Emotional stimuli and motor conversion disorder

Abstract

Conversion disorder is characterized by neurological signs and symptoms related to an underlying psychological issue. Amygdala activity to affective stimuli is well characterized in healthy volunteers with greater amygdala activity to both negative and positive stimuli relative to neutral stimuli, and greater activity to negative relative to positive stimuli. We investigated the relationship between conversion disorder and affect by assessing amygdala activity to affective stimuli. We conducted a functional magnetic resonance imaging study using a block design incidental affective task with fearful, happy and neutral face stimuli and compared valence contrasts between 16 patients with conversion disorder and 16 age- and gender-matched healthy volunteers. The patients with conversion disorder had positive movements such as tremor, dystonia or gait abnormalities. We also assessed functional connectivity between the amygdala and regions associated with motor preparation. A group by affect valence interaction was observed. Post hoc analyses revealed that whereas healthy volunteers had greater right amygdala activity to fearful versus neutral compared with happy versus neutral as expected, there were no valence differences in patients with conversion disorder. There were no group differences observed. The time course analysis also revealed greater right amygdala activity in patients with conversion disorder for happy stimuli (t = 2.96, P = 0.006) (with a trend for fearful stimuli, t = 1.81, P = 0.08) compared with healthy volunteers, with a pattern suggestive of impaired amygdala habituation even when controlling for depressive and anxiety symptoms. Using psychophysiological interaction analysis, patients with conversion disorder had greater functional connectivity between the right amygdala and the right supplementary motor area during both fearful versus neutral, and happy versus neutral 'stimuli' compared with healthy volunteers. These results were confirmed with Granger Causality Modelling analysis indicating a directional influence from the right amygdala to the right supplementary motor area to happy stimuli (P < 0.05) with a similar trend observed to fearful stimuli (P = 0.07). Our data provide a potential neural mechanism that may explain why psychological or physiological stressors can trigger or exacerbate conversion disorder symptoms in some patients. Greater functional connectivity of limbic regions influencing motor preparatory regions during states of arousal may underlie the pathophysiology of motor conversion symptoms.

Figure 1

Amygdala activity to emotional stimuli in conversion disorder (CD). (A) Patients with motor conversion disorder (CD) were compared with healthy volunteers (HV) using an incidental affective task with a mixed measures ANOVA with patient Group as a between-subjects factor and Valence as a within-subjects factor. The glass brain, statistical parametric map image and contrast estimates show the significant patient Group by Valence interaction of fearful versus rest (F–R) and happy versus rest (H–R) contrasts between patients with conversion disorder and healthy volunteers localized to the right amygdala (mixed measures ANOVA) (right amygdala local peak Montreal Neurological Institute coordinates x, y, z = 24, −4, −24 mm, Z = 3.83, P < 0.001 uncorrected, P < 0.05 region of interest corrected). The glass brain is shown at P < 0.001 uncorrected cluster threshold >4. The statistical parametric map image is shown at P < 0.005 uncorrected cluster threshold > 4. (B) Right amygdala time course activity. The area under the curve for the right amygdala time course (Finite Impulse Response function time-locked to block onset) was compared between patients with conversion disorder and healthy volunteers for the fearful (top; t = 1.81, P = 0.08) and happy (bottom; t = 2.96, P = 0.006) conditions. Error bars represent standard deviation.

Figure 2

Depression scores and functional connectivity. (A) The statistical parametric map image shows the regression analysis of the Beck Depression Inventory (BDI) scores and the happy versus rest (H–R) contrast of the left amygdala in patients with motor conversion disorder (CD). The scatter plot show the regression analyses of the depression scores and the % BOLD signal change of the left amygdala in patients with motor conversion disorder during fearful versus rest (F–R) (solid line: R² = 0.31, P < 0.001) and happy versus rest (dashed line: R² = 0.66, P < 0.001). The statistical parametric map image is shown at P < 0.005 uncorrected cluster threshold >4. (B) The glass image, scanning probe microscopy image and plot show the significant Group effect of the functional connectivity map of the right amygdala (seed voxel not shown) [mixed measures ANOVA with within-subjects Valence factor (F–N and H–N) and between-subjects Group (motor conversion disorder and healthy volunteers) of the psychophysiological interaction analysis]. The glass image is shown at P < 0.001 uncorrected cluster threshold >4. The statistical parametric map image is shown at P < 0.005 uncorrected cluster threshold > 4. Error bars are in standard deviation. VCA = vertical anterior commisure line.