The brain is undoubtedly the most mysterious organ in the human body, protected by many biological barriers such as the skullcap, the meninges, the blood-brain barrier, among others. A real trench that keeps you safe and, thus, preserves who we are, because it is in this intelligent unknown with about a kilo and a half that we keep our self. And more: you, reader, are only reading this text because it is being processed by the brain. However, this unique machinery has not yet been replicated by even the most modern artificial intelligence algorithms. Indeed, how does physical matter become thought?
Understanding how the brain works is one of the biggest challenges for scientists. Neuroscientist Eric Kandel, Nobel laureate in Physiology and Medicine in 2000, goes further and in his very interesting book “Different Minds: What Different Brains Reveal About Us” he suggests that understanding brains that are not working properly may be the way to understand their functioning a little better. Understanding the diseased brain is one of the greatest challenges of modern medicine, which begins when we need to access it, as it is under lock and key.
In recent decades, however, several imaging techniques have been developed that allow the visualization of this organ in a non-invasive way. The best known is MRI, which allows us to examine brain structures. But what about the functioning of the brain, how could we assess it? It does not have a rhythmic cycle of beats like the heart, but it communicates through the famous synapses that can be evaluated by another non-invasive test called positron emission tomography, better known as PET Scan.
PET Scan is an image exam that uses a radioactive molecule that, after being administered to the patient, emits radiation and is detected by the equipment. The technical explanation of this exam looks like a science fiction movie – what do you mean, injecting a radioactive compound into our body? The reader may remember the “adamantium”, a fictitious metallic alloy, administered in the veins of the character Wolverine from the famous “X-Men” film franchise, but in the exam the amount is so small that there is no danger or chance of the individual becoming a mutant.
The radioactive molecules administered can vary, but the most commonly used is radioactive glucose—the familiar glucose, only coupled to a radioactive molecule. Glucose is the brain’s main energy fuel – every 100 grams of brain consumes about 5 milligrams of glucose per minute. This glucose all comes from the diet or from some reservoirs that we have in our body. In fact, it’s a good thing that the brain doesn’t depend on gasoline like automobiles, because currently in Brazil it would be impossible to bear the “costs of thinking”.
With this radioactive glucose we can estimate the amount of fuel that the brain is using and define whether it is working correctly or not. For example, a brain that is consuming too little glucose is interpreted as a brain whose neurons are having difficulty communicating, a phenomenon that occurs in some neurodegenerative diseases, such as Alzheimer’s disease.
This biological interpretation of the radioactive glucose PET scan was defined about forty years ago. Until recent studies showed that another brain cell seems to have a preference for glucose, a star-shaped cell called an astrocyte. The astrocyte seems to be the neuron’s cook: it looks for glucose in the blood, prepares a tasty food, lactate, and sends it to the neurons. This lactate is readily used by neurons to produce energy for synapses to function properly. This neuron-astrocyte coupling appears to have a very special evolutionary function and is certainly related to the unique cognitive particulars that we, Homo sapienswe have.
This discovery has caused confusion in the biological interpretation of this test, which has been used for decades in clinical medicine. Are changes in brain glucose consumption really caused by diseased neurons? Or is it the cooks who are not being able to prepare the neurons’ dinner? A “gastronomic” revolution in the neurosciences is coming, and the next chapters could completely change how we understand the brain and treat neurological disorders.
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Eduardo Zimmer is a biochemist and professor at the Department of Pharmacology at the Federal University of Rio Grande do Sul.
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