title: Neurosensory effects of transcranial alternating current stimulation.
abstract: BACKGROUND
  Electrical brain stimulation can elicit neurosensory side effects that are unrelated to the intended stimulation effects. This presents a challenge when designing studies with blinded control conditions.
  
  
  OBJECTIVE
  The aim of this research was to investigate the role of different transcranial alternating current stimulation (tACS) parameters, i.e. intensity, frequency, and electrode montage, on the probability, duration and intensity of elicited neurosensory side effects.
  
  
  METHODS
  In a first study, we examined the influence of tACS on sensations of phosphenes, dizziness, pressure, and skin sensation in fifteen healthy subjects, during 8 s of stimulation with different amplitudes (1500 μA, 1000 μA, 500 μA, 250 μA), frequencies (2 Hz, 4 Hz, 8 Hz, 16 Hz, 32 Hz, 64 Hz), and montages (F3/F4, F3/C4, F3/P4, P3/F4, P3/C4, P3/P4). In a second study, ten healthy subjects were exposed to 60 s of tACS (1000 μA, 2 Hz versus 16 Hz, F3/F4 versus P3/P4) and were asked to rate the intensity of sensations every 12 s.
  
  
  RESULTS
  The first study showed that all stimulation parameters had an influence on the probability and intensity of sensations. Phosphenes were most likely and strongest for frontal montages and higher frequencies. Dizziness was most likely and strongest for parietal montages and at stimulation frequency of 4 Hz. Skin sensations and pressure was more likely when stimulation was performed across central regions and at posterior montages, respectively. The second study also revealed that the probability and the intensity of sensations were neither modified during more extended periods of stimulation nor affected by carry-over effects.
  
  
  CONCLUSIONS
  We demonstrated that the strength and the likelihood of sensations elicited by tACS were specifically modulated by the stimulation parameters. The present work may therefore be instrumental in establishing effective blinding conditions for studies with tACS.
authors.affiliation: Division of Functional and Restorative Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Division of Translational Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Neuroprosthetics Research Group, Werner Reichardt Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany.
authors.forename: Valerio
authors.initials: V
authors.lastname: Raco
authors.affiliation: Division of Functional and Restorative Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Division of Translational Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Neuroprosthetics Research Group, Werner Reichardt Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Bauer
authors.affiliation: Division of Functional and Restorative Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Division of Translational Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Neuroprosthetics Research Group, Werner Reichardt Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Olenik
authors.affiliation: Division of Functional and Restorative Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Division of Translational Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Neuroprosthetics Research Group, Werner Reichardt Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany.
authors.forename: Diandra
authors.initials: D
authors.lastname: Brkic
authors.affiliation: Division of Functional and Restorative Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Division of Translational Neurosurgery, Department of Neurosurgery, Eberhard Karls University, Tuebingen, Germany; Neuroprosthetics Research Group, Werner Reichardt Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany. Electronic address: alireza.gharabaghi@uni-tuebingen.de.
authors.forename: Alireza
authors.initials: A
authors.lastname: Gharabaghi
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D004244:Dizziness / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D010719:Phosphenes / Q000502:physiology; D011312:Pressure; D012677:Sensation / Q000502:physiology*; D012867:Skin / Q000503:physiopathology; D065908:Transcranial Direct Current Stimulation / Q000009:adverse effects*; D055815:Young Adult
keywords: Electrode montage; Frequency; Intensity; Neurosensory side effects; Parameter setting; Study design; Transcranial alternating current stimulation