Differential effects of left/right neuropathy on rats' anxiety and cognitive behavior.

Chronic pain is frequently accompanied by a deterioration of emotional behavior and cognitive function. A small number of studies in humans concluded that pain-associated negative affect is more pronounced when pain is localized in the left side of the body. It has been suggested that such side bias results from cortical function lateralization. It is not known, however, if other pain-associated behavioral changes are differentially affected by left- and right-sided pain. To test this hypothesis, the performance of rats with a unilateral spared nerve injury neuropathy installed in the left (SNI-L) or in the right (SNI-R) side was compared in anxiety (elevated-plus maze) and cognitive (spatial working and reference memory, attentional set-shifting task, and delay-to-signal impulsivity task) behavioral paradigms. Results show that SNI-L animals presented an increased anxiety-like profile while maintaining preserved cognitive function. On the contrary, SNI-R animals presented cognitive deficits in all tasks except in the reference memory, but displayed a normal anxiety-like profile. Our results show that left- and right-sided neuropathic pain differentially affects emotional behavior, which is in accordance with previous observations in human subjects, both in experimentally induced pain and in chronic pain conditions. Additionally, our results demonstrate that the cognitive function deterioration associated with unilateral neuropathic chronic pain conditions is also differentially affected.