What term is used to describe a state of temporary confusion which results from misleading information sent to the brain by various sensory organs?

Learn about medical disorders that can interfere with cognition and mimic dementia.

Even as a sleep-deprived and inexperienced intern, several decades ago, I knew something was wrong when I was asked to evaluate Mrs. M, a woman well into her 90s who was admitted for care of “dementia.” She was reputed to have been sharp as a tack until the preceding week. Following the operation that repaired her cataracts, which in those days meant a period of patched eyes and bedrest, her behavior changed quickly and dramatically. Her lovely personality became irritable and angry. Her language became abusive. She scratched a caregiver in her nursing home who was trying to help her get dressed.

It seemed very likely to me that Mrs. M’s sudden change in behavior had more to do with her operation than with a progressive neurological condition.

A Condition that Can Fool Even Experienced Doctors

In fact, Mrs. M was suffering from delirium, at that time called acute organic brain syndrome that results in rapidly changing mental states, and causes confusion and changes in behavior. She returned to her previous healthy cognitive status very quickly after her eye patches were removed and her post-operative recovery continued.

The lesson I learned from her recovery was that delirium can fool even experienced doctors into misdiagnosing dementia, which is now called Major Neurocognitive Disorder (and which I’ll abbreviate after this as MaND). Confusion, disorientation, and memory impairment are signs of delirium that are shared with MaND.

Delirium looks very different, though, in other ways. It comes on rapidly, often after a medical or surgical event or toxic combination of medications. It is accompanied by shifting alertness, resulting in moments of sleepiness alternating with moments of agitation. Delirium is more often associated with visual hallucinations or psychotic delusions than MaND. And, most importantly, delirium can often be reversed once the cause is found and treated.

Its causes are many and include infection, metabolic disturbances, toxic medication reactions, withdrawal from alcohol, and the effects of head injury, just to name a few.

Delirium is only one of a long list of reversible or partly reversible medical conditions that can mimic MaND and mislead the doctors into assigning the wrong diagnosis. When the patient’s condition is labeled incorrectly, some terrible things begin to happen. The search for treatable conditions may be stopped too early. Hopelessness can set in. The wrong medication might be prescribed. The opportunity to improve the patient’s health and quality of life may be lost, perhaps forever.

What makes this especially tragic is that distinguishing delirium from MaND is usually not too difficult and just requires careful attention to history, symptoms, physical and mental status examinations, and the results of common laboratory tests.

I’m going to discuss a few of the many medical disorders that can interfere with cognition and mimic MaND. I’ll leave discussion of the medications that interfere with cognition for another article. The systems and organs of the body are so dependent upon each other that it will not surprise you to learn that many different kinds of disorders can present with real or apparent memory disturbances.

Head Trauma

Starting at the top of the body, head injury tops the list because of the risk of trauma to the brain. A fall, even one that seemed less serious, can be followed by significant cognitive problems. When this is due to a concussion, symptoms usually improve over time with supportive care. A limited post-traumatic bleed inside the skull can interfere with cognitive functioning by leading to a collection of blood called a subdural hematoma.

Normal Pressure Hydrocephalus

Another condition that can create cognitive impairment is normal pressure hydrocephalus (NPH), a disorder in which cerebrospinal fluid accumulates in the ventricles (cavities) of the brain and interferes with thinking, memory, walking, and control of urination.

Problems with Vision and Hearing

Sensory limitations, too, can create a picture like cognitive impairment that worsens as the affected person becomes increasingly isolated as a result of hearing or vision problems. Recent research has emphasized that there is a relationship between hearing loss and the risk for development of cognitive impairment.

Disorders of the Heart and Lungs

The heart and lungs provide the brain with oxygen and nutrients that are necessary for proper functioning. Age is often accompanied by vascular (blood vessel) disease that interferes with cardiac output or lung disease that interferes with the delivery of oxygen to the brain. These underlying diseases can cause MaND as well as what’s commonly known as vascular dementia (which can sometimes occur along with Alzheimer’s-related dementia). They can also affect alertness, memory, and executive function..

