Matches, mismatches, and the experience of supernumerary body parts: Comment on "Left and right temporal-parietal junctions (TPJs) as "match/mismatch" hedonic machines: A unifying account of TPJ function", by Doricchi et al.

Abstract

The temporal-parietal junction (TPJ) has been implicated in a bewildering array of cognitive abilities, from at-tention to theory of mind, from memory to humour. This apparent diversity of function might seem to preclude any general theory of the TPJ. In this light, the paper by Doricchi and colleagues [1] makes an ambitious attempt to provide such a theory. They propose that the right TPJ codes matches between expected and actual events, whereas the left TPJ has separate neural populations coding for matches and mismatches. This deceptively simple interpretation allows them to provide elegant interpretations of the TPJ’s role in several domains, including theory of mind, humour, and bodily awareness. This is an impressive achievement, which provides insight not only into TPJ function, but also into deep mechanistic similarities in superficially different cognitive domains. Here, we will focus on the role of the TPJ in bodily awareness, focussing on one form of abnormal experience of the body not discussed by Doricchi and colleagues, namely the experience of supernumerary body parts. To maintain a coherent sense of the embodied self, Doricchi and colleagues argue that the right TPJ stores a template of the body against which to compare new stimuli, as a long-term updating belief system about our bodies. They discuss the involvement of the TPJ in several abnormal conditions involving altered bodily awareness, including out-of-body experiences, denial of hemiplegia (anosognosia), and claims that one’s