Effects of Gamma-tACS on EEG Periodic Activity

Study Overview
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Brief Summary
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In this study on healthy subjects, the effect of transcranial alternating current stimulation (tACS) will be investigated. In particular, the distinction between periodic and aperiodic electroencephalogram (EEG) activity will be considered, as well as the state-dependency phenomenon. Participants will take part in two experimental sessions that will include tACS stimulation (one real, one control). Before, during, and after stimulation, subjects will have their EEG recorded during rest or during tasks. The aim of this study is to investigate how the modulatory effects of gamma-tACS interact with intrinsic neural activity, measured in terms of periodic and aperiodic activity, as well as neurophysiological and behavioral modulation, taking into consideration the state-dependency phenomenon, which refers to the brain's activation state prior to stimulation.

Official Title
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Evaluation of the Effects of Gamma-tACS on the Periodic Activity of Neural Signals as a Function of State-dependency

Conditions
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Transcranial Alternating Current Stimulation

Intervention / Treatment
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* Device: real tACS
* Device: sham tACS


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: - Healthy adults Exclusion Criteria: Common exclusion criteria Left-handedness (assessed through the Oldfield test) Diagnosis of neurological or psychiatric disorders Vision problems that prevent reading, not correctable with lenses Diagnosis of substance dependence on drugs or alcohol Presence of hearing aids/prostheses Diagnosis of epilepsy or family history up to the second degree with it Episodes of febrile convulsions or recurrent fainting Head trauma Presence of surgical clips or metal implants in the head Diagnosis of heart disease Presence of a cardiac pacemaker or artificial heart valve Presence of hearing aids/prostheses Hearing problems or tinnitus Vision problems not corrected with lenses (such as color blindness) Taking tricyclic antidepressant medications Taking neuroleptic medications Diagnosis of headache or migraine Taking more than 3 alcoholic units in the last 24 hours Taking 2 or more cups of coffee or caffeine from other sources in the last 2 hours

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: real tACS<br> | Device: real tACS<br>* tACS is a non-invasive method to induce brain modulation. It will be applied at a frequency of 40 Hz (gamma-tACS) with a peak-to-peak intensity of 2 mA. During the real tACS condition, the alternating current will be administered for 20 minutes.<br>|
| Sham Comparator: sham tACS<br> | Device: sham tACS<br>* In the sham tACS condition, the current will be delivered only for the first 30 seconds and then stopped, in order to simulate the same somatosensory sensations as real tACS, but without inducing modulation.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| resting-state electroencephalography (EEG) signal | The periodic and aperiodic activity of the EEG signal will be estimated through Brainstorm (i.e., EEG analysis software) and quantified in terms of numerical values representing the periodic/aperiodic component of the EEG signal. The periodic and aperiodic activity of the EEG signal will be assessed during three time frames: baseline, during the intervention, and immediately after the intervention (real or sham tACS) | baseline | 
| resting-state electroencephalography (EEG) signal | The periodic and aperiodic activity of the EEG signal will be estimated through Brainstorm (i.e., EEG analysis software) and quantified in terms of numerical values representing the periodic/aperiodic component of the EEG signal. The periodic and aperiodic activity of the EEG signal will be assessed during three time frames: baseline, during the intervention, and immediately after the intervention (real or sham tACS) | during the intervension | 
| resting-state electroencephalography (EEG) signal | The periodic and aperiodic activity of the EEG signal will be estimated through Brainstorm (i.e., EEG analysis software) and quantified in terms of numerical values representing the periodic/aperiodic component of the EEG signal. The periodic and aperiodic activity of the EEG signal will be assessed during three time frames: baseline, during the intervention, and immediately after the intervention (real or sham tACS) | immediately after the intervention | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| behavioral performance (response times) | Participants' motor performance at a computerized task will be measured in terms of response times (how fast the participants press a computer button, according to the task's instructions). The participants' motor performance will be assessed during two time frames: baseline and immediately after the intervention (real or sham tACS) | baseline | 
| behavioral performance (response times) | Participants' motor performance at a computerized task will be measured in terms of response times (how fast the participants press a computer button, according to the task's instructions). The participants' motor performance will be assessed during two time frames: baseline and immediately after the intervention (real or sham tACS) | immediately after the intervention | 
| behavioral performance (accuracy) | Participants' motor performance at a computerized task will be measured in terms of accuracy (% of correct responses at the computerized task, according to the task's instructions). The participants' motor performance will be assessed during two time frames: baseline and immediately after the intervention (real or sham tACS) | baseline | 
| behavioral performance (accuracy) | Participants' motor performance at a computerized task will be measured in terms of accuracy (% of correct responses at the computerized task, according to the task's instructions). The participants' motor performance will be assessed during two time frames: baseline and immediately after the intervention (real or sham tACS) | immediately after the intervention | 
| auditory steady state response (ASSR) | The auditory steady state response will be measured via EEG during entrainment through exposure to amplitude-modulated 40Hz sounds (5 min, sequence of amplitude-modulated tones at 40 Hz, delivered via earplug binaurally). The auditory steady state response will be measured as power of the EEG gamma band. The auditory steady state response will be assessed during two time frames: baseline and immediately after the intervention (real or sham tACS) | baseline | 
| auditory steady state response (ASSR) | The auditory steady state response will be measured via EEG during entrainment through exposure to amplitude-modulated 40Hz sounds (5 min, sequence of amplitude-modulated tones at 40 Hz, delivered via earplug binaurally). The auditory steady state response will be measured as power of the EEG gamma band. The auditory steady state response will be assessed during two time frames: baseline and immediately after the intervention (real or sham tACS) | immediately after the intervention |