Liver and Kidney Disease

Diseases of the kidney or liver can result in an accumulation of toxic metabolic waste products in the blood, dulling the mind or poisoning mental activity and sometimes resulting in MaND.

Hormone Disruption

Disorders of the endocrine organs, responsible for making hormones that are transported through the bloodstream in order to control many metabolic activities, are additional causes of MaND-like symptoms. An excess or deficiency of thyroid hormone interferes with thinking. Disturbances in the regulatory effects of insulin, a hallmark of diabetes mellitus, harm cognition along with other bodily functions.

Infections

Some infections produce a prolonged change in mental functioning that lacks signs clearly linked with delirium. Lyme disease, syphilis, or HIV for example, are capable of mimicking MaND.

Cancers

Some cancers are associated with cognitive and behavioral changes. These can occur through local effects of a tumor (for example by invading or compressing brain tissue) or as a result of tumor effects on the immune system in which antibodies against the brain are formed, producing a “paraneoplastic syndrome”.

Toxic Metals

Heavy metal toxicity, too, can create more stable changes that could go unrecognized without specific testing.

How Doctors Make an Accurate Diagnosis

Fortunately, many of these medical conditions are treatable and some are even curable. An assessment for MaND should always include tests to look for these treatable conditions so that no patient has to suffer needlessly from an untreated and debilitating condition. The mental status examination should give clues to the presence of a delirium or certain other medical disturbances, and this examination is followed up by physical examination and tests of the blood and urine.

Blood count, thyroid tests, kidney functions, liver enzymes, metabolic screening, and urinalysis are routine elements of the MaND diagnostic workup. Lyme or syphilis tests, lumbar puncture, heavy metal screen, urine culture, chest X-ray, EEG, or neuroimaging with MRI and/or PET scanning may be appropriate tests for patients whose symptoms suggest the need for these additional, more costly, and sometimes more invasive tests.

Summary

Mrs. M’s recovery from delirium showed her caregivers that sometimes even a severe cognitive disturbance can be effectively treated. It is the clinician’s job to think beyond the diagnosis of MaND and consider other possible causes of symptoms, some of which may be treatable. Recognizing the medical mimics of MaND opens the door to treatment, recovery, and better quality of life for patients and those who care for them.
 

Inability of a person to correctly determine their body position in space

Spatial disorientation results in a person being unable to determine their position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibular system (within the inner ear), and proprioceptive system (sensory receptors located in the skin, muscles, tendons and joints) collectively work to coordinate movement with balance, and can also create illusory nonvisual sensations, resulting in spatial disorientation in the absence of strong visual cues.

In aviation, spatial disorientation can result in improper perception of the attitude of the aircraft, referring to the motion of the aircraft (whether turning, ascending or descending). For aviators, proper recognition of aircraft attitude is most critical at night or in poor weather, when there is no visible horizon, and spatial disorientation has led to numerous aviation accidents. Spatial disorientation can occur in other situations where visibility is reduced, such as diving operations.

Flight safety, history, and statistics

Spatial orientation in flight is difficult to achieve because numerous sensory stimuli (visual, vestibular, and proprioceptive) vary in magnitude, direction, and frequency. Any differences or discrepancies between visual, vestibular, and proprioceptive sensory inputs result in a sensory mismatch that can produce illusions and lead to spatial disorientation. The visual sense is considered to be the largest contributor to orientation.[1]: 4 

While testing an early turn and slip indicator devised by his friend Elmer Sperry in 1918, United States Army Air Corps pilot William Ocker entered a graveyard spiral while flying through clouds without visual references; the turn indicator showed he was in a turn, but his senses told him he was in level flight. Emerging from the clouds, Ocker was able to recover from the dive.[2] In 1926, Ocker was subjected to a Bárány chair equilibrium test by Dr. David A. Myers at Crissy Field; the resulting duplication of the somatogyral illusion he had experienced and a subsequent re-test, which he passed using the turn indicator,[3] led him to develop and champion instrumented flight.[4] Sperry would go on to invent the gyrocompass and attitude indicator, both of which were being tested by 1930.[5]: 8  With Lt. Carl Crane, Ocker published the instructional text Blind Flying in Theory and Practice in 1932.[4] Influential advocates of instrumented flight training included Albert Hegenberger and Jimmy Doolittle.[5]: 8 

