I know that neurons can exhibit tonic and phasic firing, and also that a neuron is sometimes called an integrator. This makes me interested to know if there are activities in the brain that depend on two or more signals of different frequency occurring at the same time. For example, in a telephone system, two signals with a different frequencies at once(DTMF) are interpreted as 1. Is there anything similar in the human brain?
Remembering that neurons don't generate sinusoids, just spikes (mostly)....
It depends on exactly how you want to define "depend on". For instance, a downstream neuron receiving inputs from two neurons will be more likely to fire as it spatially/temporally sums the inputs from the two neurons. Regardless of their specific rates, if their interaction is such that an impulse from each neuron arrives within a certain timing of the other, it may be sufficient to cause the downstream neuron to spike. In this case, particular sets of frequencies of the two upstream neurons would be more likely to activate the downstream neuron and would do so at a particular rate for the downstream neuron. Of course, the phase delay between the two neurons would be important too.
In a more general sense, one might consider the binding problem, by which many sensory inputs are bound into a single, higher level experience, such as an object or a biographical memory, which can then later be recalled (and thus activate all the lower sensory regions that encoded the memory in the first place, nearly recreating the experience).
There is a somewhat-hypothetical phenomenon called cross-frequency coupling which has generated some interest recently. This has mostly been described in the hippocampus and in interactions between the hippocampus and neocortex.
In general, drawing analogies of how the brain might work from engineered telecommunication/computing system can be quite misleading.
I just wanted to add Izhikevich's FM modulation theory of communication, but I would say it is controversial.
- Izhikevich E.M. (1999) Weakly Pulse-Coupled Oscillators, FM Interactions, Synchronization, and Oscillatory Associative Memory. IEEE Transactions On Neural Networks, 10:508-526
- Hoppensteadt F.C. and Izhikevich E.M. (1998) Thalamo-Cortical Interactions Modeled by Weakly Connected Oscillators: Could Brain Use FM Radio Principles? BioSystems, 48:85-94