高精度經顱電刺激是一種非侵入性神經調控技術，可透過客製化多電極配置，對大腦皮質進行較具聚焦性的刺激。然而，高精度經顱電刺激通常需將刺激電極放置於接近目標刺激區域的位置；當該位置位於頭髮覆蓋區時，便需仔細整理頭髮，以確保電極與頭皮之間具有良好接觸。本研究提出並建立一套以左側背外側前額葉皮質為目標、且避開頭髮覆蓋區域的高精度經顱電刺激電極配置，並評估其對前額葉血流動力學反應及斯特魯普任務表現的影響。電極配置透過基於真實體積法的經顱電刺激模擬器 （Realistic vOlumetric-Approach-based Simulator for Transcranial electric stimulation, ROAST） 進行最佳化，以維持左側背外側前額葉皮質足夠的電場強度、減少電流向右半球擴散，並避免將電極放置於頭髮覆蓋的頭皮區域。最終配置以 F3 為陽極並輸入 +2.1 毫安，AF3、F5 與 FC5 為回流電極，各輸入 −0.7 毫安，在左側背外側前額葉皮質產生 0.23 V/m 的電場強度，且右半球外溢程度極低。
本研究共納入 10 名健康受試者，採交叉設計完成真刺激與假刺激兩個實驗時段，兩次實驗間隔兩週，以降低殘留效應。刺激採用 20 分鐘的間歇性 θ 爆發刺激模式電刺激波形。受試者於刺激前、刺激期間與刺激後完成情緒型與原始型斯特魯普任務，同時持續記錄功能性近紅外光譜，以評估氧合血紅素與去氧血紅素濃度的變化。
功能性近紅外光譜結果顯示，最一致的血流動力學反應出現在目標左側背外側前額葉皮質。在真刺激時段中，左側背外側前額葉皮質的氧合血紅素濃度於前測、單獨刺激、刺激合併斯特魯普任務及後測條件下皆顯著高於基線。此外，右側背外側前額葉皮質與右側前額葉區域亦觀察到氧合血紅素濃度增加。去氧血紅素雖在後期實驗條件中呈現數值上的增加，但未出現顯著的條件相關變化。行為結果顯示，反應時間與正確率皆具有顯著的條件主效應。經霍姆校正後，真刺激時段的後測正確率顯著高於前測，而反應時間在各時段內未呈現顯著差異。然而，由於實驗時段與條件之間的交互作用未達顯著，因此無法將行為改善明確歸因於刺激本身。
為比較避開頭髮區域與頭髮覆蓋區域電極配置的刺激結果，本研究另針對 4 名受試者進行案例研究。結果顯示，兩種電極配置在所有實驗條件下的氧合血紅素與去氧血紅素功能連結模式皆呈現顯著相似性。上述結果進一步支持所提出之避開頭髮區域高精度經顱電刺激電極配置，在本研究設定刺激強度下的可行性。
整體而言，本研究結果支持所提出之避開頭髮區域高精度經顱電刺激電極配置，可針對左側背外側前額葉皮質進行刺激，並產生可量測的前額葉血流動力學反應。此方法可作為未來重複刺激與居家型神經調控研究的實用基礎，並可進一步應用於輕度認知障礙與失智症族群。

High-definition transcranial electrical stimulation (HD-tES) is a non-invasive neuromodulation technique that enables relatively focal cortical stimulation through customized multi-electrode configurations. However, HD-tES typically requires stimulation electrodes to be placed close to the target activation site, which may lie within a hair-covered area and therefore require careful hair preparation to ensure adequate electrode–scalp contact. This study proposed the development of hair-free HD-tES montage targeting the left dorsolateral prefrontal cortex (DLPFC) and evaluated its effects on prefrontal hemodynamic responses under Stroop tasks. The montage was optimized using the Realistic vOlumetric-Approach-based Simulator for Transcranial electric stimulation (ROAST) to maintain sufficient electric-field intensity in the left DLPFC, minimize current spread to the right hemisphere, and avoid electrode placement over hair-covered scalp regions. The final configuration consisted of F3 at +2.1 mA and AF3, F5, and FC5 at −0.7 mA each, producing an electric-field intensity of 0.23 V/m in the left DLPFC with minimal right-hemisphere spillover.
Ten healthy participants completed stimulation and sham sessions using a crossover design with a two-week washout period. A 20-minute electrical waveform patterned at intermittent theta-burst stimulation (iTBS) protocol was delivered. Participants performed emotional and original Stroop tasks before, during, and after stimulation, while functional near-infrared spectroscopy (fNIRS) was continuously recorded to assess changes in oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR) concentrations.
The fNIRS results showed the most consistent hemodynamic responses in the targeted left DLPFC. During the stimulation session, HbO concentration was significantly higher than baseline during the pretest, stimulation-only condition, stimulation with the Stroop task, and posttest. In addition, the increase of HbO was observed in the right DLPFC and right prefrontal region. Although numerical increases were observed during the later experimental conditions, HbR did not show significant condition-related changes. Behavioral performance showed significant condition effects for both reaction time and accuracy. Posttest accuracy was significantly higher than pretest accuracy within the stimulation session after Holm correction, whereas no significant within-session changes were observed for reaction time. However, the absence of a significant session × condition interaction indicated that the behavioral improvement could not be attributed specifically to stimulation.
To compare stimulation outcomes between hair-free and hair-covered montages, additional case studies involving four participants showed significant similarity in HbO and HbR functional connectivity patterns across all experimental conditions. These observations further support the feasibility of the proposed hair-free montage of HD-tES under designed stimulation intensities.
Overall, our findings support the feasibility of the proposed hair-free HD-tES montage for targeting the left DLPFC and producing measurable prefrontal hemodynamic responses. This approach may provide a practical foundation for future repeated and home-based neuromodulation studies in individuals with mild cognitive impairment and dementia.

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