Most often telepathy occurs spontaneously in incidents of crisis where a relative or friend has been injured or killed in an accident. An individual is aware of the danger to the other person from a distance. Such information seems to come in different forms as in thought fragments, like something is wrong; in dreams, visions, hallucinations, mental images, in clairaudience, or in words that pop into the mind. Often such information causes the person, the receiver, to change is course of action, such as changing his travel plans or daily schedule, or to just call or contact the other person. Some incidents involve apparent telepathy between humans and animals.
Telepathy seems to be related to the individual's emotional state. This is true of both the sender and receiver. Most women were receivers, as case findings showed, and one possible explanation is that women are more in touch with their emotions and rely on intuition more than men. Geriatric telepathy is fairly common, this may be due, it is speculated, to the impairment of the senses with age.
Telepathy can be induced in the dream state. It appears to be related to some biological factors: blood volume changes during telepathic sending, and electroencephalogram monitoring show that the brain waves of the recipient change to match those of the sender.
Dissociative drugs adversely affect telepathy, but caffeine has a positive effect on it.
Telepathy, like the other forms of psychic phenomena is elusive and difficult to test systematically. Enough evidence is available to reasonably substantiate the phenomenon does exist. But, quantifying it seems to be another matter. The phenomenon is closely connect to the emotional states on both the sender and receiver which creates difficulty in replicating experimental results. Attitudinal factors also influence the phenomenon. The best that researchers can hope for is to have supportive and receptive subjects in experiments that produce similar results
However the most profound and far-reaching implications to be able now to claim that telepathy, clairvoyance and precognition are indubitable hard facts; that the evidence for them is as well-founded and reliable as for the basic facts of physics and chemistry. The second section of this book is designed to outline the sort of evidence upon which this statement is founded, to point towards some of the laws governing para-normal phenomena - or, at least, towards helpful theories of their nature - and finally to consider the implications. What sort of a universe is it in which these things are facts? What do they tell us of the nature of Man himself?
http://www.survivalafterdeath.org/articles/johnson/telepathy.htm