In an earlier post (“Correlated Response Fluctuations Between Cortical Neurons Rare“) I discussed a research paper that challenged a large body of literature that claimed a high degree of synchrony or correlated responses between brain cells (neurons) in the cerebral cortex. They concluded that either 1) “adjacent neurons share only a few percent of their inputs” or 2) “their activity is actively decorrelated.”
In the same issue of Science a paper by different team of researchers addresses the question of active decorrelation of signals (action potentials) in the cerebral cortex. (“The Asynchronous State in Cortical Circuits” was published January 29, 2010 in Science.)
These researchers used a combination of theory, computer modeling, and actual recordings from rat somatosensory and auditory cerebral cortex to address the relationship between correlations and shared input.
They found that neurons displayed a high degree of correlated (synchronous) activity if the neurons receiving shared input were either all excitatory or all inhibitory. However, neural circuits in the cerebral cortex contain both types of neurons. When both excitatory and inhibitory neurons were driven by common excitatory input their spiking activity was actively decorrelated.
The authors provide a plausible mechanism for the active decorrelation. They explain that asynchronous activity persists in the presence of shared input because the two types of neurons (inhibitory and excitatory) spontaneously track one another with a time lag that is inversely proportional to the number of neurons in the cortical circuit.
The sum of the evidence suggests that careful recording techniques will show more asynchrony (less synchrony or correlation) between signals in nearby cortical neurons than previously thought. Circuit dynamics will assure a great deal of asynchrony even in the presence of significant common input. These findings suggest that asynchronous signals predominate in the cerebral cortex and, therefore, efficient signal processing (most would say information processing) is possible.
Other related blog posts:
Correlated Response Fluctuations Between Cortical Neurons Rare
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