The sopite syndrome (; ) is a

neurological disorder Neurological disorders represent a complex array of medical conditions that fundamentally disrupt the functioning of the nervous system. These disorders affect the brain, spinal cord, and nerve networks, presenting unique diagnosis, treatment, and ...

that relates symptoms of

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

, drowsiness, and mood changes to prolonged periods of motion. The sopite syndrome has been attributed to motion-induced drowsiness such as that experienced by a baby when rocked.Lawson, B. D., & Mead, A. M. (1998). The sopite syndrome revisited: Drowsiness and mood changes during real or apparent motion. Acta Astronautica, 43(3-6), 181-192. Researchers Ashton Graybiel and James Knepton at the US Naval Aerospace Medical Research Laboratory first used the term "the sopite syndrome" in 1976, to refer to the sometimes sole manifestation of

motion sickness Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include ...

, though other researchers have referred to it as "Sopite syndrome."

Signs and symptoms

Several symptoms are associated with the sopite syndrome. Typical responses include: *drowsiness *yawning *disinclination for work *lack of social participation *mood changes *apathy *sleep disturbances *other fatigue-related symptoms The sopite syndrome is distinguished from other manifestations of motion sickness (i.e. nausea, dizziness, etc.) in that it may occur before other symptoms of motion sickness or in their absence. The sopite syndrome may persist even after an individual has adapted to the other symptoms associated with motion-induced sickness.

Severity

The effects of the sopite syndrome may range from minor physical inconveniences to hazardous conditions. People who operate automobiles, airplanes, etc., may experience impaired motor function due to the motions of the vehicle. These impairments often result in a decreased attention span; those who consider themselves well-rested may still succumb to drowsiness at inopportune moments. The sopite syndrome may therefore contribute to motor vehicle accidents in which automobile operators fall asleep at the wheel. However, the sopite syndrome itself does not directly result in death.Kennedy, R. S. (5 October 2010). (A. V. Paschall, Interviewer) A subject experiencing the sopite syndrome on a frequent basis may increase the number of hours spent sleeping by fifty percent. A study of motion sickness occurrences in workers on an offshore oil vessel showed a large majority of participants experienced mild symptoms of fatigue. Many participants also experienced severe sleep disturbances. These symptoms were associated with impaired task performance.Haward, B. M., Lewis, C. H., & Griffin, M. J. (2009). Motions and crew responses on an offshore oil production and storage vessel. '' Applied Ergonomics'', 40(5), 904-914.

Causes

The sopite syndrome has been associated with visually-induced and vestibular motion sickness. Other factors associated with drowsiness such as darkness or physical fatigue may intensify the effects of motion-induced sleepiness. The sopite syndrome may occur with little motional stimulus (though the greatest effects tend to be observed in subjects who have been exposed for longer periods of time), and often persists for a time after the motional stimulus has ceased.

Susceptibility

A study of certain aspects of motion sickness among medical transport attendants showed that the onset of the sopite syndrome is likely to occur independently of the mode of transportation; little difference was observed in the frequency of sopite symptoms for ground transport compared to air transport. Also, the length of time exposed to vehicular motion did not appear to affect the occurrence (or lack thereof) or severity of the sopite syndrome. No difference was observed in the incidence of the sopite syndrome for men versus women.Wright, M. S., Bose, C. L., & Stiles, A. D. (1995). The incidence and effects of motion sickness among medical attendants during transport. Journal of Emergency Medicine, 13(1), 15-20. The sopite syndrome is likely a cumulative disorder. For instance, when a subject has the flu, a

hangover A hangover is the experience of various unpleasant physiological and psychological effects usually following the consumption of alcohol (beverage), alcohol, such as wine, beer, and liquor. Hangovers can last for several hours or for more than ...

may exacerbate the symptoms of the illness. A subject normally resistant to motion sickness may experience symptoms of motion sickness when also experiencing flu-like (or hangover-like) symptoms.

Mechanism

The exact mechanism for the induction of the sopite syndrome is still unknown; however, a leading theory asserts that the sopite syndrome (and perhaps motion sickness in general) is somehow related to the

reticular formation The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks ...

