Know thyself: Exploring interoceptive sensitivity in Parkinson's disease

BACKGROUND: Although Parkinson's disease (PD) is defined by its motor symptoms, it is now well recognised that cognitive, affective and emotion domains are also impaired. The pathophysiology of these disabling non-motor symptoms (NMS) remains unclear; recently the involvement of limbic areas, including the insula, in the neurodegenerative process has been suggested to have a key role. These areas, and the insula in particular, are also been suggested as key regions for interoception; interoceptive sensitivity (IS) is a measure of the accuracy of perception of sensations from inside the body related to the function of internal organs. OBJECTIVES: To evaluate IS in PD patients by means of a well-established task: the heartbeat perception task. Moreover, we evaluated possible correlations between IS and psychological, affective and disease-related characteristics as well as fatigue perception in PD patients. METHODS: Twenty PD patients and 20 healthy subjects (HS) were included and underwent the heartbeat perception task. An extensive evaluation of motor, non-motor, affective and emotion domains was carried out. RESULTS: PD patients showed lower IS than HS (0.58±0.2 vs 0.72±0.1; p=0.04). PD reported higher scores in scales assessing depression (Hamilton depression scale: 8.7±5.8 vs 6.2±7.5; p=0.04); anhedonia (Snaith-Hamilton Pleasure Scale: 26.8±9.7 vs 15.4±2.9; p=<0.001) and apathy (Apathy Evaluation Scale: 35.8±8.6 vs 27.8±6.8; p=0.008). No significant correlations were detected between IS and motor, non-motor, affective and emotion symptoms. CONCLUSIONS: PD patients have reduced interoceptive sensitivity. Future studies are encouraged to evaluate the importance of interoception in understanding the pathophysiology of affective/emotional symptoms in PD.