Nov 13 2009

Tracking Down Consciousness

The holy grail of modern neuroscience, and perhaps one of the toughest scientific problems we face, is understanding at a fundamental level the nature of consciousness. What is it about our brain function that makes us aware of our own existence?

It is not simply an emergent property of having enough neurons wired together. A popular notion in science fiction is that artificial intelligence may unexpectedly emerge out of a sufficiently powerful computer – such as Vger or SkyNet. But this scenario is highly unlikely. Consciousness appears to be a specific function of thinking systems, not just a consequence of complexity.

For example, the cerebellum is a specialized part of the brain involved with motor coordination. It contains about the same number of neurons and connections that the cortex does, but the cerebellum itself is not conscious nor does it appear to contribute to consciousness.

Neuroscientists and psychologists have also been able to demonstrate experimentally for years that some brain processes are conscious – we experience them as our own thoughts and sensations; while others are entirely subconscious – we have no awareness of them. While it is clear that it is brain processes that are generating consciousness, we do not know what it is precisely that is different about conscious and subconscious processes.

This question is of far more than academic interest. In some patients who are comatose but retain some brain function it is difficult to say exactly how much consciousness they may have. Our inferences from the neurological exam are probably accurate in most cases, but there is a twilight zone of brain function where a shadow of consciousness may remain but be undetected by standard exam. Studies with fMRI scans are beginning to show that such patients may actually be processing sensory input in a conscious way. This does not mean that they are fully awake and just trapped in a comatose body – consciousness is not a binary state, you can be a little conscious. Imagine yourself extremely sleepy, barely awake and on the brink of falling asleep. Or, alternatively, imagine someone who is so drunk they can barely stand. They have some consciousness, but clearly not full consciousness, and likely will not remember much in the morning.

Understanding consciousness will likely also be helpful if we ever want to build true AI. We can accomplish this by simply copying the brain, in which case we can create AI without fully understanding it, but that is a suboptimal situation. It will be to our advantage to have a very high degree of control over the properties of any AI.

Another application of understanding consciousness would be to explore the minds of animals with whom we cannot directly converse. How conscious is a cow, actually?

A new study by neuroscientists at Cambridge claims to have found a possible signature of conscious processing. What they did is compare two tasks – looking at pictures of houses and faces so that they are consciously experienced, and looking at the same pictures in a way that they are not consciously experienced. In the latter case, each eye was presented with a separate picture – one with the house or face in green on orange, and the other with the colors reversed. The conscious brain perceives these overlapping images as just a yellow blur, but the images are still processed subconsciously. In this way the researchers hoped to isolate the variable of conscious experience of the images.

This seems like a reasonable technique to me, although I am not sure how complete the isolation of the conscious variable is. Differences in visual processes are also likely to be present – separate from conscious awareness.

In any case, what they found was that with the conscious images fMRI responses were very consistent from trial to trial – each time the subject looked at the picture they displayed a similar pattern of brain activity. When the subconscious images were viewed, however, there was a much more random pattern of brain activity. From this they conclude that one signature of conscious processing is a consistency of patterns of brain activation.

If this property is reproducible across other experimental designs (you cannot really conclude much from a single such experiment) it may provide one additional piece to the puzzle of consciousness. Perhaps the consistency comes from the fact that certain brain networks core to the function of conscious awareness are always involved in consciousness. It would be nice, of course, to discover what those core networks are.

Previous studies have focused on the intensity of neural activation as a property of consciousness. This makes sense also, as it certainly appears clinically that a minimal level of cortical activity is necessary in order to generate wakefulness. Consciousness therefore appears to be a very energetic function, perhaps because it requires coordinated activation across a broad area of the cortex (not just the function of one small piece of the brain).

Slowly the nature of consciousness is coming into focus. If confirmed, this is just a baby step, but slow steady small steps is the norm for scientific progress these days (the press prefers breakthroughs and eureka moments, but these are rare).

Consciousness is likely to be a problem like the origin of life or even curing cancer – a many decade long project that will see mostly incremental advances, too slow to perceive, like watching the hour hand of a clock. But when we step back and look at the big picture, it is clear that we are slowly advancing.

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