# [Eeglablist] convert EEG montage from bipolar to unipolar

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Fri May 12 16:26:39 PDT 2017

```Dear Mubaraki,

Ok this is the solution I learned from my colleague.
Let X be the (single-channel referenced) original EEG data and Xb be the
bipolar-montage version of it.
Using a bipolar-referencing transform matrix M, the relation of X and Xb
can be written as

Xb = M * X

Now M is a known matrix: if your bipolar montage is referenced as F1 - F3
for example, then F1 is 1 and F3 is -1. I guess the directions of the signs
do not matter as long as they are consistent with other pairs, such as
C1-C3 etc.
After making M, you multiply M^-1 from left, you obtain

X = M^-1 * Xb

Thus, by multiplying the inverse matrix of the known bipolar-referencing
transform matrix M, you obtain the original signal.

What a smart solution! I'm proud of him.

Makoto

On Wed, May 10, 2017 at 1:45 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
wrote:

> Dear Mubaraki,
>
> I've recently seen a solution (and a surprisingly simple solution) one of
> my colleague used in SCCN. I'll ask him about it and will get back to you.
>
> Makoto
>
> On Tue, Feb 14, 2017 at 7:12 PM, Ibtissem KHOUAJA <
> ibtissem.Khouaja at live.fr> wrote:
>
>>
>> Dear Mubaraki,
>>
>>
>> I think it will be not the same.
>>
>>
>> The EEG, in this case, records the potential difference between two
>> active electrodes.
>>
>>
>>
>> Yours, Ibtissem
>>
>>
>>
>> ----------------
>> ------------------------------------------
>> ----------------------------------------------------------
>> PhD in computer science
>> Speciality: Biomedical Signal Processing
>> Laboratory: LTIM, University of Monastir, Tunisia
>> http://www.labtim.org/accueil.php
>> Laboratory: LIGM, Univerisity of Paris-East, France
>> http://ligm.u-pem.fr/
>>
>>
>> ------------------------------
>> *De :* eeglablist-bounces at sccn.ucsd.edu <eeglablist-bounces at sccn.ucsd.edu>
>> de la part de Mubaraki A.A.H. <aahm1v15 at soton.ac.uk>
>> *Envoyé :* lundi 13 février 2017 12:06:13
>> *À :* EEGLAB List ‎[eeglablist at sccn.ucsd.edu]‎
>> *Objet :* [Eeglablist] convert EEG montage from bipolar to unipolar
>>
>> I am using data from https://physionet.org/pn6/chbmit/ for EEG research
>> on EEGLAB. The channels here are provided in terms of a bipolar montage
>> (ex: FP1-F7 instead of FP1). How can I convert this bipolar montage to the
>> standard, unipolar channel data
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>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>

--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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