However, both anatomical and physiological measurements
indicate that sensory integration begins at subcortical levels, providing a compelling argument against a labeled-line theory of somatosensation. Today, with the use of molecular genetics, and equipped with strategies for acute ablation and/or silencing of neuronal subtypes, we can test the idea that the exquisite combination of ion channels, organizational properties of cutaneous LTMR endings, and CNS circuits are the substrate of tactile perception. This Review describes the anatomical and physiological characteristics of LTMRs and their associated spinal cord circuits responsible for translating mechanical selleckchem stimuli acting upon the skin into the neural codes that underlie touch perception. We begin by highlighting key features that endow each LTMR subtype with its unique ability to extract salient characteristics of mechanical stimuli and then describe the neuronal components of the spinal cord that receive LTMR input and how these components are assembled into circuits that process innocuous touch information. Pain and touch are intricately related, and insights into pain processing may
reveal fundamental principles of normal touch sensations. Thus, whenever possible, we have highlighted pain pathways as they relate to our understanding of the processing of innocuous touch information. Interested readers should consult more comprehensive reviews on Apoptosis inhibitor pain circuits and processing (Basbaum et al., 2009, Smith and Lewin, 2009 and Todd, 2010). Combined psychophysical and neurophysiological studies have resulted in a complex picture of the peripheral neural pathways involved in tactile perception. Psychophysical and microneurography techniques in humans and nonhuman primates have offered the most comprehensive view of how stimuli give rise to perceptions and what fiber types may elicit those perceptions. However, neither of these strategies
is designed to elucidate the sensory circuits and pathways underlying touch perception. On the other hand, electrophysiological recordings from model organisms have provided a wealth of information regarding the unique physiological properties of cutaneous somatosensory receptors and, in the most case of the ex vivo preparation and postrecording intracellular labeling, compelling physiological correlations to anatomical features of touch receptors (Koerber and Woodbury, 2002 and Woodbury et al., 2001). More recently, transgenic mice engineered to express molecular markers in LTMR subtypes have broadened our understanding of touch receptor biology. In combination with physiological recordings in skin-nerve preparations, mouse transgenic tools have enabled definition of LTMRs by their anatomical and physiological attributes (Li et al., 2011 and Seal et al., 2009).