Keypoint: Established focal neuromodulation therapies are generally considered safe from a cognitive standpoint.
Focal neuromodulation therapies for psychiatric and neurological conditions are not generally associated with adverse cognitive effects, according to a review published in Nature Reviews Psychology. In fact, focal direct-to-brain neuromodulation has the potential to improve aspects of cognition by treating the underlying disorder.
Health care providers and researchers are increasingly using focal neuromodulation therapies – such as transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), and ablative techniques – to disrupt aberrant brain networks that contribute to clinical symptoms in neurological and psychiatric disorders. However, there is still concern that these approaches may also negatively affect normative cognitive processes.
To address these concerns, investigators from Sunnybrook Research Institute in Canada conducted a systematic review to assess the effects of repetitive TMS, DBS, and ablative techniques on cognition among patients with major depressive disorder (MDD), obsessive-compulsive disorder (OCD), schizophrenia, Parkinson disease (PD), essential tremor, and Alzheimer disease (AD).
Most studies employing repetitive TMS target the dorsolateral prefrontal cortex with the motivation of improving executive function. This treatment approach has been granted regulatory approval for use by the United States Food and Drug Administration (FDA) for treatment-resistant MDD.
The body of research about repetitive TMS indicated that this approach likely did not impair cognition among patients with MDD, treatment-resistant OCD, schizophrenia, PD, or AD. Some studies reported improvements in cognition, however, the studies had conflicting findings and differing lengths of follow-up.
Deep brain stimulation is an invasive modality that involves implanting electrodes unilaterally or bilaterally into target regions or fiber tracts. The implanted electrodes are connected to a power stimulator implanted in the chest. The FDA approved this technique for the treatment of PD and essential tremor and has regulatory approval by the US FDA for the treatment of OCD.
In general, no evidence indicated that DBS changed or improved cognition among patients with MDD or OCD. However, some evidence indicated verbal fluency declined among patients with PD and essential tremor. In AD there was limited evidence supporting the use of DBS to slow cognitive decline.
Ablative techniques involve surgically creating focal lesions in the brain. Some examples of lesional techniques include radiofrequency ablation, Gamma Knife radiosurgery, and magnetic-resonance-guided focused ultrasound.
Ablative techniques are not associated with substantial impairments to cognition among patients with MDD, OCD, PD, and essential tremor. However, the risk for post-operative cognitive decline was lower after magnetic resonance-guided focused ultrasound relative to other approaches.
Review authors concluded, “Overall, clinicians and patients can be reassured that the neuromodulation therapies used to treat the psychiatric and neurological conditions discussed in this Review do not generally cause cognitive impairment.”
The review authors noted that cognitive effects were often assessed as a secondary outcome which may have decreased the power for the studies to detect cognitive changes. In addition, many studies had small sample sizes, lacked a control group, and did not have long-term follow-up data to evaluate outcomes after a sufficient amount of time.
Note: This article originally appeared on Psychiatry Advisor
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