Christof Koch and the Neural Correlates of Consciousness
Posted by dlende on September 29, 2008
Scholarpedia has an entire entry on the neural correlates of consciousness, which argues for including the neural correlates for conscious precepts (that’s a dog!) as any part of understanding how we are consciously aware. In this case, the neural correlates of both basal arousal (see image below) and activity in the inferior temporal cortex are necessary for us to be consciously aware.
This Scholarpedia page is maintained by Christof Koch and Florian Mormann, both at Caltech. Mormann is a post-doc; his latest article on “Latency and selectivity of single neurons indicate hierarchical processing in the human medial temporal lobe” (pdf) appeared in the Journal of Neuroscience.
Koch wrote the popular book The Quest for Consciousness: A Neurobiological Approach based on his collaborative work with Francis Crick. Here is Michael Shermer reviewing the book at Scientific American:
A rock climber adorned with a tattoo of the Apple Computer logo on his arm, Koch takes an unabashed neurobiological approach, the natural extension of what his longtime collaborator Francis Crick started in 1994 when he wrote in The Astonishing Hypothesis “that ‘you,’ your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules.” To me, the most astonishing aspect of this theory is that it is astonishing to anyone. Where else could the mind be but in the brain? Nevertheless, finding the neuronal correlates of consciousness (NCC) has proved elusive, so instead of concocting a grand unified theory, Koch and Crick undertook a very specific research program focusing on the visual system, to understand precisely how photons of light striking your retina become fully integrated visual experiences. Koch and his colleagues, for example, discovered a single neuron that fires only when the subject sees an image of President Bill Clinton. If this neuron died, would Clinton be impeached from the brain? No, because the visual representation of Clinton is distributed throughout several areas of the brain, in a hierarchical fashion, eventually branching down to this single neuron. The visual coding of any face involves several groups of neurons–one to identify the face, another to read its expression, a third to track its motion, and so on. This hierarchy of data processing allows the brain to economize neural activity through the use of combinatorics: “Assume that two face neurons responded either not at all or by firing vigorously. Between them, they could represent four faces (one face is encoded by both cells not firing, the second one by firing activity in one and silence in the other, and so on). Ten neurons could encode 210, or about a thousand faces…. It has been calculated that less than one hundred neurons are sufficient to distinguish one out of thousands of faces in a robust manner. Considering that there are around 100,000 cells below a square millimeter of cortex, the potential representational capacity of any one cortical region is enormous.” Given that the brain has about 100 billion neurons, consciousness is most likely an emergent property of these hierarchical and combinatoric neuronal connections. How, precisely, the NCC produce qualia remains to be explained, but Koch’s scientific approach, in my opinion, is the only one that will solve the hard problem.
Reducing symbols and qualia to just neural connections forgets that there is a body and environment involved, and that the dynamic and emergent property emerges in conjunction with those. This approach to consciousness is also rather blind to evolution. Nicholas Humphrey’s book A History of the Mind: Evolution and the Birth of Consciousness is foundational there. Still, the brain does most of the heavy lifting, I imagine…
Koch also has a Glossary of Consciousness on his website (not a direct link – you’ll see where to click on the left hand side). You can even get this 56 minute lecture by Koch on his quest at You Tube – wow, did his hair grab my conscious attention! Koch also gives us a clip of Francis Crick discussing consciousness and then takes us through his ideas and research.
The hattip for this particular entry goes to Deric Bownds, who covered this Scholarpedia entry earlier.