Background Interoception describes the predictive representation and control of the internal physiological state of the body. Disturbances in interoception have been demonstrated in people with functional seizures. Little is known about interoception in epilepsy.

Aim To compare dimensions of interoception across three groups - people with functional non-epileptic seizures (FS), people with epileptic seizures (ES) and healthy controls (HC). We hypothesised that people with ES would display deficits in interoception compared to HC, given the neuroanatomical correlates of interoception are frequently implicated in epilepsy.

Methods We included 37 participants with FS, 48 with ES and 34 HC. All participants completed measures of (1) interoceptive accuracy (IA) – objective performance on a heartbeat tracking task (HTT) and heartbeat discrimination task (HDT); (2) trait interoceptive sensibility – subjective sensitivity to internal sensations (measured using the Porges Body Perception Questionnaire) and (3) state interoceptive sensibility – subjective trial-by-trial measures of confidence in heartbeat detection. These were used to calculate interoceptive awareness (metacognitive measure). All completed self-report ratings of dissociation (MDI, SDQ), depression (BDI), and anxiety (BAI).

Results Across the groups, there was a statistically significant difference in IA measured through the HTT (χ² (2)=12.474, p=0.002) with the highest mean score demonstrated in HC (&xbar;=76.76), followed by ES (&xbar;=54.29) and then FS groups (&xbar;=50.14). Pairwise comparisons revealed significant differences in IA when comparing HC to both ES (p=0.010) and FS (p=0.003), but not between ES and FS groups (p=0.582). Interoceptive sensibility also differed significantly between groups (F (2, 116)=11.769, p<0.001) and was highest in FS, followed by ES, then HC but did not differ between ES and FS groups (p=0.969). Significant differences in HDT awareness were found between groups (F=5.182, p=0.007). Pairwise comparisons revealed significant differences between ES and FS (p=0.005). Mean HDT awareness for FS (&xbar;=0.495) was lower than for ES (&xbar;=0.598) and HC (&xbar;=0.548). People with FS displayed the highest levels of dissociation, depression, and anxiety with dissociation and depression scores being significantly higher than those with ES (p<0.001 and p=0.030 respectively).

Conclusions Both ES and FS groups demonstrated deficits in interoception (reduced IA and increased interoceptive sensibility) compared to HC. Interoceptive awareness on the HDT significantly differed between ES and FS groups. Whilst interoceptive deficits in people with ES could be related to the effects of epilepsy on interoceptive networks, interoceptive awareness in ES appears to be higher compared to those with FS. The role of interoception merits further study in these patient populations.