Efficacy of Adjuvant Cerebellar Theta Transcranial Alternating Current Stimulation In Cognitive Symptoms of Schizophrenia: An EEG-Based Randomized Sham-Controlled Trial

Cognitive impairment in schizophrenia is one ofthe most difficult symptom domains to treat with pharmacotherapy andpsychotherapy available at present.

Noninvasive neuromodulation techniques useeither magnetic or electrical stimulation to directly target specific brainareas, alter neuronal oscillations, cause long-term neuroplasticity changes. Variousneuromodulation techniques including rTMS, tDCS, tRNS, tACS etc. are found tobe well tolerated. Their effect in improving cognitive impairments inschizophrenia is found to be equivocal. Evidence is limited due to majority ofresearch having small sample size, some having contradictory findings and lackof evidence regarding long-term efficacy. (Kar and Singh, 2022) tACS is moreeffective at entraining the endogenous brain oscillations as compared to tDCS asit mimics the alternating nature of brain oscillations. (Elyamany et al., 2021)

According to a study by Parker et. al. (2014),considering the extensive anatomical connection between cerebellum, thalamus, prefrontaland anterior cingulate cortex, cerebellar stimulation may restore prefrontalfunction and improve cognition in schizophrenia. No serious adverse event wasreported in any study administering tACS to cerebellum in healthy or diseasedpopulation. Singh et. al. conducted a study where single session of theta tACSwas applied on cerebellar vermis in schizophrenia patients which led to changesin theta activity in frontal cortex but no significant change in performance ona core cognitive-timing task, concluding that repeated or longer duration tACSsessions may induce long-lasting or more robust changes in midfrontal oscillatoryactivity at lower frequency bands that may lead to significant behaviouralimprovement. (Singh et al., 2019)