Encefalus

Spheres of Influence: Scientific American.

The above was article was published in Scientific American Mind

Its author is Michael Gazzaniga one of the most respected figures in neuropsychology.

Michael Gazzaniga

If you don’t know him, he’s the guy who made the most important work in the lateralization of the two hemispheres. You’ve probably heard before that the left hemisphere is sequential and logical, while the right holistic and sentimental (even if this is not always true). These discoveries belong to this man.

How he did that? Back in to 60’s (starting from the 40’s) it was a common procedure to cut in half the corpus callosum, the part of the brain that connects the two hemispheres, thus splitting the cerebral cortex in half. Everything below the cerebral cortex remained unaffected, since lateralization is met only in in the cerebral cortex. The scientists at first expected the patients to meet problems in their everyday activities, however they did not. Gazzaniga (along with Roger Sperry) decided to study these patients (called split-brain patients in lay terms).

 Roger Sperry, Nobel prize in medicine (1981) for his work about split-brains

The patients seemed to cope with their every day activities because the two hemispheres could work in parallel as they received the same stimuli. Once Gazzaniga and Sperry put the subject in trials where the two hemispheres could not communicate the patients showed up the effects of lateralization.

So for example, if a word was shown on the left visual field, the patient could not read it, because the right hemisphere, to where the left visual field belongs, was unable to read. What is most interesting however is this (taken from http://physics.weber.edu/carroll/honors-time/split_brain.htm)

• The left brain dominates for language, speech, and problem solving

• The right brain dominates for visual-motor tasks

1.  Each hemisphere was presented a picture that related to one of four cards placed in front of the split-brain subject.  The right hemisphere saw the picture on the left (a snow scene), and the left hemisphere saw the picture on the right (a chicken foot).  Both hemispheres could see all of the cards.

2.  The left and right hemispheres easily picked the card that related to the picture it saw.   The left hand pointed to the right hemisphere’s choice, and the right hand pointed to the left hemisphere’s choice.

3.  The patient was then asked why the left hand was pointing to the shovel.  Only the left hemisphere can talk, and it did not know the answer because the decision to point to the shovel was made in the right hemisphere.

4.  Immediately the left hemisphere made up a story about what it could see — the chicken.  It said the right hemisphere chose the shovel to clean out a chicken shed.

Does this reveals the left brain’s interpreter in action?

 Source:  Gazzaniga, Michael S., "The Split Brain Revisited," Scientific American, July 1998

(An official edition by Michael Gazzaniga explaining the whole procedure can be found in Scientific American Digital)

The left hemisphere just made a story out of nowhere to explain what the subject had chosen!

So, we see that beyond lateralization, a much important issue was raised by this experiments. Maybe the most important issue of all: That of consciousness.

Does each hemisphere have a different consciousness? How consciousness can emerge through what seems to be two different brains? If these brains really had two consciousnesses, then which of the two the patient experienced. Was it the left hemisphere’s? Or was it the right’s? If it was the left hemisphere, then the right hemisphere was doomed to eternal silence (since it could not speak) and who experienced it?

Obviusly, split-brain experiments can freak you out.

Don’t try splitting your brain like that kids

Consciousness is a subject that I am directly interested in, but it can’t be covered in full detail in just one post. So, in this one,we will focus on the implications of the split-brain experiments on consciousness and the commentary of Michael Gazzaniga

In the article Spheres of Influence published in Scientific American Mind (which was mentioned in the beggining) Gazzaniga writes the following:

"When we triggered a negative mood in the right hemisphere by a visual stimulus, the patient denied seeing anything but suddenly said that she was upset and that it was the experimenter who was upsetting her. She felt the emotional response to the stimulus—all the autonomic results—but had no idea what caused it. Ah, lack of knowledge is of no importance, the
left brain will find a solution."

So, Gazzaniga goes on to postulate his own theory of consciousness. What he believes constitutes consciousness is the left hemisphere’s ability to interprete events. So, in his own point of view, our brain simply experiences events in seperate circuits and then the left hemisphere connects them into a whole.

To recapitulate (again from http://physics.weber.edu/carroll/honors-time/split_brain.htm)

The Left Brain’s Interpreter

This and other split-brain experiments show that …

• Each of us has an interpreter in our left hemisphere.

• This interpreter constructs theories about why we act and behave the way we do.

• Thousands (perhaps millions) of brain activities go on relatively independently of one another and all outside the realm of conscious experience.  They affect body movements, emotions, thoughts, ….

