Somatosensation in the Brain: A Theoretical Re-evaluation and a New Model

This Opinion article presents a comprehensive review of the human and animal literature on somatosensory processing of the past 10 years.We propose a new model of the functional architecture of somatosensory processing, entailing several dedicated pathways or networks subserving different functions that rely (partly) on somatosensory information.In contrast to previous models, these pathways or networks are thought to be much less independent or ‘information encapsulated’ and much more multimodal in nature.The model includes a ‘cylinder block’ of basic somatosensory processing and higher-order networks involved in: (i) haptic object recognition and memory; (ii) body perception; (iii) body ownership; (iv) affective processing; and (v) action. The somatosensory system is important for many functions, such as tactile recognition, the perception of our body, and motor actions. We present a comprehensive review of the human and animal literature on somatosensory processing over the past 10 years and evaluate how well existing models can accommodate the new observations. Based on these observations and a survey of the brain structures involved in somatosensation, we suggest that a new model is needed that describes multiple networks involved in separate subfunctions. These networks are highly interconnected and often multimodal in nature. The model includes basic somatosensory processing and five higher-order networks involved in haptic object recognition and memory, body perception, body ownership, affective processing, and action. The somatosensory system is important for many functions, such as tactile recognition, the perception of our body, and motor actions. We present a comprehensive review of the human and animal literature on somatosensory processing over the past 10 years and evaluate how well existing models can accommodate the new observations. Based on these observations and a survey of the brain structures involved in somatosensation, we suggest that a new model is needed that describes multiple networks involved in separate subfunctions. These networks are highly interconnected and often multimodal in nature. The model includes basic somatosensory processing and five higher-order networks involved in haptic object recognition and memory, body perception, body ownership, affective processing, and action. Somatosensory processing is central to life; a touch on the shoulder, a soft stroke on the hand – both can say more that words. We use it to be aware of the parts that belong to our body, it has an important social function, and it is crucial for socioemotional development. It is also important for almost every activity during our daily life and forms the basis of all of our motor actions. Furthermore, somatosensory processing allows us to recognize with ease different objects based on touch alone (haptic object recognition; see Glossary). Thus, the processing of touch, temperature, pain, and proprioception are important for survival, for efficient interaction with the environment, and for emotional and social functioning. A central question is how the somatosensory system is organised to perform these different functions. While the visual system has traditionally received the most attention, the functional and neural organisation of the somatosensory system is increasingly being investigated and the complexity of the system is becoming clearer. About a decade ago, the physiology of the somatosensory input to the brain had been mapped to a detailed level (e.g., 1.Burton H. Jones E.G. The posterior thalamic region and its cortical projection in New World and Old World monkeys.J. Comp. Neurol. 1976; 168: 249-302Crossref PubMed Scopus (439) Google Scholar,2.Berkley K.J. Spatial relationships between the terminations of somatic sensory and motor pathways in the rostral brainstem of cats and monkeys. I. Ascending somatic sensory inputs to lateral diencephalon.J. Comp. Neurol. 1980; 193: 283-317Crossref PubMed Google Scholar; Box 1) and several ideas about cortical processing had been formulated 3.Kaas J.H. Somatosensory system.in: Paxinos G. Mai J.K. The Human Nervous System. 2nd edn. Academic Press, 2004: 1059-1092Crossref Google Scholar. Single-case studies 4.Sirigu A. to body a of PubMed Google and for tactile object PubMed Scopus Google the of in somatosensory as well as studies of and and with several models that the functional and of the Somatosensory in the and the in the and in the and in the posterior lateral of the in of The Nervous System. Scholar. A the with and and tactile The system also to the somatosensory the the to the E.G. thalamic relationships of and cortical in monkeys.J. Comp. Neurol. PubMed Google Scholar]. 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