After providing all the funding for The Brain from Top to Bottom for over 10 years, the CIHR Institute of Neurosciences, Mental Health and Addiction informed us that because of budget cuts, they were going to be forced to stop sponsoring us as of March 31st, 2013.

We have approached a number of organizations, all of which have recognized the value of our work. But we have not managed to find the funding we need. We must therefore ask our readers for donations so that we can continue updating and adding new content to The Brain from Top to Bottom web site and blog.

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Bruno Dubuc, Patrick Robert, Denis Paquet, and Al Daigen

Monday, 20 August 2012
Do we synchronize our neurons to synchronize our thoughts?

oldradioJust as the pendulum of a clock oscillates to keep the time, the human brain’s networks of neurons oscillate together to help us encode certain memories. Or at least that is one of the functions attributed to these neuronal oscillations, which have been largely preserved throughout the history of evolution in the animal kingdom. Researchers are taking a growing interest in these oscillations, because if they do let the brain encode information in terms of time, they represent a valuable tool in addition to the mechanisms by which the brain generates its many spatial representations of the body and the world outside it.

For example, many data show that when a network of neurons emits action potentials at a certain frequency, and then synchronizes its frequency with that of other neuronal networks over time, all these networks temporarily bind to one another. In one case, the result of this transient binding of neuronal assemblies might be to influence the perception of certain sensory stimuli. In another, the assemblies might be working in parallel to represent the various attributes of an object or to form a mental image of it. These spontaneous oscillations observed in neuronal networks arise from a dynamic interaction between the intrinsic properties of the neurons’ cell membranes and the architecture of the neural circuits involved (see this other post).

Neuroscientist Laura Colgin used such neuronal circuits in the rat hippocampus to demonstrate that it used two different oscillation frequencies to select two different kinds of information alternately: information on the rat’s current position, associated with activity in the entorhinal cortex, and information on the storage of this spatial information, associated with activity in hippocampal subfield CA3.

Colgin’s study, published in the November 2009 edition of the journal Nature, showed that the fast gamma oscillations (65-140 Hz) observed in area CA1 of the hippocampus were synchronized with the same kind of fast gamma oscillations in the entorhinal cortex, while the slow gamma oscillations (25-50 Hz) in CA1 were synchronized with the slow gamma oscillations in hippocampal subfield CA3.

Colgin concluded that these observed instances of synchronization support the theory that the brain may use various frequencies of gamma oscillations to “tune in” various sources of information, somewhat the way a tuner is used to select various frequencies on the radio band. She said that the brain may use the slow gamma frequencies to tune in old memories, and the fast gamma frequencies (65-140 Hz) to tune in relevant information about what is happening right now.

If this “gamma frequency tuner” were indeed found to be a general mechanism by which the brain’s neuronal networks switch among different “channels” several times per second, that would be quite consistent with the way we perceive our thoughts to fluctuate so rapidly.

i_lien How the Brain Filters Out Distracting Thoughts to Focus On a Single Bit of Information
a_exp Frequency of gamma oscillations routes flow of information in the hippocampus
a_lien Neuronal Oscillations in Cortical Networks

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