are there 'spot detectors' in the brain?

[gib65]

I've heard the term 'spot detector' thrown around in some of the brainscience literature, but I vaguely remember learning in university that there are no spot detector neurons in the brain, only on the retina.

 

So my first question is: are there or are there not spot detector neurons in the brain?

 

My second question is: if not, then how are we actually able to see spots or know about them? Doesn't being conscious of something require some kind of brain processing of that information? Doesn't the brain have to have some kind of 'detector' mechanism in place in order for us to perceive whatever's being detected? When I look at the stars I surely feel like I'm seeing spots (or points). Same with pencil marks on paper. What brain area is responsible for my perception of these things if not spot detectors?

[Ringer]

A 'spot neuron' would be a bit of a misnomer. Neurons aren't all specifically designed for specific functions per say. It would kind of like looking for a reading neuron. You have to also take into account we don't have the brain's neuronal pattern mapped, so if there were neurons specifically used for spot detection we would be hard pressed to pin it down.

 

Your second question is assuming some sort of duality between the brain and the eye; both are apart of ourselves and should not really be separated. The reason we see spots is the same reason we see any other color, very simply because it's a different color than the area around it.

[gib65]

Your second question is assuming some sort of duality between the brain and the eye; both are apart of ourselves and should not really be separated. The reason we see spots is the same reason we see any other color' date=' very simply because it's a different color than the area around it.[/quote']

 

Yeah, that makes sense, Ringer, but whatever is picked up by the retina does get sent to the brain, does it not? From what I remember learning in school, signals are sent from the retina to area V1 in the occipital lobe, and the first types of neurons they are received by are line detectors, motion detectors, depth detectors, and I think a few others, but spot detectors was not one of them. So where it seems a little puzzling to me is when I consider what happens when the retina does pick up a spot or point. It must send a signal of some kind to area V1, and when V1 receives it, what neurons end up firing? Does the signal bypass V1 and go somewhere else? I mean, some center in the brain must be processing the signal because I'm able to think about the fact that I'm seeing a spot/point.

[Ringer]

Well it's not completely that simple. There are thousands of photoreceptors in the eyes and only a small percentage can really see color, only in the center of vision in fact. Not only that but the light from the left and right hemispheres go to different hemispheres of the occipital lobe and the same is true for both eyes. So the brain gets a scattered, partially color, overlapping input that it has to rearrange and make since out of. You never ONLY see a spot, and a spot is just a change in color. Again our ideas of what neurons do is not black and white. Saying that only one kind of neuron can see a line is a mistake, there may be neurons that respond more to lines than to motion, but that doesn't mean it's a 'line neuron'. It could just as well be an inanimate neuron seeing as the line doesn't move. In that train of thought a line neuron could just as easily see a spot as a line since the only different is the dimensions.

[CharonY]

Yeah, that makes sense, Ringer, but whatever is picked up by the retina does get sent to the brain, does it not?

Absolutely not. There is heavy modulation and editing going on before the signal reaches the brain. The way it works is not that there is a specialized cell that can spot a pattern per se (how is it supposed to do it, it only gets a signal and then transfers it). The trick is than the signal reaches an ensemble of cells that are connected in such a way that they cumulative respond to a specific stimulus.

In simplified form, imagine a row of cells. The right cells inhibit the cells to their left, whereas the left cells induce the ones right of them. What happens is that if a light source moves from left to the right, the net signal is a very strong one, as the first cell (outermost left) gives out a signal and then increases the output of the neighboring cell when the light reaches it.

On the other hand the same cells are non-responsive to movements from right to left. Thus you have a group of cells that are specialized to left-to-right movements.

Note that this kind of modulation is, with exceptions, not necessarily located on the retina itself, but also in cells on the way to the brain.

Specialized effects as e.g. cells specialized in detecting contrasts or specific patterns and movements are wired like this. The brain only gets a heavily edited version of what is going on in the retina.

Edited December 25, 2010 by CharonY