In 1965, the Federal Aviation Agency of the United States issued Advisory Circular AC 60-4, warning pilots about the hazards of spatial disorientation, which may result from operation under visual flight rules in conditions of marginal visibility.[6] A new version of the advisory was issued in 1983 as AC 60-4A, defining spatial disorientation as "the inability to tell which way is 'up.'"[7]

Statistics show that between 5% and 10% of all general aviation accidents can be attributed to spatial disorientation, 90% of which are fatal.[8] Spatial-D and G-force induced loss of consciousness (g-LOC) are two of the most common causes of death from human factors in military aviation.[9] A study on the prevalence of spatial disorientation incidents concluded that "if a pilot flies long enough ... there is no chance that he/she will escape experiencing at least one episode of [spatial disorientation]. Looked at another way, pilots can be considered to be in one of two groups; those who have been disorientated, and those who will be."[1]: 2 

Physiology

There are four physiologic systems that interact to allow humans to orient themselves in space. Vision is the dominant sense for orientation, but the vestibular system, proprioceptive system and auditory system also play a role.[citation needed]

Spatial orientation (the inverse being spatial disorientation, aka spatial-D) is the ability to maintain body orientation and posture in relation to the surrounding environment (physical space) at rest and during motion. Humans have evolved to maintain spatial orientation on the ground. Good spatial orientation on the ground relies on the use of visual, auditory, vestibular, and proprioceptive sensory information. Changes in linear acceleration, angular acceleration, and gravity are detected by the vestibular system and the proprioceptive receptors, and then compared in the brain with visual information.[citation needed]

The three-dimensional environment of flight is unfamiliar to the human body, creating sensory conflicts and illusions that make spatial orientation difficult and sometimes impossible to achieve. The result of these various visual and nonvisual illusions is spatial disorientation.[10][9][11] Various models have been developed to yield quantitative predictions of disorientation associated with known aircraft accelerations.[12]

The vestibular system and sensory illusions

Main article: Sensory illusions in aviation

The vestibular system detects linear and angular (rotational) acceleration using specialized organs in the inner ear. Linear accelerations are detected by the otolith organs, while angular accelerations are detected by the semicircular canals.

Misleading sensations

Without a visual reference or cues, such as a visible horizon, humans will rely on non-visual senses to establish their sense of motion and equilibrium. During the abnormal acceleratory environment of flight, the vestibular and proprioceptive systems can be misled, resulting in spatial disorientation. When an aircraft is maneuvering, inertial forces can be created by changes in vehicle speed (linear acceleration) and/or changes in direction (rotational acceleration and centrifugal force), resulting in perceptual misjudgment of the vertical, as the combined forces of gravity and inertia do not align with what the vestibular system assumes is the vertical direction of gravity (towards the center of the earth).

Under ideal conditions, visual cues will provide sufficient information to override illusory vestibular inputs, but at night or in poor weather, visual inputs can be overwhelmed by these illusory nonvisual sensations, resulting in spatial disorientation. Low visibility flight conditions include night,[6] over water or other monotonous/featureless terrain that blends into the sky,[6] white-out weather,[6] or inadvertent entry into instrument meteorological conditions after flying into fog or clouds.

For example, in an aircraft that is making a coordinated (banked) turn, no matter how steep, occupants will have little or no sensation of being tilted in the air unless the horizon is visible, as the combined forces of lift and gravity are felt as pressing the occupant into the seat without a lateral force sliding them to either side.[13] Similarly, it is possible to gradually climb or descend without a noticeable change in pressure against the seat. In some aircraft, it is possible to execute a loop without pulling negative g-forces so that, without visual reference, the pilot could be upside down without being aware of it.[citation needed] A gradual change in any direction of movement may not be strong enough to activate the vestibular system, so the pilot may not realize that the aircraft is accelerating, decelerating, or banking.

Gyroscopic flight instruments such as the attitude indicator (artificial horizon) and the turn and slip indicator are designed to provide information to counteract misleading sensations from the non-visual senses.

