Thalamus waves

21/12/2008 by admin.

Here is more from that article in the New York Times about Rodolfo Llinas’ by Sandra Blakeslee (here). This part is about conditions that appear to involve the loss of thalamus driven brain waves.

“When the brain is awake, neurons in the cortex and thalamus oscillate at the same high frequency, called gamma…. .Such coherent activity allows you to see and hear, to be alert and able to think…But at day’s end, cells in the thalamus naturally enter a low-frequency oscillation… .You fall asleep. Your brain is still tapping out slow rhythms, but consciousness is suspended.

So if a small part of the thalamus gets permanently stuck at a low frequency, or part of the cortex fails to respond to the wake-up call, Dr. Llinás said, an abnormal rhythm is generated, a so-called thalamocortical dysrhythmia….a maintained, abnormal low frequency in a part of the brain can generate what is called an attractor. Think about a tornado. It’s just wind that is turning on itself. In doing so, it becomes a thing that, while made out of air, has a life of its own.

“A thalamocortical dysrhythmia also has a structure. It is a thing. And it leads to the symptoms seen in a wide variety of brain diseases.”

Dr. Llinás believes that these disrupted rhythms can be set off by a variety of causes — faulty genes, brain injury, chemical imbalance…. dysrhythmias can be treated with deep brain stimulation, drugs or tiny surgical lesions that return brain oscillations to normal, he said. The goal is to wake up parts of the brain that have fallen into low-frequency sleep mode.

In Parkinson’s, chemical changes send bits of the thalamus into a low-frequency mode. If the affected part of the thalamus connects to the brain’s primary motor center, a slow tremor, at four cycles per second, appears. The patients shake at the same frequency as the oscillating motor thalamus.

If the abnormal bit of thalamus connects to a region that plans movements, the patients cannot initiate movement.

And if the piece of thalamus is involved in making smooth movements, the patients experience increased muscle tone. They become rigid.

Dr. Llinás says a patient can experience several of these symptoms or only one, depending on the site of the abnormal rhythm. By the same token, he says, normal function can be restored by acting on the right spot.

Deep brain stimulation, in which slender electrodes are implanted directly into the cortex or thalamus, has been used in 40,000 patients around the world, mostly for movement disorders, and is now being tried for schizophrenia, epilepsy, Tourette’s syndrome, dystonia, chronic pain, depression, phantom pain and traumatic brain injury.”

The interesting thing here, for our concern with understanding consciousness, is that the thalamus appears to control the existence of consciousness. It may also control the focus and nature of the conscious experience.

Posted in thalamus | 1 Comment »