Thanks for the helpful comments. So, is it correct to say that, if we inject two independent (uncorrelated) Poissonian spike trains into the two neurons, then it does not matter how many spikes are we sampling, the cross-correlation will be near zero? Consequently, neither the input nor the output firing rate does matter. However, if the two Poissonians share correlated spikes, then, because of the non-linearity kicks in, the output cross-correlation will scale not only with the injected correlation, but also with the firing rate.

According to elementary statistics, the estimated correlation coefficient of a population increases with the sample size. When applying this principle to cross-correlograms, we can consider firing rate as sample size, thus, for a cell pair with a fixed effective connectivity higher firing rates will give us higher cross-correlations. Unless something is special about cross-correlograms, I don't see the need for an experimental verification on this. If someone could explain it to me why this is not obvious, I would appreciate.

This study seems to be biased towards the "cultural intelligence" hypothesis.
Nonetheless, it is an ambitious project with very reach data.

Possible confounds:
1) Kids were better instructed and motivated in the social tasks utilizing the human interaction and language. The con-specific task presentation itself might provided an advantage to the children group in every task.
2) In the theory-of-mind experiments the differences between the two actors were clearly defined and necessary. The introduction of the second person did not force the subjects to switch point of view, as it should be, as a critical component of the concept of theory-of-mind.

Minor comments.
The large number of outliers in the h ... read more

Great study. It is calling for a follow-up with neuronal recording, especially from mirror neurons in F5, to see whether neurons modulate their responses depending on observing intentional vs. accidental displays of reaching actions.

Minor comments : It would be interesting to dissociate the reward component of the task from the intention-direction component by placing the reward to the non targeted container.

Possible confounds:
1) Tamarins in the study were presented by the action in multiple trials and rewarded after each intentional grasp condition. This reward might have conditioned a preference toward the targeted container.
2) Moreover, the cue to the targeted container was more available from the reach ... read more

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