I believe a combination of Senna's unusual mind and his spirituality had the effect of overriding the usual reflexes in response to a 'what if' moment, for want of a better word. For example, with the car on the limits, often the mind finds an internal limit it believes or estimates to exist in reality when in fact, in all physical practicality the car has a larger margin before hitting it's actual limit. The driver can't feel this limit, can't trust it and can't sense it - but it is there.
Senna overcame this barrier, because his concentration and focus was such that his consciousness simply switched off and allowed his automatic subconsciousness to take over completely. This is what he describes as happening before his Monaco crash in 88 and the 'pin prick' of awaking from his subconscious state.
An example, albeit a corny one, is that of a karate chop on a piece of wood. As the old adage goes, if you believe your hand will pass through the wood, you will break the plank in half easily. On the surface this appears to be new-age baloney. But in practicality it makes sense - if you overcome the fear of hurting your hand then this has the effect of maintaining the pressure as your hand hits the plank. The natural reflex to recoil as your hand hits the wood, or as you feel pain, is overcome.
Senna's belief in a Christian God and Jesus may seem crazy to agnostic or atheists like us, but I think it had the effect on Senna of overcoming the natural primeval human fears and reflex actions associated with danger, and driving a car close to it's limits.
This reminds me also of another Brazilian, one Filipe Massa at Monaco, taking it far too easy in damp conditions. Race engineer Rob Smedley analysed the telemetry and told him he was being 'a wimp' and to push harder. Massa couldn't believe he had any more margin remaining, but the telemetry, the physics said otherwise. He simply had to close his eyes, have faith in what the car was capable of and let his subconscious take over, rather than to listen to his rational conscious mind, and even his racer's instinct for the feel and balance of his Ferrari.
Or maybe Senna's secret was a more earthly one. I remember him suggesting his prayers and visions of Jesus left him relaxed, smiling and laughing at the start of a race, completely free of nerves. He also suggests that sex the night before a race gave him a 'who cares?' gung-ho attitude to racing the next day.

Which is understandable, considering he was dating with Xuxa at the time.
