Literally "knowing by heart": Signals from heart to brain prompt feelings of familiarity

The idea that the body affects the mind is not new. The eminent American psychologist William James famously proposed that it is actually the physical sensation of fear that causes us to feel afraid. In more recent years, researchers have extended this principle, exploring the possibility that physical sensations play an important role in moral decisions and other processes usually seen as more purely cognitive or cerebral, such as memory.

It's already known that physical markers of arousal such as dilated pupils correlate with feelings of familiarity, but this could be because of the mental effort of remembering, rather than because physical arousal triggers the feeling of familiarity. Now a pioneering study in Journal of Experimental Psychology: General gets around this problem by testing people's memory for faces presented at specific phases of the heart beat. The results provide compelling evidence that our feelings and judgments about familiarity are influenced by signals arising from the heart.

Chris Fiacconi at Western University and his colleagues began by asking 37 undergrads to look at 68 fearful faces, presented for 1.5 seconds each. Next, the participants looked at 136 more faces – half had appeared previously and half were new – and their task was to say whether they had seem them before. Crucially, the participants were wired up to an heart monitor and during the memory test some of the faces were presented at the precise moment that the heart had just pumped a burst of blood into the arteries – the so-called systole phase – while the other faces were presented while the heart was relaxing, known as the diastole phase.

This is important because the systole phase increases blood pressure, which is detected by baroreceptors in the heart's arteries, and in turn the baroreceptors signal this change in pressure to various regions in the brain, including the brain stem but also higher brain areas involved in cognition. The amazing revelation from this first study was that participants were significantly more likely to say that a face was familiar if it was presented during the systole phase. This was true for faces that were old and also for those that were actually new. A follow-up study using neutral faces made the same findings.

A final study made things a little more elaborate. During the memory test for the faces, whenever participants thought they'd seen a face before, they were asked to clarify whether they actually recollected seeing it, or if it just felt familiar but they did not actually remember seeing it. Intriguingly, presenting a face during the heart's systole phase increased participants' tendency to report a sense of familiarity, but did not affect their claims to actually recollect having seen it.

These are dramatic results because they suggest that when making memory judgments, we don't necessarily rely only on our actual memory traces in the brain, but that we also interpret our physiological sensations. By presenting faces at a specific moment in the heart beat cycle, the current research effectively hacks into this system to trick participants into thinking they've seen new faces before. As the researchers state – in such cases "participants may interpret the transient increase in arousal that results from baroreceptor mediated feedback as owing to the familiarity of the stimulus probe."

Where next for this line of research? Fiacconi and his colleagues said that an important future goal is "to determine whether other epistemic feelings, such as feelings of knowing, tip-of-the-tongue-states, and deja-vu experiences are also shaped by this type of visceral feedback."

Further reading

Fiacconi, C., Peter, E., Owais, S., & Köhler, S. (2016). Knowing by heart: Visceral feedback shapes recognition memory judgments. Journal of Experimental Psychology: General, 145 (5), 559-572 DOI: 10.1037/xge0000164