‘‘Seeing’’ through the tongue: cross-modal plasticity in the congenitally blind Ron Kupers a, * , Maurice Ptito b a Center for Functionally Integrative Neuroscience (CFIN), Aarhus University, and Aarhus University Hospital, Noerrebrogade 44, 8000 Aarhus Denmark b School of Optometry, Universite ´ de Montre ´al, CP 6128 Montreal H3C 3J7, QC, Canada Abstract. Sensory substitution refers to the capacity of the brain to replace the functions of a lost sense by another sensory modality. This cross-modal plasticity has been documented both in animals and humans deprived of a particular sensory modality, such as vision or audition. Discovering new ways to exploit this cross-modal plasticity may help to optimize the recovery of sensory loss. The most commonly used form of sensory substitution is Braille reading, which enables the blind to read by using the somatosensory system. Recently, a human–machine interface, the tongue display unit (TDU), which uses the tongue as a medium for visual substitution in blind subjects, has been developed. We trained six congenitally blind and five blindfolded, sighted controls to use the TDU to perform a visual orientation discrimination task. Subjects were positron emission tomography (PET) scanned before and after an intensive 1-week training program with the TDU. Before training, no increased activity was measured in the visual cortex of either group during the orientation detection task. However, after training, patterned stimulation of the tongue activated the visual cortex in congenitally blind subjects. Sighted controls did not show occipital activation post-training despite equivalent performance on the same task. These data reveal the development of cross-modal plasticity in the brains of congenitally blind subjects. They further show that the time course of neuroplasticity in humans can be remarkably rapid. D 2004 Elsevier B.V. All rights reserved. Keywords: Cross-modal plasticity; Congenitally blind; Transcranial magnetic stimulation; Occipital cortex; Sensory substitution 1. Introduction Sight is probably the most important of our senses. Since we live in a very visual world, the loss of vision is one of the most incapacitating events that may overcome a person. It is therefore not surprising that many attempts have been undertaken to develop artificial forms of vision. The best-known example of artificial vision is Braille reading. Although Braille is an important tool for the blind, a major limitation is that it does not allow one to convey information from objects placed outside the egocentric space. 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.04.053 * Corresponding author. Tel.: +45-8949-3081; fax: +45-8949-4400. E-mail address: ron@pet.auh.dk (R. Kupers). www.ics-elsevier.com International Congress Series 1270 (2004) 79 – 84