Both visual and auditory stimuli are sent to the brain via ganglion cells (retinal resp. spiral). Both are the first cells along their resp. pathways that produce action potentials.

My question concerns typical frequencies of action potentials sent along the axons of the visual vs. auditory ganglion cells as a reaction to a "typical stimulus", i.e. a medium long, medium strong signal of some fixed frequency (e.g. light: red, sound: 440Hz) against a white resp. silent background.

Are these frequencies of comparable range, or does one type of ganglion cell (retinal vs. spiral) fire with a significantly higher or lower rate than the other?

(The question would not make sense, if the physical frequencies of light and sound - which trigger the receptor cells - would be coded by frequencies of action potentials. But I assume that this is not the case, is it?)


1 Answer 1


The auditory brainstem shows "phase-locking" typically up to 1-3Khz at most; 3000Hz is an incredibly high firing rate for a single neuron, but this phase-locking is achieved not by individual cells firing in-phase with an auditory stimulus, but rather with a population of cells that tend to fire in-phase, such that if you average across the population you get a phase-locked population volley.

In some cases, in some animals, this phase locking can even get to the higher frequencies (see here for example).

However, this phase locking seems primarily important for sound localization via interaural time differences. Frequency itself is encoded by which population of hair cells is activated, according to the properties of the basilar membrane. Firing rates of individual spiral ganglion cells are only faster than 100 Hz at very high stimulus intensities.

Similar to the spiral ganglion cells, retinal ganglion cells primary encode intensity information in their firing rates.

However, in both cases, it's important to recognize how crucial adaptation is in sensory systems. RGCs in particular fire primarily to transients, so it is typical to use light flashes, drifting gratings, or other dynamic stimuli. The response to a "medium long, medium strong signal of some fixed (wavelength)" is going to be brief, followed by silence, not a constant response like you imply.

  • $\begingroup$ You write "phase-locking" in quotation marks, as if you were not quite sure what it means, resp. you don't want to commit to a specific definition. Can you give me a source where phase-locking is explained in detail which I can rely on? $\endgroup$ Commented Nov 22, 2017 at 15:56
  • $\begingroup$ The quotes were not to indicate I don't know what it means, but to indicate it is a specific term rather than a descriptive one. google.com/search?q=phase+locking+in+the+auditory+system gives many sources. $\endgroup$
    – Bryan Krause
    Commented Nov 22, 2017 at 16:13
  • $\begingroup$ Please don't feel offended, I know that you know what you are talking about. Alas, your hint how to google doesn't help me a lot (short-termed). There's too much to go through (and too specific: "auditory system"). Do you have a more general and concise reference? $\endgroup$ Commented Nov 22, 2017 at 16:17
  • $\begingroup$ I don't have a specific reference in my pocket, which is why I am suggesting you look at some relevant search terms and try to find the answer on your own. $\endgroup$
    – Bryan Krause
    Commented Nov 22, 2017 at 16:20
  • $\begingroup$ Just for the record: I already gained some knowledge about "phase-locking" (its meaning, its origins, its contexts, its mechanisms,..) but am still missing an overarching overview. $\endgroup$ Commented Nov 22, 2017 at 16:21

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