Erik Weihenmayer went blind when he was 13 years old, but new technology enables him to see with his tongue.

The BrainPort device gives him a sense of space and, together with a friend nearby, helps him scale Utah's formidable Castleton Tower.

Inside the Human Body - Building Your Brain is presented by Michael Mosley and can be seen on BBC One at 9pm on Thursday 19 May 2011 and after on BBC iPlayer