Why We Forget and How to Remember Better, page 18
Coronavirus Disease 2019 (COVID-19)
Have you heard the term “brain fog” being used in relation to COVID-19 infection? Brain fog is not a medical or scientific term; it is a term used by individuals to describe how they feel when their thinking is sluggish, fuzzy, and not sharp. COVID-19 infections may cause brain fog by damaging the brain in several ways—each of which can lead to memory and thinking impairments. First, it can infect the brain directly, causing encephalitis (inflammation of the brain). Second, it is a risk factor for strokes. Third, because it frequently infects the lungs, COVID-19 can deprive the brain of oxygen. In addition to these very serious problems, many individuals who were thought to have fully recovered from COVID-19 infection have persistent impairment in working memory,3 which leads to difficulties remembering new episodic and semantic information as well. Lastly, a group of German and American doctors have speculated that the combination of the direct infection with the virus, systemic inflammation, increased risk of strokes, and damage to lungs and other bodily organs might place survivors of COVID-19 at increased risk for Alzheimer’s disease in the future.4 It is too early to tell if this speculation is correct, but we hope not.
Diabetes
Diabetes can cause memory impairment in several different ways. First, diabetes is a risk factor for strokes, and strokes can cause memory problems, as described later in this chapter. Second, when the levels of blood sugar rise too high or fall too low, there can be periods of memory loss and confusion. Lastly, the hippocampus and other parts of the brain can be permanently damaged if the control of diabetes is too strict and blood sugar concentrations repeatedly drop to dangerously low levels.
Hospitalizations, Major Surgeries, and Anesthesia
Many people can become confused and delirious and experience memory problems when they are hospitalized for any serious medical problem or a major surgery, such as a life-threatening infection or a hip surgery. Sometimes the memory problems are related to the powerful medications that are given at the time, as described earlier in this chapter and in the Appendix. Other times, they are related to the effects of the stress that the body is under and the hormonal cascades triggered by those stress responses. As the individual recovers and the effects of the medications wear off, the memory should return to normal.
Sometimes the confusion and memory problems are related to anesthesia, which brings up a question we are frequently asked: Does general anesthesia cause long-lasting memory impairment or dementia? Our review of the available medical literature suggests that general anesthesia, properly administered, does not cause permanent memory impairment or dementia. It may, however, cause delirium (confusion), making a hospitalization prolonged and unpleasant. It may also bring out symptoms of memory loss in an individual when these symptoms were not yet apparent in daily life. For these last two reasons, we generally recommend that local or spinal anesthesia be used whenever the surgeon and anesthesiologist feel it is safe to do so. If, however, there is any question about the individual moving around during a delicate surgical procedure, then general anesthesia will be the safest method.
Organ Failure
It shouldn’t be surprising to hear that, in order for your brain to function properly, all of your other organs need to function properly as well. So, if you or a loved one are experiencing serious problems with the liver, kidney, heart, or lungs, the brain won’t be able to function properly, and memory impairment will likely be present. If the bodily organs recover, brain and memory function will return to normal in most cases.
Neurologic Disorders
Here we will describe some of the common brain disorders that cause memory problems. Chapter 13 has already presented dementia, mild cognitive impairment, subjective cognitive decline, Alzheimer’s disease, vascular cognitive impairment, vascular dementia, frontotemporal dementia, normal pressure hydrocephalus, Parkinson’s disease, Parkinson’s disease dementia, dementia with Lewy bodies, primary progressive aphasia, and semantic dementia and the memory problems associated with each.
Brain Tumors
Brain tumors generally cause memory problems in one of three ways. First, some tumors will directly invade and destroy one of the brain’s memory centers such as the hippocampus (for episodic memory), the cerebellum (for procedural memory), or their connections. Second, some tumors, such as those found in a brain structure above the nose called the pituitary gland, may disrupt thyroid hormone or other brain chemicals important for memory. Third, because they are growing inside the confined space of the skull, many tumors—even benign ones that are not cancerous—will compress one of the brain’s memory centers or their connections. Because tumors can cause memory loss, a brain scan looking for them is part of the standard evaluation of memory impairment.
Epilepsy and Seizures
Epilepsy and seizures can impair memory in two different ways. First, although most seizures involve complete loss of consciousness, rhythmic jerking of arms and legs, and bladder incontinence, some seizures are subtle and only manifest with a slight alteration of consciousness. These focal impaired awareness seizures (previously called partial complex or petit mal seizures) are often difficult to detect. Nonetheless, when present, they frequently interfere with the brain’s ability to encode or store new memories. Such focal seizures should be considered when memory problems appear intermittently. The typical scenario is that you may notice fairly profound episodes of memory loss in a loved one, but when they undergo extensive memory testing as part of a neuropsychological evaluation, their memory is felt to be completely normal. If this occurs, obtaining an electroencephalogram (EEG) can be helpful.
