Pain Perception in Fibromyalgia Linked to Reduced Brain Activity in Primary Motor Cortex, Study Finds

Pain Perception in Fibromyalgia Linked to Reduced Brain Activity in Primary Motor Cortex, Study Finds

People with fibromyalgia show reduced metabolic activity and altered electrical activity in the primary motor cortex — the areas of the brain that control voluntary body movements, a study has found.

These results point to a connection between an altered primary motor cortex and pain perception in fibromyalgia (FM) patients. 

The study, titled “Mutual interaction between motor cortex activation and pain in fibromyalgia: EEG-fNIRS study,” was published in the journal PLOS ONE.

Activation of the primary motor cortex interacts with parts of the brain that process pain. People who experience chronic pain, such as those with FM, appear to have an altered primary motor cortex.

Research has shown that increased physical activity can lead to an improved quality of life for people with FM. However, the complex processes that govern the interaction between movement and pain are not well-understood.  

To explore this connection more deeply, researchers based at the Bari Aldo Moro University, in Italy, designed a study to measure the activity in the primary motor cortex in people with FM during voluntary body movements in response to pain stimulation and compared those findings to people without FM. 

The team recruited 38 people with FM (average age 42 years, 35 women), and 21 people without FM (average age 32 years, 15 women) to served as controls. 

Brain activity was measured using a combination of an electroencephalogram (EEG), which measures electrical activity in the brain, and functional near-infrared spectroscopy (fNIRS), which analyzes metabolic activity by measuring hemoglobin levels — the protein that carries oxygen around the body and is elevated in active areas of the brain. 

Voluntary movements were assessed using the finger-tapping task, a common technique to evaluate muscle control and motor ability in the upper parts of the body. 

The task involved sitting in a chair and pressing a push-button panel with the right-hand thumb (all participants were right-handed). Two types of tapping tasks were used, the slow-tapping test (pressing a button every five seconds) and the fast-tapping test (clicking the button as quickly as possible).

Pain was stimulated using laser light directed at the back of the hand, and perceived pain was assessed using a visual analog scale, where zero meant no pain and 100 recorded the worst imaginable pain.

The overall experiment involved a series of randomized tapping tasks and pain stimulation with one-minute rest intervals. Brain activity was measured throughout. 

The analysis found that, compared to controls, people with FM were slower on the fast finger-tapping task, regardless of pain stimulation. 

As expected, metabolic activity, as measured by fNIRS, found motor cortex activity was centered on the left side of the brain. FM patients overall had reduced activity in the motor cortex compared to controls, especially during the fast-tapping task. Even when resting, people with FM showed a trend toward lower hemoglobin levels in this area of the brain than healthy controls. 

Pain stimulation had little effect on motor cortex metabolism in both groups, and the reduced activity seen in FM patients was independent of the duration or severity of their disorder.

Electrical brain activity, as measured by EEG, was significantly different between FM patients and healthy subjects when the pain was stimulated on the right hand, and during the fast-tapping task. In contrast, no significant changes in brain activity were observed when the left hand was stimulated. 

As expected, patients and controls differed significantly in their perception of pain intensity following laser stimulation. However, their perceived pain was unaffected by the finger-tapping task. 

“The complex mechanisms of interaction between networks involved in pain control and motor function require further studies for the important role they play in structuring rehabilitation strategies,” the authors said.