The perception-filter model: patients with somatoform disorders and major depressive disorder show stronger cardiac signals, but normal filter function and cardiac perception

In the perception-filter
model it is posited that three consecutive
stages contribute to the generation of medically-unexplained
symptoms (MUS): (I.) Stronger afferent
bodily signals, (II.) an impaired filter function to differentiate
relevant from irrelevant signals, and (III.) disturbed
perception of bodily signals, ultimately feeding into MUS.
As these assumptions have not yet been tested in the same
sample, we assessed indicators of stages (I.-III.)
based on
cardiac interoception in patients with somatoform disorders
(SFD), patients with major depressive disorder
(MDD) and healthy control (HC) individuals. Heart rate
(variability; HR/HRV) and blood pressure served as indicators
of bodily signal strength (I.); heartbeat-evoked
potentials (HEPs) assessed during a heartbeat counting
task (HCT) and a distraction task indicated filter system
function (II.); cardiac interoceptive accuracy (IAc) in the
HCT was interpreted as an index of perception of bodily
signals (III.). All indicators were assessed before and after
a socially-evaluated
cold pressor stress task (SECPT; to
manipulate bodily signal strength) and a control intervention.
SFD patients (n=24) showed higher average HR and
diastolic blood pressure, as well as lower HRV than HC
individuals (n=22), but there were no differences in HEPs
or IAc. Neither were there significant differences between
the SFD and the MDD groups (n=24), nor any stress effect
on HEPs or IAc. Our findings suggest that stronger bodily
signals (I.) is the only model assumption that could be
supported for patients with fully-developed
SFD.