Of the various organs of the body that may pop into your brain when you think about pregnancy, or about the COVID-19 pandemic, the brain is probably not one of them. But morning sickness, fatigue, changes in your mood, lactation (production of milk in your breasts) after you deliver, and certain hormonal changes all relate directly to processes occurring in your brain. Additionally, while the life-threatening complications of COVID-19 manifest most notoriously in the respiratory system, a number of patients have suffered neurological effects, including in the brain, caused by infection with SARS-CoV-2 (the virus that causes COVID-19).
Within the brain, beneath a brain structure called the thalamus, there is a command center for the body’s neuroendocrine system. This command center consists of a brain region called the hypothalamus and a pea-sized gland called the pituitary, which are connected by a complex of nerve fibers (long extensions of nerve cells that transmit electrical signals) and special blood vessels. Concentrations of cells called nuclei within the hypothalamus send nervous signals directly to the pituitary and also control the release of various hypothalamic hormones that travel through the special blood vessels to the pituitary. There, the hormones arriving from the hypothalamus are either stored or control the release of still other hormones that are made in the pituitary itself. Changes in this system over the course of pregnancy include an increase in the release of various pituitary hormones that circulate in the blood, including adrenocorticotropic hormone (ACTH), whose job is to stimulate the adrenal glands (located above the kidneys) to release the stress hormone cortisol (whose concentration thus rises) and prolactin, the hormone that stimulates milk production in the breasts.
Another hormone releasing structure in the brain is the pineal gland, which receives information from the eyes. Release of the hormone melatonin from the pineal makes you sleepy and melatonin levels in the blood normally rise and fall based on the 24 hour light dark cycle, but this cycle is often disrupted during pregnancy and following delivery, when you are getting up throughout the night to breastfeed.
Many such complications have been very severe, appearing as strokes in young people with or without severe respiratory complications of COVID-19, or as encephalitis (brain inflammation), even with death of the affected brain tissues.
Studies with a brain imaging procedure called magnetic resonance imaging (MRI) have revealed that certain areas of gray matter (concentrations of the cell bodies of nerve cells, as opposed to the long extensions of the cells that form structures called tracts that transmit signals between distant sites within the brain and spinal cord) shrink during pregnancy. Rather than being a bad thing, scientists believe that this shrinking is the result of a pruning process through which the brain streamlines its structure to produce more efficient functions similar to the process that occurs when you learn something new.
Since early spring, doctors have reported an increasing number of symptoms and signs resulting from SARS-CoV-2 affecting the central nervous system (which consists of the brain and spinal cord). Many such complications have been very severe, appearing as strokes in young people with or without severe respiratory complications of COVID-19, or as encephalitis (brain inflammation), even with death of the affected brain tissues. Additionally, affecting nerves rather than the central nervous system, there have been reports related to COVID-19 of what neurologists call Guillain–Barré syndrome in which a person suffers paralysis, or severe muscle weakness, due to the immune system attacking the affected nerves.
Researchers believe that such effects result from any of four possible mechanisms or a combination of any of these four. One such mechanism is that the SARS-CoV-2 virus infects the central nervous system, where it directly damages nervous tissue. This is the same mechanism that sometimes leads to inflammation of the brain as a complication of infection with certain other viruses, notably herpes simplex viruses (HSV).
Another mechanism that may be at play is what immunologists call the cytokine storm. Cytokines are various immune system proteins that play important roles in defending the body, but a cytokine storm is an excessive release of such proteins. Also called cytokine release syndrome, this out of whack immune response is thought to be such an important factor underlying the life-threatening respiratory effects of COVID-19 that patients showing signs of it are treated with special medications that block key cytokines from doing their job.
The condition called Guillain–Barré syndrome (GBS) that we mentioned above is an example of something caused by a third possible mechanism of damage due to the virus. In contrast with a direct assault by the virus on the nervous system, but also in contrast with a cytokine storm consisting of various proteins with no particular target, the process causing GBS and similar conditions is thought to involve the immune system identifying something on the nerves as foreign and consequently making antibodies customized to latch onto that something.
Finally, the brain and other parts of the nervous system can be damaged by disease processes happening throughout the body. For example, if inadequate amounts of oxygen are reaching the blood from the lungs, if blood is not circulating adequately to the brain due to blood clots, or if body fluids, electrolytes, or acid-base balance are disrupted, there can be neurological effects.