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Ralph Lewis is a staff psychiatrist, Matthew Burke is a cognitive neurologist, and Ari Zaretsky is vice-president, education, at Sunnybrook Health Sciences Centre.

Post-COVID-19 condition (also known as “long COVID”) is a very real and potentially debilitating problem for a great many people. It’s also a somewhat poorly defined condition, with many different symptoms that may be associated with a longer persistence of the virus in the body, abnormal immune responses, and/or inflammation. Earlier estimates for how many people suffer from the condition were higher when a greater number of the population were unvaccinated, but even recent conservative estimates suggest that 5 per cent of COVID infections can result in long COVID. While many patients ultimately have a good prognosis, some have had serious neurological complications, such as encephalitis or stroke.

Many cases of long COVID have been associated with signs of illness that are difficult to observe. Patients are often struck by persistent fatigue and difficulty concentrating (commonly known as “brain fog”), along with other non-specific ailments including palpitations, dizziness, headache, insomnia, and mood dysregulation. This constellation of symptoms is non-specific and common to other distressing syndromes and chronic illnesses from across the medical spectrum. Patients who are suffering debilitating symptoms in the absence of verifiable, objective signs of illness can understandably feel insulted and/or dismissed when doctors suggest their condition may be “psychosomatic” (traditionally viewed, too simplistically, as a physical ailment caused by mental distress as opposed to a physical condition.)

What Globe readers want you to know about living with long COVID

Newer research and a better understanding of brain circuitry has revealed a much more complex explanation – one that sufferers are likely to find far more validating. We now understand that a wide range of symptoms can be produced by biologically based abnormalities in the function, rather than the structure, of the brain. You might think of this as a problem of “software” rather than “hardware.” Software, or functional, changes in the brain can have many real impacts on the body’s hormonal, metabolic and immune-system functioning.

Neuroscientists now understand that the brain is essentially a prediction machine. To efficiently process a flood of incoming information, the brain makes predictions about what it thinks this information is going to tell it based on expectations and assumptions. Most of the time these are accurate guesses, but the cost of such an efficient system is that sometimes the brain gets it wrong. This is what creates the “magic” of optical illusions, and it also underlies the placebo effect (the real phenomenon of positive expectations leading to symptom improvement) and its counterpart, the nocebo effect (the onset of new, or worsening, symptoms in the wake of negative expectations).

In the case of a frightening, novel illness like COVID, the barrage of media reports about people afflicted by a wide array of bewilderingly non-specific, long-term symptoms collectively shaped our expectations of what having COVID, or long COVID, might feel like. Those messages, as received by our brains, may be amplified by social contagion and a variety of other complex biopsychosocial factors.

Since the act of anticipating what an illness might feel like can quickly and powerfully influence our brain’s function, it’s possible that in some cases, long COVID sufferers are experiencing symptoms due to brain-circuit changes caused by expectations. When patients report having these symptoms, they really are experiencing them, as these mechanisms are far more potent and neurologically based than “imagining” a non-existent perception. In fact, it’s crucial to note that the brain’s perception of sensation based on expectations is just as real as the brain’s perception of sensation based on input from the senses. Notice as well that we are not talking here about a mental disorder – we are talking about a normal and universal human trait. Every one of us is vulnerable to this phenomenon. There are a great many quirks of human behaviour that are explained by the ways in which expectations shape perceptions, and in a subset of long COVID patients, such mechanisms could be at play.

Unfortunately, these types of disruptions in brain-body function have been long neglected by medicine, despite being responsible for a startlingly high proportion of all visits to doctors. The primary problem now is that our evolving understanding of the relevant neurobiological underpinnings has outpaced how most of society and medicine understand this phenomenon. Many still maintain inappropriate black-and-white thinking toward symptoms, categorizing them as being either “real”/“physical” or “not real”/“psychosomatic.” Symptoms resulting from brain-circuit dysfunction, as described above, often get falsely lumped into the category of “not real/psychosomatic,” which is itself a false equivalency.

Long COVID has finally put a spotlight on this topic. We are hopeful that ongoing research in this field will not only help shed further light on complex brain-based phenomena, but also accelerate an overhaul of words like “psychosomatic” and the unfortunate stigma associated with such labels.