The Hydraulic Brain

By Neuroskeptic | September 19, 2013 4:24 pm

People used to think that nerves were literally pipes, conveying impulses in the form of pressure waves of water.

Even 100 years ago, this ‘hydraulic’ view was still influencing psychologists such as Freud, with his ideas about mental pressures building up inside the brain.

Still, after physiologists Hodgkin and Huxley explained nerve conduction as an electrical phenomenon in 1952, the hydraulic theory was killed off forever.

…or so we thought. But it’s back from the dead, in the form of a quite remarkable paper in the remarkable journal Medical Hypotheses: Impulses and pressure waves cause excitement and conduction in the nervous system

The German authors, Barz, Schreiber and Barz, argue that:

The elastic properties of cells, nerve and muscle fibres allow mechanical impulses to be carried (comparable with the blood pulse in the arterial vessel system), and therefore they can conduct energy or information.

Orthodoxy holds that as an electrical impulse travels down a nerve, it triggers a local flow of sodium ions into the cell, via voltage-gated ion channels. Since sodium ions have an electrical charge, this flow generates a voltage, and propagates the impulse.

Barz et al reinterpret all this. They propose that intracellular pressure causes ion influx, and this in turn increases intracellular pressure, because water follows the ions into the cell by osmosis:

The impulse wave stretches the membrane, which significantly reduces its resistance for ions. So, the ‘‘explosive’’ influx of sodium ions (with associated water) into the cell can create or can reinforce a mechanical impulse.

On this view, all the electrical fields are merely a side-effect. “Voltage-gated ion channels”, they say, are actually pressure-gated, and open in response to mechanical forces.

I never thought I’d live to see the day that “Voltage-gated ion channels” was put in scare quotes.

When it comes to explaining synaptic transmission between cells, Barz et al are rather vague, but they seem to suggest that this, too, is mechanical, and that neurotransmitters are unimportant.

They conclude by admitting that there is no direct evidence for any of this, but:

Until now it appears that  scientists have not had a sufficient stimulus to prove the pressure wave theory, but the authors hope that this paper may give this.

I have to say this is a lovely idea. It’s obviously not true, not least because you can stimulate a nerve without touching it, just by applying an electrical (or magnetic) field. But it is rather cute.

ResearchBlogging.orgBarz H, Schreiber A, & Barz U (2013). Impulses and pressure waves cause excitement and conduction in the nervous system. Medical Hypotheses PMID: 23953966

  • Dimokratis Karamanlis

    The soliton model ( is a similar(?) hypothesis.

    • Neuroskeptic

      That’s fascinating – thanks!

  • Y V Chawla

    You feel the force when you feel angry, when
    you feel confusion, when you meet any unexpected positive or negative
    happening. There is ‘nothing’ behind this feeling, this vibration.
    Mind is continuously being stirred. There is
    not a single moment when this stir is not there. The stir is essentially
    positive, negative or neutral. This stirring happens on the Original ground.
    There is nothing behind the stirring.
    Y V Chawla

  • Han

    Whenever there are two hypotheses, we can always ask “Can it be both?”

    The pressure wave / soliton idea and the electrical one are not mutually exclusive. They can both be operating in the brain. Also, the fact that electrical stimulation can excite neurons only shows that this is a possible laboratory intervention. Similarly, Transcranial Magnetic Stimulation, for instance, is not proof that the brain uses magnetic fields for communication in non-lab situations.

    If this is experimentally verified, you could describe pressure waves and electrical waves as two sides of the same coin – which one is “real” could end up being a matter of convention and experimental tractability.

    • Neuroskeptic

      It is plausible that pressure waves do accompany electrical activity but they might be merely an epiphenomenon.

      We know that electrical activity isn’t one, because it can trigger cell firing. It might be that pressure variations (within the range that could plausibly occur in vivo) can also trigger cell firing (not just in mechanosensitive sensory neurons) but that’s an open question AFAIK…

      • Yohan

        Right. I guess all I am pointing to is the biophysical possibility that mechanical and ionic waves in a neuron could be 100% correlated. If this were true, then either could be seen as epiphenomenal — pressure could reliably cause electrical signaling and vice versa. There would be some choice in deciding which to call epiphenomenal.

        Similarly, does electrical signaling cause neurotransmitter release or is it the other way round? The real answer is that each can cause the other in the right circumstances. Nonlinear coupled systems are often hard to parcellate into neat causal chains — they’re more like loops!

  • Richard

    Interesting their comparison with mechanical waves in the circulatory system; surely the mechanical forces exerted by pulsating arteries & capillaries in the brain would seriously affect brain function if their idea were true..?

  • Joan Torelló Mas

    Very interesting article and all coments so.
    Throughout times some people wrote on a kind of “pneumatic mind” that could be related to the “hydraulic mind”, did specially Michael Servetus.
    I’m collecting that in my blog:

    I think that is really fascinating. It could be a global theory.

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About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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