Friday, September 12, 2008

From Spikes to Decisions: Part 1

In 1799, in the Nile Delta town of Rosetta, Napoleon’s army came across three passages inscribed in a slab of black basalt. Each segment was actually the same message written three times, each in a different language. Hieroglyphics were on the top, then demotic, and Greek at the bottom. The demotic was deciphered rather easily, but the hieroglyphics remained a mystery for several years. At the time, no one had a clue what the glyphs meant; the predominant view held that it was just picture writing, not a phonetic alphabet. This view was challenged by James Young, and then shown to be false by a man named Jean-François Champollion.

Champollion, who could read both Greek and Coptic, was able to figure out the seven ancient demotic signs that were still alive in the Coptic language. Looking at how these signs were used, he was able to work out their meaning. He then began tracing the demotic signs back to hieroglyphics. By working out what some hieroglyphs stood for, he could then make inroads into the rest of the passage.

With his deciphered passage in hand, Champollion traveled to Egypt and removed the shroud which had covered ancient Egyptian language and history for so long.

At first glance, a scribbled-on slab of black basalt has little in common with brain research. However, one of the major approaches to neural science—deciphering neural code from sensory input—is essentially the same process linguists used with the Rosetta Stone. Simply speaking, as long as there is a sensory input that changes neural firing, there is the potential to decipher that firing. For vision, this could be a white screen with a black vertical bar, for hearing, a “bah bah” as opposed to a “gah gah” sound, for touch, a tap on the finger, and so on. Although the technical side is quite complicated, it is at its core a process of translation.

Over the past hundred years, science has been able to discover a lot about the brain and how it functions. It’s no small wonder that some of the greatest advances in our understanding have been in the area of vision, where it’s relatively easy to control experiments in order for the subject to see only what the researcher is looking to study. If the picture being projected onto the retina is known, then adding, removing or changing the picture in a systematic way can illuminate how and where in the brain neurons change their firing patterns.

The problem is, many of the things we are most interested in—consciousness, problem-solving, emotion, episodic memory, even adding or subtracting—are intangible states or mechanisms of the mind. These are things that happen inside a creature’s head, and there are not necessarily any outward signs that anything is occurring.

For instance, even figuring out the mood of a person is a precarious undertaking. Take something like happiness. Someone can say they’re happy, but what are they feeling when they say they’re happy? How about an animal’s emotional state? There is no sure way to objectively know what any creature is thinking or feeling; it’s even impossible to know that other people are conscious. This makes it significantly challenging to find an inroad into the biological basis of some of the biggest questions about ourselves.

Brain research is complicated by this factor, but that doesn’t mean people haven’t been trying to figure it out anyway. A lot of psychology and neuroscience experiments are actually designed to discover neural and behavioral signs of a mental state, so we can make some significant progress in these areas. I would like to focus on one area in which I think we are about to put the biological basis of two separate mental phenomena.

These abstract mental functions are, I think, well defined in terms of neural firing. By well defined, I mean that neuroscientists have known about them for decades and done thousands of experiments to both directly and indirectly confirm the correlation between the biology and the psychological construct.

The first concept, spatial awareness, has found a correlate in place cells, which are located throughout the hippocampus. The second is the reward prediction signal, produced by the dopaminergic neurons of the midbrain.

In upcoming posts, I’ll summarize the functioning of these two systems, describe a paper that asks if they could be integrated, and discuss why I think it would be an exciting development.


Rosetta Stone Sites:

BBC - -

One of my paragraphs is a summary/paraphrase of the bottom of this site -

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