Review
Touch and the body

https://doi.org/10.1016/j.neubiorev.2009.04.004Get rights and content

Abstract

The dual nature of touch has long been understood. The sense of touch seems to carry information at the same time about the external object touching our skin, and also about our body itself. However, how these two interact has remained obscure. We present an analytic model of how tactile information interacts with mental body representations in the brain. Four such interactions are described: the link between the body surface and the maps in primary somatosensory cortex, the contribution of somatosensory cortical information to mental body representations, the feedback pathway from such higher representations back to primary tactile processing in somatosensory cortex, and the modulation of tactile object perception by mental body representations.

Section snippets

Introduction and model

Touch is often considered by neuroscientists under the general heading of somatosensation. This already reveals a strong link between tactile sensation and perception on the one hand, and the body on the other. Indeed, the receptor organ for touch, the skin, also forms the surface of the physical body. Although the interdependence between the sense of touch and the body is well recognised, this interaction can take place at a range of different levels within the nervous system, with quite

Pathway 1—the physical body structures tactile sensation

The sense of touch is the phenomenal counterpart of afferent input from mechanoceptors on the body surface. Peripheral signals from the skin are transmitted through the dorsal columns of the spinal cord to the medulla, and project via the postero-lateral thalamus, to contralateral primary (SI; area 3b and 1 in the monkey) and secondary (SII) somatosensory cortices. These are located, respectively in the postcentral gyrus and parietal operculum. Somatosensory cortical areas, and SI in

Pathway 2—tactile sensations contribute to a mental body representation

Processing of tactile information does not end at the primary somatosensory cortex. Broadly speaking, brain areas showing tactile responses beyond SI can be classified in two ways, following Katz's (1925) distinction between exteroceptive and interoceptive touch. On the one hand, areas such as SII are concerned with further processing of tactile object features. Neurons in these areas have larger receptive fields but more precise tuning properties than SI, suggesting a role in feature

Pathway 3—mental body representations reciprocally influence primary tactile processing

So far we have reviewed evidence showing that the tactile representation of the body contributes to more abstract, multimodal representations of the body in the brain. In this section we will show how MBRs in turn influence primary levels of tactile processing. In particular, we focus on how visual information related to the body affects tactile sensation (Fig. 2).

Pathway 4—MBRs mediate the formation of object representations from primary tactile sensations

The tactile interpretation of an object touching the skin is often mediated by a description of one's own body. That is, exteroceptive tactile perception depends on, and implicitly includes, information from MBRs. In this sense, tactile perceptions are always referenced to the body, even if the content of the perception is an external object.

This body-referencing can take at least four forms, which we argue are conceptually quite distinct. First, touch is inevitably body-referenced in the sense

Overall conclusion

To conclude, we have shown that the sense of touch has a close and interactive relation with higher cognitive representations of our own body. Indeed, studies of tactile perception offer one of the few ways to study mental body representations in a well-controlled and quantitative way. Modulations of tactile perception often reflect the contribution of a mental body representation. We have presented an analytic and neurally plausible model, suggesting four key pathways whereby touch and the

Acknowledgements

PH's contribution was supported by BBSRC project grant D009529, and by a research grant from Bial Foundation.

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