Startle reflex hyporeactivity in Parkinson's disease: An emotion-specific or arousal-modulated deficit?

Abstract

We previously reported that patients with Parkinson's disease (PD) demonstrate reduced psychophysiologic reactivity to unpleasant pictures as indexed by diminished startle eyeblink magnitude (Bowers et al., 2006). In the present study, we tested the hypothesis that this hyporeactivity was primarily driven by diminished reactivity to fear-eliciting stimuli as opposed to other types of aversive pictures. This hypothesis was based on previous evidence suggesting amygdalar abnormalities in PD patients coupled with the known role of the amygdala in fear processing. To test this hypothesis, 24 patients with Parkinson's disease and 24 controls viewed standardized sets of emotional pictures that depicted fear, disgust (mutilations, contaminations), pleasant, and neutral contents. Startle eyeblinks were elicited while subjects viewed these emotional pictures. Results did not support the hypothesis of a specific deficit to fear pictures. Instead, the PD patients had reduced reactivity to mutilation pictures relative to other types of negative pictures in the context of normal subjective ratings. Further analyses revealed that controls displayed a pattern of increased startle eyeblink magnitude for "high arousal" versus "low arousal" negative pictures, regardless of picture category, whereas startle eyeblink magnitude in the PD group did not vary by arousal level. These results suggest that previous findings of decreased aversion-modulated startle is driven by reduced reactivity to highly arousing negative stimuli rather than to a specific category (i.e., fear or disgust) of emotion stimuli.

Subthalamic nucleus stimulation affects incentive salience attribution in Parkinson's disease

“…Nevertheless, other imaging and neurophysiological studies indicated the existence of a common subcortical network involved in the incentive salience attribution processing 29,37 and suggested the influence of arousal level on affective and motivational physiological responses. 38,39 In the present study the pictures of victims were stronger stimuli than pictures from the other content categories according to the valence and arousal ratings in all groups and conditions and may represent the most salient pictures that signal threat to one's own bodily integrity. This is in line with the finding that the mesolimbic dopamine system responds to both rewarding and aversive stimuli that are of high intensity.…”

Apathy and Emotional Blunting in Parkinson’s Disease

“…In spite of these limitations, this study is unique due its examination of different apathy dimensions in a PD participant group without dementia. In the future, it will be of interest to use objective measures, such as the startle reflex, to assess apathy dimensions, in order to further elucidate underlying pathophysiology and clinical associations [30].…”

EEG Correlates of Emotional Experience in Huntington’s Disease

“…Affective stimuli may therefore elicit not only attention and perceptual processes but also motor effects [16], which functions may be compromised in basal ganglia disorders [17]. This hypothesis is also supported by Functional Magnetic Resonance (FMRI) findings in regard to the activation of caudate under negative pictures, as a key element in social withdrawal [18,19]. Event related potentials may be an easy and cheap method to explore cognitive deficit in the course of HD [20], and additional information may come from EEG activity related to affective stimuli processing.…”