, an area of the brainstem associated with arousal. A study of motion-induced effects on the P50 potential (a measure of arousal) showed that subjects exposed to motion environments experience decreased sensory gating, which involves the filtering of information in the brain.Dornhoffer, J. L., Mamiya, N., Bray, P., Skinner, R. D., & Garcia-Rill, E. (2002). Effects of rotation on the sleep state-dependent midlatency auditory evoked P50 potential in the human. Journal of Vestibular Research-Equilibrium & Orientation, 12(5-6), 205-209. In the case of Space Motion Sickness, the unweighting of

otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...

organs can lead to a sensory mismatch between the visual, vestibular, and somatosensory systems. Motion studies in which the subjects lacked vestibular systems did not experience symptoms of the sopite syndrome or other manifestations of motion sickness.

Vestibular system

The role of the

vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...

in the inducement of the sopite syndrome or related symptoms may be difficult to ascertain. Researchers must compare the results of test subjects experiencing a motion environment to a control environment lacking motion. Experimental subjects who suffered increased fatigue in a rotating environment apparently recovered from this side effect when the same environment ceased motion. In similar studies, control subjects lacking vestibular function did not experience the motion-induced drowsiness associated with the sopite syndrome, while subjects with normal-functioning vestibular systems did experience increased fatigue in the rotating environments.

Visual stimulus

The relation of the visual-vestibular stimulus to the sopite syndrome may be observed when comparing airline cockpit crew with cabin crew. While the former typically experience more confined conditions, the airline cabin crew tend to experience more symptoms associated with sopite syndrome; this effect may be attributed to the lack of visual validation and increased movement of the cabin crew.

Biochemicals

Certain

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

s or

biochemical Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, ...

s likely affect the pathways associated with motion sickness in general and the sopite syndrome in particular. Studies reported by Kennedy, Drexler and Kennedy (2010) have investigated the role of

cortisol Cortisol is a steroid hormone in the glucocorticoid class of hormones and a stress hormone. When used as medication, it is known as hydrocortisone. Cortisol is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal corte ...

and

melatonin Melatonin, an indoleamine, is a natural compound produced by various organisms, including bacteria and eukaryotes. Its discovery in 1958 by Aaron B. Lerner and colleagues stemmed from the isolation of a substance from the pineal gland of cow ...

(a hormone associated with the maintenance of

circadian rhythm A circadian rhythm (), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., Endogeny (biology), endogenous) and responds to the env ...

s) in motion-induced drowsiness. Subjects were exposed to vection-producing environments (virtual reality, for example) and symptoms were evaluated using a ''Simulator Sickness Questionnaire''. Sopite symptoms were also measured using a developed scale. The levels of endogenous cortisol and melatonin were then compared with levels before the subjects were tested in the vection environments. Most subjects showed increased levels of

endogenous Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell. For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...

cortisol and melatonin post-vection. Melatonin may therefore be involved in the drowsy state associated with the sopite syndrome.Kennedy, R. S., Drexler, J., & Kennedy, R. C. (2010). Research in visually induced motion sickness. Applied Ergonomics, 41(4), 494-503.

Noradrenergic pathways

The inhibition of noradrenergic pathways has also been associated with symptoms of the sopite syndrome. Studies have shown that animals exposed to motion environments commonly exhibit drowsiness and disinclination for activity. These animals show slowed

electroencephalography Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignal, bio signals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in ...

waves, which are involved in the firing of

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s in the brain. The locus coeruleuses of these animals are apparently deactivated.Nishiike, S., Takeda, N., Kubo, T., & Nakamura, S. (2001). Noradrenergic pathways involved in the development of vertigo and dizziness - A review. Acta Oto-Laryngologica, 61-64. The sopite syndrome is therefore linked to inhibition of the locus coeruleus-noradrenergic pathways. As such, noradrenaline releasers may be useful in counteracting these symptoms.

Diagnosis

Classification

The sopite syndrome is classified as a symptom-complex centered on drowsiness. It may be distinguished from ordinary fatigue. Researchers have previously studied this effect through the use of rotating rooms. When subjects who had previously shown minimal susceptibility to general motion sickness and fatigue (in this particular case, four military officers) were recruited to live in a rotating room for several days, they exhibited several signs of drowsiness, such as yawning and frequent napping. Despite numerous activities designed to promote awareness and excitability, the subjects showed decreased motivation to socialize or perform physical activities. Many of these symptoms could be attributed to the vestibular stimulation of the rotating rooms.

