| Paper authors: | Elizabeth Gregory, Ivan Torres, Daniel Blumberger, Jonathan Downar, Zafiris Daskalakis, Fidel Vila-Rodriguez |
| Year of paper publication: | 2021 |
| Post authors: | Alice Erchov, Sarah Kesler, Fidel Vila-Rodriguez |
| Download the research article: | Gregory (2021) Repetitive Transcranial Magnetic Stimulation Shows Longitudinal Improvements in Memory in Patients With Treatment-Resistant Depression |
Introduction
Did you know that poor mood is not the only way to diagnose depression? In fact, cognitive impairment – worsened thinking, concentration, and decision making – is one of nine criteria for the disorder. This impairment is even more common and severe among those who have treatment-resistant depression: a particular case where someone does not improve with standard antidepressant medications.
Repetitive transcranial magnetic stimulation (rTMS) is a neurostimulation treatment that is effective even for those with treatment-resistant depression. Interestingly, rTMS stimulates the same regions of the brain thought to be responsible for cognition, meaning it may improve thinking and decision-making for those with depression. We know this from past studies which have tested cognition in short-term periods immediately after treatment. Whether or not these changes persist over time is unknown.
This study assessed changes to cognition 3 months post-rTMS among a group of people with treatment-resistant depression and compared it to people without depression.
Methods
47 people with depression completed cognitive assessments before rTMS and 3 months after. To be classified as treatment-resistant, each of these 47 people had to have not responded to at least one antidepressant, or have tried but were not able to continue 2 or more due to side effects. These people were divided into two groups: those who were cognitively impaired (significantly worse cognitive function due to their depression, taking into account their pre-illness IQ) or relatively cognitively unimpaired (no worse cognitive function due to their depression, after taking into account pre-illness IQ).
Those with treatment-resistant depression received either standard rTMS or its accelerated version, iTBS. Treatments were delivered daily on weekdays, for 4-6 weeks. People received 20-30 treatments total.
Changes in cognition were compared between these 47 people with treatment-resistant depression and 43 “healthy controls”. These healthy controls were people without depression who were similar in age, sex, and IQ. This way, this study could identify the way rTMS affected those with depression specifically, and not just natural fluctuations in cognition or test performance over time.
| Cognitive Domain | Definition |
| Pre-illness IQ estimate | An estimation of an individual’s overall intelligence before the onset of depression |
| Verbal learning and memory | The ability to repeat back a list of words read out loud after a delay |
| Working memory | The ability to remember information while processing or using it to complete a task |
| Attention and set-shifting | The ability to keep or switch your focus on-demand throughout a task |
| Verbal fluency | The ability to easily and efficiently produce a list of related words from memory |
| Inhibitory control | The ability to control your impulses and ignore information that is irrelevant to a task at hand |
Results
Among those with treatment-resistant depression, 51% (24 people) were significantly cognitive impaired before rTMS across all domains. 49% (23 people) only experienced worse attention and task switching than healthy controls and were considered relatively cognitive unimpaired.
- Benzodiazepine medications were more common among those who were cognitively impaired
- For those who were cognitively impaired, rTMS significantly improved verbal learning and memory, 3 months post-treatment
- Improvements in verbal memory among this group were also related to improvements in depressive symptoms, overall
Those who were cognitively impaired and older tended to have higher improvements on their verbal learning and memory in response to treatment
Conclusion
rTMS was found to selectively improve verbal learning and memory in patients with treatment-resistant depression who experienced cognitive impairment. Possibly, rTMS can be used to help treat cognitive symptoms in other disorders through its theorized effects on brain structure and function. Some studies have found it can increase brain matter in regions responsible for memory.
Future studies with larger amounts of people are needed to confirm these effects. Knowing how rTMS may benefit cognition and how age and certain medications (i.e., benzodiazepines) can affect these outcomes may be important for clinicians to know.