Whether it’s reading the words on this page, remembering your breakfast, or tickling the hair on your skin, your experiences and sensations are the work of nerve cells. Just like your feelings, your chains of reasoning, your good and less good habits. It is the same for your anxieties, your moods, your tremors and your memory lapses which, if they do not afflict you yet, risk to do so one day. The full panoply of human experience is found in the electrochemical impulses transmitted along and between the 90 billion nerve cells, also called neurons, that make up a person’s brain.
When minds change, so do brains – and the reverse is also true. Factors that alter the brain and central nervous system, or the behavior of specific types of neurons and supporting cells within these structures, can also alter the mind, for better or worse. When the brain ages, is damaged, or hijacked by recreational drugs, the mind also changes. Sometimes entire personalities change. This means that drugs and other treatments that target neurons can be used to treat both physical illnesses – neuron degeneration, for example – and mental illnesses.
“When minds change, so do brains – and the reverse is also true. When the brain ages, is damaged, or hijacked by recreational drugs, the mind also changes. Sometimes whole personalities change”
A hundred years ago, a single discipline, neuropsychiatry, dominated the study and treatment of brain dysfunction. A schism occurred from the 1930s. Today, the departments of neurology, which deal with organic dysfunctions of the nervous system, and the departments of psychiatry, which deal with the human mind, remain separate. Many believe that a merger between these two disciplines is long overdue. This becomes all the more important as the biological links to mental disorders such as depression and anxiety become evident. As thoughts and feelings, and therefore the way the brain has been wired, have a role to play in the brain, they also play a role in disease.
The science that feeds into these two fields is both advanced and quite primitive. The brain is so complex that its scientific understanding may seem decades behind that of other organs. In addition to its billions of neurons, the brain has a similar number of non-neuronal cells, called glial cells, which provide the insulation needed to separate neural currents, as well as the nutrients neurons need to generate those currents, responses immune and waste disposal services the brain needs to stay healthy. Glial cells even help eliminate unwanted connections in the brain during development. The story of the role these cells play in brain health is only just beginning to be told.
Neurons communicate with each other through spaces called synapses, places where a signal transmitted electronically along the body of a cell is translated into a chemical message to be transmitted to the next cell. More than 100 of these neurotransmitters have been discovered so far. But while some, like serotonin and dopamine, have become household names, much more needs to be done to understand how they and their more obscure comrades work.
“The brain has a similar number of non-neuronal cells, called glial cells, which provide the insulation needed to separate neural currents, as well as the nutrients neurons need to generate those currents. The story of the role these cells play in brain health is only just beginning to be told.”
In the second half of the 20th century, doctors discovered a whole series of psychiatric drugs. But each of the three main classes of psychiatric drugs – antidepressants, antipsychotics and anxiolytics – were discovered by chance. Scientific accounts of their operation were absent, incomplete or erroneous. Ten years ago, no new drug had been on the market for more than three decades. There was talk of a crisis in psychopharmacology.
But new knowledge in neuroscience is now arriving at an impressive speed. Genetics and a growing knowledge of molecular circuitry underlie much of this progress. Other drivers of progress include tools such as optogenetics, organoids and new forms of imaging, as well as a growing interest in the underlying functioning of the brain. One of the most exciting recent discoveries is the extent to which the brain is plastic, giving rise to new neurons throughout human life, which holds great potential for treating, if not curing, many brain diseases.
These advances make it possible to consider innovative approaches to target brain diseases. Optimism also comes from the success of new treatments for disorders such as depression, epilepsy, migraine, postnatal depression and spinal muscular atrophy (SMA).
Psychiatry is finally getting closer to neurobiology
New approaches include neuroimmunology, which targets immune cells in the brain; gene therapy, which involves replacing faulty genes with functional genes; and a renewed interest in psychedelics, neuromodulation, and precision drugs based on genetic or molecular pathways. Other innovative approaches, such as gene editing, stem cell transplants and RNA therapies, could also lead to new treatments, as could studies of recreational drugs, which try to learn and therapeutic approaches to their manifest mind-altering power. Psychiatry is being redesigned, with efforts to improve the classification and diagnosis of disease, and through closer links with neurobiology. Investors, biotech companies, and forward-thinking pharmaceutical companies are showing renewed interest in neuroscience. Drug pipelines are filling up.
“Psychiatry is being redesigned, with efforts to improve the classification and diagnosis of disease, and through closer links with neurobiology”
And that’s good. According to the Global Burden of Disease Project, 12 mental health disorders affect approximately 970 million people. Their prevalence has increased by 48% since 1990 due to population growth. With more than one in ten people affected on the planet, it is a global problem, although available data suggests it is more pronounced in Western countries.
Neurological problems take their toll. Strokes, dementias, migraines, Parkinson’s disease, epilepsy and traumatic brain injury are collectively the world’s number one cause of disability. Due to the aging of the population, the number of deaths from neurological diseases is increasing rapidly, especially in low- and middle-income countries.
The brain is often described as the most complex structure in the known universe. It is perhaps unsurprising that medicine has struggled to remedy its many and varied ailments. Yet, thanks to new scientific approaches and innovative treatments, the sector is experiencing renewed energy and enthusiasm. The discoveries to come will change brains, minds – and many lives.
© 2022 The Economist Newspaper Limited. All rights reserved. Source The Economist, translation The new Economist, published under license. The article in the original version: www.economist.com.