Cataplexy is characterized by a sudden loss of muscle tone, either generalized over the entire body or localized to specific muscle groups. According to MayoClinic.com, a number of physical changes occur during a cataplectic attack such as slurred speech, head droop or arm weakness. Cataplexy is often a symptom of the sleep disorder narcolepsy. However, in rare cases, cataplexy occurs without the co-occurrence of narcolepsy. Cataplexy is a neurological condition, lasting from a few seconds to several minutes, without warning. The exact cause of cataplexy is unknown, but the condition is strongly linked to experiencing intense emotions and reduced levels of the neurochemical hypocretin.
Narcolepsy
The National Institute of Neurological Disorders and Stroke estimates approximately one in every 2,000 Americans experiences narcolepsy, with 70 percent of these individuals experiencing co-occurrence of cataplexy. Narcolepsy results from the brain's inability to regulate normal sleep cycles, and sudden onset of daytime sleepiness occurs. This condition is disabling for most because it can occur during any point of daily activity. A bout of narcolepsy may last from seconds to minutes and occurs one to several times a day. The cause of narcolepsy is unknown, but brain abnormalities, genetic variants and disruptions in immune system functions are associated with development of narcolepsy.
Emotional States
Emotions such as humor, laughter and excitement are correlated with cataplectic episodes in people with co-existing narcolepsy. A 2005 study in the "Journal of Neuropsychiatry and Clinical Neurosciences" concluded that the emotional trigger of laughter was most strongly correlated with provoking cataplexy. This included emotional states related to laughter such as feeling excitement, elation and recalling moments of happiness. This study further indicated that laughter is linked to fluctuations in muscle activity, which is highly disrupted in moments of cataplectic episodes. During cataplectic states, however, the individuals reported awareness of outside stimuli, such as noise and conversation, yet a virtual muscle paralysis deterred movement for the duration of the episode.
Hypocretin
The hypothalamus region of the brain regulates basic functions of hormone release, emotional expression and sleep. A 2006 study in the "Tohoku Journal of Experimental Medicine" concluded that the neurochemical hypocretin-1, which is regulated by the hypothalamus, was significantly reduced in study participants with symptoms of cataplexy. Hypocretin is a primary chemical important in regulating sleep as well as states of arousal. Hypocretin deficiency is further associated with decreased levels of histamine and epinephrine, which are chemicals important in promoting wakefulness, arousal and alertness.
References
- "Journal of Neuropsychiatry and Clinical Neurosciences": Characterizing the Emotions That Trigger Cataplexy; Lois E. Krahn, MD, et al; February 2005
- Public Library of Science:Anomalous Hypothalamic Responses to Humor in Cataplexy; Allan L. Reiss, et al; 2008
- "Tohoku Journal of Experimental Medicine": Niemann-Pick Disease Type C: Cataplexy and Hypocretin in Cerebrospinal Fluid; Oyama K, et al; July 2006
- Mayo Clinic: Narcolepsy
- National Institute of Neurological Disorders and Stroke: Narcolepsy Fact Sheet
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