Dear all,
We are happy to annouce our recent publication in PNAS in which BrainStorm is featured:
Coherent neural representation of hand speed in humans revealed by MEG imaging.
K. Jerbi, J.-P. Lachaux, K. N Diaye, D. Pantazis, R.M. Leahy, L. Garnero & S.Baillet - PNAS, Volume 104, Number 18, page 7676--7681 - may 2007
Please contact Sylvain Baillet for information and reprints.
[QUOTE=Sylvain;862]Dear all,
We are happy to annouce our recent publication in PNAS in which BrainStorm is featured:
Coherent neural representation of hand speed in humans revealed by MEG imaging.
K. Jerbi, J.-P. Lachaux, K. N Diaye, D. Pantazis, R.M. Leahy, L. Garnero & S.Baillet - PNAS, Volume 104, Number 18, page 7676--7681 - may 2007
Please contact Sylvain Baillet for information and reprints.[/QUOTE]
hello sylvain
could you send me a reprint of your work?
thankyou
Daniele Arisi
UO Neuropsichiatria dell'Infanzia e dell'Adolescenza
Azienda Ospedaliera di Cremona - Italy
d.arisi@ospedale.cremona.it
Hi
I wondered if someone could kindly explain in more details as to how the map displaying the coherence between M1 and other brain areas was derived?
"The difference maps were thresholded at P<0.001 using group-level (n=15), one-tailed paired permutation tests, which randomly exchanged the estimated values of coupling in R and VM for each subject."
What does it all mean? I guess I don’t understand what this exhaustive permutations analysis is.
Why was the permutation 2^15 instead of 2^12,000 for number of tessellations?
Was the coherence between cortical areas calculated separately for R and VM? Or was the VM signal subtracted? from the R condition which acted as a baseline?
Thanks.
May
Hi May,
first, thanks for your interest in the methods we used in this paper.
[QUOTE=hengrumay;1182]Hi
I wondered if someone could kindly explain in more details as to how the map displaying the coherence between M1 and other brain areas was derived?
"The difference maps were thresholded at P<0.001 using group-level (n=15), one-tailed paired permutation tests, which randomly exchanged the estimated values of coupling in R and VM for each subject."
What does it all mean? I guess I don’t understand what this exhaustive permutations analysis is.
Why was the permutation 2^15 instead of 2^12,000 for number of tessellations?
[/QUOTE]
The coherences were computed between M1 and all vertices for each subject in the rest ® condition and in the visuomotor (VM) condition. This gives for each node of the tesselation (12000 in total) a value of coherence between its activity and that of M1 (Reminder: M1 is defined as the vertex displaying maximum coherence with hand speed in the first analysis, see Fig. 1 of the paper), both for R and VM conditions. In other words, for a given subject you have at each vertex 2 values of coherence, one for each condition. Now you have 15 subjects across which you want to test whether the magnitude of coherence changes significantly in VM compared to R. Therefore, using the permutation approach, you construct the null distribution by swapping the values of R and VM. For 15 subjects you have 15 coherence pairs (VM:R) for each vertex. This gives you a total of 2^15 possible permutations.
For more information on how to use permutations to test for statistical significance please refer to these papers:
[I][B]Pantazis D, Nichols TE, Baillet S, Leahy RM.[/B]
"A comparison of random field theory and permutation methods for the statistical analysis of MEG data."
Neuroimage. 2005 Apr 1;25(2):383-94
[B]Nichols TE, Holmes AP.[/B]
"Nonparametric permutation tests for functional neuroimaging: a primer with examples."
Hum Brain Mapp. 2002 Jan;15(1):1-25[/I]
[QUOTE=hengrumay;1182]Was the coherence between cortical areas calculated separately for R and VM? Or was the VM signal subtracted? from the R condition which acted as a baseline?
Thanks.
May[/QUOTE]
Yes, the cortico-cortical coherence between M1 and the rest of the brain was computed for R and VM separately, we then used permutation tests to find the vertices that displayed significant differences between the two conditions. Note that we used z-transformed coherence values (as explained in the paper).
Hope this helps.
Karim
Hi Karim,
Thanks for clarifying! Yes it is a little clearer in my wee head.
I will try to find those references.
Thanks!
May