The transformation to painful touch is also intimately tied to the actions of non-neuronal cells (e.g., microglia, astrocytes, and oligodendrocytes) in the dorsal horn that also serve to maintain the persistent pain state. The transformation of touch into pain results from peripheral nerve or tissue damage and involves changes in key dorsal horn circuits that stem from aberrant primary afferent input and altered descending supraspinal input. While some forms of touch can feel pleasant, touch can also become painful after injury. Touch input from the periphery is then transmitted centrally to the spinal cord and ultimately relayed to the somatosensory cortex through a series of neuronal circuits that conserve body somatotopy. Contradicting this, recent work indicates that initial detection involves non-neuronal cells in the skin, which in turn communicate with nearby sensory neurons. Central dogma indicates that sensory neurons are the sole and initial responders to mechanical stimuli in the skin. Despite the vital importance of touch in our lives, our understanding of exactly how mechanical stimuli are detected in the skin and converted into action potentials is still in nascent stages. In humans, tactual acuity and postural stability decrease with age, which leads to difficulties with tasks that require fine manipulations and an increase in falls due to reduced tactile sensation in the feet ( Dannenbaum and Jones, 1993 Ken-shalo, 1986 Tanaka et al., 1996 Tremblay et al., 2003). Gentle touch is critical for the healthy development of a newborn baby ( Ardiel and Rankin, 2010 Hopper and Pinneau, 1957). Our ability to sense touch is indispensable for daily activities throughout our lives.
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