From the Guidelines
A proposed mechanism by which motor cortex stimulation works to relieve pain is descending serotonin-mediated presynaptic inhibition of spinal dorsal horn. Motor cortex stimulation activates pathways that release serotonin, which then travels down the spinal cord to inhibit pain transmission at the dorsal horn level. This presynaptic inhibition works by reducing the release of excitatory neurotransmitters from primary afferent pain fibers, effectively blocking pain signals before they can be relayed to higher brain centers. The serotonergic system is particularly important in this process, as it forms part of the body's endogenous pain control system. When the motor cortex is stimulated, it enhances this natural pain-inhibiting mechanism, providing relief for patients with chronic pain conditions that have not responded to other treatments.
Some key points to consider in the context of motor cortex stimulation for pain relief include:
- The role of descending pathways in modulating nociceptive transmission, as highlighted in studies on the periaqueductal grey matter and its connections to the spinal cord 1
- The potential for motor cortex stimulation to activate these descending pathways and enhance pain inhibition, as suggested by its effectiveness in reducing pain in patients with central poststroke pain 1
- The importance of considering the underlying mechanisms of pain modulation when evaluating the efficacy of different treatments for chronic pain conditions.
In terms of the specific mechanism by which motor cortex stimulation relieves pain, descending serotonin-mediated presynaptic inhibition of spinal dorsal horn is the most plausible explanation, given the available evidence on the role of serotonin in pain modulation and the effects of motor cortex stimulation on pain transmission. This is supported by studies demonstrating the effectiveness of motor cortex stimulation in reducing pain in patients with chronic pain conditions, including central poststroke pain 1.
From the Research
Proposed Mechanism of Motor Cortex Stimulation for Pain Relief
- The proposed mechanism by which motor cortex stimulation works to relieve pain is related to the modulation of pain-signaling pathways.
- Studies have shown that motor cortex stimulation (MCS) can activate the descending analgesic pathways, leading to the inhibition of spinal dorsal horn neurons 2, 3.
- The specific mechanism involves the increase of serotonin in the nucleus raphe magnus (NRM) and the consequent inhibition of spinal neurons and astrocytes 2.
- MCS has been found to modulate c-fos and serotonin expression, and alter brain activity in areas such as the striatum, thalamic area, and cerebellum 4.
- The most likely answer is: Descending serotonin-mediated presynaptic inhibition of spinal dorsal horn, as supported by the study that found MCS induces analgesia by restoring the descending serotonergic pathway with consequent inhibition of spinal neurons and astrocytes 2.