3.5.5 Pain

The Neural Circuits Involved in Pain and Chronic Pain

Pain:

The transmission of pain signals from the periphery to the brain is mediated by specialized cells called nociceptors, which are activated by tissue damage or the potential for tissue damage. When nociceptors are activated, they send signals through sensory neurons to the spinal cord, which is a long, tube-like structure that extends from the brain down through the centre of the back. The spinal cord is involved in the processing and integration of sensory information, including pain.

Once the pain signals reach the spinal cord, they are transmitted to the brain, where they are processed and interpreted. The thalamus, a brain region that acts as a hub for sensory information, plays a key role in the transmission of pain signals to the cerebral cortex. The somatosensory cortex, which is a part of the cerebral cortex, is involved in the conscious perception of pain.

The amygdala, a brain region involved in emotional processing, is also thought to play a role in pain perception. The amygdala receives input from the thalamus and other brain regions that are involved in sensory processing, and it can modulate the intensity of pain signals and help regulate the expression of pain behaviours.

Other neurotransmitter systems that are involved in pain include the opioid system, which is involved in pain relief, and the sympathetic nervous system, which is involved in the body’s stress response. The opioid system includes neurotransmitters such as endorphins and enkephalins, which can inhibit pain signals and produce a feeling of euphoria. The sympathetic nervous system, on the other hand, activates the “fight or flight” response and can increase the perception of pain.

Overall, the neural circuits involved in pain processing are complex and involve the interaction of multiple brain regions and neurotransmitter systems. These circuits help to process and regulate pain signals in the body and influence the perception of pain (Craig, 2003).

Chronic pain:

Chronic pain is a complex and poorly understood phenomenon that involves the interaction of many different neural circuits in the body. Chronic pain is defined as pain that lasts for more than three months. These circuits are influenced by a variety of factors, including genetics, environment, and psychological stress, and they help to regulate the perception and experience of chronic pain.

One key brain region that is involved in the development of chronic pain is the amygdala, which is a brain region involved in emotional processing. The amygdala receives input from the thalamus and other brain regions that are involved in sensory processing, and it can modulate the intensity of pain signals and help regulate the expression of pain behaviours. Chronic pain can lead to changes in the structure and function of the amygdala, as well as other brain regions that are involved in emotional processing, such as the anterior cingulate cortex and the insula. These changes can increase the intensity of pain signals and contribute to the development and maintenance of chronic pain (Apkarian, 2011).

Other brain regions and neurotransmitter systems that are involved in chronic pain include the prefrontal cortex, which is involved in decision-making and impulse control, and the opioid system, which is involved in pain relief. Chronic pain can lead to changes in the function of these brain regions and neurotransmitter systems, which can further contribute to the development and maintenance of chronic pain. For example, chronic pain can lead to changes in the function of the prefrontal cortex, which can impair the ability to regulate pain and contribute to the development of negative emotional states such as depression and anxiety. Chronic pain can also lead to changes in the opioid system, which can impair the ability to relieve pain and contribute to the development of opioid tolerance and dependence.

References:

(1) Apkarian, A. V., Hashmi, J. A., & Baliki, M. N. (2011). Chronic pain as a disease of the brain: Underlying mechanisms. Dialogues in Clinical Neuroscience, 13(3), 365-379.

(2) Craig, A. D. (2003). Interoception: The sense of the physiological condition of the body. Current Opinion in Neurobiology, 13(4), 500-505.