Most mental health diagnoses are made without ever looking at the brain. Clinicians and researchers have debated for decades whether brain imaging is helpful and, while research on the technology is promising, there’s still much to be learned before it becomes a routine part of care.
The current approach to diagnosing mental illness is informed by the Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychological Association. During an evaluation, a patient self-reports their symptoms, and the clinician uses the manual to find which disorder matches best.
Because the DSM was not developed with neuroscience (it was created before the invention of brain imaging tools available today), billions of dollars have gone towards research to identify biomarkers that can explain the biological causes of mental illnesses. That attempt produced little, but research on brain imaging technology carried on and a couple tools in particular have made notable headway.
The first is magnetic resonance imaging (MRI). MRIs can detect subtle abnormalities in structure and function in the brain between healthy subjects and patients with mental illness.
For example, MRI studies have found that those with bipolar disorder and major depressive disorder have thinner gray matter in various parts of the brain than healthy patients. Other studies have found atypical neural responses related to emotional processing and regulation in patients with mood disorders.
Beyond potential for diagnosis, brain imaging may also be able to validate clinical treatment. For example, MRI scans have even shown tangible differences in the brain after talk therapy.
One randomized study of 14 participants reported that 70% of patients with panic disorder showed visible healing in their brains after four therapy sessions, compared to 7% in the control group. Comparably, a randomized study of 59 patients found that those who received therapy for depression had increased amounts of gray matter in the cortex compared to those who did not receive therapy.
The second technology that has shown potential is single-photon emission computed tomography (SPECT). These nuclear tests capture three-dimensional images of blood flow activity in different regions of the brain. They can find abnormalities invisible on anatomical scans, such as ultrasounds.
While originally used to evaluate strokes and seizures, SPECT brain scans have recently been used in some psychiatric cases. For example, they are one of the most reliable tools to differentiate between diagnoses of post-traumatic stress disorder and traumatic brain injury, which have similar symptoms.
Brain imaging can also be a crucial tool to determine whether symptoms are a result of mental illness or other physical causes, like toxic exposure and head trauma.
For example, a review of 12 studies (over 1,600 participants) found that 6% of patients originally thought to be experiencing an episode of psychosis had a MRI scan abnormality that led to a change in their diagnosis or treatment. Some of the conditions found to explain their symptoms were encephalitis, brain tumors, and dementia.
A qualitative study found that SPECT scans help uncover brain trauma in complicated psychiatric cases as well. Since patients may fail to remember or report head trauma to their clinicians during a mental health assessment, SPECT can be used for diagnosis, prognosis, and treatment for patients with suspected traumatic brain injury.
All that said, there remain many unknowns.
For example, while there is evidence that brain imaging can reliably monitor brain function, there are no adequate large-scale studies to prove it helps diagnose psychiatric disorders. All studies to date have had small patient groups, and biomarker research requires large sample sizes to be more certain that what smaller studies have suggested aren’t erroneous.
There’s also more work to be done to clarify the extent to which findings generalize. For example, researchers at Yale University replicated a study monitoring brain activity of trauma-exposed, emergency department patients with a new population: Israeli trauma survivors. While they could match clusters of brain activity observed in the first study, they couldn’t find an association with post-traumatic stress disorder symptoms like the other had.
There also are limitations of current imaging technology. For example, it can’t be used by itself to differentiate disorders when they present similarly. One study found that white matter alterations in various parts of the brain were almost identical in patients with attention deficit/hyperactivity disorder and autism spectrum disorder.
It seems unlikely that brain imaging will become a routine diagnostic tool in mental health care anytime soon – there is too much still to learn. But the research that does exist is promising. For now, imaging is at least a helpful tool for clinicians to rule in or out causes other than mental health conditions.
Research for this piece was supported by Arnold Ventures.
