[Unboxing Lab] 'The brain moved faster than the tongue'... The hidden culprit behind our 'salt addiction'

[The Financial News] Researchers have discovered that when our body runs low on salt, a special neural circuit in the brain kicks in and directly checks the blood for sodium, regardless of what the tongue tastes. Hormones in the brain act like sensors to finely tune salt intake, and this mechanism is expected to offer a new key to tackling chronic diseases such as hypertension and diabetes.

We often say we are "craving" a certain taste. But there is actually an invisible hand behind the scenes that controls that craving. This study reveals the fundamental reason why we keep reaching for salty foods even when we know they are bad for our health.
What if we could subtly adjust this switch inside the brain? Instead of relying on sheer willpower to resist salty foods, patients suffering from salt addiction could have their brain signals modulated so that they naturally return to a healthier diet. Such a treatment is no longer just a fantasy.

To uncover this secret, Professor Young-Seok Lee of Kookmin University and his team turned to the brains of fruit flies, which are genetically similar to us in many ways. They kept the flies in a completely salt-free environment for 48 hours and then observed what changes occurred in their brains.
They used a technique called calcium imaging, which makes neurons light up when they are active, allowing real-time tracking of brain activity. Under the microscope, the researchers saw a specific circuit in the brains of salt-deprived flies flashing on and off like an emergency light, sending out strong signals.
The intensity of this response was particularly striking. Normally, fruit flies perceive a salt concentration of around 100 mM (millimolar) as too salty and quickly avoid it. But once the brain switch was turned on, the flies actively sought out and enjoyed that same salty taste. Even when faced with a high salt concentration of 300 mM—about the level of seawater—the signaling pathway known as Protein Kinase A (PKA) in the brain was highly active, effectively steering their behavior with the message, "We need this salt right now!"

Recognizing its significance, this study was published in the prestigious international journal Proceedings of the National Academy of Sciences of the United States of America (PNAS). The treasure the team found after opening this box can be summed up in two major points.
The first twist is that the brain directly checks blood salt concentration. We usually assume the brain responds only after the tongue detects something salty. In reality, when there is not enough salt in the blood, the brain declares an emergency even before the mouth has a chance to taste anything.
The second twist is the "perfect teamwork" of hormones. When salt levels drop, a hormone in the brain called leucokinin stimulates cells that secrete Insulin. The Insulin signal then spreads throughout the brain like a messenger, resetting the system so that salty foods, which were previously rejected, now taste delicious. Once enough salt has been consumed, this circuit shuts down almost eerily precisely. Our body is constantly, without a break of even 0.1 seconds, maintaining a delicate golden balance for the sake of our health.
How was today’s unboxing? Behind that casual bite of a salty snack you just grabbed, there is a precision sensor in your brain working fiercely out of sight to keep you alive. We will be back next time with more research that will make you slap your knee in amazement!

monarch@fnnews.com Kim Man-gi Reporter