How The Brain Senses Signals From the Body

Week 2 of the Withdrawal Symptoms series

How the brain detects signals from the body through pathways involved in interoception.

---

Recognizing the Experience

Many withdrawal symptoms involve sensations that seem to come directly from the body.

People may notice their heartbeat more strongly, feel changes in their breathing, or experience sensations such as pressure, vibration, or tingling.

Some people also notice changes in balance, digestion, or body temperature.

These experiences raise an important question: How does the brain detect what is happening in the body?

In the previous article, we explained how changes in inhibitory stability can increase signal activity across the body.

The next step is understanding how those signals travel to the brain.

The Brain Continuously Monitors the Body

The brain processes information not only from the outside world, but also from within the body.

It constantly monitors signals from internal organs and tissues.

Signals from the heart, lungs, blood vessels, digestive system, and muscles travel to the brain through sensory pathways.

These signals provide ongoing information about how the body is functioning, including heart activity, breathing, and organ function.

The brain uses this information to help regulate the body and maintain internal stability.

This process of sensing signals from within the body is called interoception.

During benzodiazepine withdrawal, activity across body systems can increase.

This can lead to a higher volume of signals being sent to the brain.

When these signals become strong or frequent enough, they may begin to enter awareness as noticeable sensations.

Through this process, the brain continuously monitors signals from the body in real time.

Pathways Carrying Signals to the Brain

Signals from the body reach the brain through two main pathways.

One pathway involves the vagus nerve, which carries signals from organs such as the heart, lungs, and digestive system.

Another pathway involves spinal sensory pathways, which carry signals from muscles, joints, and other tissues.

These signals are first processed in the brainstem, in areas such as the nucleus of the solitary tract and the parabrachial nucleus.

From the brainstem, signals are sent through the thalamus to higher brain regions that monitor the body’s internal state.

Together, these pathways form the main routes by which signals travel from the body to the brain.

Brain Regions That Monitor the Body

After passing through the brainstem and thalamus, signals from the body are sent to higher brain regions that monitor the body’s internal state.

Two regions are especially important:

The insula brings together signals from different organ systems and represents the body’s overall condition.⁴

The anterior cingulate cortex helps coordinate the body’s response to these signals.

These regions monitor incoming signals and help determine whether those signals enter awareness.

Interoception and Symptom Awareness

Most signals generated within the body remain outside awareness and are processed automatically by the brain.

However, when activity in body systems increases, the signals from those systems may become stronger or more frequent.

During benzodiazepine withdrawal, inhibitory stability is reduced, which can increase activity across multiple body systems.

This increased activity leads to more signals being sent to the brain.

Interoceptive pathways carry these signals to the brain. When signals become strong or frequent enough, they may begin to enter awareness as noticeable sensations.

For example:

• signals from the heart may be felt as palpitations

• signals from breathing may be felt as air hunger

• sensory signals may be felt as tingling, internal vibration, or dizziness

These sensations reflect the detection of signals from the body, not yet what those signals mean.

Diagram

Figure 2. Simplified body-to-brain interoceptive pathway.

Signals from internal organs travel through the vagus nerve and spinal pathways to the brainstem, including areas such as the nucleus of the solitary tract and the parabrachial nucleus. These signals are then sent through the thalamus to higher brain regions, including the insula and anterior cingulate cortex, where they are monitored and may enter awareness.

Looking Ahead

Understanding how the brain senses signals from the body raises another important question:

Where do these signals come from during withdrawal?

In the next article, we will explain how reduced inhibitory stability during benzodiazepine withdrawal can activate multiple body systems, generating signals throughout the body.

Selected Scientific References

1. Khalsa SS, et al. Interoception and mental health: A roadmap. Biol Psychiatry. 2018;84(3):197–208.

2. Chen WG, et al. The emerging science of interoception: Sensing, integrating, interpreting, and regulating signals within the self. Trends Neurosci. 2021;44(1):3–16.

3. Craig AD. How do you feel? Interoception: The sense of the physiological condition of the body. Nat Rev Neurosci. 2002;3(8):655–666.

4. Critchley HD, Harrison NA. Visceral influences on brain and behavior. Neuron. 2013;77(4):624–638.