The brain maps input to output; a signal processing element maps input to output. The brain has feedback, both internally and externally; signal processing elements may have feedback. Feedback in a filter causes resonance, where certain frequencies are amplified and others attenuated. At extreme settings of resonance, on some filters, the output is self-oscillation: the output of the filter is completely dominated by the resonant properties of the filter. Near self-oscillation, the filter is heard to ring strongly at its resonant frequency. I suspect something similar occurs in the brain when in psychotic mania: the resonant properties of the feedback loops dominating the normal process of relating input to output, this pulling one away from reality. That's the picture.
