Two experiments conducted in Italy demonstrated that exposing participants to falsely accelerated cardiac feedback prior to administering electric shocks caused them to perceive the shocks as more painful. This artificial feedback also triggered an enhanced physiological response in anticipation of the shock, resulting in a slower heartbeat in participants. The study was published in Neuroscience.
Pain is a complex sensory and emotional experience typically associated with tissue damage or a threat of harm to the body. It serves as a crucial protective mechanism, alerting an individual to potential danger and promoting behaviors that help avoid or mitigate harm. The sensation of pain involves a sophisticated interplay of physiological and psychological processes.
These processes involve pain receptors in body tissues that detect harmful stimuli and transmit signals to the brain, but whether a person experiences pain and how intense also depends on what one expects to experience. Because of this, pain can sometimes occur even when no damage to the body has been done.
Scientists propose that our brain acts as a complex prediction device constantly making inferences about what is happening and what is about to happen. Sensations largely depend on these inferences. However, brain’s predictions do not always mirror reality. They are often inaccurate, although the human brain constantly tries to adapt its predictions and make them accurate.
Study author Eleonora Parrotta and her colleagues noted that previous research indicates the human perception of pain might be significantly influenced by bodily sensations (i.e., interoceptive sensations). This led them to hypothesize that manipulating cardiac feedback – information about heart function – could alter pain perception. One method of doing this is through false auditory feedback, such as playing heartbeat sounds that participants mistakenly believe are their own.
In the first experiment, researchers attached electrocardiography electrodes (ECG) to the participants’ skin and provided them with headphones. The ECG equipment recorded the participants’ heart activity, while during one phase of the experiment, heartbeat sounds were played through the headphones. These sounds either matched the participant’s actual heartbeat or were artificially faster or slower.
After some time, participants received a painful electric shock. There were five different levels of electric shock, and participants were asked to rate the intensity of each. The experiment had two phases: a no-feedback phase, where no cardiac feedback sounds were played, and a feedback phase when they were. The no-feedback phase consisted of 10 trials, and the feedback phase had 18. Post-experiment, participants completed the Body Perception Questionnaire to assess bodily awareness and reactivity.
In the second experiment, the researchers investigated whether sounds clearly external to the body, such as non-organic sounds, would have similar effects to heartbeat sounds. The experiment mirrored the first, but instead of heartbeats, participants listened to percussive sounds created by knocking wood together during the feedback phase. These percussive sounds varied in speed, similar to the heartbeat manipulations.
The results of the first experiment indicated that participants found electric shocks more painful when exposed to faster cardiac feedback (heartbeat sounds) compared to slower feedback or feedback matching their real heartbeat rate. They also rated the pain as more unpleasant in the faster feedback condition. Notably, their actual heart rate decreased when listening to the faster cardiac feedback, an effect not observed with the other feedback types.
In the second experiment, participants again rated the pain from electric shocks as more intense when they were listening to faster paced sounds (faster clapping of the two woods), but the effect was smaller in magnitude. Pain unpleasantness and real heartrate were unaffected by these sounds – they were the same for all three paces.
“These findings show for the first time that cardiac feedback manipulation can be conceptualized in terms of an interoceptive inference that modulates both our perception and the physiological state of the body, thereby actively generating the interoceptive and autonomic consequences that have been predicted,” the study authors concluded.
The study sheds light on the psychological mechanisms of pain perception. However, it also has limitations that need to be taken into account. Notably, the study samples were small and consisted almost exclusively of young people. Studies on larger samples and participants of different age might not yield equal results.
The paper, “Exposure to false cardiac feedback alters pain perception and anticipatory cardiac frequency”, was authored by Eleonora Parrotta, Patric Bach, Giovanni Pezzulo, Mauro Gianni Perrucci, Marcello Costantini, Francesca Ferri.
