An Investigation of Emotion Processing Impairments in Huntington’s Disease

2017-03-16T01:37:50Z (GMT) by Catarina Ciala Kordsachia
Huntington's disease (HD) is a neurodegenerative disorder associated with altered processing of emotional stimuli. Altered emotion processing in HD includes a well-established deficit in the ability to recognize emotions from facial expressions. Subjective experience of emotion is also altered, although previous studies have indicated both diminished and exaggerated subjective experiences. The overarching purpose of this thesis was to improve current knowledge on the processing of emotional stimuli in HD, by answering three research questions, which are addressed in three papers. For the thesis, data were collected from 25 participants with the gene-expansion for HD (late pre-manifest and early diagnosed) and 25 HD gene-negative healthy control participants.
   
   The first paper addressed the question of whether individuals with HD, compared to controls, show altered facial muscle responses to emotionally-evocative scenes and emotionally-expressive faces. Using electromyography (EMG) to examine facial muscles activity, we found that HD participants displayed lower activation of the levator labii muscle when viewing disgusting scenes than control participants, providing evidence for reduced disgust experience in HD. HD participants also displayed lower EMG responses of the zygomaticus major and orbicularis oculi muscles in reaction to happy faces and of the frontalis muscle in reaction to fearful faces. The finding of diminished responsivity to disgust is relevant to current controversies regarding whether disgust processing is affected in HD, and the reduced responsivity to happy stimuli may have implications for social functioning in HD.
   
   The second paper addressed the question of whether individuals with HD visually scan emotionally-evocative natural scenes differently than healthy controls. We found that HD participants fixated for a smaller portion of picture viewing time, and that their scan paths were longer than those of controls. These findings suggest an enhanced, but unfocussed search for information in HD. This search for information may constitute a strategy used by HD participants to compensate for difficulties in evaluating the stimuli, perhaps due to difficulties with self-reflection.
   
   The third paper addressed the question of whether individuals with HD display reduced visual scanning of the emotionally most informative features of human faces than healthy controls. We found that, relative to the scanning of the whole pictures, the HD participants made a lower number of fixations on the eye and nose/mouth regions and spent less time looking at these regions. Further, visual scanning of the eye region was associated with emotion recognition performance in the HD group, raising the possibility that scanning of the eyes is insufficient for accurate emotion recognition in HD. Alternatively, people with HD may show reduced scanning of the eyes because they are less emotionally engaged with other people, in line with the significance of eye-contact in social interactions.
   
   Taken together, findings from this research project yielded several new insights into how individuals with HD process emotion-related visual stimuli differently than healthy control participants. Some of the effects observed in HD may be related to similar underlying processes, but overall the findings suggest that alterations in emotion processing in HD are nuanced and complex.