We were recently asked for a design to do an unusual type of bipolar training on the Atlantis. The client wanted to take one bipolar pair as one channel, and a different bipolar pair as another channel, then train the difference between these channels. For example, one channel might be Fp1-T3. Another channel might be Fp2-T4. Then, with these as two channels, train the difference between them, as a virtual channel. What was wanted was to do this twice, so that it is repeated with T3-P3 and with T4-P4, creating yet another virtual channel. Then the difference between the two virtual channels is desired, to do whole-head bipolar training. As another variation, the sum of these two virtual channels was also desired. This produces a unique combination of intrahemispheric and interhemispheric training.
In order to configure this on an Atlantis 4×4 and use the sum-channel mode to do the channel combinations, the following description shows how to connect the leads. Note that all sites are still being acquired monopolar, so if a linked ear reference is used, for example, it is still possible to do 4-channel live Z-Scores along with this type of training.
Note the following algebra for one of the desired combinations:
(A – B) – (C – D) (what you want)
= A – B – C + D
= A + D – B – C
= (A + D) – (B + C) (what the software produces)
Note how the minus signs inside the parentheses have turned into plus signs, by rearranging the terms.
Now the last arrangement, (A + D) – (B + C) is the type of equation that channel 3 becomes, when using 4-channel sum-channel mode with the Combine Option. Only now, A is channel1, D is channel 2, B is channel 3, and C is channel 4.
One equation wanted was:
((T3 – Fp1) minus (T4 – Fp2)) MINUS ((T3 – P3) minus (T4 – P4))
Se let A=T3-Fp1, D=T4-Fp2, B=T3-P3, and C=T4-P4. Then you get what you wanted. Therefore, set so:
acquired channel 1 = T3-Fp1
acquired channel 2 = T3-P3
acquired channel 3 = T4-P4
acquired channel 4 = T4-Fp2
So the way to do it is connect as follows:
A1 T3
R1 Fp1
A2 T3
R2 P3
A3 T4
R3 P4
A4 T4
R4 Fp2
A similar exercise will produce the other combination you wanted:
(A – B) + (C – D) (what you want)
= A – B + C – D
= A + C – B – D
= (A + C) – (B + D) (what the software produces)
You wanted:
((T3 – Fp1) minus (T4 – Fp2)) PLUS ((T3 – P3) minus (T4 – P4))
So let A=T3-Fp1 C=T4-Fp2, B=T3-P3, and D=T4-P4.
So in this case,
acquired channel 1 = T3-Fp1
acquired channel 2 = T3-P3
acquired channel 3 = T4-Fp2
acquired channel 4 = T4-P4
So connect:
A1 T3
R1 Fp1
A2 T3
R2 P3
A3 T4
R3 Fp2
A4 T4
R4 P4
In both cases, you would use sum-channel mode, “combine,” and train using “channel 3” as the training channel.
