Trending Clinical Topic: Brain Stimulation

Ryan Syrek


September 02, 2022

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New findings regarding the potential of brain stimulation to boost memory, improve attention-deficit/hyperactivity disorder (ADHD) symptoms, and treat depression resulted in this week's top trending clinical topic. A new study in 150 adults aged 65-88 years found that transcranial alternating current stimulation (tACS) for 20 minutes over 4 consecutive days had a lasting effect on memory (see Infographic).

Most patients involved in the study had typical memory loss or mild cognitive impairment (MCI). Electrical currents were delivered through electrodes embedded in a cap. Targeting the inferior parietal cortex at a low frequency of 4 Hz selectively improved working (short-term) memory without affecting long-term memory. Alternatively, targeting the dorsolateral prefrontal cortex at 60 Hz selectively improved long-term memory without affecting short-term memory. The rate of memory improvement during the 4-day intervention predicted the size of the memory benefit at the 1-month timepoint. Participants who had lower baseline cognitive function demonstrated larger, more enduring improvements in memory.

Instead of tACS, separate research recently found that transcranial direct current stimulation (tDCS) improved attention among patients with ADHD who were not taking stimulants. In the study, 64 adults were randomly assigned to receive either active or sham stimulation. All participants had moderate or severe symptoms of inattention, with an inattention score of 21 or higher on the clinician-administered Adult ADHD Self-Report Scale version 1.1 (CASRS). The scale includes nine questions related to inattention symptoms (CASRS-I) and nine related to hyperactivity-impulsivity symptoms (CASRS-HI). The score can vary from 0 to 36 for each domain. The mean inattention score on CASRS-I at week 4, the primary outcome, was 18.88 in the active tDCS group vs 23.63 in the sham tDCS group. The estimated Cohen d was 1.23 (95% CI, .67-1.78), indicating at least a moderate effect. About one third of patients (34.3%) in the active tDCS group achieved a 30% reduction in CASRS-I score compared with 6.2% in the sham tDCS group.

Noninvasive brain stimulation may also be beneficial in treating chronic anosmia or hyposmia associated with COVID-19. Approximately 1% of patients with COVID experience long-term smell loss, which represents a substantial number, given the global spread. Results of a small, double-blind, sham-controlled study showed that anodal tDCS (A-tDCS) combined with olfactory training (OT) provided notable and durable improvement in seven patients with persistent COVID-19–related hyposmia or anosmia. The participants had a score of less than 12 on the Sniffin' Sticks identification subtest and were not using medications for alleviating olfactory symptoms. Smell performances were assessed immediately prior to stimulation (t0) and rated on a scale of 0-10. In the 20-minute OT session, patients sniffed 10 odors in a random order for 10 seconds each and were then asked to identify the smell and rate its intensity. A-tDCS or sham therapy was administered at the same time. The smell assessment was repeated immediately after sham therapy (t1), A-tDCS (t2), and 3 months from the end of stimulation (t3). Both subjective and objective measures showed a statistically significant improvement at t2 and t3, with average measurements doubled or even tripled compared with t0 and t1. In addition, all patients demonstrated notable improvement in smell performance.

Not all of the news about brain stimulation was positive. A recent study found that tDCS did not augment cognitive-behavioral therapy (CBT) in patients with major depressive disorder (MDD). Results of a multicenter, placebo-controlled, randomized clinical trial showed that adjunctive tDCS was not superior to sham tDCS plus CBT or CBT alone. The multicenter study included adults aged 20-65 years with a single or recurrent depressive episode who were either not receiving medication or receiving a stable regimen of selective serotonin reuptake inhibitors or mirtazapine. A total of 148 participants (89 women, 59 men) with a mean age of 41 years were randomly assigned to receive CBT alone (n = 53), CBT+ tDCS (n = 48), or CBT + sham tDCS (n = 47). A total of 126 patients completed the study. The primary outcome was the change in Montgomery-Åsberg Depression Rating Scale (MADRS) from baseline to post-treatment in the intention-to-treat sample. At baseline, the average MADRS score was 23.0. In each of the study groups, MADRS scores were reduced by a mean of 6.5 points (95% CI, 3.82-9.14 points). The Cohen d value was -0.90 (95% CI, -1.43 to -0.50), indicating a significant effect over time, the researchers report. However, they add, "there was not significant effect of group and no significant interaction of group x time, indicating the estimated additive effects were not statistically significant."

Although brain stimulation may not have improved upon CBT in MDD, the potential effects on memory, ADHD symptoms, and smell impairment after COVID were enough to garner much attention. Those findings resulted in the emerging intervention becoming the top trending clinical topic of the week.

Learn more about deep brain stimulation.


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