When most people hear about electroconvulsive therapy, or ECT, it usually conjures up terrifying images of cruel, outdated, and pseudo-medical procedures. This perception of ECT, formerly known as electroshock therapy, as dangerous and ineffective has been reinforced in pop culture for decades — consider the 1962 novel turned Oscar-winning film, “One Flew Over the Cuckoo’s Nest,” in which an unruly patient is subjected to ECT as punishment by a tyrannical nurse.
Despite this stigma, ECT is a highly effective treatment for depression – up to 80% of patients experience a reduction in symptom severity of at least 50%. For one of the most debilitating diseases in the world, I think it’s surprising that ECT is rarely used to treat depression.
Contributing to the stigma surrounding ECT, psychiatrists still don’t know exactly how it heals a depressed person’s brain. ECT uses highly controlled doses of electricity to induce a brief seizure under anesthesia. Often the best description you’ll get from a doctor as to why that brief bout can alleviate symptoms of depression is that ECT “resets” the brain—an answer that can be vague and disturbing to some.
As a data-obsessed neuroscientist, I was also dissatisfied with this statement. In our recently published study, my colleagues and I in Bradley Voytek’s lab at UC San Diego discovered that ECT might work by resetting the brain’s background electrical noise.
Listening to brain waves
To study how ECT treats depression, my team and I used a device called an electroencephalogram, or EEG. It measures the brain’s electrical activity – or brain waves – via electrodes placed on the scalp. You can think of brain waves as music played by an orchestra. Orchestral music is the sum of many instruments together, just as EEG measurements are the sum of the electrical activity of millions of brain cells.
Two types of electrical activity form brain waves. The first, oscillations, resemble the highly synchronized, melodic music you might hear in a symphony. The second, aperiodic activity, is more like the asynchronous sound you hear when musicians tune their instruments. These two types of activities coexist in the brain and together create the electrical waves that an EEG records.
It is important that vocal sounds and symphonic music should not be confused with each other. They clearly arise from different processes and serve different purposes. The brain is similar in this way: aperiodic activity and oscillations are different because the biology that drives them is different.
However, the methods that neuroscientists have traditionally used to analyze these signals are unable to distinguish between the oscillations (symphony) and the aperiodic activity (tuning). Both are critical to the orchestra, but until now neuroscientists have mostly ignored – or missed altogether – aperiodic signals because they were thought to be just background noise from the brain.
In our new research, my team and I show that ignoring aperiodic brain activity likely explains the confusion about how ECT treats depression. It turns out we’ve been missing this signal all along.
Connecting aperiodic activity and ECT
Since the 1940s, ECT has been associated with an increase in slow oscillations in patients’ brain waves. However, these slow oscillations have never been linked to the way ECT works. The extent to which slow oscillations occur is not consistently related to the extent to which symptoms improve after ECT. Also, ideas about how the brain produces slow oscillations have no link between these processes and the pathology underlying depression.
Because these two types of brain waves are difficult to separate in measurements, I wondered whether these slow oscillations were indeed mismeasured aperiodic activity. Returning to our orchestral analogy, I believed that scientists had incorrectly identified the mood sounds as symphony music.
To investigate this, my team and I collected three EEG data sets: one from nine patients with depression who underwent ECT in San Diego, another from 22 patients in Toronto who received ECT, and a third from 22 patients in Toronto who participated in a clinical trial of magnetic seizure therapy. , or MST, a newer alternative to ECT that starts an attack with magnets instead of electricity.
We found that aperiodic activity increases on average by more than 40% after ECT. In patients receiving MST treatment, aperiodic activity increases more modestly, by approximately 16%. After taking into account changes in aperiodic activity, we found that slow oscillations don’t change much at all. In some patients, slow oscillations were not even detected, and instead aperiodic activity dominated their EEG recordings.
How ECT treats depression
But what does aperiodic activity have to do with depression?
A long-standing theory about depression states that severely depressed patients have too few brain cells called inhibitory cells. These cells can turn other brain cells on and off, and maintaining the balance between these on and off states is critical to healthy brain function. This balance is especially relevant in depression, because the brain’s ability to shut down cells plays an important role in how it responds to stress, a function that makes people particularly vulnerable to depression if it’s not working properly.
Using a mathematical model of cell type-based electrical activity, I linked increases in aperiodic activity, such as that observed in ECT patients, to a dramatic change in the activity of these inhibitory cells. This change in aperiodic activity can restore the crucial on/off balance in the brain to healthy levels.
Although scientists have been recording EEGs of ECT patients for decades, this is the first time that brain waves have been linked to this specific brain malfunction.
Although our sample size is relatively small, our findings indicate that ECT and MST likely treat depression by resetting aperiodic activity and restoring the function of inhibitory brain cells. Further research may help to destigmatize ECT and highlight new directions for the research and development of depression treatments. Listening to the brain’s non-musical background noise can help solve other mysteries, such as how the brain changes with aging and diseases like schizophrenia and epilepsy.
This article is republished from The Conversation, an independent nonprofit organization providing facts and analysis to help you understand our complex world.
It was written by: Sydney E. Smith, University of California, San Diego.
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Sydney E. Smith does not work for, consult with, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.