Second, some individuals with chronic epilepsy may intermittently have prolonged seizures lasting more than a few minutes. If these prolonged seizures are difficult to stop, they are sometimes referred to as status epilepticus. Such prolonged seizures may damage the hippocampus permanently, leading to scarring of the hippocampus called hippocampal sclerosis. Not surprisingly, individuals with hippocampal sclerosis generally show impaired episodic memory.
Multiple Sclerosis
Multiple sclerosis is an autoimmune disease that affects patches of the white matter, the wiring of the brain. Because most of the brain’s white matter is going to or from the frontal lobes, it is frontal lobe function that is most affected. This leads to difficulties similar to vascular cognitive impairment. Working memory capacity is diminished, and there is reduced ability to acquire new information and retrieve previously learned information from episodic memory. See the vascular cognitive impairment section of Chapter 13 for more information regarding the types of memory difficulties seen with damage to the white matter of the brain.
Strokes and Bleeds
Most strokes occur when an artery sending blood from the heart to the brain becomes blocked by a clot and a part of the brain doesn’t receive enough blood and dies. There can also be bleeding strokes when a brain artery ruptures and blood suddenly accumulates inside the brain. Lastly, there are two types of bleeds between the brain and skull, called subdural and epidural hematomas. All of these strokes and bleeds can cause memory problems, usually due to one of three mechanisms.
First, the stroke or bleed may directly damage one of the memory centers, such as the hippocampus or its connections. Second, the stroke or bleed may put pressure on one of the memory centers or their connections. Third, an accumulation of strokes may cause vascular cognitive impairment or vascular dementia, as described in Chapter 13.
Strokes and bleeds can cause different types of memory problems depending upon where the damage occurs. If the stroke damages the hippocampus or its connections, episodic memory problems will usually be seen. If the damage occurs to the lower and outside part of the temporal lobe, then problems with semantic memory may be seen. And if the damage occurs to the basal ganglia or cerebellum, procedural memory problems are generally seen.
Strokes, whether clotting or bleeding, occur suddenly and are noticeable if large enough to cause memory problems. On the other hand, although subdural hematomas generally start after a fall, they may grow slowly over days or weeks and only then become large enough to cause memory problems.
The bottom line is that if you or a loved one experience memory loss suddenly or in the days or weeks after a fall, call the doctor immediately as a stroke or a bleed may have occurred.
Traumatic Brain Injury, Concussions, and Chronic Traumatic Encephalopathy
A traumatic brain injury occurs when there is an injury to the brain caused by an external force. When traumatic brain injuries are moderate or severe, many types of memory are affected, with the specifics depending upon which parts of the brain are injured. For example, injury to the cerebellum will affect procedural memory, whereas injury to the left temporal lobe will affect episodic and semantic memory.
A concussion is a mild traumatic brain injury that temporarily affects brain functioning. Memory loss around the time of injury is one of the most common symptoms of concussion, and the duration of amnesia has even been used as one of the criteria to define the severity of concussion. Individuals recovering from concussion frequently have difficulty concentrating, which affects their working memory, as well as their ability to acquire new information and retrieve previously learned information from episodic memory.
Individuals who have repetitive mild head impacts—not just two or three but hundreds or thousands, whether or not they meet criteria for concussion—are at risk for developing a progressive degenerative disease later in life known as chronic traumatic encephalopathy. Individuals who were boxers, American football players, or military veterans exposed to blast injuries are some of those who are at risk for chronic traumatic encephalopathy, as are those who have experienced intimate partner violence. Although this disease generally begins in microscopic regions of the frontal lobes, by the middle stage of the disease it spreads to the hippocampus. For this reason, individuals with chronic traumatic encephalopathy generally first experience trouble concentrating, affecting their working memory. As the disease progresses, their episodic memory abilities can be devastated, and they can end up with memory performance similar to that of individuals with Alzheimer’s disease.
Transient Global Amnesia
Transient global amnesia is an unusual neurologic disorder in which individuals develop a sudden inability to form new memories along with the loss of a few hours or days of prior memories. They repeatedly ask questions like, “Where am I?” and “What’s going on?” Approximately 5 minutes after giving the answers to them, they invariably repeat the same questions again. After ruling out other causes of sudden memory loss such as strokes, seizures, blood chemistry problems, and almost everything in this chapter, we are able to reassure the individual and their family that this type of memory loss is usually temporary and that their memory is likely to return within 24 hours (except for the time in which they could not form any new memories). Although no one is completely sure what causes transient global amnesia, it is more common in those with migraines and is often precipitated by the same things that trigger migraines.
