Conjoined twins Krista and Tatiana have stunned the world's medical experts by seeing through each other's eyes.
The pretty four-year-old twins have two separate bodies but share the same brain.
The girls have a conjoined thalamus, the part of the brain that sends physical sensations and motor functions to the cerebral cortex, allowing them to hear each other's thoughts and see through each other's eyes.
But it wasn't until their proud mum Felicia Simms saw them playing that she discovered that they could see through each other's eyes.
She said: 'When they are playing, one of the girls will reach over and grab something from her sister's side and know exactly where it is without possibly being able to see it.
'It's absolutely awesome to watch them sometimes because there's no way she can see the toy she is reaching for and it's just incredible.' The girls also seem to experience each other's emotions.
'If one of the girls is hurt, the other can feel it and if you discipline one the other will also cry.'
The girls, from Vernon, British Columbia, Canada,have been receiving constant medical care since they were born.
Paediatric neurosurgeon Doug Cochrane, who has looked after them from birth, confirmed they can see through each other's eyes.
He said: 'The twins are sharing signals from the other twin's visual field.
'One twin may see what the other twin does, as the brain of one of the girls receives electronic impulses from the retina of the opposite twin.'
Felicia and her childhood sweetheart, Brendan 26, were unaware their daughters were conjoined until she was five months pregnant.
She underwent an ultrasound scan which diagnosed the twins as having a condition known as Craniopagus.
Felicia said: 'The doctors told me: 'The twins are joined together. Further tests are needed, but at the moment we know they are linked in some way'. ...
via Doctors stunned by conjoined twins who share same brain and thoughts | Mail Online.
I've wondered in the past if such a thing is possible, to have two brains connected. These girls will have some fascinating things to teach us about the human brain. Since thoughts we can hear in our minds all go through the thalamus, it will be interesting to learn to what degree they share one consciousness.
The bilateral removal of the centromedian nucleus (part of the Intra-laminar nucleus of the Thalamus) appears to abolish consciousness, causing coma, PVS, severe mutism and other features that mimic brain death. The centromedian nucleus is also one of the principal sites of action of general anaesthetics and anti-psychotic drugs. This evidence suggests that a functioning thalamus is necessary, but not sufficient, for human consciousness.
Some have suggested the controversial notion that human consciousness resides fully or at least mainly in the centromedian nucleus.
The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain. ... The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, probably in the ILN of the thalamus, but no one can say how it works.