How The Brain Senses Signals From the Body

Week 2 of the Withdrawal Symptoms series

How the brain detects physiologic signals from internal organs through neural pathways involved in interoception.

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Recognizing the Experience

Many withdrawal symptoms involve sensations that appear to arise directly from the body. People may notice their heartbeat more strongly, become aware of changes in breathing, or feel internal sensations such as pressure, vibration, or tingling. Some individuals also notice changes in balance, digestion, or temperature regulation.

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

In the previous article, we examined how changes in inhibitory stability can increase physiologic signaling across body systems. 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 external environment but also from within the body.

Signals from the heart, lungs, blood vessels, gastrointestinal system, and muscles travel through specialized sensory pathways to the brain. These signals provide continuous information about physiologic conditions such as cardiovascular activity, breathing patterns, and internal organ function.¹

The brain uses this information to coordinate physiologic regulation and maintain internal stability.

This process of sensing internal body signals is known as interoception.

Pathways Carrying Signals to the Brain

Signals from the body reach the brain through two primary sensory pathways.

One pathway involves the vagus nerve, which carries information from organs such as the heart, lungs, and digestive system.²

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

These signals are first processed in brainstem integration centers, including the nucleus of the solitary tract and the parabrachial nucleus.³

From these brainstem centers, signals are relayed through thalamic pathways to cortical regions involved in monitoring the body’s internal state.

Brain Regions That Monitor the Body

After passing through brainstem centers and thalamic relay, physiologic signals are transmitted to cortical regions that monitor the body’s internal state.

Two regions are particularly important:

The insula integrates signals from multiple organ systems and represents the body’s physiologic condition.⁴

The anterior cingulate cortex participates in coordinating responses to changes in internal signals.⁵

These regions contribute to the brain’s ongoing monitoring of the body rather than determining interpretation of signals.

Interoception and Symptom Awareness

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

However, when activity within body systems increases, the signals generated by those systems may become stronger.

During benzodiazepine withdrawal, changes in inhibitory stability can increase activity across multiple physiologic systems. This can increase the volume of signals traveling to the brain.

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

For example:

• cardiovascular signals may be experienced as palpitations

• respiratory signals may be experienced as air hunger

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

These sensations reflect detection of physiologic signals rather than interpretation of their significance.

Diagram

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

Physiologic signals from internal organs travel through vagal and spinal sensory pathways to brainstem integration centers such as the nucleus of the solitary tract and parabrachial nucleus. These signals are relayed through thalamic pathways to cortical regions, including the insula and anterior cingulate cortex, where they are monitored and may enter conscious awareness.

Looking Ahead

Understanding how the brain senses signals from the body raises another important question: where do these signals originate during withdrawal?

In the next article, we will examine how changes in inhibitory stability can activate multiple regulatory systems, generating physiologic signals throughout the body.

Selected Scientific References

1. Khalsa SS, et al. Biol Psychiatry. 2018.

2. Berthoud HR, Neuhuber WL. Auton Neurosci. 2000.

3. Chen WG, et al. Trends Neurosci. 2021.

4. Craig AD. Nat Rev Neurosci. 2002.

5. Critchley HD, Harrison NA. Neuron. 2013.