Clouding of consciousness (also known as brain fog or mental fog)
occurs when a person is slightly less
wakeful or
aware
Awareness is the state of being conscious of something. More specifically, it is the ability to directly know and perceive, to feel, or to be cognizant of events. Another definition describes it as a state wherein a subject is aware of some inform ...
than normal.
They are not as aware of time or their surroundings and find it difficult to pay
attention
Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Atte ...
.
People describe this
subjective sensation as their mind being "
fog
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
gy".
Background
The term ''clouding of consciousness'' has always denoted the main
pathogenetic
Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...
feature of
delirium
Delirium (also known as acute confusional state) is an organically caused decline from a previous baseline of mental function that develops over a short period of time, typically hours to days. Delirium is a syndrome encompassing disturbances in ...
since physician Georg Greiner
pioneered the term (') in 1817.
The ''Diagnostic and Statistical Manual of Mental Disorders'' (DSM) has historically used the term in its definition of delirium. However, the
DSM-III-R
The ''Diagnostic and Statistical Manual of Mental Disorders'' (DSM; latest edition: DSM-5-TR, published in March 2022) is a publication by the American Psychiatric Association (APA) for the classification of mental disorders using a common langua ...
and the
DSM-IV
The ''Diagnostic and Statistical Manual of Mental Disorders'' (DSM; latest edition: DSM-5-TR, published in March 2022) is a publication by the American Psychiatric Association (APA) for the classification of mental disorders using a common langua ...
replaced "clouding of consciousness" with "disturbance of consciousness" to make it easier to
operationalize
In research design, especially in psychology, social sciences, life sciences and physics, operationalization or operationalisation is a process of defining the measurement of a phenomenon which is not directly measurable, though its existence is in ...
, but it is still fundamentally the same thing.
Clouding of consciousness may be less severe than delirium on a spectrum of
abnormal consciousness.
Clouding of consciousness may be synonymous with ''subsyndromal delirium''.
Subsyndromal delirium differs from normal delirium by being overall less severe, lacking acuteness in onset and duration, having a relatively stable sleep-wake cycle, and having relatively stable motor alterations.
The significant clinical features of subsyndromal delirium are inattention, thought process abnormalities, comprehension abnormalities, and
language
Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
abnormalities.
The full clinical manifestations of delirium may never be reached.
Among intensive care unit patients, subsyndromal subjects were as likely to survive as patients with a Delirium Screening Checklist score of 0, but required extended care at rates greater than 0-scoring patients (although lower rates than those with full delirium)
or have a decreased post-discharge level of functional independence vs. the general population but still more independence than full delirium.
In clinical practice, there is no standard test that is exclusive and specific; therefore, the diagnosis depends on the
subjective impression of the physician. The
DSM-IV-TR
The ''Diagnostic and Statistical Manual of Mental Disorders'' (DSM; latest edition: DSM-5-TR, published in March 2022) is a publication by the American Psychiatric Association (APA) for the classification of mental disorders using a common langua ...
instructs clinicians to code subsyndromal delirium presentations under the miscellaneous category of "
cognitive disorder
Cognitive disorders (CDs), also known as neurocognitive disorders (NCDs), are a category of mental health disorders that primarily affect cognitive abilities including learning, memory, perception, and problem solving. Neurocognitive disorders in ...
not otherwise specified".
Psychopathology
The
conceptual model
A conceptual model is a representation of a system. It consists of concepts used to help people knowledge, know, understanding, understand, or simulation, simulate a subject the model represents. In contrast, physical models are physical object su ...
of clouding of consciousness is that of a part of the brain regulating the "overall level" of the consciousness part of the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
, which is responsible for awareness of oneself and of the environment.
Various etiologies disturb this regulating part of the brain, which in turn disturbs the "overall level" of consciousness.
This system of a sort of general activation of consciousness is referred to as "arousal" or "wakefulness".
It is not necessarily accompanied by
drowsiness
Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...
, however.
Patients may be awake (not sleepy) yet still have a clouded consciousness (disorder of wakefulness).
Paradoxically, affected individuals say that they are "awake but, in another way, not".
Lipowski points out that decreased "wakefulness" as used here is not exactly synonymous with drowsiness. One is a stage on the way to
coma
A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
, the other on the way to
sleep
Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...
which is very different.
The affected person experiences a subjective sensation of mental clouding described in the patient's own words as feeling "
fog
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
gy".
One patient described it as "I thought it became like
mist
Mist is a phenomenon caused by small droplets of water suspended in the cold air, usually by condensation. Physically, it is an example of a dispersion. It is most commonly seen where water vapor in warm, moist air meets sudden cooling, such a ...
y, in some way... the outlines were sort of fuzzy".
