Figure 1.

Subthreshold synaptic inputs. The substrate for receptive field plasticity. Intracellular in vivo recordings from a nociceptive-specific rat dorsal horn neuron revealing subthreshold synaptic inputs. The output of somatosensory neurons is determined by those peripheral sensory inputs that produce sufficiently large-amplitude monosynaptic and polysynaptic potentials to evoke an action potential discharge (A and B). This constitutes the receptive field or firing zone of the neuron. However, stimuli outside the receptive field can evoke synaptic inputs that are too small normally to produce action potential outputs (C), and this constitutes a subliminal fringe or low-probability firing fringe, which can be recruited if synaptic efficacy is increased, to expand and change the receptive field. In this particular neuron, a standard pinch stimulus applied to points A, B, and C evoked only action potentials at points A and B but clear subthreshold synaptic inputs at C. Modified from Reference 365.