Science

ADHD and pain sensitivity are linked and exacerbated by each other – Sciences et Avenir

Attention deficit hyperactivity disorder (ADHD) increases pain sensitivity, which in turn exacerbates ADHD, French mouse researchers show. Reciprocal impairment due to alteration of the cerebral pain control network, according to this paper published in PNAS.

Attention and its disturbances modulate pain sensations.

Difficulty concentrating, inattention, impulsivity, and potential hyperactivity are among the well-known symptoms of ADHD, which affect about 2.5% of adults, according to the HyperSupers Specialist Association. Less well known, hypersensitivity to pain is also one of the features reported by these patients and is supported by the importance of their withdrawal reflexes when confronted with a painful stimulus. “Our work began with a 2013 study in which this hypersensitivity in adults with ADHD was partially reduced with Ritalin or methylphenidate, which are reference drugs,” explains Science et Avenir neurologist Mark Landry, who led this new work. Thus, this sensitivity to pain is clearly related to the disorder itself, as it is reduced by treatment.

The link between pain and ADHD may seem nebulous. In fact, there is a direct connection, although it has not yet been demonstrated. “In the brain, and in particular the cortex, certain areas involved in pain perception are also known to control emotions or executive functions such as attention,” Landry explains. The anterior cingulate cortex (ACC) and the insular cortex (or insula) are among these areas linking pain and attention. This is a connection that we can intuitively understand: “on the one hand, we can distract from part of our pain by focusing our attention on something else, or concentrate on it and perceive it in a more important way, and on the other hand, pain limits the ability to concentrate attention,” the researcher concludes.

Mice that suffer faster and harder

This is what the team is seeing in very special mice, designed to show all the basic and accompanying symptoms of human ADHD, and which took several years to develop. “By measuring the withdrawal reflex of these mice when confronted with a painful stimulus, we assessed their sensitivity to pain, hot, cold and mechanical stimuli,” explains Mark Landry. The team makes two important findings. Primarily, pain sensitivity was reinforced in the house these mouse ADHD under normal conditions. The effects of the pathological pain condition were then amplified in mice with ADHD: nope Only them threshold from sensitivity to pain was lower than among animals healthy, but from Besides gap Between them states normal and painful was the most important. “We are already starting from a lower level, and we adds a differential more raised, So in finality is a state Indeed very sensitive” annotation Mark Landry. Second conclusion : this is increase sensitivity through a increase activity belonging neurons belonging Bone marrow dorsal, loaded from transmit pain stimulus from in periphery before brain.

Areas of the brain responsible for attention and pain are hyperactivated.

It remained to determine the areas of the brain underlying these disorders of the spinal networks (relating to the spinal cord). Since the CCA and the insula are well known to be involved in both pain and attention, they are the first suspected by researchers. “Indeed, CCA was hyperactivated in mice with ADHD and even more so in induced pain,” reports Mark Landry. Conversely, by modulating the activity that binds the CCA and the insula, the researchers observed an effect on pain. The more the pathway between the CCA and the insula is activated, the more neurons in the spinal cord are activated and the more pain is felt. On the contrary, the inhibition of CCA and its association with the islet caused the opposite effect. “But above all, this pain control via the CCA-insula is enhanced in ADHD mice when they are already more active than in healthy mice at the base,” Landry notes. Thus, in people with ADHD, these areas of the brain that influence pain are not only more active, but also respond abnormally to pain. “ADHD and persistent pain exacerbate each other,” the researchers conclude, “and new treatments need to target overlapping mechanisms to be more effective.”

Possible neuroinflammation

For Mark Landry, the cause of these brain dysregulations in ADHD is probably localized inflammation in the CCA and insula. “This concept of neuroinflammation has been extensively researched in several neurological pathologies. In addition, some papers already describe changes in inflammatory markers in people with ADHD,” says Mark Landry. In collaboration with Inserm in Tours, he and his team are already working to correlate these findings with blood and urine tests from ADHD patients to find the same variations in inflammatory markers, with initial results scheduled for 2024.

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