|MadSci Network: Neuroscience|
Dear Shannon, You ask an interesting question about the mechanisms of crying. Although the exact mechanism underlying the crying response to stimuli interpreted as sad is not known, several hypotheses have been proposed. The general idea is that crying is produced by a number of (not yet precisely identified) brain regions located in the brain stem. Crying is a highly stereotyped behaviour; it is characterised by a set of facial expression and respiratory patterns that are already seen in the very first moments of the life and seem to be common to all humans. One interesting way to know more about crying mechanisms is to look at brain damaged patients suffering from pathological crying and laughing. These patients experience episodes of uncontrolled crying or laughing that, importantly, are not associated with a particular stimulus. Moreover, the crying or laughing behaviour can sometimes be triggered by a non-correspondent stimulus (ex. : patient cried after someone told him a joke). In early observations of pathological crying and laughing, Wilson (1924) proposed that the problem emerges because of a disinhibition of crying and laughing centres in the brain stem, normally under inhibitory control of the higher (cortical) motor centres of the brain. The fact that in 30 patients suffering from pathological crying and laughing all had lesions in the internal capsule (Poeck, 1985) support Wilson’s idea that a descending motor pathway toward lower regions is involved. In a recent case study (Parvizi et al., 2001), the putative mechanisms underlying normal and pathological crying and laughing are discussed. It is noted that patients with such pathology sometimes change from laughing to crying and may respond in a totally incongruent manner (ex. crying) to a banal stimulus (ex. a hand movement in the visual field). The patient observed by Parvizi et al. (2001) has lesions in the brain stem as well as in the cerebellum. Authors proposed that the pathology arises from damage to the cerebro (cortical)-ponto-cerebellar pathway. It is argued that several brain regions are involved, including regions known to play a role in emotions (ex. amygdala, cingulum and others), motor regions of the brain stem and the cerebellum. This last structure, traditionally known to participate in motor control may, according to authors, play a modulation role in the crying/laughing response by adjusting it with social context. For example, a person may laugh very loudly in a given circumstance (ex. party) while in other situation the response would have been restricted to a smile or totally inhibited. In that sense, I found that this idea has a point in common with the view of Wilson in that a « crying or laughing centre » is under the control of other brain structures. Regards, Eric See also this related question : ID: 994346025.Gb Related papers : Wilson (1924) J. Neurol. Psychopathol. IV : 299-333 Poeck (1985) In : Vinken et al. (Eds) Handbook of clinical neurology Vol. 3 p343-367 Parvizi et al. (2001) Brain 124 : 1708-1719.
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