Computer-Based Models of tDCS and tACS

Transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) are noninvasive neuromodulatory techniques that deliver low-intensity currents facilitating or inhibiting spontaneous neuronal activity. These techniques have a number of advantages that have been applied in clinical settings; in particular, tDCS/tACS dose in principle is easily customized by varying electrode number, position, size, shape, and current. However, the ability to leverage this customization depends on how tDCS/tACS dose modulate the underling brain current flow. This relationship is not simple and can benefit from the use of computational models of current flow, personalized to individual subjects and cases. Tools for modeling range from Finite Element Method models to stand-alone GUI based software for clinicians. Many software packages can load individual’s MRI scans, allowing individualized therapy design. However, the challenge remains to design and interpret these models while remaining aware of their limitations. Current flow models alone cannot “make dose decisions,” but rather inform the rational design of electrotherapy. This is evidenced in exemplary studies combining computer modeling and clinical data, several examples of which are outlined in this chapter. Though modeling software is now widely available, newer generations of algorithms promise more precision and flexibility, and thus it is predicted that with increased validation, dissemination, simplification and dissemination of modeling tools, computational forward models of neuromodulation will become useful tools to guide the optimization of clinical electrotherapy. Essential for this adoption and refinement is an appreciation by clinicians of the uses and limitations of computational models, and conversely understanding by engineers and programmers of what software functions are relevant to clinical practice.