Otoliths and somatogravic illusions

Two otolith organs, the saccule and utricle, are located in each ear and are set at right angles to each other. The utricle detects changes in linear acceleration in the horizontal plane, while the saccule detects linear accelerations in the vertical plane; humans have evolved to assume the vertical acceleration is caused by gravity. However, the saccule and utricle can provide misleading sensory perception when gravity is not limited to the vertical plane, or when vehicle speeds and accelerations result in inertial forces comparable to the force of gravity, as the otoliths only detect acceleration, and cannot distinguish inertial forces from the force of gravity.[8] Some examples of this include the inertial forces experienced during a vertical take-off in a helicopter or following the sudden opening of a parachute after a free fall.[citation needed]

Illusions caused by the otolith organs are called somatogravic illusions and include the Inversion, Head-Up, and Head-Down Illusions. The Inversion Illusion results from a steep ascent followed by a sudden return to level flight; the resulting relative increase in forward speed produces an illusion the aircraft is inverted.[8] The Head-Up and Head-Down illusions are similar, involving sudden linear acceleration (Head-Up) or deceleration (Head-Down), leading to a misperception the nose of the aircraft is pitching up (Head-Up) or down (Head-Down); the aviator could be fooled into pitching the nose down (Head-Up) or up (Head-Down) in response, leading to a crash or a stall, respectively.[8]

Typically, the Head-Up illusion occurs during take-off, as a strong linear acceleration is used to generate lift over the wing and flaps. Without a visual reference, the pilot may assume from the vestibular system the nose has pitched up and command a dive; if this occurs during take-off, the aircraft may not have sufficient altitude to recover before crashing into the ground.[1]: 7 

Semicircular canals and somatogyral illusions

In addition, the inner ear contains rotational accelerometers, known as the semicircular canals, which provide information to the lower brain on rotational accelerations in the pitch, roll and yaw axes. Changes in angular velocity are detected from the relative motion between the fluid in the canals and the canal itself, which is fixed to the head; because of inertia, the fluid in the canals tends to lag when the head moves, signaling a rotational acceleration. However, semicircular canal output ceases after prolonged rotation (beyond 15–20 s) as the fluid has now been entrained into motion through friction, matching the motion of the head. If the rotation is then stopped, the perceived motion signal from the inner ear indicates the aviator is now turning in the opposite direction from actual travel, as the fluid continues to move while the canal has stopped.[8] In addition, the inertia of the fluid means the detection threshold of rotational acceleration is limited to approximately 2°/sec2; angular accelerations below this value cannot be detected.[1]: 5  Specific common somatogyral illusions induced by the semicircular canals are the Leans, Graveyard Spin, Graveyard Spiral, and Coriolis.

Main article: The leans

If the aircraft enters an unnoticed, prolonged turn gradually, then suddenly returns to level flight, the leans may result. The gradual turn sets the fluid into the semicircular canals into motion, and rotational acceleration of two degrees per second (or less) cannot be detected. Once the aircraft suddenly returns to level flight, the continued fluid motion gives the sensation the aircraft is banking in the opposite direction of the turn that just ended; the aviator may attempt to correct the misperception of the vertical by banking into the original turn.[8] The leans is considered the most common form of spatial disorientation.[1]: 9 

Main articles: Graveyard spiral and Graveyard spin

The graveyard spiral and graveyard spin are both caused by the acclimation of the semicircular canals to prolonged rotation; after a banked turn (in the case of the graveyard spiral) or spin (for the graveyard spin) of approximately 20 seconds, the fluid in the semicircular canals has been entrained into motion by friction, and the vestibular system no longer perceives a rotational acceleration. If the aviator then ends the turn or spin and returns to level flight, the continued motion of the fluid will cause a sensation the aircraft is turning or spinning in the opposite direction, and the pilot may re-enter the original turn or spin inadvertently; the aviator may not recognize the illusion before the aircraft loses too much altitude, resulting in a collision with terrain[8] or the g-forces on the aircraft may exceed the structural strength of the airframe, resulting in catastrophic failure. One of the most infamous mishaps in aviation history involving the graveyard spiral is the crash involving John F. Kennedy Jr. in 1999.[14]

