Emotional processing in Huntington´s disease

Patients suffering from Huntington`s disease (HD) have repeatedly demonstrated deficits in recognizing disgust in facial expressions. Findings on the selectivity of patients` disgust impairment are however inconsistent and might be influenced by different moderating variables such as symptom severity, emotion traits and gender. Furthermore, it is unclear whether the disgust recognition dysfunction is associated with atrophy in specific brain regions (e.g. striatum, insula). As of yet, it is striking to note that there have been no investigations on whether or not the disgust decoding deficit in HD is paralleled by impairment in visually induced disgust experience. This aspect is the primary research question of the planned study with test-retest-design. Sixty HD gene carriers (20 individuals without clinical symptoms, 20 with mild symptoms, and 20 with moderate clinical symptoms), and 60 healthy controls; matched for age, gender and socioeconomic status will participate in the study. The subjects will view 24 emotion-relevant scenes for the induction of happiness, fear, disgust, and affectively neutral states. Additionally, subjects will be presented with 42 pictures depicting emotional facial expressions (happy, fearful, sad, angry, disgusted, surprised, neutral). The subjects will rate the intensity of the scene-induced emotions as well as the intensity of the emotions expressed by the depicted persons. A questionnaire set will be used for examining emotion traits (trait disgust, disgust sensitivity, trait anxiety, anxiety sensitivity, aggression, depression, extraversion). Neurological and cognitive tests will also be performed within the context of the study (Unified Huntington Disease Rating Scale, apraxia tests of Goldenberg and de Renzi, Rey Complex Figure Memory Test, Trail Making Test, California Verbal Learning Test, Stroop Colour and Word Test). Morphometric brain data of the insula, striatum, amygdala, orbitofrontal cortex will be obtained. Temporal stability of the findings will be examined by means of a retest with the same design after one year. A second retest with a patient sub-sample will be conducted after two years. We predict that patients with HD will show impairments in disgust recognition and experience relative to healthy controls. With increasing symptom severity the disgust processing dysfunctions are expected increase as well.

Huntington`s disease (HD) is an autosomal dominant, neurodegenerative disorder caused by an abnormal expansion of the tri-nucleotide repeat cytosine-adenine-guanine (CAG) on chromosome 4. CAG expansion beyond 35 repeats is associated with the expression of HD. Cerebral degeneration starts within the basal ganglia, resulting in increasing deterioration of motor function, in psychiatric disturbance and cognitive impairment. One particular deficit relates to the recognition of affective facial expressions. Previous studies found a selective or a disproportionately severe disgust recognition deficit of symptomatic HD patients and pre-symptomatic carriers of the Huntingtin-gene. Objectives of this study were to determine if impairment in disgust recognition is disproportionately more pronounced than for other basic emotions, and if this deficit extends to disgust experience. We investigated emotion recognition and emotion experience in pre-clinic gene-carriers and symptomatic HD patients compared to mentally healthy controls, who were matched for sex, age and education. Symptomatic patients were retested after one year. The participants were asked to judge the intensity of affective facial expressions depicting six basic emotions (anger, disgust, fear, sadness, happiness, surprise), and a neutral affective state. Furthermore, participants were asked to report the intensity of emotional experiences elicited by affective scenes (disgust, fear, and happiness), and for an affectively neutral state. Choices were graded (1 `very little` to 9 `very intense`) over the six basic emotions. Additionally, measures of habitual emotional reactivity and patients` symptom severity were obtained. Furthermore, symptomatic patients and matched controls underwent a structural magnet resonance imaging (MRI) on a 3T scanner to examine associations between emotion recognition ability and grey matter volume loss. The analysis of the recognition task revealed lower intensity ratings of target emotions for angry, disgusted, sad and surprised faces in symptomatic HD patients compared to controls, which might point to a quantitative recognition deficit in HD patients. Moreover, patients and controls misclassified fear with surprise, but only patients misclassified disgust with anger. Thus, disgust was the only emotion with a quantitative (reduced intensity) as well as a qualitative (misclassification as anger) recognition deficit in HD patients. But we found no rating differences relative to controls concerning reported experience of affective scenes or habitual emotional reactivity. Neutral faces and scenes were estimated by patients as happier than by controls suggesting an estimation bias to positive valence for ambiguous visual stimuli. Furthermore, associations between patients` functioning in everyday life and emotion recognition deficits displayed the importance of a sound emotion processing for life quality. Pre-symptomatic gene-carriers showed intact quantitative emotion recognition but more misclassifications than controls concerning anger and disgust as well as an estimation bias to positive valence. This indicates that uncertainty of emotion classification may appear earlier during development of the disease than changes in intensity judgment of affective facial expressions. Our findings also reveal that in the course of one year emotion recognition ability of HD patients does not worsen indicating a slow progress of this deficit. MRI data revealed an extended reduction of patients` grey matter compared to controls. Recognition deficits of disgust, sadness and surprise correlated with grey matter loss of brain regions which were affected in HD patients. Moreover, deficits of daily life functionality were associated to grey matter loss in the affected regions. Relations between our rating data and MRI findings indicate involvement of emotion-specific brain regions as well as brain areas which are concerned to of the working memory.