To him the number nine is a towering presence, pi is a breathtaking landscape, and David Letterman looks like the number 117. This episode explores the life of British writer, linguist and savant Daniel Tammet, whose synesthesia and extraordinary memory challenge our understanding of the human brain.

We trace his journey from a boy with childhood seizures in East London to a writer who translates the savant experience for the world.

• His large family, early epilepsy, and the name change to Tammet, derived from the Estonian word for oak tree.
• His diagnosis with Asperger's syndrome and rare classification as a prodigious savant.
• His European record reciting 22,514 digits of pi by walking through a mental landscape.
• His fluency in more than ten languages and learning conversational Icelandic in a single week. ...