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Transcranial alternating current stimulation enhances individual alpha activity in human EEG.

Zaehle T, Rach S, Herrmann CS - PLoS ONE (2010)

Bottom Line: We delivered tACS over the occipital cortex of 10 healthy participants to entrain the neuronal oscillatory activity in their individual alpha frequency range and compared results with those from a separate group of participants receiving sham stimulation.The results show that spike-timing-dependent plasticity (STDP) selectively modulates synapses depending on the resonance frequencies of the neural circuits that they belong to.Thus, tACS influences STDP which in turn results in aftereffects upon neural activity.The present findings are the first direct electrophysiological evidence of an interaction of tACS and ongoing oscillatory activity in the human cortex.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Otto-von-Guericke University, Magdeburg, Germany.

ABSTRACT
Non-invasive electrical stimulation of the human cortex by means of transcranial direct current stimulation (tDCS) has been instrumental in a number of important discoveries in the field of human cortical function and has become a well-established method for evaluating brain function in healthy human participants. Recently, transcranial alternating current stimulation (tACS) has been introduced to directly modulate the ongoing rhythmic brain activity by the application of oscillatory currents on the human scalp. Until now the efficiency of tACS in modulating rhythmic brain activity has been indicated only by inference from perceptual and behavioural consequences of electrical stimulation. No direct electrophysiological evidence of tACS has been reported. We delivered tACS over the occipital cortex of 10 healthy participants to entrain the neuronal oscillatory activity in their individual alpha frequency range and compared results with those from a separate group of participants receiving sham stimulation. The tACS but not the sham stimulation elevated the endogenous alpha power in parieto-central electrodes of the electroencephalogram. Additionally, in a network of spiking neurons, we simulated how tACS can be affected even after the end of stimulation. The results show that spike-timing-dependent plasticity (STDP) selectively modulates synapses depending on the resonance frequencies of the neural circuits that they belong to. Thus, tACS influences STDP which in turn results in aftereffects upon neural activity.The present findings are the first direct electrophysiological evidence of an interaction of tACS and ongoing oscillatory activity in the human cortex. The data demonstrate the ability of tACS to specifically modulate oscillatory brain activity and show its potential both at fostering knowledge on the functional significance of brain oscillations and for therapeutic application.

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Stimulation details and results.A: Location of stimulation and EEG electrodes: The tACS electrodes were placed bilaterally over the occipital cortex (PO9, PO10, international 10/10 system); EEG is measured from parieto-occipital midline electrodes CPz, Pz, and POz. B: Timeline of experimental events: The experiment started with the determination of the individual alpha frequency during a 1-minute period in which the participants were in a relaxed state with eyes closed followed by an evaluation of an individual phosphene threshold. Subsequently, the participants performed a simple detection task for 16 minutes. During this period, EEG recording was stopped after 3 minutes (Pre-measure) and a 10 minute stimulation (either tACS or Sham) was given, followed by a further 3 minute EEG recording (Post-measure). C: Group averaged EEG activity: Average FFT power spectra for the 3 minute intervals preceding (pre, dotted line) and following (post, solid line) the stimulation condition separately for the tACS-group (left) and the Sham-group (right). D: mean individual alpha amplitude for tACS and sham group: There is an increase in individual alpha power from pre- to post-stimulus measurement in the subjects that received tACS (solid line), but not for the subjects that received sham-stimulation (dotted line). No tACS related alpha modulation can be observed in the upper and lower frequency band. Data are normalized to the pre-stimulation alpha power. Asterisks indicate statistical significance. Data are the means ±s.e.m.
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pone-0013766-g001: Stimulation details and results.A: Location of stimulation and EEG electrodes: The tACS electrodes were placed bilaterally over the occipital cortex (PO9, PO10, international 10/10 system); EEG is measured from parieto-occipital midline electrodes CPz, Pz, and POz. B: Timeline of experimental events: The experiment started with the determination of the individual alpha frequency during a 1-minute period in which the participants were in a relaxed state with eyes closed followed by an evaluation of an individual phosphene threshold. Subsequently, the participants performed a simple detection task for 16 minutes. During this period, EEG recording was stopped after 3 minutes (Pre-measure) and a 10 minute stimulation (either tACS or Sham) was given, followed by a further 3 minute EEG recording (Post-measure). C: Group averaged EEG activity: Average FFT power spectra for the 3 minute intervals preceding (pre, dotted line) and following (post, solid line) the stimulation condition separately for the tACS-group (left) and the Sham-group (right). D: mean individual alpha amplitude for tACS and sham group: There is an increase in individual alpha power from pre- to post-stimulus measurement in the subjects that received tACS (solid line), but not for the subjects that received sham-stimulation (dotted line). No tACS related alpha modulation can be observed in the upper and lower frequency band. Data are normalized to the pre-stimulation alpha power. Asterisks indicate statistical significance. Data are the means ±s.e.m.

Mentions: The aim of the present study was to provide direct electrophysiological evidence for the interaction of tACS and endogenous oscillatory neural activity. We applied tACS over the occipital cortex at the individual alpha frequency of 10 healthy participants, as well as a sham stimulation in a separate sample of 10 participants, and measured the alpha power from 3 parieto-central midline electrodes (Figure 1a). We hypothesized that tACS would interact with the ongoing neuronal activity and entrain the individual alpha oscillations.


