Tuesday, January 22, 2008

Polyvagal Theory and developmental psychopathology

Beauchaine, T.P., Gatzke-Kopp, L., & Mead, H.K. (2007). Polyvagal Theory and developmental psychopathology: Emotion dysregulation and conduct problems from preschool to adolescence. Biological Psychology, Vol 74, 174-184.

Polyvagal Theory specifies two distinct branches of the vagus, each originating in the medulla. The evolutionarily older branch originates in the dorsal motor nucleus (DMX), while the newer branch originates in the nucleus ambiguus (NA). Both branches provide inhibitory input to the viscera, including the heart. However, each does so in service of distinct evolutionary functions. The DMX branch is tasked with primary survival strategies, enacting defensive behaviors such as fighting, flighting, or freezing. The NA branch, only found in mammals, is used in modulating the fight/flight response towards the execution of social affiliation behaviors (read: emotional regulation).

Functional organization of the autonomic nervous system is thought to be phylogenetically hierarchical, with response strategies to threat dictated by the newest neural structures first, then falling back on older structures when a given response strategy fails. Therefore, polyvagal theory predicts that the NA branch will inhibit acceleratory sympathetic nervous system (SNS) input to the heart when attention and social engagement are adaptive, and withdraw this inhibitory influence when fighting or fleeing are adaptive.

Beauchaine et al argue that an under-responsive central reward system coupled with deficient vagal modulation of emotion leads to sensation-seeking and aggressive behaviors characteristic of externalizing disorders, such as conduct disorder and delinquency, while an over-responsive central inhibition system coupled with deficient vagal modulation of emotion leads to withdrawal behaviors characteristic of internalizing disorders, such as anxiety and panic.

True to form, vagal deficiencies were observed in aggressive children and adolescents, manifested in attenuated respiratory sinus arrhythmia (a measure of vagal activity and thus an index of parasympathetic influence) at baseline and while watching sad and threatening films. Onset of motivational deficiencies appear as early as preschool years (central dopamine systems maturing quite early), but the study reveals that reduced vagal tone and excessive vagal reactivity don't appear until after preschool and into the middle school years. Therefore, socialization of strong emotion regulation skills during these formative years may buffer at-risk children from going on to develop conduct disorders and delinquency.

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