However, in some other patients, the character of the emotional display can be incongruent with, and even contradictory to, the emotional valence of the provoking stimulus or may be incited by a stimulus with no clear valence. For example, a patient may laugh in response to sad news or cry in response to stimuli with no emotional undertone, or, once provoked, the episodes may switch from laughing to crying or vice versa.The symptoms of PBA can be severe, with persistent and unremitting episodes. Characteristics include:

The onset can be sudden and unpredictable, and has been described by some patients as coming on like a seizure;
The outbursts have a typical duration of a few seconds to several minutes; and,
The outbursts may happen several times a day.Many people with neurologic disorders exhibit uncontrollable episodes of laughing, crying, or anger that are either exaggerated or contradictory to the context in which they occur. Where patients have significant cognitive deficits (e.g., Alzheimers) it can be unclear whether it is true PBA as opposed to a grosser form of emotional dysregulation, but patients with intact cognition often report the symptom as disturbing. Patients report that their episodes are at best only partially amenable to voluntary control, and unless they experience a severe change of mental status, as in traumatic brain injury they often have insight into their problem and judge their emotional displays as inappropriate and out of character.
Overall, the trial showed a statistically significant benefit from taking a combination of dextromethorphan and quinidine, with both dosages being safe and well tolerated. For a secondary objective measuring a participants "perceived health status...measuring eight health concepts: vitality, physical functioning, bodily pain, general health perceptions, physical role-, emotional role-, social role functioning, and mental health," the higher dosage showed improvement, especially on measures of social functioning and mental health. Epidemiology
Prevalence estimates place the number of people with PBA between 1.5 and 2 million in the United States alone, which would be less than 1% of the U.S. population even at the high end of the estimate. Some argue that the number is probably higher and that clinicians underdiagnose PBA. However, the prevalence estimate of 2 million is based on an online survey. Self-selected computer-savvy patients in at-risk groups evaluated their own symptoms and submitted their self-diagnoses. No doctor or clinic confirmed the data. Motivation to participate could have been influenced by the presence of symptoms, which would have skewed the results. The actual prevalence could very well be quite a bit lower than estimated. History
The Expression of the Emotions in Man and Animals by Charles Darwin was published in 1872. In Chapter VI, "Special Expressions of Man: Suffering and Weeping", Darwin discusses cultural variations in the acceptability of weeping and the wide differences in individual responses to suffering.