Toward the unknown: consciousness and pain

Pain is a conscious sensation that can be studied more tractably than general consciousness. Three neural systems are required: the somatosensory system relays injury information to the thalamus, where awareness of injury arises without painfulness; the affective system modulates pain intensity; and the cognitive system directs attention. Imaging reveals two essential cortical circuits for pain and attention in the anterior cingulate cortex, activated when high-frequency input induces long-term potentiation at synapses on pyramidal neuron apical dendrites, involving AMPA and NMDA receptors and type-1 adenylate cyclase. The apical dendrites form a network where serious injury input produces a local field potential. The author proposes experiments in mouse models to test whether this local field potential is necessary and sufficient for pain consciousness.

Study at a glance

Abstract

Abstract Studies of consciousness are hindered by the complexity of the brain, but it is possible to study the consciousness of a sensation, namely pain. Three systems are necessary to experience pain: the somatosensory system conveys information about an injury to the thalamus where an awareness of the injury but not the painfulness emerges. The thalamus distributes the information to the affective system, which modulates the intensity of the pain, and to the cognitive system that imparts attention to the pain. Imaging of patients in pain and those experiencing placebo and hypnosis-induced analgesia shows that two essential cortical circuits for pain and attention are located within the anterior cingulate cortex. The circuits are activated when a high-frequency input results in the development of a long-term potentiation (LTP) at synapses on the apical dendrites of pyramidal neurons. The LTP acts via α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors, and an anterior cingulate cortex–specific type-1 adenylate cyclase is necessary for both the LTP and the pain. The apical dendrites form an extensive network such that the input from serious injuries results in the emergence of a local field potential. Using mouse models, I propose experiments designed to test the hypothesis that the local field potential is necessary and sufficient for the consciousness of pain.