[FieldTrip] How to understand the cross-correlogram and its feature comparison against the one obtained by shuffling the trials

[Kai Yu]

Hi,

I have been using your FieldTrip Intracranial Spike Analysis package for a
while. However, I am still confused by the statement listed on your website.

"Cross-correlations between neurons can either arise because of common,
time-locked fluctuations in the firing rate (Brody et al., 1999). These
correlations are invariant to a change in the order of trials. The
shuffling of trials in ft_spike_xcorr always pertains to two subsequent
trials, in order to avoid an influence of slow changes in the firing rate
across trials. We refer to this cross-correlogram that is obtained under a
permutation of subsequent trials as the 'shift-predictor'
cross-correlogram. If the observed features of the cross-correlogram that
are not present in the shift-predictor cross-correlogram, then this
indicates that they arise because of induced synchronous activity."

For the last sentence, would you please explained more about the "induced
synchronous activity"? In my own understanding, this is the activity after
the task or external stimulation. But if I want to know the synchronous or
de-synchronous activity during the stimulation, how can I get the evidence
from these cross-correlations and also the jpsth figures?

Thank you so much!

Best,
-Kai

-- 
Kai Yu
Biomedical Functional Imaging and Neuroengineering Laboratory
Department of Biomedical Engineering
University of Minnesota - Twin Cities
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