Proceedings #32: Effects of cerebellar delta and theta frequency tACS on cognitive performance in patients with schizophrenia

Abstract

Schizophrenia is associated with impairments across several cognitive functions, including reaction time, prospective time estimation, working memory, verbal learning and memory, attention, and executive functions. Transcranial alternating current stimulation (tACS) to the dorsolateral prefrontal cortex (DLPFC) is an effective non-invasive technique that may hold clinical relevance for the treatment of neuropsychiatric symptoms such as psychosis (delusions and hallucinations), depressive mood, anxiety, irritability/lability, apathy, euphoria, disinhibition, and agitation/aggression. However, DLPFC stimulation may not be very effective for cognitive and executive functions. Recent evidence has been suggested the role of cerebellum in cognitive and executive tasks but the effects of cerebellar tACS in patients with schizophrenia are ambiguous. The aim of the current study was to investigate the therapeutic potential of delta and theta frequency tACS of the cerebellar vermis on cognition in patients with schizophrenia. We used interval-time-estimation task (3 s and 12 s) that could represent both cognitive and executive functions. EEG signals were collected from the centro-medial (“Fz/Cz”) and other locations during interval- timing tasks before and after the tACS. We applied anodal stimulation on cerebellar region and cathodal lead was located on the shoulder. We also examined the efficacy of stimulation based on cognitive scores pre/post cerebellar stimulation. Patients with schizophrenia showed reduction in accurately estimation of 3 and 12 second intervals as compared to healthy control subjects. Single session of either delta or theta frequency cerebellar tACS did not influence interval-timing performance in patients. Time-frequency spectrograms showed no significant changes in oscillatory activity around 3 s and 12 s cue events after delta frequency cerebellar tACS at the centro- medial cortical region. However, theta tACS increased oscillatory activity around cues. Change in activity was more prominent in lower frequency band (4-8 Hz) between 500-1000 ms from the cue events. Increased oscillatory activity was observed around the response time. These results speculate that theta tACS improved task-related lower frequency oscillations but did not affect behavioral response due to the delayed (at 500-1000 ms) cue-related evoked activity as compared to normal subjects (at 0-500 ms). We suggest that cerebellar neuromodulation approach, with appropriate stimulation parameters, could be an alternative therapeutic strategy to improve cognitive and executive functions in patients with schizophrenia and other neuropsychiatric diseases.