A General Anesthetic can work by causing confusion in the brain

How exactly do narcotics erase our perception of the world? A new study focusing on the common surgical drug Propofol suggests that anesthesia doesn’t just «turn off» the brain; it temporarily destabilizes its activity, preventing it from processing information effectively.

This groundbreaking research, which uses advanced mathematical principles, offers a fresh perspective on how we lose consciousness and sensation during medical procedures.

Anesthesia: More Than Just Being «Asleep»

The term «anesthesia» itself comes from the ancient Greek words meaning «without sense.» Medically, it is defined as a chemically induced state encompassing four key components:

1. Paralysis (lack of movement)
2. Analgesia (lack of pain)
3. Amnesia (lack of memory)
4. Unconsciousness

In everyday life, our brain constantly shifts between states like wakefulness and sleep. A key difference between these states lies in how they react to emotional stimuli. For example, a phone notification causes a sharp spike in nerve activity when you are awake. That same sound has virtually no conscious effect when you are asleep—or under anesthesia.

The central question for researchers was: How does the anesthetized brain respond to these stimuli, and why are we not consciously aware of it?

Measuring Consciousness with Dynamical Systems Theory

To answer this, the study used principles from a branch of mathematics called Dynamical Systems Theory to measure the stability of brain activity.

Stability, in this context, is the system’s ability to recover from disturbances and return to its baseline.

• Stable System Example: A pendulum with friction will always return to rest in the same place, no matter how hard you push it.
• Unstable System Example: The weather—a small disturbance (the metaphorical butterfly’s wing flap) can lead to massive, chaotic changes.

Professor Earl Miller, one of the study’s lead authors, emphasized the brain’s need for balance: «The brain has to operate on a knife edge between stability and chaos. It has to be stable enough for its neurons to excite each other, but if it is too excitable, it becomes chaotic.» Measuring stability is a crucial metric for overall brain health.

Propofol Destroys the Excitatory-Inhibitory Balance

In the study, researchers recorded brain activity from two macaques while they were administered Propofol, a powerful injectable anesthetic. As the monkeys drifted deeper into anesthesia, their brain activity became noticeably more erratic and unstable.

This instability is traced back to Propofol’s direct action on brain cells:

• The Awake Brain: Stability relies on a precise balance between excitatory neurons (which increase activity) and inhibitory neurons (which decrease activity).
• The Anesthetized Brain: Propofol works primarily on the inhibitory system, strengthening it and pushing the entire system out of balance.

When researchers played sounds to the anesthetized macaques, they found that the brain’s sensory responses were drastically slower and much longer-lasting. This sensory impact led to long-term confusion at the executive level. This unstable, prolonged reaction means the brain can no longer effectively process incoming information, which is likely the reason we cannot perceive our surroundings or feel pain under anesthesia.

Future Applications for Mental Health

This novel method of describing brain states through their stability offers a powerful new tool for neuroscience.

Professor Ila Fiete, another senior author, believes this approach can be broadly applied to study:

• Different areas of the brain.
• The effects of various types of anesthetics.
• Neuropsychiatric conditions such as depression and schizophrenia, potentially offering a new way to diagnose and track the stability (or lack thereof) in these conditions.

By viewing the brain as a dynamic system, researchers are unlocking deeper secrets about the nature of consciousness and the chemical conditions that disrupt it.