Distinctive body perception mechanisms in high versus low symptom reporters: a neurophysiological model for medically-unexplained symptoms

OBJECTIVE: The neurophysiological processes involved in the generation of medicallyunexplained
symptoms (MUS) remain unclear. This study tested three assumptions of the
perception-filter model contributing to MUS: (I.) increased bodily signal strength (II.) decreased
filter function, (III.) increased perception.
METHODS: In this cross-sectional, observational study, trait MUS was assessed by a webbased
survey (N=486). The upper and lower decile were identified as extreme groups of high
(HSR; n=29; 26 women; Mage=26.0 years) and low symptom reporters (LSR; n=29; 21 women;
Mage=28.4 years). Mean heart rate (HR) and heart rate variability (HRV), and cortisol awakening
response (CAR) were assessed as indicators of bodily signal strength (I.). Heartbeat-evoked
potentials (HEPs) were assessed during rest and a heartbeat perception task. HEPs reflect
attentional resources allocated towards heartbeats and served as index of filter function (II.).
Interoceptive accuracy (IAc) in heartbeat perception was assessed as an indicator of perception
(III.).
RESULTS: HSR showed higher HR and lower HRV (RMSSD) than LSR (I.), but no
differences in CAR. HSR exhibited a stronger increase of HEPs when attention was focused on
heartbeats than LSR (II.); there were no group differences in IAc (III.).
CONCLUSIONS: The perception-filter model was partially confirmed in that HSR showed
altered bodily signals suggesting higher sympathetic activity (I.); higher HEP increases indicated
increased filter function for bodily signals (II.). As more attentional resources are mobilized to
process heartbeats, but perception accuracy remains unchanged (III.), this overflow could be
responsible for detecting minor bodily changes associated with MUS.