I'm not a full blown neuroscientist like ND, but I do have some background in it. As I understand it, hallucinogens form connections within the brain that do not normally form while sober. The chaotic nature of a hallucinogen trip makes it difficult to pinpoint parts of the brain that are interacting. Looking at the glowing areas in an fMRI is not enough to form a concrete conclusion about ... anything really. There are too many factors at play, and all we can rely on is a traditional reductionist model (which is severely lacking, mind you). For example, if a part of the brain lights up on LSD that is associated with visual acuity, one may safely say that the LSD is contributing to it. This can be verified by first-hand accounts of an acid trip. But what about more ethereal (for lack of a better term) effects of LSD, such as this "telepathy" phenomena? The absolute best way I can think of for testing this is chucking two people in an fMRI machine while tripping on acid, and instruct them to perform the memory tasks as ND described. However, the machine could interfere with the "telepathic" signals, if this is the mechanism of action. Same thing with a MEG (magnetoencephalography).

The best method to examine this "telepathy" phenomena is as ND described, a sample study. However, this wont explain the mechanism of action. All we can do is hypothesise given the current literature on the effects of hallucinogens on a neurological level.

I'm one of those people who think it is impossible to fully understand the brain. There are more neuronal connections in the brain than there are stars in our galaxy. All we can see are trends.