Virtual reality (VR) is a powerful tool for simulating aspects of the real world. The success of VR is thought to depend on its ability to evoke a sense of "being there", that is, the feeling of "Presence". In view of the rapid progress in the development of increasingly more sophisticated virtual environments (VE), the importance of understanding the neural underpinnings of presence is growing. To date however, the neural correlates of this phenomenon have received very scant attention. An fMRI-based study with 52 adults and 25 children was therefore conducted using a highly immersive VE. The experience of presence in adult subjects was found to be modulated by two major strategies involving two homologous prefrontal brain structures. Whereas the right DLPFC controlled the sense of presence by down-regulating the activation in the egocentric dorsal visual processing stream, the left DLPFC up-regulated widespread areas of the medial prefrontal cortex known to be involved in self-refl ective and stimulus-independent thoughts. In contrast, there was no evidence of these two strategies in children. In fact, anatomical analyses showed that these two prefrontal areas have not yet reached full maturity in children. Taken together, this study presents the fi rst fi ndings that show activation of a highly specifi c neural network orchestrating the experience of presence in adult subjects, and that the absence of activity in this neural network might contribute to the generally increased susceptibility of children for the experience of presence in VEs.

Grapheme-color synesthetes perceive particular colors when seeing a letter, word or number (grapheme). Functional neuroimaging studies have provided some evidence in favor of a neural basis for this type of synesthesia. Most of these studies have reported extra activations in the fusiform gyrus, which is known to be involved in color, letter and word processing. The present study examined different neuroanatomical features (i.e. cortical thickness, cortical volume and cortical surface area) in a sample of 48 subjects (24 grapheme-color synesthetes and 24 control subjects), and revealed increased cortical thickness, volume and surface area in the right and left fusiform gyrus and in adjacent regions, such as the lingual gyrus and the calcarine cortex, in grapheme-color synesthetes. In addition, we set out to analyze structural connectivity based on fractional anisotropy (FA) measurements in a subsample of 28 subjects (14 synesthetes and 14 control subjects). In contrast to the findings of a recent neuroanatomical study using modern diffusion tensor imaging measurement techniques, we did not detect any statistically significant difference in FA between synesthetes and non-synesthetes in the fusiform gyri. Our study thus supports the hypothesis of local anatomical differences in cortical characteristics in the vicinity of the V4 complex. The observed altered brain anatomy in grapheme-color synesthetes might be the anatomical basis for this particular form of synesthesia but it is also possible that the detected effects are a consequence (rather than the primary cause) of the life-long experience of grapheme-color synesthesia.

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Background: "The feeling of being there" is one possible way to describe the phenomenon of feeling present in a virtual environment and to act as if this environment is real. One brain area, which is hypothesized to be critically involved in modulating this feeling (also called presence) is the dorso-lateral prefrontal cortex (dlPFC), an area also associated with the control of impulsive behavior.

Individuals with synaesthesia experience certain stimuli in more than one sensory modality. Most common is the linkage of letters and digits (graphemes) to colors. Whereas synaesthesia might be partly genetically determined, the linkages to specific colors are assumed to be learned. We present a systematic statistical analysis of synaesthetic color perception based on subjects' reproduction of individual colors for each grapheme, instead of simple verbal categorizations. The statistical analysis revealed that the color perceptions, measured with the HSL (hue, saturation, and luminance) scale, varied systematically among the different digits and letters. The frequencies of the digits and letters (in the German language) partly explained these systematic variations. However, digit frequency was more strongly related to color perception in the synaesthetes than was letter frequency. The results for digit and letter frequency indicate that experience with graphemes may shape synaesthetic color perception.