Referee 1's review:

**********
N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication, the manuscript has been revised in light of these comments and to address other editorial requirements.
**********

This is an interesting paper, perhaps not so new in its findings, that focuses on the gender differences of mu rhythm desynchronization. Apart from some minor points I will discuss later, there is a main concern that should, in my view, be addressed by the authors.

All the paper focuses on the difference found in mu rhythm desynchronization during action observation between males and females. It is obvious, therefore, that other indexes of female or male typicality correlate with mu rhythm desynchronization. However, it is not demonstrated that such an asymmetry of desynchronization is specific for action observation and is not present also during action execution or motor imagery (two other conditions known to depress the mu rhythm).

In other word, if the asymmetry in the mirror neuron system is paralleled by an analogue asymmetry in motor execution, the theoretical framework built on the present results would fall down. I therefore ask the authors to address this specific point by performing a control experiment.

Minor points

Abstract: I don't like the expression 'extreme male brain theory', and it is not true that this work gives support to that theory.

Introduction, please, remove the acronym 'aka' and explain better what mirror neurons are
Introduction, p 3, conceivably not conceivable
Introduction, p 3, the paragraph starting with "The MNS, a basic sensory-motor......" presents hypotheses as if they were experimental data. I would smooth that.

Results, p 7, Correlation of Mu suppression and dispositional measures. It is obvious that these parameters correlate with the degree of mu suppression. Simply because both, the parameters and the mu suppression correlate with gender. I found quite tautological this part of the work.

Discussion: too long, verbose and somehow unsubstantiated. The association between MNS and autism seems here quite hard.

Methods, p 14, electro not eletro
Methods, p 15, the part on the 'clean data' is poorly written
Methods, p 15, if the authors normalyze the data on the baseline, baseline data themselves should be provided in the results and a t-test should be performed on them to control for a possible gender-related effect on baseline.

Bibliography, too many citations...