A transcranial magnetic stimulation protocol of the inferior frontal gyrus to manipulate activity in the interoceptive brain network: a pilot study on heartbeat-evoked potentials

Interoception, the processing and perception of internal
bodily signals, plays an important role in symptom perception.
As interoception is mediated by the interoceptive
brain network (IBN), whereas dysfunctions in the IBN
may contribute to symptom generation, a manipulation
of activity in the IBN by transcranial magnetic stimulation
(TMS) could be a promising approach to normalize potential
dysfunctions. Using a network stimulation approach
targeting the inferior frontal gyrus (IFG), four participants
underwent a TMS protocol to enhance (intermittent theta
burst stimulation/iTBS), or to inhibit (continuous/cTBS)
IBN activity or a neutral condition (intermediate/imTBS).
Heartbeat-evoked
potentials (HEPs) from 455-595ms
after
the cardiac R-wave
in a 3x3 cluster around electrode C2,
assessed during a heartbeat counting task, served as indicator
of IBN activity. HEPs were recorded before and directly
after TMS sessions. Average HEP amplitudes descriptively
increased after the inhibition (cTBS: +42%; pre: .23; post:
.33 μV) and the neutral (imTBS: +102%; pre: .41; post: -.
57
μV) protocol, but decreased after undergoing the enhancement
(iTBS: -60
%; pre: .65; post: .26 μV) protocol. However,
none of these differences were significant due to the small sample size. Future studies in larger samples sizes have to
validate the current findings that iTBS may enhance IBN
activity, whereas cTBS has no effect as compared to a neutral
condition. In case this validation is successful, the current
TMS protocol may be a future approach to normalize
IBN activity in somatic symptom disorders.