Neuroscience - Neuronal plasticity: Increasing the gain in pain

We describe those sensations that are unpleasant, intense, or distressing a s painful. Pain is not homogeneous, however, and comprises three categories : physiological, inflammatory, and neuropathic pain. Multiple mechanisms co ntribute, each of which is subject to or an expression of neural plasticity -the capacity of neurons to change their function, chemical profile, or str ucture. Here, we develop a conceptual frame- work for the contribution of p lasticity in primary sensory and dorsal horn neurons to the pathogenesis of pain, identifying distinct forms of plasticity, which we term activation, modulation, and modification, that by increasing gain, elicit pain hypersen sitivity.