Once an aircraft enters conditions under which the pilot cannot see a distinct visual horizon, the drift in the inner ear continues uncorrected. Errors in the perceived rate of turn about any axis can build up at a rate of 0.2 to 0.3 degrees per second.[citation needed] If the pilot is not proficient in the use of gyroscopic flight instruments, these errors will build up to a point that control of the aircraft is lost, usually in a steep, diving turn known as a graveyard spiral. During the entire time, leading up to and well into the maneuver, the pilot remains unaware of the turning, believing that the aircraft is maintaining straight flight.[15]: 125 

In a 1954 study (180 – Degree Turn Experiment), the University of Illinois Institute of Aviation found that 19 out of 20 non-instrument-rated subject pilots went into a graveyard spiral soon after entering simulated instrument conditions. The 20th pilot also lost control of his aircraft, but in another maneuver. The average time between onset of instrument conditions and loss of control was 178 seconds.[16]

Main article: Coriolis effect (perception)

Spatial disorientation can also affect instrument-rated pilots in certain conditions. A powerful tumbling sensation (vertigo) can result if the pilot moves his or her head too much during instrument flight. This is called the Coriolis illusion. Because the semicircular canals are set in three different axes of rotation, if the aviator suddenly moves their head during a rotational acceleration, one canal may abruptly start to detect an angular acceleration while another ceases, resulting in a tumbling sensation.[1]: 9 

Visual illusions

Even with good visibility, misleading visual inputs such as sloping cloud decks, unfamiliar runway grades, or false horizons can also form optical illusions, resulting in the pilot misjudging the vertical orientation, aircraft speed or altitude, and/or distance and depth perception; these could even combine with nonvisual illusions from the vestibular and proprioceptive systems to produce an even more powerful illusion.[17]

Examples

See also

• Balance disorder – Physiological disturbance of perception
• Bárány chair – Device used for aerospace physiology training
• Broken escalator phenomenon – The sensation of losing balance or dizziness when stepping onto an escalator which is not working
• Brownout (aeronautics) – In-flight visual impairment by pilots
• Dizziness – Neurological condition causing impairment in spatial perception and stability
• Equilibrioception – Physiological sense regarding posture
• Ideomotor phenomenon – Concept in hypnosis and psychological research
• Illusions of self-motion – Misperception of one's location or movement
• Motion sickness – Nausea caused by motion or perceived motion
• Pilot error – Decision, action or inaction by a pilot of an aircraft
• Proprioception – Sense of the relative position of one's own body parts and strength of effort employed in movement
• Sense of direction
• Sensory illusions in aviation – Misjudgment of true orientation by pilots
• Situation awareness – Adequate perception of environmental elements and external events
• Spatial ability
• Topographical disorientation

