I was reading this paper * about the arithmetic task and EEG correlations of the flow state.
I am not sure about the negative amplitudes in Figure 3 where alpha and beta bands are discussed. Does anyone understand why?
Thanks a lot!
*Katahira, K., Yamazaki, Y., Yamaoka, C., Ozaki, H., Nakagawa, S., & Nagata, N. (2018b). EEG Correlates of the Flow State: A Combination of Increased Frontal Theta and Moderate Frontocentral Alpha Rhythm in the Mental Arithmetic Task. Frontiers in Psychology, 9, 1–14. https://doi.org/10.3389/fpsyg.2018.00300
Hello Melanie Baumgartner ,
The amplitudes plotted in Figure 3 are amplitudes measured relative to a baseline period. So, a negative amplitude represents a decrease in alpha/beta amplitude during the task/mathematical processing. It is actually quite common to see decreases in amplitude in the alpha/beta frequencies in occipital (and to an extent, parietal) cortex during visual processing. The mechanisms are not yet fully understood, but many researchers believe that these desynchronizations (and therefore decreased amplitudes) represent the disinhibition of neural populations in visual cortices, allowing for robust processing of visual stimuli. I hope this helps!
Hi Melanie Baumgartner ,
I have read this article two weeks ago. I am not expertise but what I generally understood from this figure is that low working memory load can be cause negative amplitudes in alpha and beta band .In this figure it can be seen that decreased alpha and beta amplitude especially in boredom and flow condition. Tuladhar et al. (2007) says that the high alpha activity in the parieto-occipital area is related to the load on working memory; so, lower frontal and right central alpha activity can be because of the lower load on the working memory in the boredom and flow condition. I am not sure that answer is your question but I hope this answer gives you a different perspective.
Tuladhar, A. M., ter Huurne, N., Schoffelen, J. M., Maris, E., Oostenveld, R., and Jensen, O. (2007). Parieto-occipital sources account for the increase in alpha activity with working memory load. Hum. Brain Mapp. 28, 785–792. doi: 10.1002/hbm.20306
My guess is that the data is baseline corrected. This can explain a negative value, i.e. a drop relative to the baseline period. Interestingly, the paper does not say whether and which baseline correction was applied. So it remains speculation.
While I have not seen the paper from which this figure is taken, as EEG's are normally measure with a differential amplifier and specific electrode(s) selected as a reference electrode, the voltages are usually varies from positive to negative with respect to the reference electrode(s) selected. So it should not be surprising that voltages grouped by some chosen period can be negative or positive.
Melanie Baumgartner thanks for asking this super helpful question. Brittany K. Taylor I'm really interested in "desynchronizations (and therefore decreased amplitudes) represent the disinhibition of neural populations in visual cortices." Are there any references that you could recommend? Many thanks!
Hi Ethan Kutlu,
Here are a few references to get you started!
Article Alpha Frequency Entrainment Reduces the Effect of Visual Distractors
Article From local inhibition to long-range integration: A functiona...
Article Event-related dynamics of cortical rhythms: Frequency-specif...
Brittany K. Taylor Thank you so much! I really appreciate it. Have a good day!
Dear experts:
Brittany K. Taylor
Zehra Ülgen
Melanie Baumgartner
Ethan Kutlu
Franklin Lue
Kathrin Ohla
May I ask one question?
For example, in alpha, if some output FFT values are negative and some values are positive, how to calculate the alpha absolute power? Should we integrate all negative and positive values? Or do we need to convert negative values into absolute values first? And then calculate the relative power value.
Thank you!
Zhepeng
As before since the signal is a differential voltage, one need to consider how you aim to view the alpha power with respect to the source; is your interest is in the relative alpha power from active to reference than yes by all means calculate the absolute value first, however if you are not interest in the relative electrical difference from active ti reference electron the I'd not convert to absolute.
Dear Franklin Lue
Thank you for such a quick reply! We ask this question because the relative power value should be a percentage around 0-100% (or 0-1). However, when we integrated some negative and positive amplitude data in five EEG bands (delta, theta, alpha, beta, gamma), the relative power became huge (i.e., 440%(44.44) or even over 1000%). The reason is that the integration result of five EEG bands with negative and positive values could be 1 or 2 as the denominator, but the numerator could be very large for the integration of one specific band(i.e., delta).
Therefore, we thought we needed to transfer negative value to absolute value first to consider relative power. Is the same way to transfer negative value to absolute value for calculating absolute power also? Do you have some reference or tutorial website to support this viewpoint in case reviewer concerns?
Again, thank you!
Franklin Lue
Zhepeng :)
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