The Pursuit of DLPFC: Non-neuronavigated Methods to Target the Left Dorsolateral Pre-frontal Cortex With Symmetric Bicephalic Transcranial Direct Current Stimulation (tDCS).

BACKGROUND The dose of transcranial direct current stimulation (tDCS) is defined by electrode montage and current, while the resulting brain current flow is more complex and varies across individuals. The left dorsolateral pre-frontal cortex (lDLPFC) is a common target in neuropsychology and neuropsychiatry applications, with varied approaches used to experimentally position electrodes on subjects. OBJECTIVE To predict brain current flow intensity and distribution using conventional symmetrical bicephalic frontal 1 × 1 electrode montages to nominally target lDLPFC in forward modeling studies. METHODS Six high-resolution Finite Element Method (FEM) models were created from five subjects of varied head size and an MNI standard. Seven electrode positioning methods, nominally targeting lDLPFC, were investigated on each head model: the EEG 10-10 including F3-F4, F5-F6, F7-8, F9-F10, the Beam F3-System, the 5-5 cm-Rule and the developed OLE-System were evaluated as electrode positioning methods for 5 × 5 cm(2) rectangular sponge-pad electrodes. RESULTS Each positioning approach resulted in distinct electrode positions on the scalp and variations in brain current flow. Variability was significant, but trends across montages and between subjects were identified. Factors enhancing electric field intensity and relative targeting in lDLPFC include increased inter-electrode distance and proximity to thinner skull structures. CONCLUSION Brain current flow can be shaped, but not focused, across frontal cortex by tDCS montages, including intensity at lDLPFC. The OLE-system balances lDLPFC targeting and reduced electric field variability, along with clinical ease-of-use.