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The goal of this Rpackage is to allow neuroscientists to reproduce andtest the neural fragility method described in (Li et al. 2017, 2021).This method implements an intracranial EEG (iEEG) marker of theepileptogenic zone localization. In this method, seizures areconceptualized as transitions from a stable networked system to anunstable one. To quantify this, node fragility is computed from linearnetwork models, measuring each node’s susceptibility to destabilization.There are significant details missing in (Li et al. 2017, 2021) toreproduce the neural fragility method and adjust the parameters. ThisRpackage aims to identify and fill up the implementation details. Itwill also allow users to test the method parameters on their data.

To install the package from GitHub

devtools::install_github("Jiefei-Wang/EZFragility")

To load the package

library(EZFragility)

If you are working with the source code, you can load the package with

devtools::load_all()

The package contains an example data. To see the first 5 rows andcolumns of the data, type

pt01EcoG[1:5,1:5]

The package contains an example results. To see it, type

pt01Frag

For explanations on how to use the package please refer to the vignette.

vignette("Intro_to_EZFragility",package="EZFragility")

The method is based on building a discrete time linear system computinga stable adjacency matrix A for the evolution of x(t).
$x(t+1)=A x(t)$ with$x_i(t)$ the iEEG signal at time$t$ for electrode$i$. A is computed for a series of time windows to derive the fragilityrow.
In this package, we are applying a ridge regression to solve the matrixA. In (Li et al. 2017, 2021), a regularization parameter value of 1e-4is recommended, however testing on the data from patient pt01 from theFragility data set (data subset available in this package) this valuedoes not ensure that A is always stable. To tackle this issue, we haveimplemented a dichotomy to search for the lowest stable lambda valuerendering the matrix A stable (see R function ridgeSearch in fileridge.r).

The method to compute the row perturbation is also not clear. To computethe fragility row, a minimum 2-induced norm additive row perturbation$\Delta$ is computed to destabilize the linear network placing aneigenvalue of$A+\Delta$ at$\lambda=\sigma+j\omega$. The minimum normis a function of$\lambda$ given in (Li et al. 2017) (see functionfragilityRow in the scrip fragility.r), however the paper does notdescribe how to choose$\lambda$ with$|\lambda|=1$. To tackle thisissue, we search for the value that minimize the norm of$\Delta$.