Transcranial electrical stimulation (tES) of the brain can have variable effects, plausibly driven by individual differences in neuroanatomy and resulting differences of the electric fields inside the brain. Here, we integrated individual simulations of electric fields during tES with source localization to predict variability of transcranial alternating current stimulation (tACS) aftereffects on α-oscillations. In two experiments, participants received 20-min of either α-tACS (1 mA) or sham stimulation. Magnetoencephalogram (MEG) was recorded for 10-min before and after stimulation. tACS caused a larger power increase in the α-band compared to sham. The variability of this effect was significantly predicted by measures derived from individual electric field modeling. Our results directly link electric field variability to variability of tACS outcomes, underline the importance of individualizing stimulation protocols, and provide a novel approach to analyze tACS effects in terms of dose-response relationships.

It has been stated that active-transmission electrodes should improve signal quality in mobile EEG recordings. However, few studies have directly compared active-and passive-transmission electrodes during a mobile task. In this repeated measurement study, we investigated the performance of active and passive signal transmission electrodes with the same amplifier system in their respective typical configurations, during a mobile auditory task. The task was an auditory discrimination (1,000 vs. 800 Hz; counterbalanced) oddball task using approximately 560 trials (15% targets) for each condition. Eighteen participants performed the auditory oddball task both while standing and walking in an outdoor environment. While walking, there was a significant decrease in P3 amplitude, post-trial rejection trial numbers, and signal-tonoise ratio (SNR). No significant differences were found in signal quality between the two electrode configurations. SNR and P3 amplitude were test-retest reliable between recordings. We conclude that adequate use of a passive EEG electrode system achieves signal quality equivalent to that of an active system during a mobile task.

Variability of transcranial electrical stimulation (tES) effects is one of the major challenges in the brain stimulation community. Promising candidates to explain this variability are individual anatomy and the resulting differences of electric fields inside the brain. Here, we integrated individual simulations of electric fields during tES with source-localization to predict variability Individual differences in electric fields explain tES variability 2 of transcranial alternating current stimulation (tACS) aftereffects on α-oscillations. Forty participants received 20 minutes of either α-tACS (1 mA) or sham stimulation. Magnetoencephalo-

Background Several studies examined the influence of subthalamic nucleus–deep brain stimulation (STN‐DBS) on quality of life (QoL) in patients with Parkinson's disease (PD). However, it is unclear whether this effect differs between age groups and disease durations and whether it stays consistent over time. Objectives We assessed the influence of stimulation duration, disease duration, and age at surgery on QoL after STN‐DBS. Methods We systematically searched for studies reporting the results of the Parkinson's Disease Questionnaire 39 or 8. Studies were included if they investigated the time passed since STN‐DBS or if their study cohort fell into the range of one of the following age groups: younger than 60 years or between 60 and 70 years. For each condition, a standardized mean difference meta‐analysis was performed. Furthermore, all studies were categorized into short or long disease duration at surgery using a median split. Results A total of 23 studies reporting the cumulative outcome of 76 to 802 PD patients were included in this analysis. The results demonstrate a substantial improvement of QoL after DBS that remains stable over 36 months. QoL falls to preoperative scores 60 months after surgery. However, only 3 studies could be included in this analysis. Both younger and older PD patients profit in QoL from STN‐DBS, independent of the disease duration. Conclusions The results of this analysis show an impressive improvement in QoL after STN‐DBS, with a loss of QoL 60 months after DBS surgery. This highlights the need to explore the factors influencing QoL after STN‐DBS to prevent or delay a decline in QoL.

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