References

1. ^ a b c d e f Newman, David G. (3 December 2007). An overview of spatial disorientation as a factor in aviation accidents and incidents (PDF) (Report). Australian Transport Safety Bureau. ISBN 978-1-921165-52-8. Retrieved 11 February 2021.
2. ^ Wolverton, Mark (Fall 2008). "The Father Of Blind Flying". Invention and Technology. American Heritage Institute. 23 (3). Retrieved 11 February 2021.
3. ^ Chivalette, William I. (1998). "Sergeant William Charles Ocker: The Army's third enlisted pilot" (PDF). Air Force Enlisted Heritage Research Institute. Retrieved 11 February 2021.
4. ^ a b LeCompte, Tom (September 2008). "The Disorient Express". Air & Space. Smithsonian Institution. Retrieved 11 February 2021.
5. ^ a b McIntosh, David M. (1988). The evolution of instrument flying in the U.S. Army (PDF) (Report). Air Command and Staff College. Archived (PDF) from the original on November 1, 2019. Retrieved 11 February 2021.
6. ^ a b c d Moore, George S. (February 9, 1965). "AC 60-4: Pilot's Spatial Disorientation". Federal Aviation Agency. Retrieved 11 February 2021.
7. ^ Hunt, Kenneth S. (February 9, 1983). "AC 60-4A: Pilot's Spatial Disorientation" (PDF). Federal Aviation Administration. Retrieved 11 February 2021.
8. ^ a b c d e f g Antuñano, Melchor J. "Medical Facts for Pilots: Spatial Disorientation, safety brochure AM-400-03/1" (PDF). Federal Aviation Administration. Retrieved 9 February 2021.
9. ^ a b Jedick, Rocky 'Apollo' (1 April 2013). "Spatial Disorientation". Go Flight Medicine. Retrieved 30 July 2016.
10. ^ Previc, Fred H.; Ercoline, William R. (2004). Spatial disorientation in aviation. Reston, Virginia: American Institute of Astronautics and Aeronautics. doi:10.2514/4.866708. ISBN 978-1-60086-670-8.
11. ^ "Spatial disorientation - physiology". Britannica. Retrieved 30 July 2016.
12. ^ Newman, Michael C.; Lawson, Ben D.; Rupert, Angus H.; McGrath, Braden J. (August 13–16, 2012). "The role of perceptual modeling in the understanding of spatial disorientation during flight and ground-based simulator training". AIAA Modeling and Simulation Technologies Conference. AIAA modeling and simulation technologies conference. Minneapolis, Minnesota: American Institute of Aeronautics and Astronautics. doi:10.2514/6.2012-5009. ISBN 978-1-62410-183-0.
13. ^ "ANA pilots unaware for 17 seconds that plane was almost turning upside down". Japan Today. August 31, 2012. Retrieved 11 February 2021. The aircraft tipped more than 130 degrees to the left at one point, but the darkness outside meant many of those on board did not realize the craft had almost flipped over.
14. ^ a b Jedick, Rocky 'Apollo' (April 15, 2014). "JFK Jr Piper Saratoga Mishap". Go Flight Medicine.
15. ^ Campbell, Douglas E. (2018). VPNavy! USN, USMC, USCG and NATS Patrol Aircraft Lost or Damaged During World War II (2018 ed.). Syneca Research. ISBN 978-1-387-49193-3.
16. ^ Aulls Bryan, Leslie; Stonecipher, Jesse W.; Aron, Karl (1954). 180-degree turn experiment. University of Illinois. ASIN B0007EXGMI. LCCN a54009717. OCLC 4736008. OL 207786M.
17. ^ Antuñano, Melchor J. "Medical Facts for Pilots: Spatial Disorientation, Visual Illusions; safety brochure AM-400-00/1" (PDF). Federal Aviation Administration. Retrieved 9 February 2021.
18. ^ Landsberg, Bruce (February 1, 2009). "Safety Pilot Landmark Accidents: The Day the Music Died". Aircraft Owners and Pilots Association. Retrieved 11 February 2021.
19. ^ NTSB Identification: NYC99MA178 (Report). National Transportation Safety Board. Retrieved 11 February 2021.
20. ^ Aircraft Accident Brief AAB-02/02, Accident Number CHI01MA011 (PDF) (Report). National Transportation Safety Board. 2002. Retrieved 28 February 2021.
21. ^ "Spatial disorientation doomed Carnahan flight". Aircraft Owners & Pilots Association. June 6, 2002. Retrieved 28 February 2021.
22. ^ "NTSB releases Atlas Air freighter crash findings". 15 July 2020.
23. ^ "DCA19MA086.aspx".
24. ^ "Remains of Japan ASDF pilot found, two months after F-35A fighter crash off Aomori". The Japan Times. June 7, 2019. Retrieved 11 February 2021.
25. ^ Yeo, Mike (June 10, 2019). "Japan blames spatial disorientation for F-35 crash". Defense News. Retrieved 11 February 2021.
26. ^ "Japan pilot crashed after 'spatial disorientation'". BBC News. 2019-06-10. Retrieved 2019-06-10.
27. ^ Steinbuch, Yaron (2021-02-09). "Kobe Bryant helicopter pilot had 'spatial disorientation' before crash: NTSB". New York Post. Retrieved 2021-02-09.
28. ^ "Investigators report Kobe Bryant's pilot got disoriented in clouds". 2021-02-09. Retrieved 2021-02-10.

External links

• "Ashton Graybiel Spatial Orientation Laboratory – Brandeis University". Retrieved 30 July 2016.

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