ashennell

Hi, I assume that you mean unchecked production of the endonuclease proteins. There are different types of DNA endonuclease that perform different roles. The ones I know about are produced by bacteria to defend from viral infection. So these endonucleases target DNA that is not part of the cells own chromosomes and they cut at very specific sites. I think some DNA endonucleases are produced during cell apoptosis (cell suicide), they target the cells own DNA and (as far I remember) are not to fussy where they cut. So before I could answer what would happen following unchecked production I think I would need a little more detail. I'm sure there are people around here who more about this than me though. I think that DNA endonucleases are ineffective while the DNA is folded into chromosomes. So again, I think you would need to narrow down the situation you are talking about. I hope I havn't completely misunderstood what you are asking.

I'm not too sure about curve detection. I don't think that there are cells in the primary visual cortex that respond specifically to curves of different orientation or 'radius'. I think that curve detection is probably achived in the next layer up in the cortical hierarchy - the secondary visual areas. Probably through recognition of patterns of short line segments that are produced from the primary cortical area. It may be worth noting that some neurons in the primary visual cortex actually respond to end-stopped lines. Lines of a certain orientation that stop within the cells receptive field. These may assist in curve detection as a curve can be approximated by a series of short lines. I'm not sure if this is clear - but I must dash. I you want any more info please feel free to ask.

Maybe I should get back on topic;- I agree, there is something in the brain that makes us overlook the pointlessness of it all. Our brains evolved as a solution to keeping us alive as best as possible rather than as a a general 'computer-like' reasoning machine. We can reason that this is all pointless but that wont stop a good joke from being funny or a car accident from scaring us and wanted to stay alive etc,etc. So I think our emotions are the part of our mind that prevents this from occuring. I am an atheist and therefore share this view that at the end there will be nothing. Does this mean that life is pointless? No, I think that it just means that the point is not at the end. (yes lovebug, another opinion )

roughly, yes. It's not a perfect mapping where every retinal neuron gets a perfect set of orientation cells just for itself. It is an approximation of this pattern. We call this organisation retinotopic. Neurons that are next to each other in the retina will project to adjacent parts of the visual cortex (with overlap). note : to detect a line in the cortex, a cortical neuron must receive input from a set of adjacent retinal cells - a line of them at least. SO line detection 'per se' requires that there is some overlap in the projection. Do you understand? I think I need I diagram.

Hi, I agree that this discussion is going nowhere. You say that you're not being offensive but accuse me of not wanting to see logic and being full of opinions. I can't see how these comments relate to the rest of the discussion or main part of your last reply. You seem to have misunderstood every part of my last post, deliberately or otherwise - I don't know. Maybe I should just stop but I dont like being accused of not wanting to see logic. So- You seem to be saying that we are at the top of the food chain because we are more determined. Assuming that we are at the top of the food chain then our ability to learn, use language and our opposable thumbs put us there. If motivation is all you need then why would any species have less than the maxmimum possible? My point was that evolution should select for determination to survive in all species. Non of any of this is a proof of natural selection - I don't understand what you mean here. Your arguement here is, as a far I can tell, that determination or will to survive is proportional to intelligence.I am saying is that the instinctual drive is similar across species - i.e. the determination. Intelligence determines which dangers we are aware of but not how hard we try to avoid them. So no not "precisely" these things are completely different. Like you say - the suicide bomber has a belief that becoming a martyr is better than life. I was using this as an example (as I stated) of humans ability to ignore their survival instinct (determination to survive). My point - our "complex brains" allow us to hold complex religeous beliefs that enable us to be more determined to die than to live. The nobility of their actions is not the important factor in this arguement. Anyway. If you think that someone is completely avoiding reason then I would guess it is more likely that you just don't understand what they are saying. Secondly, perhaps I have some opinions - this is not a discussion where it would be easy to provide references. Are opinions not allowed in a discussion forum? By the way 'determinism' is a philosophical doctrine that states that every act and decision is the inevitable consequence of its antecedants. I assume, therefore, that you mean 'determination'. (If you really do mean determinism then no wonder were not getting anywhere)

Firstly, I should mention that it is accepted that this reply is annoyingly augumentative and full of nit-picking. One thing, as humans, that we do NOT share with animals is our determination to win an arguement I'm sure that there have been many instances where an animal has had to work very hard to survive and accomplished some comparatively amazing feats. Afterall, they live in the "wilderness" every day. Strangely they never choose to publish their experiences. I think the problem here is that animals don't really have other things to forget about. SO I would say that this trait is not really seen at all in animals. But surely if a variant of a species evolved that is prepared to try harder or be more determined to survive then it would quickly dominate the population. The concept of "determination" is in a sense a very human thing. If we talk about survival instinct then I think there is no different between humans and animals. The difference is that we have a more complex world model. We can often predict danger a long time in advance. So, yes, working to avoid death when you are in no immediate danger is mainly a human characterisitic. But this is due to animals ignorance of possible dangers and not their lack of a love for life. If animals had the same need for social interaction as we do then perhaps they would. I'm not sure to what extent lonely animals risk going insane. Another topical example: Suicide bombers. As a species I think we show a the greatest ability to actually overcome our survival instinct. I think most animals would only risk their life for their offspring (this is a simplification- altruism and natural selection is complex I think). This results from our ability to have a complex understand of our environment and to hold complex beliefs. The same reason why we may appear to be more determined. In summmary. Clearly the way we percieve threats differs from other speicies. The fact the our brains allow us to consider things that might happen (to worry) and to think about other things (our family or a nice hot up of coffee) means that we must be focused on survival when we find ourselves floating in the middle atlantic ocean. However, the idea that in general animals just dont work as hard as possible with the abilities that they have to avoid death dosn't seem to make evolutional sense. I hope it's OK to shorten the quotes as I have done in this reply.

Well, how much depth do you want to go into? The amount of research on the visual system is immense. This page gives a pretty good intro to colour processing from the retina up: http://www.psych.ucalgary.ca/pace/va-lab/Brian/neuralbases.htm Most modern neuroscience textbooks will also cover the subject. If you google a few key terms then you can probably find as much as you would get in text book on the internet. If you want more detail than this please let me know. I'll see what I can do.

Why do you think this? we certainly have a wider range of behaviour we can use to avoid death but does this mean we are more determined? I think the problem is that we did not evolve in environment that we are now expected to succed in. Our stressors are very different from our ancestors.

I don't think that the occipital lobe has colour specific cells as you describe. The retina certainly has three types of cone cell that are sensitive to different parts of the spectrum. These correspond to red, blue and green. However, I think that colour information is coded in terms of colour opponancy. There are three colour-opponent neural channels - red-green, blue-yellow and white-black. So the colour of a particular point is coded in terms of its position within each of these axis. The result of this is we cannot see certain colour combinaitons at one point e.g. a reddish-green. is this clear? If you want more detail about colour processing let me know. I seem to remember it gets quite complex as you progress to the cortex. From memory i think that colour info is processed by double-opponent cells in the blob regions in areas 17 of the cortex. But im not sure.

The projection from the retina via the thalamus to the cortex is topographic. So the organisation of visual information in the occipital lobe is retinotopic. So the short answer is that each point on the retina goes to different 'line detector' neurons. However, this is unlikely to be perfectly point-to-point. In fact, there are many retinotopic maps in the primary visual areas - i.e. there are parallel projections that form multiple retinotopic maps. I fail to recall how many there are and to what extent they differ in resolution.