论文标题

L1-norm vs. L2-norm拟合在优化焦点多通道TES刺激方面:线性和半决赛编程与加权最小二乘

L1-norm vs. L2-norm fitting in optimizing focal multi-channel tES stimulation: linear and semidefinite programming vs. weighted least squares

论文作者

Prieto, Fernando Galaz, Rezaei, Atena, Samavaki, Maryam, Pursiainen, Sampsa

论文摘要

这项研究的重点是多通道经颅电刺激,这是一种在低强度电流影响下刺激神经元活性的非侵入性脑方法。我们介绍了数学公式,以找到当前模式,该模式优化了给定焦点靶标分布与大脑内部密度的体积电流密度之间的L1-norm拟合。与L2-Norm(最小二乘)拟合的估计值相比,L1-Norm众所周知,有利于良好的定位或稀疏分布。我们提出了一种线性编程方法,该方法执行L1-norm拟合和当前模式(L1L1)的惩罚以控制非零电流的数量。优化器使用预先过滤的候选物中使用两阶段的元启发式搜索过滤了大量候选解决方案。用8通道电极蒙太奇获得的数值模拟结果表明,我们对L1-Norm数据拟合益处的假设是有效的。与L1-norm正则L2-norm拟合(L1L2)相比,通过半决赛编程和加权Tikhonov最小二乘法相比,L1L1结果总体优先于最大化目标位置的聚焦电流密度以及聚焦和滋扰电流的比率。我们提出元启发式L1L1优化方法作为一种潜在技术,以在给定的目标位置以可控幅度获得良好的刺激。 L1L1在阳极和阴极电极之间找到了一种当前模式,同时抑制了大脑中的滋扰电流,因此为调节刺激的影响(例如,受试者所经历的感觉)提供了潜在的替代方法。

This study focuses on Multi-Channel Transcranial Electrical Stimulation, a non-invasive brain method for stimulating neuronal activity under the influence of low-intensity currents. We introduce mathematical formulation for finding a current pattern which optimizes a L1-norm fit between a given focal target distribution and volume current density inside the brain. L1-norm is well-known to favor well-localized or sparse distributions compared to L2-norm (least-squares) fitted estimates. We present a linear programming approach which performs L1-norm fitting and penalization of the current pattern (L1L1) to control the number of non-zero currents. The optimizer filters a large set of candidate solutions using a two-stage metaheuristic search in from a pre-filtered set of candidates. The numerical simulation results, obtained with both a 8- and 20-channel electrode montages, suggest that our hypothesis on the benefits of L1-norm data fitting is valid. As compared to L1-norm regularized L2-norm fitting (L1L2) via semidefinite programming and weighted Tikhonov least-squares method, the L1L1 results were overall preferable with respect to maximizing the focused current density at the target position and the ratio between focused and nuisance current magnitudes. We propose the metaheuristic L1L1 optimization approach as a potential technique to obtain a well-localized stimulus with a controllable magnitude at a given target position. L1L1 finds a current pattern with a steep contrast between the anodal and cathodal electrodes meanwhile suppressing the nuisance currents in the brain, hence, providing a potential alternative to modulate the effects of the stimulation, e.g., the sensation experienced by the subject.

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