Abstract
Objective
While interoceptive abnormality in patients with functional seizure (FS) has been demonstrated using explicit tasks, implicit measurements of interoception such as the effect of interoception on perceptual brain processes, have not been investigated. It has been shown that perception
is
normally modulated by interoceptive signals related to the
different phases (systole v diastole) of the
cardiac cycle (cardiac modulation
effect
). Given our previous findings using explicit measures of interoception, we hypothesized that cardiac modulation would be impaired in FS.
Methods
Thirty-two patients with FS and 30 age/sex matched non-clinical individuals conducted a face intensity judgment task, in which their intensity rating when
fearful
or neu
t
ral faces was presented was compared between systolic and diastolic phases. They also conducted the heartbeat discrimination task as a measure of their capacity to integrate both interoceptive and exteroceptive information.
Results
Patients with FS had impaired cardiac modulation of the perception of neutral faces
(corrected p = 0.044).
Individual differences in the heartbeat discrimination task predicted the degree to which cardiac modulation occurred across the whole group (p = 0.028).
This cardiac modulation effect was significantly associated with seizure severity (p = 0.021).
Regardless of cardiac phase, patients rated fearful facial expressions as less intense compared to control participants (p = 0.006).
Significance
These findings highlight impaired implicit cardiac modulation effects in patients with FS. This reflects interoceptive dysfunction in patients with FS, and an inability of the brain to
integrate interoceptive signaling with perceptual processing. This may have implications for our understanding of the pathophysiology in FS and inform novel diagnostic approaches.
AGO