This recent article by Susan Dominus in the New York Times is very intriguing. The two twins, Tatiana and Krista Hogan, are joined at the skull (craniopagus) and their brains have developed in a very curious way. Doctors believe that the two thalamus’ are joined by a “thalamic bridge”, which could, perhaps, allow one twin to experience the sensory stimulation initiated by the other, which appears to be evidenced by one of the twins having a drink and the other twin reacting as if she has just drunk something. Both of the corpus callosum’s are unusually short, too, and Tatiana’s left hemisphere is smaller than her right, and Krista’s right hemisphere is smaller than her left.
Dr. Cochrane, a neurosurgeon, performed a test on the two girls, whereby one had their eyes covered and light was flashed across the other’s eyes. Dr. Cochrane detected activity in the occipital cortex of the girl who had her eyes covered, perhaps suggesting that the sensory information from the light-stimulated twin passed across the “thalamic bridge” and stimulated cells in the other brain.
This certainly seems to suggest that components of a mind can be shared in a craniopagus twin.