Introduction: The ability to understand and actively modulate the perception of others emotions may have important implications in the treatment of a variety of disorders such as autism, sociopathy and traumatic brain injury. Here we investigate the possible role of the periaqueductal grey (PAG) in modulating the perception of the emotional states of others.

Methods: Medically intractable pain patients who were implanted with deep brain stimulation (DBS) electrodes in the ventrolateral PAG performed a behavioral task. Subjects were shown images of morphed facial expressions across multiple axes each crossing a pair of 2 different emotional states including: anger, happiness and sadness. An axis of male-female faces was added to test for non-emotional perception. DBS was pseudorandomly turned on/off while individuals were asked to report the perceived emotional state. Ensuring that comfort level was not compromised throughout the experiment, a control trial testing for the perceived pain level was performed for every ten trials. In addition, subjects were confirmed not to be able to reliably identify whether the pulse generator is turned on or off.

Results: PAG stimulation lead to emotion perception bias across all tested axes . Under conditions of maximal ambiguity, the facial expressions were perceived as sad rather than happy or angry and angry rather than happy. In addition, the subjects’ response rate of happy decreased by 19 % in the “happy-sad” axis and by 7% in the “happy-angry” axis. Stimulation did not affect gender discrimination and no association was found between stimulation and perceived pain levels.

Conclusions: We discover a role for the human PAG in modulating emotional perception. Our findings may lay the ground for further research investigating the effectiveness of DBS in the treatment of several disorders such as depression, autism and antisocial personality disorder.

Patient Care: These results encourage further investigations of the potential role of PAG deep brain stimulation as a treatment for several mental disorders.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Understand the behavioral task. 2) Understand the significance of used controls. 3) Realize the role of the PAG in modulating emotion perception, the potential uses of DBS in patients with disorders such as autism, traumatic brain injury and antisocial personality disorders.

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