Optimization of multifocal transcranial current stimulation for weighted cortical pattern targeting from realistic modeling of electric fields

• Published in: NeuroImage (Orlando, Fla.) Vol. 89; pp. 216 - 225
• Main Authors: Ruffini, Giulio, Fox, Michael D., Ripolles, Oscar, Miranda, Pedro Cavaleiro, Pascual-Leone, Alvaro
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.04.2014; Elsevier; Elsevier Limited
• Subjects: Algorithms; Behavior; Biological and medical sciences; Brain; Brain Mapping; Cerebral Cortex - physiopathology; Disease; Electric fields; Electric Stimulation Therapy - methods; Electrodes; Electroencephalography; Electromagnetic Fields; fMRI; Fundamental and applied biological sciences. Psychology; Human head model; Humans; Inventors; Models, Neurological; Multifocal stimulation; Nerve Net - physiopathology; NIBS; Optimization algorithms; PET; rs-fcMRI; Science; tACS; Targeted stimulation; tCS; tDCS; TES; Transcranial alternating current stimulation; Transcranial direct current stimulation; Vertebrates: nervous system and sense organs; Multifocal stimulation; TES; tCS; tACS; NIBS; Transcranial direct current stimulation; Human head model; fMRI; Targeted stimulation; rs-fcMRI; tDCS; Transcranial alternating current stimulation; Electric fields; PET; Human; Stimulation; Nuclear magnetic resonance imaging; Electric field; Models; Functional imaging
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2013.12.002

Recently, multifocal transcranial current stimulation (tCS) devices using several relatively small electrodes have been used to achieve more focal stimulation of specific cortical targets. However, it is becoming increasingly recognized that many behavioral manifestations of neurological and psychiatric disease are not solely the result of abnormality in one isolated brain region but represent alterations in brain networks. In this paper we describe a method for optimizing the configuration of multifocal tCS for stimulation of brain networks, represented by spatially extended cortical targets. We show how, based on fMRI, PET, EEG or other data specifying a target map on the cortical surface for excitatory, inhibitory or neutral stimulation and a constraint on the maximal number of electrodes, a solution can be produced with the optimal currents and locations of the electrodes. The method described here relies on a fast calculation of multifocal tCS electric fields (including components normal and tangential to the cortical boundaries) using a five layer finite element model of a realistic head. Based on the hypothesis that the effects of current stimulation are to first order due to the interaction of electric fields with populations of elongated cortical neurons, it is argued that the optimization problem for tCS stimulation can be defined in terms of the component of the electric field normal to the cortical surface. Solutions are found using constrained least squares to optimize current intensities, while electrode number and their locations are selected using a genetic algorithm. For direct current tCS (tDCS) applications, we provide some examples of this technique using an available tCS system providing 8 small Ag/AgCl stimulation electrodes. We demonstrate the approach both for localized and spatially extended targets defined using rs-fcMRI and PET data, with clinical applications in stroke and depression. Finally, we extend these ideas to more general stimulation protocols, such as alternating current tCS (tACS). •We provide a method for optimizing the configuration of multifocal tDCS.•Optimization cortical target maps are based on fMRI, PET or other data.•Algorithm optimizes electrode currents and locations subject to safety constraints.•We highlight clinical applications in stroke and depression.•We discuss the generalization of these methods to tACS.