Connectivity with Imaginary Coherency and Corrected with ft_sourcestatistics plotting issues

Francois · June 28, 2019, 8:05am

Using imaginary coherency in Brainstorm, I would like to show that two regions do have some sort of connectivity with each other, using the Destrieux atlas for my two regions. I added my individual subject coherency files to process 1, and attempted to do a one-sample student's t-test in the frequency range of 4 - 12 Hz,

Your coherence value IS different from zero, it is always strictly positive. This test would not be of much interest.
You need to formulate this as a contrast across conditions: eg. the coherence between ROI A and B is significantly higher in condition A than in condition B.

but I get the following error which I'm assuming is related to the imaginary part

The imaginary coherence is a real value. See the description in the header of the coherence computation function:

github.com

brainstorm-tools/brainstorm3/blob/master/toolbox/connectivity/bst_cohn.m#L17


      
          %    - X       : Input signals [Nsignals x Ntimes]

          %    - Y       : Input signals [Nsignals x Ntimes]

          %    - Fs      : Sampling frequency of X and Y (in Hz)

          %    - nFFT    : Length of the window used to estimate the coherence (must be a power of 2 for the efficiency of the FFT)

          %    - Overlap       : [0-1], percentage of time overlap between two consecutive estimation windows

          %    - CohMeasure    : {'mscohere', 'icohere' , 'icohere2019', 'lcohere2019'}

          %    - isSymmetric   : If 1, use an optimized method for symmetrical matrices

          %    - ImagingKernel : If not empty, calculate the coherence at the source level

          %    - waitMax       : Increase of the progress bar during the execution of this function

          %

          % CohMeasure (Definitions):

          %     In Late 2019, the fft-based coherence functions were updated. The

          %     lagged and Imaginary coherence have different definitions among two

          %     versions. The recent changes are set as default. Please consider this

          %     if you want to reproduce your former analyses. 

          %     

          %     Gxy:  cross-spectral density between x and y

          %     Gxx:  autospectral density of x

          %     Gyy:  autospectral density of y

          %     Coherence function (C)            : Gxy/sqrt(Gxx*Gyy)

          %     Magnitude-squared Coherence (MSC) : |C|^2 = |Gxy|^2/(Gxx*Gyy) = Gxy*conj(Gxy)/(Gxx*Gyy)