Cross-modal transfer of information between the tactile and the visual representations in the human brain: A positron emission tomographic study.

Positron emission tomography in three-dimensional acquisition mode was used to identify the neural populations involved in tactile-visual cross-modal transfer of shape. Eight young male volunteers went through three runs of three different matching conditions: tactile-tactile (TT), tactile-visual (TV), and visual-visual (VV), and a motor control condition. Fifteen spherical ellipsoids were used as stimuli. By subtracting the different matching conditions and calculating the intersections of statistically significant activations, we could identify cortical functional fields involved in the formation of visual and tactile representation of the objects alone and those involved in cross-modal transfer of the shapes of the objects. Fields engaged in representation of visual shape, revealed in VV-control, TV-control and TV-TT, were found bilaterally in the lingual, fusiform, and middle occipital gyri and the cuneus. Fields engaged in the formation of the tactile representation of shape, appearing in TT-control, TV-control and TV-VV, were found in the left postcentral gyrus, left superior parietal lobule, and right cerebellum. Finally, fields active in both TV-VV and TV-TT were considered as those involved in cross-modal transfer of information. One field was found, situated in the right insula-claustrum. This region has been shown to be activated in other studies involving cross-modal transfer of information. The claustrum may play an important role in cross-modal matching, because it receives and gives rise to multimodal cortical projections. We propose here that modality-specific areas can communicate, exchange information, and interact via the claustrum.