Dysfunctional Relationship Between the Prefrontal Cortex and Amygdala for Explaining Posttraumatic CRPS Syndrome.

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Dear Editor, After limb trauma, the first short lasting response corresponds to a facilitatory supraspinal influence exerted at the spinal cord with sympathoexcitation. A descending sympathoexcitatory response with analgesia, peripheral vasoconstriction, and facilitated motor reflexes could be an active adaptive response for helping to maintain the capacity to use an injured body part for flight or fight in case of emergency. After that, a descending sympathoinhibitory response with hyperalgesia, vasodilatation, and muscle weakness could be a passive adaptive response, where facilitation of pain might promote protection from new injury and vasodilatation and immobilization might help the healing process of the injured region. Persistent sympathoinhibition has been implicated for developing posttraumatic complex regional pain syndrome (CRPS). However, there is little known about the underlying neuroanatomical pathways involved in persistent sympathoinhibition in CRPS patients. Periaqueductal gray (PAG) has been seen as a center for defensive reactions that is capable of coordinating the sensory, motor, and autonomic outputs of the stress response. According to Vianna [1], four main longitudinal cell-rich subdivisions exist in the PAG, namely the dorsomedial (dmPAG), dorsolateral (dlPAG), lateral, and ventrolateral (vlPAG) subdivisions. Activation of neurons in the lateral/dorsolateral column of the PAG (l/dlPAG) results in sympathoexcitation that accompany the fight-or-flight response [2,3]. Activation of neurons in the vlPAG results in the sympathoinhibition that can accompany deep pain [2,3]. These PAG columns have extensive, viscerotopically organized, descending projections to sympathetic premotor neurons in the rostroventral medulla (RVM) [4]. Differential activation of l/dlPAG columns and vlPAG columns could provide a substrate for the parallel activation or inhibition of premotor neurons in the RVM and Locus Coeruleus thus explaining different patterns of autonomic activity supporting active and passive coping behaviors. Afferent signals from the autonomic nervous system terminating in lamina …