Source Localization Using Recursively Applied and Projected MUSIC with Flexible Extent Estimation

Abstract

Magneto- and electroencephalography (M/EEG) are widespread techniques to measure neural activity in-vivo at a high temporal resolution but low spatial resolution. Locating the neural sources underlying the M/EEG poses an inverse problem, which is ill-posed. We developed a new method based on Recursive Application of Multiple Signal Classification (MUSIC). Our proposed method is able to recover not only the locations but, in contrast to other inverse solutions, also the extent of active brain regions flexibly (FLEX-MUSIC). This is achieved by allowing it to search not only for single dipoles but also dipole clusters of increasing extent to find the best fit during each recursion. FLEX-MUSIC achieved the highest accuracy for both single dipole and extended sources compared to all other methods tested. Remarkably, FLEX-MUSIC was capable to accurately estimate the level of sparsity in the source space (r = 0.82), whereas all other approaches tested failed to do so (r ≤ 0.18). The average computation time of FLEX-MUSIC was considerably lower compared to a popular Bayesian approach and comparable to that of another recursive MUSIC approach and eLORETA. FLEX-MUSIC produces only few errors and was capable to estimate the extent of sources reliably. The accuracy and low computation time of FLEX-MUSIC renders it an improved technique to solve M/EEG inverse problems both in neuroscience research and potentially in pre-surgery diagnostic in epilepsy.

Spontaneous Necker-cube reversals may not be that spontaneous

“…As a first step, we concatenated the reversal- and stability-ERPs of all participants. Next, we identified a global set of active sources by calculating the flexible multi-signal classification (FLEX-MUSIC) inverse solution on the concatenated ERPs ( Hecker et al, 2023 ). FLEX-MUSIC is a recently developed improvement of the well-established recursive MUSIC approach to solve EEG inverse problems, that can accurately estimate not only the location but also the spatial extent of neural sources.…”

Localization of Spatially Extended Brain Sources by Flexible Alternating Projection (Flex-AP)

“…We evaluated the FLEX-AP method by comparing it to (non-FLEX) AP, RAP-MUSIC and FLEX-RAP-MUSIC. Note, that the smoothing of forward matrices in the FLEX-RAP-MUSIC algorithm as described in [6] was corrected by the heat diffusion model. Therefore, both FLEX-AP and FLEX-RAP-MUSIC share the same set of smoothed forward models (Eq.…”

“…In this iterative approach, individual dipoles are successively added to the set of active sources, and their signals are systematically removed from the measurements through an out-projection operation until a predefined criterion is met. A natural extension of this approach, the recent introduction of FLEX-RAP-MUSIC, allowed for the estimation of the spatial extent of neural sources [6]. The results showed that extent estimation is possible by smoothing the forward matrix with increasing order, thereby reducing localization errors significantly.…”