Others may describe a "spaced out" feeling. Affected individuals compare their overall experience to that of a
dream
A dream is a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. Humans spend about two hours dreaming per night, and each dream lasts around 5 to 20 minutes, althou ...
because as in a dream consciousness, attention, orientation to time and place, perceptions, and awareness are disturbed. Barbara Schildkrout, MD, a board-certified psychiatrist and clinical instructor in psychiatry at the Harvard Medical School described her subjective experience of clouding of consciousness, or what she also called "mental fog", after taking a single dose of the
antihistamine chlorpheniramine for her
cottonwood allergy
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...
while on a cross-country road trip. She described feeling "out of it" and being in a "dreamy state". She described a sense of not trusting her own judgment and a dulled awareness, not knowing how long
time
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...
went by.
Clouding of consciousness is not the same thing as ''
depersonalization
Depersonalization can consist of a detachment within the self, regarding one's mind or body, or being a detached observer of oneself. Subjects feel they have changed and that the world has become vague, dreamlike, less real, lacking in significa ...
'' even though people affected by both compare their experience to that of a dream. Psychometric tests produce little evidence of a relationship between clouding of consciousness and depersonalization.
This may affect performance on virtually any cognitive task.
As one author put it, "It should be apparent that
cognition
Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
is not possible without a reasonable degree of arousal."
Cognition includes perception, memory, learning,
executive functions
In cognitive science and neuropsychology, executive functions (collectively referred to as executive function and cognitive control) are a set of cognitive processes that are necessary for the cognitive control of behavior: selecting and succe ...
,
language
Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
, constructive abilities, voluntary motor control, attention, and mental speed. The most significant, however, are inattention, thought process abnormalities, comprehension abnormalities, and language abnormalities.
The extent of the impairment is variable because inattention may impair several cognitive functions. Affected individuals may complain of forgetfulness, being "confused",
or being "unable to think straight".
Despite the similarities, subsyndromal delirium is not the same thing as ''
mild cognitive impairment
Mild cognitive impairment (MCI) is a neurocognitive disorder which involves cognitive impairments beyond those expected based on an individual's age and education but which are not significant enough to interfere with instrumental activities of ...
''; the fundamental difference is that mild cognitive impairment is a
dementia
Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...
-like impairment, which does not involve a disturbance in arousal (wakefulness).
In diseases
The emerging concept of
sluggish cognitive tempo
Sluggish cognitive tempo (SCT) is a syndrome related to attention deficit hyperactivity disorder (ADHD) but distinct from it. Typical symptoms include prominent dreaminess, mental fogginess, hypoactivity, sluggishness, staring frequently, incons ...
has also been implicated in the expression of 'brain fog' symptoms.
Patients recovering from COVID-19 report experiencing 'brain fog', which can reflect a wide variety of
neurological and psychological symptoms linked to COVID-19.
Many people with
fibromyalgia
Fibromyalgia (FM) is a medical condition defined by the presence of chronic widespread pain, fatigue, waking unrefreshed, cognitive symptoms, lower abdominal pain or cramps, and depression. Other symptoms include insomnia and a general hyp ...
experience cognitive problems
(known as "fibrofog" or "brainfog"), which may involved impaired concentration,
[ ] problems with
short
Short may refer to:
Places
* Short (crater), a lunar impact crater on the near side of the Moon
* Short, Mississippi, an unincorporated community
* Short, Oklahoma, a census-designated place
People
* Short (surname)
* List of people known as ...
- and
long-term memory
Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to short-term and working memory, which persist for only about 18 to 30 seconds. Long-t ...
, short-term
memory consolidation
Memory consolidation is a category of processes that stabilize a memory trace after its initial acquisition. A memory trace is a change in the nervous system caused by memorizing something. Consolidation is distinguished into two specific processe ...
,
[ working memory, impaired speed of performance,][ inability to multi-task, cognitive overload,][ and diminished attention span. About 75% of fibromyalgia patients report significant problems with ]concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', ''number concentration'', an ...
, memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
, and multitasking. A 2018 meta-analysis
A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...
found that the largest differences between fibromyalgia patients and healthy subjects were for inhibitory control
Inhibitory control, also known as response inhibition, is a cognitive process – and, more specifically, an executive function – that permits an individual to inhibit their impulses and natural, habitual, or dominant behavioral res ...
, memory, and processing speed
Mental chronometry is the scientific study of processing speed or reaction time on cognitive tasks to infer the content, duration, and temporal sequencing of mental operations. Reaction time (RT; sometimes referred to as "response time") is meas ...
.[ Many of these are also common symptoms of ]ADHD
Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by excessive amounts of inattention, hyperactivity, and impulsivity that are pervasive, impairing in multiple contexts, and otherwise age-inapp ...
(attention deficit hyperactivity disorder), and the two conditions have been linked via studies, to the point that a diagnosis of fibromyalgia has been proposed as an indication to also screen for ADHD. In particular, the "brain fog" of ADHD has been linked to "fibro fog". It is alternatively hypothesized that the increased pain compromises attention
Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Atte ...
systems, resulting in cognitive problems.[
In chronic fatigue syndrome, also known as myalgic encephalomyelitis, the ]CDC
The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency, under the United S ...
