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What the Claustrum Does—How One Makes Up One’s Mind

By: , Posted on: August 26, 2014

The Claustrum
Scroll down for two chapters from the book!

The claustrum consists of a thin yet broad sheet of neurons buried in the depths of the brain. Until recently its function has been obscure. Because it is directly connected to nearly every other region of the brain – especially the cortex – Francis Crick and Christof Koch suggested a decade ago that it might have something to do with consciousness. The brain consists of a large number of small machines that do their own computations, whereas consciousness is a single entity whereby we access seeing, hearing, touch, smell, feelings, emotions, thoughts and make decisions, in order that coherent trains of thought and behaviors emerge. So perhaps the claustrum gets it all together and acts, as Crick and Koch suggested, as the conductor of the brain’s orchestra.

Recently, my colleagues (Smythies and Ramachandran) and I have suggested that the claustrum operates by strengthening the synchronized gamma frequency oscillations in the cortex that play a key role in coordinating the brain’s input and output. For example, two different sensory inputs will activate and set-up synchronized oscillations in two particular zones within the claustrum. These will be subject to further modulation by saliency mechanisms that signal the importance (i.e., significance and reward value) of what is going on. These two groups of cortico-claustro-cortical oscillations then compete on a “winner-takes-all” basis. The winner gets to activate the motor cortex (in essence, to “make it so!”) and a particular behavior results.

Two recent experiments support this hypothesis. In one, a toxin selective for the claustrum was given to rats which effectively eliminated it, and their behavior in a radial maze was observed. In this test the rat is placed on a central platform from which eight tunnels branch-off. An otherwise normal rat will rapidly explore each tunnel in turn, sniffing, watching and listening every step of the way. The lesioned or “aclaustral” rat sits dithering on the central platform with sporadic short runs limited to the entrance of a given tunnel. It appears unable to make up its mind. In the second test, a human patient during a work-up for their intractable epilepsy underwent electrical stimulation of various brain regions via implanted electrodes for mapping purposes.  When the left claustrum was stimulated, this resulted in an immediate complete loss of conscious awareness and movement. The patient became immobile with a fixed staring gaze and failed to respond to stimuli. As soon as the current was switched-off the patient returned to normal consciousness with complete amnesia regarding the episode.

Thus we suggest that the claustrum provides the mechanism in which conscious sensations are integrated and by which conscious decisions are formulated and executed.

About the Book

The Claustrum is the first book to explore the cognitive and clinical implications of the claustrum’s functionality. Published in January 2014, this book brings together leading experts from the varied disciplines of neuroscience, providing a state-of-the-art presentation of what is currently known about the claustrum, promising lines of current research, and projects of new lines of investigation on the horizon.

Here are two chapters from The Claustrum for you to read. Let us know what you think in the comments below!

Chapter 8: Delayed Development of the Claustrum in Autism

Download (PDF, 826KB)

Chapter 11: The Claustrum and Alzheimer’s Disease

Download (PDF, 1.04MB)

 

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