Figure 9

Diagrams of nociceptive inputs and STP in the ACC under acute normal and abnormal chronic pain conditions. A. Synaptic responses of ACC neurons to regular discharging thalamic afferents. B. Responses of ACC neurons to bursting thalamic afferents. C. ACC circuit organization during two conditions of thalamic output (cortical layers shown on right). In the acute pain state, the nociceptive signals are conveyed to the ACC through normal thalamic activity to dendritic targets of pyramidal neurons in layer V (blue dashed lines) and evoke a weak discharge. STP in these synapses regulates ACC neuron output to the striatum and PAG. In contrast, abnormal thalamic bursting occurs following persistent nociceptive inputs from the periphery (solid red lines) and these bursting impulses initiate and facilitate multiple action potentials in ACC neurons. The enhanced and maintained activities in these neurons facilitate the intracortical nociceptive transmission and descending outputs which further influence ACC targets in other brain regions.