Tuesday, March 20, 2007

Neuroscience watch: Another controversial new finding about nerves

In a controversial new finding, written up at Science Daily, physicists at the Niels Bohr Institute at Copenhagen University
Danish scientists challenge the accepted scientific views of how nerves function and of how anesthetics work. Their research suggests that action of nerves is based on sound pulses and that anesthetics inhibit their transmission.

Surprisingly, although anaesthetics have been in use for about 150 years, no one knew exactly how they work. The physicists argue that they work by changing the melting point of nerve membranes, so that they cannot transmit waves.

The standard textbook view has been that nerves send electrical impulses along their length (and presumably anaesthetics disrupt that). That explanation troubled physicists because the process should generate heat, but it doesn't.

David deWitt, however, writes to me urging caution:
I am quite skeptical of the claim (without reading the original paper). There is a good deal of electrophysiological studies that clearly demonstrate that an action potential is triggered electrically. You can attach electrodes to neurons and hyper/hypo polarize them and alter the activity. There are ligand gated and voltage gated ion channels that can be activated or blocked and it is the depolarization of the synaptic membrane that triggers the calcium channels that activate the machinery associated with vesicular docking and release of neurotransmitter at the synapse. You can electrically stimulate the neuron and this will trigger the action potential. It has been shown to be necessary and sufficient. Scientists have long worked out the process of opening and closing of potassium, sodium and calcium channels. You can block these and prevent proper functioning of the neuron.

Note that it is described as "theoretical" in other words they didn't actually measure any mechanical pulses or sound--they merely suggested it as a possibility and an explanation for the effects of anesthesia.

One of the rationales was the fact that different chemicals worked as anesthesia and they depend on the solubility in olive oil. No doubt this solubility is related to how it can penetrate the cell membrane. Just because different compounds have the same effect on a neuron does not mean that they work by the same mechanism. There can be several different mechanisms that are impacted, but all resulting in the same effect.

This is significant because anesthesia does not affect all neuronal populations in the same way. If it were just a matter of a non-specific sound blocking mechanism, then ALL neurons should be simultaneously affected. This should include all of your motor and autonomic neurons as well (the ones that control breathing, peristalsis etc.) However, this is not the case.

It is possible that a rush of ions into the neuron could generate a mechanical pulse as well as an electrical signal, so I want to be careful here. But it would seem that it would have more to do with a change in volume/density than it would in the production of sound.

Instead of what is the sound of one hand clapping, what is the sound of a 100 million potassium ions flowing through a ~2 angstrom hole in a second?

This is all kind of interesting, especially in view of an earlier new finding that brain cells communicate with each other not just at the synapses but along their length.

Anaesthetics exist to relieve pain, and pain is, after all, an experience of the mind as well as a state of the brain. Understanding the true relationship between the mind and the brain will certainly require neuroscientists to develop a more accurate account of how neurons operate.

Toronto-based Canadian journalist Denyse O'Leary ( is the author of the multiple award-winning By Design or by Chance? (Augsburg Fortress 2004), an overview of the intelligent design controversy, and of Faith@Science. She was named CBA Canada's Recommended Author of the Year in 2005 and is co-author, with Montreal neuroscientist Mario Beauregard, of the forthcoming The Spiritual Brain: A neuroscientist's case for the existence of the soul (Harper 2007).

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