Anodal tDCS Over Left PPC Enhances Visuospatial Attention and Alpha Power Among Young Adults

Background: Visuospatial attention enables individuals to detect and process relevant stimuli efficiently. The posterior parietal cortex (PPC), a core hub of the dorsal attention network, exerts top-down control over visual scanning and is closely linked to alpha-band oscillations (8-13 Hz), which index attentional allocation and inhibition of distractors. Transcranial direct current stimulation (tDCS) offers a noninvasive method to alter cortical excitability transiently, but evidence for its effects on PPC-mediated attention and alpha power remains mixed.

Objective: This randomized, single-blind trial examined whether anodal tDCS over the left PPC modulates visuospatial attention and resting-state alpha power in young adults, and whether EEG changes predict behavioral performance.

Method: Thirty-two healthy participants (18-40 years) were randomized to anodal (2 mA, 20 min; n=15) or sham (n=17) stimulation. Cancellation Test performance and resting-state EEG were assessed pre- and post-stimulation. EEG analyses focused on artifact-free alpha power; regression models probed associations between neural and behavioral changes.

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Key information

Conditions

tDCS EEG Posterior Parietal Cortex Visual Attention

Age range

18 year–40 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Istanbul Medipol University

Beykoz, İ̇stanbul, 34820, Turkey (Türkiye)

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

Age between 18 and 40 years
Score of 21 or higher on the Montreal Cognitive Assessment Scale (MoCA)

Exclusion criteria

History of neurological or psychiatric illness
Uncorrected visual impairments
MoCA score of 21 or lower
Use of medications affecting cortical excitability
History of seizures or epilepsy
Presence of intracranial metal objects, implanted stimulating devices, or pacemakers

Treatment and study plan

Anodal tDCS

Device

Anodal tDCS Protocol: In the Anodal tDCS participant group, a direct current of 2 mA was applied for 20 minutes in accordance with the safety guidelines. To provide cortical stimulation, the superficial anodal electrode of the device was placed on the P3 region (left PPC), which is located in the left superior parietal lobe, corresponds to Brodmann area (BA) 40, and is associated with the dorsal visual pathway according to the international 10-20 EEG system. The reference electrode was placed on the contralateral (opposite) shoulder.

Sham tDCS

Device

Sham tDCS Protocol: The anode superficial electrode of the device was placed on the P3 region (left PPC), located in the left superior parietal lobe, corresponding to Brodmann area (BA) 40, and associated with the dorsal visual pathway according to the international 10-20 EEG system. The reference electrode was placed on the contralateral (opposite) shoulder. In the Sham tDCS group, a single 20-minute sham session was administered over the left posterior parietal cortex (P3) without delivering current, in accordance with the safety guidelines.

Primary outcomes

EEG recording and power in alpha band

Time frame: Before and immediately after applying tDCS

EEG recordings were acquired in a semi-dark, electrically shielded Faraday room using a BrainAmp 32-Channel DC System (Brain Products, Munich, Germany). Signals were sampled at 500 Hz with a 0.01-250 Hz bandpass filter and recorded using BrainVision Recorder software. A 32-channel Ag/AgCl electrode cap (Easycap) was positioned according to the international 10-20 system. Resting-state EEG data were collected for 4 minutes with eyes open and 4 minutes with eyes closed. Numerical evaluation of artifact-free EEG data for power density calculation is performed using Fast Fourier Transform (FFT) with 0.5 Hz frequency resolution, and alpha (8-13 Hz) bands were calculated and then averaged over these power spectrum values. The amplitude values, measured from peak to peak, were recorded for each individual, and the necessary data for statistical analysis were collected.
Cancellation Test

Time frame: Before and immediately after applying tDCS

The Cancellation Test is one of the most widely used tools for assessing visuospatial attention. IT consists of four subtests arranged on A4-sized sheets. Each subtest includes 60 target stimuli distributed among 300 total stimuli. For each subtest, separate scores are calculated for the right and left sides, including the number of correctly marked targets (IT1), omitted targets (IT2), incorrectly marked letters/shapes (IT3), total error score (IT4), and scanning time (IT5). The total error score is calculated as the sum of omitted targets and incorrectly marked letters/shapes. Achieving a high score (i.e., a high number of correctly marked targets and a low number of errors) and a short completion time (time score) indicate better performance. İn the present study, the paper-and-pencil version of the Cancellation Test was chosen to reliably assess visuospatial attention and subtle tDCS-induced changes.

Sponsors and collaborators

Lead sponsor

Medipol University

Other

Registry information

Important dates

Study start: 2021
Primary completion: 2021
Study completion: 2021
First posted: Jun 4, 2026
Registry last updated: Jun 4, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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