2023-05-29 07:41:34
How transcranial magnetic stimulation alters the brain in ways that dispel depression has until now remained a mystery. This new research reveals that the treatment works by reversing the direction of abnormal brain signals. Furthermore, research suggests that these contra-flows of neural activity between key areas of the brain might be a biomarker for the diagnosis of depression.
Neural signals in the wrong direction
“The hypothesis retained is that TMS modifies the flow of neuronal activity in the brain”explains Dr. Anish Mitra, researcher in psychiatry and behavioral sciences.
The study: the team of bioengineers and neurologists developed a mathematical tool to analyze functional magnetic resonance imaging, or fMRI – commonly used to locate active areas in the brain. This new analysis technique focuses on minute differences in timing between the activation of different brain areas, which can indicate the direction of this activity.
An approved treatment, over 5 days: today, the US FDA-approved treatment, known as Stanford Neuromodulation Therapy, incorporates advanced imaging technologies to guide stimulation with patterns of high-dose magnetic pulses capable of altering the brain activity linked to major depression. Compared to traditional stimulation techniques that require daily sessions over several weeks or even months, the new technique involves 10 sessions per day for only 5 days.
New sightings: the analysis is carried out on 33 patients diagnosed with treatment-resistant major depressive disorder, 23 of whom received the new treatment and 10 a placebo treatment, whose data were compared with those of 85 controls without depression. Analysis of whole-brain fMRI data reveals that one specific connection stands out:
- in the normal brain, the anterior insula, a region that integrates bodily sensations, sends signals to another region the anterior cingulate cortex, which regulates emotions;
- in the depressed brain, this flow of activity turns out to be reversed: the anterior cingulate cortex sends signals to the anterior insula;
- the more severe the depression, the higher the proportion of signals flowing in the wrong direction.
In practice :
“It’s almost as if you’ve already decided ‘how you’re going to feel’, and how you feel is already predetermined,”
explain the researchers. “In clinical practice, this fits well with how many patients react: even positive things suddenly don’t bring them any pleasure.”
How does the new TMS work? It manages to redirect the flow of neuronal activity in the right direction, and in just 1 week, which induces the alleviation of depressive symptoms in patients. Those with the most severe depression, with the most misdirected brain signals, were found to be the most likely to benefit from treatment.
A new biomarker for depression? These neural signals in the opposite direction, quite observable on imaging, indeed constitute a possible biomarker.
“And this is the first time in psychiatry where this particular change in a biology – the flow of signals between these two regions of the brain – predicts the change in clinical symptoms.”
A characteristic present in all depressive patients? Unfortunately no. Not all patients with depression exhibit this abnormal flow of neural activity, especially in milder cases of depression. However, for more severe cases, the biomarker helps predict the response to TMS.
The trial will be replicated in a larger group of patients with new interest in the direction of brain activity hidden in fMRI data.
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