• Once these brain activities are expressed, the expressions become events that the conscious system takes note of and that the interpreter must explain.

— "tip of the tongue" phenomena

— "unconscious" problem solving

• The interpreter constructs our conscious reality by interpreting the (limited and fragmentary) data available to it.

• Your conscious life is an "afterthought" constructed by the interpreter.

Source:  Gazzaniga, Michael S., Mind Matters

Consciousness can sometimes be a problem

This is a very interesting theory and a very realistic one as well. Michael Gazzanina drives the left brain’s interpretive property to a whole new level through his theory, proposing that the left brain does not simply interprete events about the external reality, but about our own consciousness.

However, what this theory doesn’t do, is to explain how the hard problem of consciousness, as it was described by David Chalmers, can be solved (Hard Problem on Wikipedia). This theory does not explain how consciousness is emerged through the neuronic chaos of our brains. However, Gazzaniga offers a second step into the whole debate of consciousness.

The problem of consciousness has been separated into the aformentioned hard problem and the easy problem. The easy problem of consciousness is constituded simply by the functions that give rise to experience. The hard problem explains how the subjective experience emerges and why.

David Chalmers (photo) has a hard problem to solve

Consciousness has also been seperated into two parts: Primary and secondary. Primary consciousness is what we can call self-awareness. It’s the ability to recognize our existence, to know that we exist and that we are different beings from each other. Very few animals are believed to possess this ability (like dolphins or some other primates). Secondary consciousness is the simple existence of awareness and feelings.

Consciousness can also be categorized as phenomenal consciousness (what we described as secondary consciousness) and as access consciousness. Access consciousness is the consciousness that can be used for rational behavioral control and verbal report.

Ned Block has theorized that phenomenal consciousness is simply the existence of a stimulus and its awareness without conscious awareness. Access consciousness comes once the awareness is conscious.

Maybe the last sentences don’t make much sense to you. How can we be aware and not self-aware. Ned Block gives the example of a clock that ticks in the background, when we suddenly become aware of its presence. In that case, we have a-consciousness (whereas before we had only p-consciousness).

Interestingly enough, not much time ago this research showed up on PLoS Biology : Neural Correlates of Auditory Perceptual Awareness under Informational Masking

It describes this very procedure: how an object can be audible without us knowing. Actually, what is interesting with this research is that it finds the neural correlates of the whole procedure: which areas of the brain function when sounds enter into the proccessing stage, before getting to the aware stage, and which areas of the brain function when awareness occurs.

No, it’s not an intergalactic weapon. It’s an fMRI used to study the neural correlates of conscious experience

And so Gazzaniga introduces a new dimension to the whole problem of consciousness: the gestalt dimension, or, how the parts become a whole. Even though there is no complete theory of consciousness yet, there is a huge amount of scientific data directing to the brain performing certain functions at certain spots. Gazzaniga’s theory is a way to explain how these different spots can emerge as a whole.

There have been two very popular neurological theories concerning this subject (the easy problem of consciousness) that of Christof Koch’s and that of Susan Greenfield’s. Koch believes that the center of consciousness lies inside a specific part of the brain, and Greenfield speaks of "assemblies" made of neurons that give rise to consciousness.

(For more visit Scientific American: How Does Consciousness Happen)

Gazzaniga offers with his theory another perspective, not on the neural correlates of consciousness, but a way that different neural correlates can become a whole and be subjectively understood as such. So, he has proposed his own theory of how a split brain, becomes one.

I hope this was not too much information on just one post With this article I just tried to scrape the surface of consciousness along with some of its historical roots. There have been many theories that we did not access in this post (like the theory of quantum consciousness for example) and will be covered in future posts. As always, feel free to comment

Further Reading: 

Online Papers on Consciousness (by David Chalmers)

Mind Papers at Fragments of consciousness (run by David Chalmers)

Consciousness in the news

Consciousness matters at Harvard University Press Publicity

Koch on (= against) quantum consciousness theory

Kuhnian and Conceptual Reflections on Dennett’s Critique of the Hard Problem

Cognition, Brain and Consciousness

Access consciousness and language

Cognitive Neuroscience of Consciousness

Lectures on Neuroscience and Consciousness

X-Phi meets A-Phi

Will Solving The ‘Hard Problem’ of Consciousness Unweave the Rainbow?

This entry was posted on Wednesday, July 30th, 2008 at 4:28 pm and is filed under Cognitive, Consciousness, Neuro-biological, Philosophical. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.