BOLD signal effects of transcranial alternating current stimulation (tACS) in the alpha range: A concurrent tACS–fMRI study

• Published in: NeuroImage (Orlando, Fla.) Vol. 140; pp. 118 - 125
• Main Authors: Vosskuhl, Johannes, Huster, René J., Herrmann, Christoph S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.10.2016; Elsevier Limited
• Subjects: Adult; Alpha Rhythm - physiology; Alpha-tACS; Behavior; Brain Mapping - methods; Cerebral Cortex - physiology; Event-related fMRI; Evoked Potentials - physiology; Female; Humans; Magnetic Resonance Imaging - methods; Male; Oxygen - metabolism; Reproducibility of Results; Resting-state fMRI; Sensitivity and Specificity; Studies; Tomography; Transcranial alternating current stimulation; Transcranial Direct Current Stimulation - methods; Visual Cortex - physiology; Visual Perception - physiology; Event-related fMRI; Resting-state fMRI; Alpha-tACS; Transcranial alternating current stimulation
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2015.10.003

Many studies have proven transcranial alternating current stimulation (tACS) to manipulate brain activity. Until now it is not known, however, how these manipulations in brain activity are represented in brain metabolism or how spatially specific these changes are. Alpha-tACS has been shown to enhance the amplitude of the individual alpha frequency (IAF) and a negative correlation between alpha amplitude and occipital BOLD signal was reported in numerous EEG/fMRI experiments. Thus, alpha-tACS was chosen to test the effects of tACS on the BOLD signal. A reduction thereof was expected during alpha-tACS which shows the spatial extent of tACS effects beyond modeling studies. Three groups of subjects were measured in an MRI scanner, receiving tACS at either their IAF (N=11), 1Hz (control; N=12) or sham (i.e., no stimulation — a second control; N=11) while responding to a visual vigilance task. Stimulation was administered in an interleaved pattern of tACS-on runs and tACS-free baseline periods. The BOLD signal was analyzed in response to tACS-onset during resting state and in response to seldom target stimuli. Alpha-tACS at 1.0mA reduced the task-related BOLD response to visual targets in the occipital cortex as compared to tACS-free baseline periods. The deactivation was strongest in an area where the BOLD signal was shown to correlate negatively with alpha amplitude. A direct effect of tACS on resting state BOLD signal levels could not be shown. Our findings suggest that tACS-related changes in BOLD activity occur only as a modulation of an existing BOLD response. •Transcranial alternating current stimulation (tACS) can manipulate the BOLD signal.•tACS at the individual alpha frequency reduces signal strength most effectively.•Current intensity modulates the tACS effect.•Only task related activity was modulated, not the resting state BOLD signal.