Since there are two threads going concerning this issue, I thought it would be easier to add this one to provide the results of my search:

Dissociation and EEG
My search basically revealed that in some cases different alters show some differences in EEG readings , but not in everyone. It really seems to be inconclusive, but I think that it is clear that some persons with Dissociative disorders do exhibit some “abnormal” patterns, but no one is drawing any definitive conclusions. However, you are not alone. Could that be helpful or reassuring?

https://scholarsbank.uoregon.edu/xmlui/handle/1794/1827

http://cat.inist.fr/?aModele=afficheN&cpsidt=13563376 Résumé / Abstract
This is the first study to apply EEG coherence analysis to the study of Dissociative Identity Disorder (DID). EEG coherence is argued to be an objective measure of cortical connectivity. Five DID patients were compared to five controls, who were professional actors. Fifteen dissociated DID alter states were studied, as were 15 alters simulated by the actor control participants. Comparisons of EEG coherence were made between DID participants and controls. Significant differences in EEG coherence were found in comparing DID host and alter personalities, with coherence found to be lower in the alter personalities. No significant differences were found in comparing DID host personalities and controls. The acted alters matched for age and gender, showed no significant differences in coherence compared to DID alter personalities. The results indicate that EEG coherence may be an objective measure of the neuronal cortical connectivity associated with DID.
Revue / Journal Title
Journal of trauma & dissociation ISSN 1529-9732
Source / Source
2002, vol. 3, no1, pp. 75-88 (1 p.3/4)
http://findarticles.com/p/articles/m.../ai_n29157071/