The Consciousness of Pain: A Thalamocortical Perspective

Abstract

Deep, dreamless sleep is considered the only "normal" state under which consciousness is lost. The main reason for the voluntary, external induction of an unconscious state, via general anesthesia, is to silence the brain circuitry of nociception. In this article, I describe the perception of pain as a neural and behavioral correlate of consciousness. I briefly mention the brain areas and parameters that are connected to the presence of consciousness, mainly by virtue of their absence under deep anesthesia, and parallel those to brain areas responsible for the perception of pain. Activity in certain parts of the cortex and thalamus, and the interaction between them, will be the main focus of discussion as they represent a common ground that connects our general conscious state and our ability to sense the environment around us, including the painful stimuli. A plethora of correlative and causal evidence has been described thus far to explain the brain's involvement in consciousness and nociception. Despite the great advancement in our current knowledge, the manifestation and true nature of the perception of pain, or any conscious experience, are far from being fully understood.

Keywords: anesthesia; consciousness; cortex; pain; thalamus.

Figure 1

The basic parameters of consciousness. Corticocortical interactions are generally thought to contribute to the aspect of awareness, whereas thalamocortical interactions contribute to the aspect of wakefulness. Both are necessary for manifesting a “normal” state of consciousness. TH: thalamus, CT: cortex.