For thousands of years, people have spoken as though the heart knows things. We describe courage as heartfelt. We suffer heartbreak. We follow our hearts. Fear makes the heart race, while relief seems to soften it.
Science has often treated this as metaphor. The brain thinks and feels; the heart is a pump responding to instructions. But the body is more interesting than that.
The heart contains its own network of neurons, known as the intrinsic cardiac nervous system. It is sometimes called the heart’s “little brain”, although we should be careful with the phrase. The heart does not think, remember or make decisions in the way the brain does. What it does have is a local nervous system capable of helping regulate its own activity.
Scientists have known about this network for some time. The important new finding is that it may be much more organised and specialised than previously understood. A recent study in Cell identified two genetically distinct groups of neurons inside the heart. Rather than all performing the same general task, the two groups appeared to have different jobs [1].
One group, identified by a gene called Npy, helped control normal heart rate. When these neurons were disrupted, cardiac function deteriorated dramatically. The second group, marked by Ddah1, seemed less important under ordinary conditions. But during severe stress, its role became clear. Without these neurons functioning normally, the heart became more vulnerable to dangerous electrical instability [1].
In simple terms, some neurons appeared to help the heart manage everyday life, while others helped it remain stable when the system was under pressure. The research is still at an early stage, and more work is needed before we know exactly how these mechanisms apply across human health and disease. But it changes the way we should think about communication between brain and body.
The brain does not control the organs like a puppeteer pulling strings. The relationship is more like a conversation. The brain sends signals to the heart, lungs, gut and other organs. But those organs also contain local nervous systems that process information, regulate activity and send signals back. Recent research suggests that organs even help shape the specialised nerve networks that develop within them [2].
This may help explain something humans have understood intuitively for a very long time: emotions are not experienced only in the head. Anxiety can feel like a pounding heart, tight chest, altered breathing and unsettled stomach. Fear changes blood pressure, muscle tension and attention. Calm is also physical: breathing slows, the heart settles and the body’s threat systems reduce their activity.
These are not imaginary symptoms added to an emotion afterwards. They are part of the emotion itself.
The scientific term for our perception of signals from within the body is interoception. The brain is continuously receiving information about heartbeat, breathing, temperature, hunger, digestion and other internal states. It uses this information to help decide whether we are safe, threatened, tired, excited or unwell. This creates feedback loops.
A stressful thought can accelerate the heart. The brain then detects that faster heartbeat and may interpret it as further evidence that something is wrong. Equally, slowing the breath and reducing physical tension can send information in the opposite direction.
This does not mean we can think our way out of every cardiac problem or breathe away serious illness. Nor does it mean heart disease is simply caused by stress. The biology is considerably more complicated. But it does mean the boundary between “mental” and “physical” health is often artificial.
Stress is not merely an idea. It is a coordinated state involving the brain, heart, breathing, hormones and autonomic nervous system. Relaxation is also not simply a thought. It is a shift across the same connected systems.
Perhaps this is why the language of the heart has survived for so long. People could feel that emotion lived there, even before they understood nerves, genes or electrical rhythms. The heart is not a second brain. But neither is it a passive machine waiting for instructions from the head.
It contains specialised neural machinery of its own, and that machinery may help it respond differently to ordinary life and moments of extreme pressure. The old intuition was not literally correct. But it may have been pointing towards something real: we feel with the whole body.
—Professor David Nutt
References
[1] Xu, Q. J., Applegate, M. C., Hsu, I-U. Y., Kogan, R. P., et al. “The intrinsic cardiac nervous system is essential for cardiac function and survival.” Cell, 2026.
[2] Hsu, I-U. Y., et al. “Organ-derived signals shape the development and identity of organ-intrinsic nervous systems.” Nature, 2026.
[3] Peeples, L. “The heart has a ‘little brain’ — and it protects against stress.” Nature, 22 July 2026.
