Much like perception and memory, certain forms of human communication are dependent on the communicators' state of consciousness. For instance, even the most proficient mathematician will have trouble understanding a complex mathematical statement spoken to him when he is in a groggy half-asleep, or low theta, state of consciousness. Likewise, someone in a hyperattentive high beta state would most likely be annoyed trying to listen to someone speaking from a slow theta state of consciousness, no doubt gritting their teeth thinking "Jesus! Hurry up and just say it already! You're wasting my time!!" and miss that "slow wave" message completely.
In this way, effective communication is an empathic process, whereby communicators "hone in" on each other's subjective state, and gradually naturally come to match it, within reason. State of consciousness extremely different from our own can be alienating, based on the nature of the relationship, and no attempt is made to match. For instance, a stranger crying on a subway train is experiencing a state of consciousness far and away from what is typical for that given social situation, and others will resist being "pulled in" to the unpleasantness of that state.
The jump in this understanding of brainwave frequency, state of consciousness, and communication is made via the state-dependent nature of cognition, perception, and memory. A change in state of consciousness can dramatically change the nature of one's thoughts; their speed, character, intensity, or mood being subject to that given state. That being said, thought associations created in a certain state of consciousness are best received by a person in that same state -- in that way the state of consciousness is, in some cases, necessary to facilitate the communication of some types of messages. Certain messages are bound to discrete "bandwidths" of consciousness, and cannot be received unless that oscillatory state is achieved. In that way, it makes sense that individuals who induce non-ordinary states often describe, all at once, suddenly "getting it," or seeing and understanding things which they previously had not been able to. It is not that their stimulus stream has changed, but rather that, say in the case of LSD, their state of consciousness is heightened and, in that induced hyper-sensitive state, aspects of their surroundings or of messages they receive are suddenly meaningful in new ways, or rather they are able to, all at once, perceive subtle aspects of those phenomenon which, in their normal state of consciousness, were ignored or "filtered" from awareness.
As I hinted at, this phenomenon of state-dependent perceptions can be thought of in terms of bandwidths or, much like radio frequencies, there is a vast range of possible perceptions we may "tune into" at any given point in time. Changes in an individual's consciousness, either upwards or downwards in frequency, allow them to become aware of new "stations," or non-ordinary ranges of communication; different aspects of the same spectrum of consciousness which we may traverse subjectively.