I have questions regarding the signal between the retina and other parts of the brain. There are two types bipolar cells which are excited by light or darkness to the retina.

Question: Do these form different signal frequencies over the nerve channels?

This is my understanding from resources.

Wikipedia states:

Retinal ganglion cells spontaneously fire action potentials at a base rate while at rest. Excitation of retinal ganglion cells results in an increased firing rate while inhibition results in a depressed rate of firing.

It’s my understanding the photoreceptors in the eye have an opsin pigment molecule which experiences a change in geometry when an electromagnetic wave passes through, pushing on the photoreceptor’s body. A potential difference in voltage occurs which causes the photoreceptor to release glutamate, an exciting neurotransmitter, or GABA an inhibitory one to the electric synapses of the bipolar cells via synapses.

One type of bipolar cell gets excited by light while the other inhibited. Either one releases a neurotransmitter to the synapses of an ion channel. The ion channel creates potential difference, sending a signal or action potential through from the soma, to the axon, to dendrites and to its receptor destination. The above quote suggests that the action potential is “frequency shit key” modulated, with a baseline frequency, then a higher or lower frequency depending on presence of a particular light wavelength. The photoreceptor outputs an exciting neurotransmitter with no light, inhibitory with light.

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    $\begingroup$ In the edit, you've added a couple of other questions, we deal with single questions, one per post. Ideally you can place the others in their own threads, and link back here to the place you've shown your researches. $\endgroup$ Commented May 30, 2022 at 23:50

1 Answer 1


Frequency-shift keying is an electronic communications approach, part of a broader set of frequency modulation strategies for conveying information.

These strategies relate to the difficulty in communicating over what is really a single available physical channel: the electromagnetic spectrum. If you're communicating by radio or other similar frequencies, you can't really sort out an individual signal from all the background except by knowing something about its structure and using that structure to filter out the noise.

It seems like you're trying to apply what you've learned about these forms of electronic communication to brains. However, none of that is necessary in brains, because each neural process represents a separate physical channel. There's no need to encode and decode signals that way: communication within the nervous system is massively parallel.

Sometimes "rates" and "frequencies" are interchangeable concepts, but not here. When people talk about a "firing rate", they literally mean a rate: discrete events. See for example "rate code". More action potentials means more neurotransmitter release at the end of an axon. No frequency encoding or decoding is necessary. Different messages are conveyed through different "cables". This is also called the "labeled line principle" or theory: the idea that information in nervous systems is conveyed largely based on the physical structure of where it comes from and where it transmits to. There is no difference in the electrical properties of an axon conveying information about one part of the visual field versus another, except that they are connected respectively to a part of the retina and a part of the brain each also dedicated to processing information about that part of the visual field.

  • $\begingroup$ Thanks, I wasn't aware of how parallel the axons were and ion channels. So everything comes in parallel from the bipolar cells after the retina? I also understand there is multiple layers in geniculate which may do some signal processing between both eye images for a side itself before reaching the visual cortex. $\endgroup$
    – Nick
    Commented May 16 at 10:53

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