Psychiatric Disorders
Here we will describe the memory problems that may be seen in some common psychiatric disorders, along with one psychiatric treatment, electroconvulsive therapy (ECT).
Anxiety
We’ve discussed anxiety and stress in several parts of this book (see Chapters 3, 7, and 9) because it can impair multiple types of memory in several different ways. First, when you’re anxious or stressed, you may find yourself thinking about and preoccupied with whatever you are anxious or stressed about. These recurrent—and often intrusive—thoughts will diminish your ability to focus on what you want to, impairing your working memory capacity to keep information in mind and your episodic memory ability to learn new information and to retrieve previously learned information. Second, anxiety and stress cause hormones to be released into your bloodstream, such as adrenaline, that trigger your “fight or flight” response. This response forces your brain to pay attention to those things in your environment that could represent a threat—even if those things have absolutely nothing to do with your current goals. Again, your attention is diverted away from what you are trying to do with your working or episodic memory and is focused on what you are anxious about. High levels of the stress hormone cortisol can be detrimental to hippocampal function, making it harder to retrieve information from memory in the moment and, in cases of chronic stress and anxiety, relating to longer-lasting impairments in memory (see Chapter 15). Lastly, because information first needs to enter your episodic memory before it can become generalized, consolidated, and part of your long-term semantic memory, anxiety disrupts semantic memory as well—making it more difficult for you to learn that list of vocabulary words or biological pathways.
Depression
Like anxiety, depression can impair several types of memory in several different ways. If you’re feeling sad, you may be preoccupied with thoughts about whatever is upsetting you. These sad thoughts may make it difficult for you to focus on what you’re trying to learn or remember, impairing your ability to keep that desired information in your working memory, learn it with your episodic memory, or make it part of your semantic memory. Additionally, depression causes biological changes in the brain’s chemistry and circuitry that can interfere with the proper function of the frontal lobes and the hippocampus—critical structures for working, episodic, and semantic memory.
Attention-Deficit/Hyperactivity Disorder (ADHD)
ADHD affects 8% to 12% of children worldwide,5 making it the most common psychiatric disorder that affects memory. ADHD is a heterogeneous disorder with many different causes. Some researchers and clinicians believe that ADHD simply represents one end of a continuum of normal human behavior, with its symptomology perhaps a reflection of societal requirements for young children to sit still in a classroom for many hours each day. However, in certain cases it appears to be related to delayed maturity of the frontal lobes or their connections, and in others it may be related to a mild brain disorder affecting the frontal lobes, its connections, or related brain structures.
Whatever its cause and whether it is normal or abnormal, the majority of individuals who meet the diagnostic criteria for ADHD have diminished working memory compared to their age-matched peers. This diminished working memory leads to impaired ability to acquire new information with episodic memory, and therefore impaired ability to generalize and consolidate that new information into semantic memory. It is for this reason that children with ADHD have difficulty learning in school, as much of school involves acquiring new semantic information, such as vocabulary words, dates, facts, formulas, rules, and so forth.
Bipolar Disease
Formerly known as manic-depressive disorder, individuals with bipolar disease experience highly elevated happy moods that can rise into mania, as well as sad, depressed moods. We’ve already spoken about how depression can impair memory, and mania can impair memory as well. Although a happy, energetic mood often augments memory and productivity—perhaps enabling you to memorize your lines for your performance in the play in record time—when people are truly manic they have too much energy. They are overactive, cannot concentrate, and cannot focus on goal-directed activities. Thus, working, episodic, and semantic memory are all impaired.
Schizophrenia
In addition to other symptoms, individuals with schizophrenia experience hallucinations (typically hearing voices), delusions (such as paranoia), and disorganization in thinking and behavior. Not surprisingly, the majority of these individuals show impairments in working memory and thus episodic and semantic memory. The exact mechanism of these memory impairments is an active area of research. In fact, some researchers believe that understanding the nature of their memory impairment will also provide a better fundamental understanding of the disorder itself.
Nonetheless, there is a general consensus that some of the memory impairment stems from being distracted by internal stimuli—that is, it is hard to pay attention to what someone is saying to you if you are, at the same time, hearing voices in your head. And if your paranoia makes you think that everyone is deceiving you, you may be so preoccupied with trying to figure out how someone you just met is trying to trick you that you don’t pay attention to their name.
In addition, research using functional magnetic resonance imaging (MRI) suggests that the brains of individuals with schizophrenia have abnormalities as well. Reduced activations are seen in the prefrontal cortex, hippocampus, and related structures in those with schizophrenia compared to healthy individuals.6 Given the importance of the prefrontal cortex for working memory, both prefrontal cortex and hippocampus for episodic memory, and intact episodic memory for the creation of new semantic memories, it is not surprising that individuals with schizophrenia show impairment in working, episodic, and semantic memory.
