25 November 2009

Consciousness: Big brains not necessary

by Kate Melville

A bigger brain doesn't mean more intelligence, say biologists at the University of London who suggest that insects could be as intelligent as much bigger animals and that only a few thousand neurons may be necessary to generate consciousness.

Differences in brain size are extreme. A whale's brain can weigh up to 9 kg (with more than 200 billion nerve cells), and human brains vary between 1.25 kg and 1.45 kg (with an estimated 85 billion nerve cells). A honeybee's brain weighs only 1 milligram and contains fewer than a million nerve cells.

Past research has shown that insects are capable of intelligent behaviors that scientists previously thought were unique to larger animals. Honeybees, for example, can count, categorize similar objects, understand concepts like "same" and "different," and differentiate between shapes that are symmetrical and asymmetrical.

"We know that body size is the single best way to predict an animal's brain size," explains researcher Lars Chittka in the journal Current Biology. "However, contrary to popular belief, we can't say that brain size predicts their capacity for intelligent behavior. Animals with bigger brains are not necessarily more intelligent."

Research suggests that bigger animals may need bigger brains simply because there is more to control - for example they need to move bigger muscles and therefore need more and bigger nerves to move them. The size increase allows the brain to function in greater detail, finer resolution, higher sensitivity or greater precision: in other words, more of the same.

"In bigger brains we often don't find more complexity, just an endless repetition of the same neural circuits over and over. This might add detail to remembered images or sounds, but not add any degree of complexity. To use a computer analogy, bigger brains might in many cases be bigger hard drives, not necessarily better processors," Chittka suggested.

Chittka posits that much of what we would class as advanced thinking can actually be done with very limited neuron numbers. He claims that computer modeling shows that consciousness can be generated with very small neural circuits, which could in theory easily fit into an insect brain. In fact, these models suggest that counting could be achieved with only a few hundred nerve cells and only a few thousand could be enough to generate consciousness.

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Source: University of London