Creating ERPs contralateral and ipsilateral to response hand

[JeshuaT]

Hi! I’m doing a surface laplacian (or current source density) analysis over the motor cortex for a task where participants had to respond with either their right hand or their left hand. What I want now is to combine the ipsilateral signals over the motor cortex and the contralateral signals over the motor cortex, and compare those. So for the ipsilateral signal: combine the potentials of the C4 channel in the right-hand response trials with the potentials of the C3 channel in the left-hand response trial. For the contralateral signal: combine the potentials of the C3 channel in the right-hand response trials with the potentials of the C4 channel in the left-hand response trials.

Basically, I want to end up with a plot that looks like this:

I’ve already tried to put the ipsilateral signals (C3 right hand and C4 left hand) in two different evoked objects, and then combine them with grand_average, but it gives the error that the channel names don’t match. Is there another way to average two signals from two different channel names and two different objects? Or is there an easier way to achieve what I want?

(my question is a lot like this question from eeglab but I couldn’t find anything in MNE for this)

[JeshuaT]

Perhaps this question is a bit simpler to answer: how can I merge the contralateral signals from these plots? Basically, how can I merge a signal of two different channels of two different sets of data

Let me know if anything is unclear in my question. I’ve been stuck with this for some time so I could really use your help!

[wmvanvliet (Marijn van Vliet)]

In this case, we need to abandon the existing channel names (C3, C4) and instead name them something like ‘ipsilateral’ and ‘contralateral’:

evoked_left.rename_channels({'C3': 'ipsilateral', 'C4': 'contralateral'})
evoked_right.rename_channels({'C4': 'ipsilateral', 'C3': 'contralateral'})

Then, we can combine them:

evoked = mne.combine_evoked([evoked_left, evoked_right], weights='nave')