Management

Many drugs taken to relieve typical symptoms of motion sickness (including nausea, dizziness, etc.) contain compounds that may exacerbate drowsiness.

Antihistamines Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provides r ...

are commonly used to treat motion sickness; however, side effects include drowsiness and impaired cognitive abilities.

Anticholinergic Anticholinergics (anticholinergic agents) are substances that block the action of the acetylcholine (ACh) neurotransmitter at synapses in the central nervous system, central and peripheral nervous system. These agents inhibit the parasympatheti ...

s such as scopolamine have also proved effective against motion sickness, but may induce drowsiness.Hoyt, R. E., Lawson, B. D., McGee, H. A., Strompolis, M. L., & McClellan, M. A. (2009). Modafinil as a Potential Motion Sickness Countermeasure. Aviation, Space, and Environmental Medicine, 80(8), 709-715. These treatments may be combined with stimulants to counteract typical motion-induced nausea and dizziness while also preventing sedation. However, many stimulants possess addictive properties, which result in a high potential for substance abuse. Some stimulants also tend to interfere with normal sleep patterns. Modafinil has been studied as a possible treatment for the sopite syndrome that does not appear to have the same side effects of normal stimulants. Modafinil appears to be effective when taken in combination with anticholinergics such as scopolamine, but studies of Modafinil-only treatments for motion sickness remain inconclusive.

Research

The sopite syndrome may be difficult to test due to the nature of the symptoms. Indicators such as drowsiness, mood changes, and apathy must be observed and graded objectively. Therefore, many of the results obtained from studies of the sopite syndrome are not sufficiently repeatable for the purposes of scientific writing.

Questionnaires

A typical method for determining the effects of the sopite syndrome is through the use of one or several questionnaires. The available questionnaires for motion sickness and sopite syndrome are described by Lawson. Two such questionnaires widely used to evaluate motion sickness are the Pensacola Diagnostic Index and the Motion Sickness Questionnaire. These questionnaires are limited, however, in that they group symptoms of drowsiness with other non-sopite related effects, such as nausea and dizziness.Gianaros, P. J., Muth, E. R., Mordkoff, J. T., Levine, M. X., & Stern, R. M. (2001). A questionnaire for the assessment of the multiple dimensions of motion sickness. Aviation, Space, and Environmental Medicine, 72(2), 115-119. Motion sickness is measured based on the cumulative ratings of all these symptoms without distinguishing different levels for each effect. A Motion Sickness Assessment Questionnaire has been developed to test the multiple dimensions of motion sickness more thoroughly; this survey defines motion sickness as gastrointestinal (involving nausea), peripheral (referring to thermoregulatory effects such as clamminess and sweating), central (involving symptoms such as dizziness and lightheadedness), and sopite-related. This questionnaire may more accurately determine how subjects experience sopite symptoms relative to other motion sickness effects. Another questionnaire designed to measure sleepiness is the Epworth Sleepiness Scale.

Optokinetic drum

An optokinetic drum may be used to study visually induced sopite effects. The optokinetic drum is a rotating instrument in which test subjects are seated facing the wall of the drum. The interior surface of the drum is normally striped; thus, as the drum rotates, the subject's eyes are subject to a moving visual field while the subject remains stationary. The speed of the drum and the duration of the test may be varied. Control groups are placed in a drum without stripes or rotation. After exposure to the rotating drum, subjects are surveyed to determine their susceptibility to motion sickness. A study in which the optokinetic drum was used to test the symptoms of the sopite syndrome showed increased mood changes in response to the visual cues, though these effects were compounded by other environmental factors such as boredom and lack of activity.Kiniorski, E. T., Weider, S. K., Finley, J. R., Fitzgerald, E. M., Howard, J. C., Di Nardo, P. A., ''et al.'' (2004). Sopite symptoms in the optokinetic drum. Aviation, Space, and Environmental Medicine, 75(10), 872-875.

References

{{Use dmy dates, date=April 2019 Neurological disorders Diseases of the ear and mastoid process Syndromes