus on whether brain scans would violate the guarantee against self-incrimination, and whether they would constitute an inappropriate search and seizure. I would say that the bigger ethical question is amount of legal weight we should place on a technology that is qualitative and subjective. Should brain scans be considered definitive proof that a person is lying? Technology helps us in many ways. DNA data has exonerated and incarcerated many individuals who might have been given the wrong sentence. But we should be careful how much we can trust the technology. Yes, the fMRI can show us brain activity, but it does not show us a man’s thoughts.

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