The brainstem is one of the oldest structures in the brain.
It is not concerned with the grand mysteries of consciousness, emotion or identity: the brainstem handles life support.
One particular group of cells in the brainstem is responsible for driving the breathing muscles. These cells work together to produce the rhythmic muscle movements that draw air into your lungs.
This rhythmic breathing pattern is essential for survival. But, sometimes, producing other patterns of activity in these same muscles can be useful.
For example, if you see a bear, or any other large, alarming stimulus, it might help your chances of survival to breathe more heavily or quickly to get ready to fight or run away (if it is a bear I strongly recommend the latter).
If the stimulus is particularly scary then you might shout involuntarily. Or you might hold your breath. All these responses are patterns of activity in your breathing muscles that are generated by your brain.
How these patterns are generated fascinates me.
One way these patterns can come about is that ‘higher’ (that is, more complex or more recently evolved) brain structures can talk to the brainstem and hijack the breathing muscles.
Recently, we looked at how the breathing pattern was changed by stimulating the midbrain in rats. We did this using
a new experimental technique, physically isolating the midbrain and brainstem from the rest of the brain.
When we activated the midbrain (with tiny injections of neurotransmitter) we found we could produce a range of different breathing patterns in the brainstem. These included heavy breathing (such as might occur during exercise) and rapid breathing (resembling sniffing).
So we now have a new tool to learn about the brainstem and how we get our respiratory muscles to perform functions other than breathing.
Think about that the next time you meet a bear!
David Farmer is a neurophysiologist
at Melbourne’s Florey Institute of
Neuroscience and Mental Health.
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