Putting aside brain injury and mushrooms, neither of which are necessary anyway, could Ueshiba have been one of the many millions of people who experience synesthesia? Sure, why not? One of my friends just revealed to me that she was blessed with this condition - and described in detail what colors she perceived when she heard various sounds.
Frankly, this thread is getting side-tracked on the subject, so let's bring it back to center.
1. Most people who are healthy who describe synesthesia, talk about either the aesthetic wonders of the experience, how distracting it is, or in some cases, savant skills (different numbers have different colors, enabling one savant to calculate at astonishing speeds). I do not recall ever reading about synesthesia contributing to physical abilities.
2. This discussion pre-supposes that Ueshiba was out-standing, in the sense that his skills surpassed those of any and all - thereby needing a special beyond human power. Most of Ueshiba's skills were not unique to him. The one's that were beg a question - are they merely fantasies that his students - and he - told? Or did he have paranormal powers as well? So, perhaps we can break down his 'powers."
He could evade attack of even multiple individuals, and grab like a vice, and break your bones if he chose. Certainly, these are skills held by many.
He had a high level of skill in "aiki" -
(there, that was quick) - but he was not alone in this. Others equaled or surpassed him, both in Japan or elsewhere.
Some, however, questioned his skills then and now. Kunii Zen'ya of Kashima Shin-ryu publicly derided Ueshiba and aikido. On of my own teachers stated to me that Ueshiba's sword work was inept, citing the way he did Yokokiuchi (striking a bundle of sticks). "When done properly, you strike one point every time. Eventually, the sticks are broken through, but the bark, except for that one point, is untouched. Ueshiba-san just whacked away like he was doing exercise."
The magic accounts - seeing beams of light, Shioda's claim that Ueshiba had soldiers fire at him and he dodged the bullets and ended up behind them, the atemi Ueshiba allegedly did to a top judo man, crippling him forever. Interestingly, Shioda was a source of a lot of these. Another example would be Terry Dobson's account of attacking him full force and finding himself wafted up in the ionosphere, gazing down at the azure ball of the earth, and then falling through the atmosphere BOOM! - to "awake" on the tatami, with Ueshiba gazing, amused, in his eyes, or the calling up of the malevolent kami that sickens Mariye Takahashi
I must say, my favorite was the time the uchi-deshi asked Ueshiba if he could teleport and he materialized at the top of the stairs and they asked him to do it again and he got mad and said that it took ten years off his life (and I can't help wondering how many years each practice rep pared away). Nonetheless, these stories are beyond aiki stories - and it's either a case of "where there's smoke, there's fire," or "smoke and mirrors."
IF such things exist, then one would be required to undertake esoteric training. Ueshiba is not the only one of whom such things have been described. I've heard of other budoka who also, allegedly, had paranormal powers. So, for those interested in such, mikkyo, shamanistic practices, lots of mushrooms - something extra is required.
However, the first two items - "aiki" included - are, by all reports, a matter of meticulous practice, good teaching and hard work.
No brain damage required.