's recommended criteria for diagnosis include that one of the following symptoms must be present:[
* Problems with thinking and memory (cognitive dysfunction, sometimes described as "brain fog")
* While standing or sitting upright; lightheadedness, dizziness, weakness, ]fainting
Syncope, commonly known as fainting, or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from ...
or vision changes may occur (orthostatic intolerance
Orthostatic intolerance (OI) is the development of symptoms when standing upright that are relieved when reclining. There are many types of orthostatic intolerance. OI can be a subcategory of dysautonomia, a disorder of the autonomic nervous sys ...
)
Lyme disease
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...
's neurologic syndrome, called Lyme encephalopathy, is associated with subtle memory and cognitive difficulties, among other issues. Lyme can cause a chronic encephalomyelitis
Encephalomyelitis is inflammation of the brain and spinal cord. Various types of encephalomyelitis include:
* ''Acute disseminated encephalomyelitis'' or ''postinfectious encephalomyelitis'', a demyelinating disease of the brain and spinal cord, p ...
that resembles multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
. It may be progressive and can involve cognitive impairment
brain fog
migraine
Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...
s, balance issues, and extensive other issues.
See also
* Cannabis use disorder
Cannabis use disorder (CUD), also known as cannabis addiction or marijuana addiction, is defined in the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and ICD-10 as the continued use of cannabis despite clini ...
* Cognitive orthotics
Cognitive orthotics are software-based personal reminder systems for people with cognitive impairment, such as memory loss. People who can benefit include the elderly, people who have experienced traumatic brain injury, and anyone who experiences m ...
* Depersonalization disorder
Depersonalization-derealization disorder (DPDR, DPD) is a mental disorder in which the person has persistent or recurrent feelings of depersonalization or derealization. Depersonalization is described as feeling disconnected or detached from one ...
* Excessive daytime sleepiness
Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompass ...
* Four boxes test
* Idiopathic hypersomnia
Idiopathic hypersomnia (IH) is a neurological disorder which is characterized primarily by excessive sleep and excessive daytime sleepiness (EDS). The condition typically becomes evident in early adulthood and most patients diagnosed with IH will ...
* Insomnia
Insomnia, also known as sleeplessness, is a sleep disorder in which people have trouble sleeping. They may have difficulty falling asleep, or staying asleep as long as desired. Insomnia is typically followed by daytime sleepiness, low energy, ...
* Mental confusion
In medicine, confusion is the quality or state of being bewildered or unclear. The term "acute mental confusion"
* Mild cognitive impairment
Mild cognitive impairment (MCI) is a neurocognitive disorder which involves cognitive impairments beyond those expected based on an individual's age and education but which are not significant enough to interfere with instrumental activities of ...
* Obtundation
Obtundation refers to less than full alertness (altered level of consciousness), typically as a result of a medical condition or trauma.
There is a huge range of potential causes including head injury, interruption of blood circulation, impaired ...
* Post-chemotherapy cognitive impairment
Post-chemotherapy cognitive impairment (PCCI) (also known in the scientific community as "CRCIs or Chemotherapy-Related Cognitive Impairments" and in lay terms as chemotherapy-induced cognitive dysfunction or impairment, chemo brain, or chemo fog) ...
* Pumphead syndrome
Postperfusion syndrome, also known as "pumphead", is a constellation of neurocognitive impairments attributed to cardiopulmonary bypass (CPB) during cardiac surgery. Symptoms of postperfusion syndrome are subtle and include defects associated wit ...
* Reactive hypoglycemia
Reactive hypoglycemia, postprandial hypoglycemia, or sugar crash is a term describing recurrent episodes of symptomatic hypoglycemia occurring within four hours"Hypoglycemia." It can also be referred to as "sugar crash" or "glucose crash." Nati ...
* Sleep inertia
Sleep inertia is a physiological state of impaired cognitive and sensory-motor performance that is present immediately after awakening. It persists during the transition of sleep to wakefulness, where an individual will experience feelings of drows ...
* Slow-wave sleep
Slow-wave sleep (SWS), often referred to as deep sleep, consists of stage three of non-rapid eye movement sleep. It usually lasts between 70 and 90 minutes and takes place during the first hours of the night. Initially, SWS consisted of both St ...
* Somnolence
Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...
* Stupor
Stupor is the lack of critical mental function and a level of consciousness, in which an affected person is almost entirely unresponsive and responds only to intense stimuli such as pain. The word derives from the Latin '' stupor'' ("numbness, inse ...
References
{{reflist
Symptoms and signs of mental disorders
Symptoms and signs: Nervous system
Cognitive disorders
Psychopathological syndromes
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