Our brain integrates information from the external environment, but also from the internal environment of the body. This environment is represented by the rest of the body, which the brain depends on and controls. In this respect, the brain is exposed to the influences of our various organs. When they do not function properly, this can lead to consequences that are sometimes very harmful. Research continues to evolve to better understand the interaction between our organs and the brain.
The effects of the Heart on the brain
We often mistakenly think that our brain is an isolated organ, when in fact it is in constant communication with the rest of the body and the various organs. For example, more and more research is being done on the connections between our heart and our brain. It has been shown that a healthy heart means a healthier brain. Researchers have shown that people with atrial fibrillation, which causes cardiac arrhythmias, lose cognitive ability faster and have a higher risk of dementia. The hypothesis is that irregular heartbeats can cause undetected microdamage and poor oxygenation of the brain, leading to a gradual accumulation of brain damage.
Changes in heart rate can also be used to detect the risk of depression. In a recent German pilot study presented at the European College of Neuropsychopharmacology conference, a wearable device was developed that measures changes in heart rate over a 24-hour period and indicates with 90% accuracy whether or not a person is depressed. Cardiovascular disease, such as hypertension, is also known to be a risk factor for stroke. A Brazilian team has shown that hypertension increases intracranial pressure, which can lead to several complications, including stroke.
The effects of the Liver on the brain
The heart is not the only organ closely linked to our brain. Liver dysfunction can also lead to severe motor and neurocognitive impairments by releasing toxic amounts of certain compounds that are no longer properly filtered. For example, severe jaundice in infants due to abnormally high concentrations of bilirubin in the blood can, in very rare cases, cause irreversible neurological damage such as developmental disorders, seizures, deafness, or intellectual retardation. Motor and cognitive delays, such as in language development, are also observed in children with biliary atresia (a blockage of the bile ducts that prevents the outflow of bile from the liver).
Similarly, Swiss researchers have also shown that chronic liver disease causes metabolic changes in the brain even before physical symptoms appear. Induction of liver dysfunction in an animal model leads to molecular dysfunction of the brain in as little as two weeks, specifically excessive ammonium levels and an abrupt decrease in two molecules, vitamin C and creatine (which serves multiple functions, including energy supply), resulting in hepatic encephalopathy (a neurological disorder caused by liver dysfunction). Other studies have also shown Alzheimer’s-like neuroinflammation and early cognitive dysfunction in patients with nonalcoholic fatty liver disease (or hepatic steatosis).
The effects of the Gut on the brain
Numerous studies are also looking at the interactions between the gut and our brain, which are proving to be far more important than scientists could have imagined just a few decades ago. Indeed, the billions of bacteria that populate our gut can sometimes be harmful and sometimes beneficial to certain neurological and psychiatric disorders. The role of the gut microbiota in depression has been demonstrated by research conducted at the Institut Pasteur in Paris. When the microbiota of an animal with mood disorders is transferred to a healthy animal, it is enough to put the latter in a depressed state (decreased motivation, loss of pleasure, apathy, etc.) within a few days. The researchers identified specific bacterial populations that were particularly reduced in these animals. They were able to show that oral treatment with the same bacteria could cure the depressive state. These antidepressant bacteria are an important step toward the development of psychobiotics.
The gut microbiota also plays a role in certain inflammatory neurological diseases. While a link between changes in the microbiota and the development of multiple sclerosis is suspected, a new study has revealed a protective role of the microbiota in this disease. The San Francisco team has shown that a subset of white blood cells (B lymphocytes) can recognize bacteria that are particularly prevalent in patients during flareups and produce specific antibodies in response. These cells are then able to migrate to the brain via the bloodstream and are thought to help reduce neuroinflammation, thereby reducing the symptoms of relapses. A final example involves people with inflammatory bowel disease (IBD). Because of this pathology, they have an increased risk of developing Parkinson’s disease later in life.
These various examples show that our brain is in constant interaction with the rest of the body. Pathological damage to our organs can negatively affect the brain and lead to the development of neurological or psychiatric diseases, so it is important to better understand these interactions in order to better prevent certain brain diseases.