Transcranial alternating current stimulation enhances individual alpha activity in human EEG.

Zaehle T, Rach S, Herrmann CS - PLoS ONE (2010)

Stimulation details and results.A: Location of stimulation and EEG electrodes: The tACS electrodes were placed bilaterally over the occipital cortex (PO9, PO10, international 10/10 system); EEG is measured from parieto-occipital midline electrodes CPz, Pz, and POz. B: Timeline of experimental events: The experiment started with the determination of the individual alpha frequency during a 1-minute period in which the participants were in a relaxed state with eyes closed followed by an evaluation of an individual phosphene threshold. Subsequently, the participants performed a simple detection task for 16 minutes. During this period, EEG recording was stopped after 3 minutes (Pre-measure) and a 10 minute stimulation (either tACS or Sham) was given, followed by a further 3 minute EEG recording (Post-measure). C: Group averaged EEG activity: Average FFT power spectra for the 3 minute intervals preceding (pre, dotted line) and following (post, solid line) the stimulation condition separately for the tACS-group (left) and the Sham-group (right). D: mean individual alpha amplitude for tACS and sham group: There is an increase in individual alpha power from pre- to post-stimulus measurement in the subjects that received tACS (solid line), but not for the subjects that received sham-stimulation (dotted line). No tACS related alpha modulation can be observed in the upper and lower frequency band. Data are normalized to the pre-stimulation alpha power. Asterisks indicate statistical significance. Data are the means ±s.e.m.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2967471&req=5

pone-0013766-g001: Stimulation details and results.A: Location of stimulation and EEG electrodes: The tACS electrodes were placed bilaterally over the occipital cortex (PO9, PO10, international 10/10 system); EEG is measured from parieto-occipital midline electrodes CPz, Pz, and POz. B: Timeline of experimental events: The experiment started with the determination of the individual alpha frequency during a 1-minute period in which the participants were in a relaxed state with eyes closed followed by an evaluation of an individual phosphene threshold. Subsequently, the participants performed a simple detection task for 16 minutes. During this period, EEG recording was stopped after 3 minutes (Pre-measure) and a 10 minute stimulation (either tACS or Sham) was given, followed by a further 3 minute EEG recording (Post-measure). C: Group averaged EEG activity: Average FFT power spectra for the 3 minute intervals preceding (pre, dotted line) and following (post, solid line) the stimulation condition separately for the tACS-group (left) and the Sham-group (right). D: mean individual alpha amplitude for tACS and sham group: There is an increase in individual alpha power from pre- to post-stimulus measurement in the subjects that received tACS (solid line), but not for the subjects that received sham-stimulation (dotted line). No tACS related alpha modulation can be observed in the upper and lower frequency band. Data are normalized to the pre-stimulation alpha power. Asterisks indicate statistical significance. Data are the means ±s.e.m.
Mentions: The aim of the present study was to provide direct electrophysiological evidence for the interaction of tACS and endogenous oscillatory neural activity. We applied tACS over the occipital cortex at the individual alpha frequency of 10 healthy participants, as well as a sham stimulation in a separate sample of 10 participants, and measured the alpha power from 3 parieto-central midline electrodes (Figure 1a). We hypothesized that tACS would interact with the ongoing neuronal activity and entrain the individual alpha oscillations.

Bottom Line: We delivered tACS over the occipital cortex of 10 healthy participants to entrain the neuronal oscillatory activity in their individual alpha frequency range and compared results with those from a separate group of participants receiving sham stimulation.The results show that spike-timing-dependent plasticity (STDP) selectively modulates synapses depending on the resonance frequencies of the neural circuits that they belong to.Thus, tACS influences STDP which in turn results in aftereffects upon neural activity.The present findings are the first direct electrophysiological evidence of an interaction of tACS and ongoing oscillatory activity in the human cortex.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Otto-von-Guericke University, Magdeburg, Germany.

ABSTRACT
Non-invasive electrical stimulation of the human cortex by means of transcranial direct current stimulation (tDCS) has been instrumental in a number of important discoveries in the field of human cortical function and has become a well-established method for evaluating brain function in healthy human participants. Recently, transcranial alternating current stimulation (tACS) has been introduced to directly modulate the ongoing rhythmic brain activity by the application of oscillatory currents on the human scalp. Until now the efficiency of tACS in modulating rhythmic brain activity has been indicated only by inference from perceptual and behavioural consequences of electrical stimulation. No direct electrophysiological evidence of tACS has been reported. We delivered tACS over the occipital cortex of 10 healthy participants to entrain the neuronal oscillatory activity in their individual alpha frequency range and compared results with those from a separate group of participants receiving sham stimulation. The tACS but not the sham stimulation elevated the endogenous alpha power in parieto-central electrodes of the electroencephalogram. Additionally, in a network of spiking neurons, we simulated how tACS can be affected even after the end of stimulation. The results show that spike-timing-dependent plasticity (STDP) selectively modulates synapses depending on the resonance frequencies of the neural circuits that they belong to. Thus, tACS influences STDP which in turn results in aftereffects upon neural activity.The present findings are the first direct electrophysiological evidence of an interaction of tACS and ongoing oscillatory activity in the human cortex. The data demonstrate the ability of tACS to specifically modulate oscillatory brain activity and show its potential both at fostering knowledge on the functional significance of brain oscillations and for therapeutic application.

Show MeSH
Related in: MedlinePlus