28 March 2007

Neuronal Behavior Confounds Expectations

by Kate Melville

The idea that the electrical signal patterns generated by neurons represent the encoding of different types of cognitive information appears to be wrong, according to scientists at the Weizmann Institute. Their research, appearing in the journal Neuron, showed that the communication signals between neurons, as measured by the experimenters, were indistinguishable from random neuronal firings. Weizmann's Dr. Ilan Lampl said the results called into question one of the key tenets used to explain how the brain works.

It had been believed that the central nervous system relied on specific patterns in neuronal electrical signals to encode different types of cognitive information. For example, in comparing objects like a table and a chair, the brain would discriminate between the different objects because each object would generate a distinct sequence of patterns within the neural system that the brain then interprets. Reinforcement of relationships between different objects and their associated signals occurred upon repeated presentation of that object, so that its pattern would be reproduced in a precise manner.

Experimental evidence supporting the pattern theory had been found in the past, but when Lampl recorded the activity of neurons in the cortex of anaesthetized rats and analyzed the data, he found no difference in the number of patterns produced or the time it takes for various patterns to repeat themselves. In fact, Lampl says, the recorded data was no different to data that was randomized.

In his conclusion, Lampl drops a bombshell by suggesting that the patterns observed could not be due to the deterministically controlled mechanisms posited in the pattern theory, but occurred purely by chance. "Since the 1980s, many neuroscientists believed they possessed the key for finally beginning to understand the workings of the brain. But we have provided strong evidence to suggest that the brain may not encode information using precise patterns of activity," Lampl concluded.

Related articles:
A Computer In A Single Neuron
Neurons Mix Digital And Analog Functionality
Chaotic Neurons Enhance Brain's Processing

Source: American Committee for the Weizmann Institute of Science