What is consciousness? A scientist’s perspective.
We all know what consciousness is. We can tell when we’re awake, when we’re thinking, when we’re pondering the universe, but can anyone really explain the nature of this perception? Or even what separates conscious thought from subconscious thought?
Historically any debate over the nature of consciousness has fallen to philosophers and religious scholars rather than scientists. However, as our understanding of the brain increases so do the number of scientists willing and able to tackle this tricky subject.
What is consciousness?
A good analogy of consciousness is explained here based on work by Giulio Tononi. Imagine the difference between the image of an apple to your brain and a digital camera. The raw image is the same whether on a camera screen or in your head. The camera treats each pixel independently and doesn’t recognise an object. Your brain, however, will combine parts of the image to identify an object, that it is an apple and that it is food. Here, the camera can be seen as ‘unconscious’ and the brain as ‘conscious’.
The bigger the better?
This example works as a simple analogy of how the brain processes information, but doesn’t explain the heightened consciousness of a human in comparison to say a mouse. Some people believe that brain size is linked with consciousness. A human brain contains roughly 86 billion neurons whereas a mouse brain contains only 75 million (over a thousand times less). A person might then argue that it is because our brains are bigger and contain more nerve cells that we can form more complex thoughts. While this may hold to a certain extent, it still doesn’t really explain how consciousness arises.
To explain why brain size isn’t the only thing that matters, we need to consider our brain in terms of the different structures/areas it consists of and not just as a single entity. The human cerebellum at the base of the brain contains roughly 70 billion neurons, whereas the cerebral cortex at the top of the brain contains roughly 16 billion. If you cut off a bit of your cerebellum (don’t try this at home) then you may walk a bit lopsided, but you would still be able to form conscious thoughts. If however, you decided to cut off a bit of your cortex, the outer-most folds of the brain, your conscious thought would be severely diminished and your life drastically impacted. So it seems that the number of brain cells we have doesn’t necessarily relate to conscious thought.
As a general rule the more primal areas of the brain, such as the brain stem and cerebellum act a bit like the camera. Like the camera, they are purely responsible for receiving individual pieces of information from our sensory organs and don’t care for linking this information together. As you move higher up the brain, links form between different aspects of our sensory experiences. This linking begins in mid-brain structures (such as the thalamus) then these links are made more intricate and permanent in the cerebrum.
Tononi believes that it is this linking of information that is the basis for consciousness. As cells become more interlinked, information can be combined more readily and therefore the essence of complicated thought can be explained. The more possible links between cells, the more possible combinations there are and therefore a greater number of ‘thoughts’ are possible.
There may be more neurons in the cerebellum than the cerebrum, but because they are not as extensively linked to each other, they cannot form as complicated thoughts
as the cerebrum. When information is relayed upwards from the cerebellum in the brain, it is passed to neurons that have more connections and can therefore make more abstract links. Perhaps a neuron responsible for telling the colour red links with a neuron responsible for the representation of a round object, giving you the notion of a red apple. If you multiply this process up a couple of times, cells soon hold a lot of combined information – smell, taste, colour etc. all come together to create your representation of the apple.
Too much connectivity
So it’s the number of connections that matter? The more connections the better? Well no, sadly it’s not quite that simple. The cells at the higher levels need to be highly interconnected but if all the cells in the brain were too interconnected then you would really be back to square one, where the whole system is either on or off. All the cells fire, or none of them do. Here, you lose all specific information and your brain doesn’t know whether it is red or round or anything, it just knows there’s something. Because along with your red apple cells, all your blue cells will fire, all your bicycle cells will fire and so on, meaning you’ll get no clear information about the apple whatsoever.
The key is that cells at the basic level need to be focused and not have their message conflicted by other information. They then pass their message up to a more connected cell that combines it with other information before passing it up a level, and so on and so forth. Now we have an entity that can build up complicated information from small bits. According to Tononi it is the ability to combine lots of information efficiently that yields the ability to analyse abstract concepts and thus gives us ‘consciousness’.
How do we become unconscious?
The true test of how good a theory of consciousness this is is whether it can also explain a loss of consciousness. Tononi believes that unconsciousness is brought on when the system becomes fragmented and connectivity in the brain decreases. This is exactly what seems to happen when in a deep sleep (when we don’t dream) or under general anaesthetic. Normally when awake and alert, fast activity can be found all over the brain and signals can be passed between areas. When we go into a deep sleep however, the brain moves to a state where signals cannot easily pass between different areas. Tononi believes that the cells temporarily shut off their connections with each other in order to rest and recuperate, therefore losing interconnectivity and associated higher thought processes.
While it may seem a far reach to suggest that consciousness is purely a state of high interconnectivity, what Tononi has done is to present the beginnings of a tangible scientific theory, backed by evidence that suggests interconnectivity is crucial for higher brain power. The question of why we can form conscious thoughts is more of a philosophical one but the scientific view seems to be that it is a fundamental property of our brains. The evolution of man has led our brains to become highly efficient at processing complex information, giving us a vast repertoire of possible thoughts. This repertoire has expanded to such an extent that we can now debate our very existence and purpose. Whatever you believe about the reasons behind consciousness, however, scientists are beginning to have their say about what rules may govern consciousness in the brain.
Post by: Oliver Freeman @ojfreemanSource: thebrainbank.scienceblog.com