Multichannel Systems NeuroExplorer - Manual (Page 71)

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2.13. Shift-Predictor for Crosscorrelograms
Shift-predictor is defined for a series of trials - you take the spikes of one neuron in trial 1 and
correlate them with the spikes of another neuron in trial 2, etc.
These "trials" are represented in NeuroExplorer as time intervals, i.e. pairs of numbers:
start of interval 1, end of interval 1
start of interval 2, end of interval 2, etc.
To use the shift-predictor, you need to create those "trials" first.
You need an external event that is fired at the beginning of each trial. Suppose Event03 is the event
that happens at the beginning of each trial and each trial lasts 20 seconds.
To create the trial intervals:
click on the New Events! button (or select Edit | Operations on Variables menu command)
in the operations list, select MakeIntervals
in the First Operand, select the external event Event03
set Shift Min to 0. and Shift Max to 20.0
in the New Var Name, type: Trials
press Run the Operation button
close the dialog.
Now, click on the Crosscorrelogram button, select Shift-predictor page and select Trials as an interval
filter and specify other shift-predictor parameters.
Shift-Predictor Algorithm
Suppose we have n trial intervals:
[t1a, t1b], [t2a, t2b], ..., [tna, tnb]
and we have 2 spike trains:
reference spike train with N timestamps r1, r2, ... , rN;
and target spike train with M timestamps s1, s2, ... , sM.
Shift-predictor for shift = 1 is calculated like this:
Step 1: find all the timestamps ri that are inside the first trial interval [t1a, t1b]
Step 2: find all the timestamps sj that are inside the second trial interval [t2a, t2b]
Step 3: shift all the timestamps ri so that thay align with the second trial:
calculate new timestamps pi = ri + (t2a-t1a)
Step 4: calculate a crosscorrelogram between pi and sj
Repeat Steps 1 through 4 with interval [t2a, t2b] in Step 1 and interval [t3a, t3b] in Step 2.
...
Repeat Steps 1 through 4 with interval [tna, tnb] in Step 1 and interval [t1a, t1b] in Step 2. Note that
we wrap around the trials: the last trial is correlated with the first one.
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