Topographical plots

[@brendadenissecorona2944]

Hi Mike!Some weeks ago i tried to make a Topographical plot, I dont know anything about Matlab and now i get it with your help, i founded the answer here in your videos. Thanks so much. Now i can continue with my thesis, i send you a big hug!

[@mikexcohen1]

Awesome. Virtual hugs are always appreciated and reciprocated :)

[@sofiaahufinger6970]

Hi, Mike, I'm following your lecturelets videos and I think that your explanations are completely awesome . When you are doing the interpolation, in the TriScatteredInterp you use elocsY' and then elocsX', so then the Y axis locations of the electrodes will be used as the points along the X axis of the interpolant. However, when you use the interpolant to generate the topodata, you use gridX and gridY. I'm not seeing why such axis change, is there a mistake or is it something that I am not seeing? Thank you in advance.

[@mikexcohen1]

Hi Sofia. The function meshgrid swaps X and Y. That's because when plotting a matrix, the rows (typically X) actually correspond to the y-axis, and vice-versa. That said, you don't need to worry too much about the mechanics here. I wanted to show the interpolation code once to dispel the idea that there is any magic involved in making topographical maps. In practice, you should always use the functions from eeglab or fieldtrip or whatever analysis package.

[@sofiaahufinger6970]

@@mikexcohen1 Hi Mike. Thank you so much for your response, now I understand everything :)

[@sayanghosh4739]

Hi, I have applied common spatial pattern algorithm on healthy and psychosis EEG data of 60 channel. And according to decending order of eigen value I took top 20 most discriminatory component. That means 20 channel..How to plot that reduced spatial filter[W] of size (20*20) or spatial pattern just inverse of W in topographical plot.

[@mikexcohen1]

Hi Sayan. You would visualize only one map at a time. And yes, it's the inverse of W.

[@pab__48]

Hi, I am working on anesthesia data classification project, and I am right now trying to plot my data (PSD) on a topographical plot, but I have trouble finding standard sensors positions (for a 129 electrode cap), as the mne tool I was using does not exist anymore. Do you have any ressources to recommend (I am using Python) ? Thank you, also for your videos. Very helpful! - Alina

[@mikexcohen1]

Hi Alina. If you know the manufacturer of the cap, it should be possible to get the standard positions based on electrode labels. Perhaps on the company's website, or perhaps in eeglab or fieldtrip (those are in MATLAB, but it wouldn't take much time to export the labels to a text file).

[@livexurxlifex3]

Hi Mike, I am trying to use EEGLAB the same way you are to create these topo plots with my data, but I have a single array of EEG data with 64 rows and 1263960 columns with a rate of 250. When I put this data into EEG lab and open the data I notice that: nbchan=64, trials=1, pnts=1263960, srate=250, xmin=0, smax=5.0558e+03, and data=64x1263960 single. I notice that your data is 3 dimensional because you have 99 trials and your chanlocs is 1x64, my chanlocs is empty [ ]. I don't think this is going to work like the way it did with your code because yours is 3 dimensional. Can you offer any help? I would love to create those beautiful head plots.

[@mikexcohen1]

Indeed, a topographical map is a 2D representation of the data. For task-based experiments, you would pick one time point, let's say 150 ms after a visual stimulus appeared on a computer screen. For continuous data, picking a single time point doesn't really make sense. What you could do is apply a spectral analysis and then make a topographical map of a prominent spectral component, for example alpha activity.

[@aumkarshah1055]

@@mikexcohen1 When we do such an operation, should absolute or relative band power be employed while generating such topo plots?

[@drpriyamiranda8801]

Thank you! Excellent explanation!!!

[@CourtneyBryceHilton]

Thanks for the videos Mike. Just checking I am understanding right: the 'pi/180' bit in the line of code: "[elocsX,elocsY] = pol2cart(pi/180*[EEG.chanlocs.theta],[EEG.chanlocs.radius]);"... that is just changing the EEG coordinates from degrees to radians, right? Also you say that that code is transforming the coordinates from cartesian to polar, but isn't it the other way around?

[@mikexcohen1]

Hi Courtney. Yes, it's just transforming from polar to Cartesian. It's possible that I said it the other way around by accident.