Vahid rakhshan, thank you for answering so quickly. Let me use a analogy to make my question clearer: imagine you look thru a microscope and somebody asks you if the microscope is necessary for your visual perception. I guess you would say: "no. It is necessary for this special mode of perceiving those real tiny things but not necessary for my visual perception in general. I could use a different device or just my eyes or even just artificial eyes that provoke electric signals in my neurons." if i ask neuroscience wether the brain is necessary for having subjective perception in general, what would they say? Best, f

You have to define what is meant by subjective experience. This is a phiiosophical question that can't be answered by neuroscience. Neuroscientists assume that what they are seeing in brain scans correlates with what a person is attending to and is suggestive of such experience. What neuroscience has confirmed is that no homunculus exists in the brain that registers subjective experience, rather higher areas of the cortex act dynamically with other areas of the brain including the amygdala, according to demands, with many functions processed pre-attentively or pre-consciously. The subjective experience may be an on-line response to the neural assemblies active at any one time.

I hardly see neuroscience as a unified field that makes definite claims about subjective perception. Quite contrary there is a huge amount of theories from neuroscience and related disciplines on the relation between conciousness and neural processes. Some are not particular metaphysical. E.g. a recent theory sees consciousness as identical to integrate information (Tononi 2008 - http://www.biolbull.org/content/215/3/216.full), which as such, does not necessarily need a brain, but is realised in the way neurons process information. Similar can be found in the "Predictive Coding" framework (Howhy, "The Predictive Mind", is a good introduction), which sees the statistical mechanics of the brain as responsible for perception.

However, I think it is safe to say that they all view the human brain as necessary for human consciousness - that is, without your brain, you would not be conscious. But they would also agree that the human brain is not necessary an requirement for consciousness as such. The disagreement is what precise the neural substrate or process that generates consciousness is. This has often been called the quest for the neural correlate of consciousness (or just NCC). What precise constitutes a NCC we do not know!

If you are interested in animal (and maybe plant) consciousness, and how we can know whether they are conscious, this article is worth a read: Edelman, Baars & Seth (2005) Identifying hallmarks of consciousness in non-mammalian species. Consciousness & Cognition 14.

Dear Derek,

In what sense do you think that neuroscience has confirmed that no homunculus exists in the brain that registers subjective experience? If subjective experience is not registered somewhere (or something along those lines) what is the point of it, or, in other words, what causal effects could it have? All that neuroscience has shown, as far as I know, is that it is very hard to see how there could be one single place where subjective experience is registered. There is no problem with there being lots and lots of such places - i.e. neurons of a particular class. I cannot see what it could mean for subjective experience, if it has some causal signalling function, to be 'an online response to the neural assemblies active at any one time' other than if some locus gets the message from this activity. The currently popular idea that you can get experience out of a mass of simultaneous events in different places is a simple violation of the locality requirements of determinate physics, as was pointed out by WIlliam James. To my mind nothing has changed about that. There would be no point in a subjective experience being made up of lots of separate events spread over the brain unless these all fed in together to co-contribute to some causal path. In neurology that is called signals arriving at a dendritic tree and setting up post synaptic potentials. Until this has happened I cannot see that the prior distributed events can be said to be an experience. We know from experiment that if output pathways from sensory cortices are cut nothing is experienced.

It seems to me likely that you could create artificially the sort of local event that corresponds to subjective experience - maybe in an artificial membrane subjected to a complex pattern of electrical potentials. The trouble is that you have no way of knowing whether it felt anything. I do not think that this need invalidate reasonable speculations about what such events are in brains, however. We have reasonable ideas about evolution and cosmogenesis that we cannot test in a simulation.