It has something to do with Kundalini, and how Kundalini adjusts the brain and nervous system from out of the subtle body, and takes consciousness beyond the subtle body to the causal body. Performing at such intensity and with such wholeness of being, the slightest inner movement of fear, nervousness, or self-doubt would bring the performance crashing down. To be in a state of consciousness that's beyond fear, hesitation or self-doubt, the brain must be functioning at a higher than normal frequency, a frequency at which the neural structures that register self are suspended.
(The minute self is allowed in it would surely say — God, what note's next? Where am I? I can't do it.)
So the frequency must be high and clear of stumbling blocks. This is in fact consciousness of the causal body. In a way, it's a state without past or future (Help, the last chord was wrong. I'm scared of the big cadenza coming up) and yet, miraculously, the whole of the twenty-nine-minute-long piece is stored there. This means that the music, and Yefim Bronfman's way into it, is stored somewhere else. Outside the body, outside the everyday brain in a high frequency state, like some sort of ubiquitous cloud storage, that works more instantaneously than doubt, fear, dread etc. Something is clearly going on with the frequency of the electrical energy in the brain, which runs at around 49,000,000 cycles per second (about half that of light). When blockages are cleared by Kundalini, the frequency at which we are conscious soars.
This clearing and heightening can spread through every action in life. Walking through the market, buying holiday clothes for Thai New Year can be like a performance of Prokofiev's Second Piano Concerto. In the market, the problem is desire. Delicious smells from the charcoal burners. Some Thai guy singing like Van Morrison. Pretty girls. The blocked-up brain says: I want to get some of that chicken down my throat. I wish I could sing like a Thai van Morrison. That's fifty women I've just seen, that I want to sleep with but never will. When causal body consciousness is active, I smell something other than delectable chicken, I hear something other than an enviable voice, I see something other than a possessable body. What this something other is cannot be put into words, but it's there and it's real, requiring a higher speed or frequency of consciousness to stay with it. There's a wonderful lightness and freedom. The senses become more, not less, acute.
The other area where staying with the causal body is beneficial is in sexual relationships and during the act of love. JJ Semple writes in depth about this in Seminal Retention And Higher Consciousness. There are various techniques for prolonging the sexual act and suspending ejaculation, but the sine qua non is control from the causal body, and staying with the causal body. It's this meditative, and transcendence-directed action that lifts self-control above a mere struggle with oneself, promotes intimate dialogue and leads to a deeper immersion in the other.