Thanks

Jim
 

Aside from the brain of an individual, may I suggest that we also have a larger "social brain", the thing by which a society, a civilization debates within itself and finally comes to a conclusion (i.e. a voted upon decision)?

Where is the center of TOD's brain?

Asking those questions really calls for a definition of consiousness, which is already quite difficult (hence my clinical approach). This was one of my first experiences in neurology : Pr Hommel in Grenoble asked me how I would tell if someone was consciouss. My first guess was to state that the person would answer more or less appropriately my questions. But then he asked, what for persons who have lost their language (aphasia) ? Ok, let's look at his behaviour. But what when he is locked-in ? And so on. Things are getting also difficult when you try to define consciousness for yourself. When you dream you can have an illusion of consciousness, same for psychotic brains in a delusional state. People with confusion don't term themselves unconscious but an outer observer can't qualify them as fully conscious.

But I can try to answer some of your questions assuming that we both have the same intuitive idea of consciousness.

* First of all, a single brain lesion isn't most often enough to induce unconsciousness. It is like memory, there isn't one region which is responsible for consciousness. This is not to be confounded with arousal, which is a function of our brain stem (the reticula of the pons and the mesencephalon to be exact). A lesion of these regions induces a state of coma because of the lack of arousal. In the same order, a lesion of the anterior thalamus can cause sleep, which is also a state of unconsciousness because of an active sleep state.

The most interesting case is confusion, which is a lack of consciousness not being induced by sleep or coma. There is no single lesion of the brain which has been ascribed to causing a confusion. Confusion results most often from altered metabolic states, diffuse lesions of the brain. Of course a right forebrain lesion can induce confusion but here also the regions injured are quite large and most often reversible.

So overall, I wouldn't ascribe consciousness to a single brain region.

* Is memory only a function of our brain signals (i.e. synaptic function)? Here I can only speculate. We have a lot of types of memories. We distinguish between procedural memory, episodic memory, semantic memory, emotional memory, short-term memory and so on. A very famous experiment is the learning of a maze by rats. You can teach a rat to find its way through a maze. After that, to sum it up quickly, there is no single region in the brain which will suppress this memory (this doesn't mean that there aren't specific regions in our brains dedicated for memorisation, especially for our episodic memory which relies on the hippocampal-limbic circuitry). On the other hand the neuroscientists have demonstrated the long term modifications of synaptic behaviour and connections in the process of learning.

In the state of reduced metabolism in hypothermia, we have shown that people can recover their memories afterwards. So if we would freeze our brains and wake it up 30 years later, I can imagine that we won't lose our memories (pure speculation, has never been done).

• Would I be consciouss if my brain where isolated ? Some experiments have adressed the deafferented brain. In a few seconds the normal alpha-rythm on the electroencephalogram disappears and is replaced with delta rythms, hallmarks of brain disease or deep sleep. Very theoretically we could imagine that we still could have some cognitive processes but the lack of sensorial feedback would quickly let our mind evade its state I think. I think sensorial input is essential and drives our consciousness (after all the aim of consciousness is to prepare our motor schemes to be as coherent as we wish with respect to our surroudings).

• Could a machine become conscious ? Some believe they can, I don't believe that. It is a favorite subject of debate among philosophers since descartes. My main objection is that our consciousness is driven by a mechanism of intention for which I don't have the beginning of an understanding but which is certainly fed by inputs from our hypothalamu and limbic lobes (and the dopaminergic connections favored by AMPOD). Machines as we make them are driven by input from a clock which doesn't exist in our brain. We can make a machine adapt to the surrounding with input based on previous knowledge or even teach them some discriminating functions in the model of neuronal networks, but we aren't able to make a machine capable of evolving from newtonian mechanics to the theory of relativity. As yet we don't know how to teach machines to be astonished. Here we return to the importance of emotions in the state of consciousness very well underscored by Antonio Damasio.

Personally I have always considered consciousness something of an exaggerated mystery. We experience it as deeply mysterious because of our own subjectivity, arising from the (meaningless) question, 'Why am I me rather than someone else?' From an objective perspective - that is, considering as a given a group of conscious individuals - this makes no sense.

But anyway, our knowledge about this and pretty much all things is so fragmentary and full of dead ends that we really know nothing about anything. It is beginning to appear to me that the universe really is deeply and fundamentally incomprehensible to us (another conclusion of Gray's, by the way).