Pain in bipolar disorder is not limited to the psychological pain of depression or agitation. Physical pain is also a symptom of bipolar disorder, usually in the form of muscle aches and joint pain. There are also chronic pain illnesses linked to bipolar disorder like migraines, fibromyalgia and arthritis. Research has shown that the way the brain perceives physical pain overlaps with the network that processes psychological pain. A new study takes this a step further, showing evidence that people with bipolar disorder and schizophrenia perceive pain differently than the general population.
Scientists are still attempting to learn more about how humans perceive and process pain. It is an evolutionarily old process, making it difficult to study. From what evidence has been found, it’s thought the brain perceives pain in five steps:
- Contact with stimulus (pressure, cuts, burns, etc.)
- Perception (nerve endings sense the stimulus)
- Transmission (nerve endings send signals to the central nervous system)
- Pain center reception (the signal reaches the brain)
- Reaction (the brain sends back a signal for action)
Most pain sensation is dealt with in the spinal cord, but is also processed in the brain. Pain is perceived in the brain by the thalamus, anterior insular cortex, anterior cingulate cortex and the prefrontal cortex. Each of these areas can also be affected in bipolar disorder. The ACC has been linked to affect regulation and processing negative emotions, each of which have been shown to be dysfunctional in schizophrenia and bipolar disorder. Dysfunction in this area has also been linked to psychosis.
The prefrontal cortex has been linked to both pain processing and bipolar disorder. In people who experience chronic pain, the prefrontal cortex appears shrunken in some patients. In bipolar disorder, the prefrontal cortex can also appear shrunken, especially when left untreated. In these cases, symptoms like problems with memory, emotional control, critical thinking and social functioning can be exacerbated.
A new study led by Amedeo Minichino and published in the journal Bipolar Disorders, has found more evidence that people with bipolar disorder and schizophrenia may experience pain differently than the general population.
They studied 17 patients with bipolar I, 21 patients with bipolar II, 20 patients with schizophrenia and 19 healthy controls. The participants were stimulated with lasers to simulate a pinprick sensation. Pain perception was then measured according participant report of 0 equaling no pain and 10 equaling the worst possible pain. Pain processing was measured through electrodes on the scalp to determine the areas of the brain stimulated during the pinprick sensation.
Those with bipolar disorder and schizophrenia showed dysfunctions in areas of the brain typically associated with processing painful stimuli as well as the part of the brain linked to psychosis.
Participants with schizophrenia showed a higher pain tolerance and reduced sensitivity. Those with bipolar disorder also showed abnormalities in pain processing, especially a lower response in the AIC and ACC. Bipolar II participants showed closer results to the healthy controls.
The authors suggest this might be related to the psychosis spectrum. A bipolar II diagnosis indicates no experiences of psychosis, whereas almost 60% of people with bipolar I experience psychosis at some point.
While this is an important step in understanding the way people with schizophrenia and bipolar disorder experience pain, there is much more research needed to fully understand the link.
Image credit: Xu-Gong