Last updated: Sun, Jul 28, 2024
Some of the experimental manipulations used in animal research aren't done in research with human subjects. It's not allowed to do “destructive testing” (as it's called in engineering) on people. On the other hand, people can report their sensations and reactions. There's never any question as to whether the experience of a human subject translates to humans, although there is often a question about how well it translates between people.
One of the more interesting types of research that takes advantage of our ability to talk takes place in the course of certain brain procedures. Surgeons use electrical probes to precisely locate areas of the brain so that they can perform operations on them, such as killing a small area of tissue to prevent dangerous seizures. In the process, which is done on anesthetized but awake patients, the surgeon applies a small electrical current to “fire” the neurons at the tip of the electrode. The patient then reports to the surgeon what he/she felt. This identifies the function of the stimulated area, or at least some of the functions that it is involved in.
We already met brain imaging technologies in Neuroimaging and Pain Measurement. Functional magnetic resonance imaging, fMRI, is used to measure blood flow within the brain. Researchers can use this technique to determine which brain areas are used while the subject is performing a task or undergoing a painful stimulus, and they can compare blood flow between groups of patients. For example, they might compare fibromyalgia patients with normal controls to detect differences between the groups. This helps by revealing what's going on inside that is different between the groups.
Over the past seven or eight years a number of research groups have used a related technology to measure the density of gray matter (neural cells) and white matter (axons) in different patient groups. They have discovered that chronic pain patients often have less gray matter in some brain areas active in pain processing than do normal patients. The gray matter loss can be significant, but seems to be at least partially recoverable if the pain can be stopped. The full significance of this is still under investigation, but may yield clues that are helpful in treating pain or in designing treatments.
A further refinement of technology has allowed researchers to explore the density and orientation of white matter in the brain. The white matter, composed primarily of myelin-covered axons, is the means of connection among the regions of the brain, so differences suggest that pain either causes or in some manner is caused by differences in brain connectivity.