Brain, Do You Have a Heart? Inside the Science of Love & Brain Health

“Not so fast,” says Paris Brain Institute neuroscientist Nicolas Renier, whose research explores the intimate dialogue between neuronal and vascular systems, opening new windows into how our bodies function.

The neuroscientist focuses on signals coming from the body, such as those carried by the blood, which can influence the organization of the brain, social behaviors, and cerebral functions. Thanks to ultra-high-resolution three-dimensional imaging of the brain’s microscopic architecture, Nicolas Renier can now take a dual perspective on the brain that is essential to understanding it: one at very large scale, and the other at microscopic scale.

“You have to be able to wander through a large organ and see the interactions between its components at a very fine scale,” explains the researcher.

There are 600 kilometers of blood vessels in our brain.
Nicolas Renier, PhD, Paris Brain Institute

This dual view allows scientists today to study both the neuronal systems of the heart and the vascular systems of the brain: two partners engaged in the same continuous dance. A biological and emotional resonance for an invisible choreography between brain and heart, united

Does the heart have a brain?
The heart has several brains. It has a muscular brain, which allows it to contract throughout an entire lifetime. But it also has a communicative brain, which allows it to interface with the main brain.

And does the brain have a heart?
The brain beats to the rhythm of our breathing, our live, our heart. It vibrates; it oscillates. Yes: the brain, too, has a heart.

With a cerebral vascular system?
A very dense network of 600 kilometers of blood vessels.

That’s equivalent to the distance between Dallas, Texas, and New Orleans, Louisiana!
Our technologies now allow us to map this network in its entirety in order to study each of its individual components with great precision, something that was not possible until recently.

What discoveries have emerged from this ability to map the brain?
We have shown that the cerebral vascular system can reorganize dynamically, even outside pathological situations.
For example, we observed a link between the organization of micro-vessels around neurons and the brain’s ability to integrate hormonal signals during gestation, which give rise to maternal behaviors.
Previously, such reorganizations were thought to occur only during neurodegenerative diseases or strokes. Today we know they can also be natural and functional.

Does this change our understanding of neurodegenerative diseases?
With neurodegenerative diseases like Alzheimer’s, the vascular system influences how the disease evolves. But we don’t yet know whether it merely reacts at late stages, when everything is already going very badly, or whether it is one of the pioneering factors of the disease.
We have shown that the vascular system reacts very quickly to changes in neuronal physiology. This allows us to position it as a likely early driver in the evolution of neurodegenerative diseases, rather than a late reactive element.

How are the vascular systems of the brain and heart connected?
There are two simultaneous links between the heart and the brain: an electrical link through the nerves, and a fluid and mechanical link through blood circulation.
The heart perfuses the brain’s 600 kilometers of blood vessels, exposing it to circulating components from the body and thus delivering information from the organs.

We have a few thousands neurones located just on top of the heart in ganglia.
Nicolas Renier, PhD, Paris Brain Institute

How does this message travel to the brain?
By passing through neurons associated with the heart, which are now the focus of extensive research. These neurons are located right next to the heart (not inside it, but resting on it, in ganglia). They are highly sensitive to cardiac function.

So, we have neurons that, instead of being in the brain, sit next to the heart?
Yes. These neurons were somewhat forgotten. But researchers have realized that they serve far more important functions than previously thought. While the brain controls the frequency and strength of heartbeats, the state of the heart can influence cerebral functions such as depression or anxiety.
It’s as if the heart sends signals to the brain, through these peripheral neurons, capable of affecting our daily lives and our emotional state.

Are we talking about a large number of neurons?
A few thousand.

Are these neurons sent from the brain?
No. They do not originate in the brain but from the development of the spinal column.

The brain has mirror neurons that allow us to synchronize with the person in front of us. 
Nicolas Renier, PhD, Paris Brain Institute

How do the neurons of the brain and those of the heart communicate, especially when we are in love?
Everything begins in the brain, because that’s where what happens in the outside world is reflected. The heart itself sees nothing.
When we see someone we are in love with, the first communication is an acceleration of the heart rate. Then comes sensory feedback from the heart, which informs the brain about the body’s general state of health and can influence the decision to engage in a social interaction.

What does that look like exactly?
The brain gives the initial impulse, but if we are tired or sick, the feeling can be dampened by the body telling us that we are not ready.
The heart shares this kind of information with the brain. By pumping blood, the heart gathers information from all the other organs. It then transmits a general health report to the brain via the neurons located beside the heart. The brain then evaluates the body’s ability to face challenges.

Can this health report eventually trigger a serious illness such as Alzheimer’s or dementia?
Cardiac health can directly influence cognitive health. Beyond the amount of blood sent to the brain, the heart can signal a state of distress to the brain that alone may lead to cerebral pathologies.

Is this automatic? Is there a delay between the cardiac signal and the onset of a cerebral problem?
Yes, and this delay went unnoticed for a long time. Until now, we thought of the heart as acting on the brain in a very direct and rapid way.

Do sadness and grief affect brain health?
We can assume that it is better to live without them, especially to maintain healthy brain activity. It has been suggested that prolonged depressive states lead to degeneration.

Do we know why, when a couple breaks up, people struggle to accept the situation and physically experience their suffering? Is it purely psychological?
It is not purely psychological. There is a direct link between how the heart functions and the brain’s emotional state.
There is both descending neural control and neuro-hormonal control. This means that the brain can send signals that release hormones into circulation, which in turn influence our stress levels.

What kinds of signals?
There are two types. The first are survival signals. They allow the brain to trigger adrenaline secretion and react immediately.
But these are not necessarily the signals that matter during a breakup, which induces a long-term state.
In that case, the brain tries to increase resilience. This signal can, for example, drive the secretion of corticosteroids, which affect how our organs and heart function over time.

So, it is inversely good for your health to tell the people you love, “I love you”?
It is obviously very good for mental health.
The brain has mirror neurons that allow us to synchronize with the person in front of us. 
If we feel love and express it, the same neurons show mirror activity in the other person’s brain.