Webbed Reprint Collection
William H. Calvin
University of Washington
Seattle WA 98195-1800 USA
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"Listening to Cortical Neurons"
Copyright ©1997 by W. H. Calvin.
Neurons run on electricity1, producing many impulses each second when they are working hard. These brief (1/1000 second, as rapid as a fast camera shutter), 0.1 volt impulses (though a hundred times smaller if recorded from outside the cell) can be amplified and heard via a loudspeaker. Neurophysiologists routinely listen to neurons via loudspeakers in their laboratories, much as anesthesiologists listen to a patient's heartbeat in the operating room.
This RealAudio file [epileptic.ra] allows you to listen to a sample of the audio monitor, amplifying the signal of several cortical neurons near the epileptic focus in an awake patient prior to removal of the epileptic region of brain2.
This RealAudio file [Interictal.ra] amplifies the signal of several cortical neurons near an experimental epileptic focus in a rhesus monkey3.
This RealAudio file [ptn-doublet.ra] is from a normal cat cortical neuron in motor cortex4, injecting steps of current into the cell, causing it to fire. Normal firing is first heard, but then you hear the transition to double-spike firing, thought to be one of the normal mechanisms that the epileptic process makes pathological5.
These files require a RealAudio player (version 2.0 or better).
Note that you can save the files to your local disk or server, to keep them handy for demos.
NOTESTeachers can simulate the sound of cortical neurons very easily. Just take a Velcro fastener, hold it up to your ear, and very slowly pull it apart, so that you hear the individual "hairs" pop loose. I once saw an entire room full of neurophysiologists break into surprised laughter when William Softky did this into a microphone, as the random intervals between the pops bears an uncanny resemblence to how cortical neurons sound.
Neurophysiologists: Don't blame the compressed audio if those units don't sound quite right. These particular sound files are not from amplification of raw recordings; I triggered a pulse generator off the largest of the spikes, and it is its output that you hear here.
1 William H. Calvin and George A. Ojemann (1994). Conversations with Neil's Brain: The Neural Nature of Thought and Language (Addison-Wesley). See Chapter 6.
2 Calvin, W. H., Ojemann, G. A., and Ward, A. A., Jr. (1973). Human cortical neurons in epileptogenic foci: Comparison of inter-ictal firing patterns to those of "epileptic" neurons in animals. Electroencephalography and Clinical Neurophysiology 34:337-351.
3 Calvin, W.H., Sypert, G.W., Ward, A.A., Jr. (1968). Structured timing patterns within bursts from epileptic neurons in undrugged monkey cortex. Experimental Neurology 21:535-549.
4 Calvin, W. H., and Sypert, G. W. (1976). Fast and slow pyramidal tract neurons: An intracellular analysis of their contrasting repetitive firing properties in the cat. Journal of Neurophysiology 39:420-434.
5 Calvin, W. H. (1980). Normal repetitive firing and its pathophysiology. In: Epilepsy: A Window to Brain Mechanisms (J. Lockard and A. A. Ward, Jr., eds.), Raven Press, New York, pp. 97-121.