A mathematical model of dorsal horn circuits' contribution to neuropathic pain.

The spinal cord is the first site for a synaptic relay in the somatosensory nervous system, where peripheral afferents synapse onto second order neurons. Noxious somatosensory afferent input is primarily transmitted to interneurons and projection neurons in the dorsal horn of the spinal cord, and projection neurons then transmit the information to supraspinal neural circuits for further processing. Despite this crucial role in pain processing, little emphasis has been placed on the dorsal horn circuits' possible contribution to neuropathic pain conditions such as phantom limb pain. Here, a mathematical model of the integration of noxious and innocuous somatosensory afferent input in the dorsal horn is presented. Dynamics of the neuronal populations are modeled using a population rate-based approach. The model successfully recreates common observations related to pain, such as wind-up and inhibition by innocuous touch. Furthermore, changes in afferent input and modifications of the synaptic connections, which are hypothesized to occur following nerve injury, give rise to output consistent with allodynia and persistent spontaneous pain. These explorations provide insights into possible mechanisms contributing to neuropathic pain conditions such as phantom limb painClinical Relevance- This model offers interesting predictions of how changes in the neural circuits at the spinal cord level may contribute to neuropathic pain conditions such as phantom limb pain and allodynia.