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The degree of functional connectivity seen in brain imaging studies during the resting state offers a window into the pathophysiology of neurologic disease, researchers said here at the 135th Annual Meeting of the American Neurological Association (ANA).

The strength and coherence of background cerebral activity appears to be a reliable biomarker for movement and behaviour deficits seen in patients who have had a stroke.

"These resting state networks are maintained even in deep anaesthesia," said Maurizio Corbetta MD, Washington University School of Medicine, St. Louis, Missouri, on September 12. "The strength of connectivity seen in these networks varies by the functional skills exhibited by the individual. Functional connectivity is a very good biomarker of activity."

New data presented over the past 5 to 10 years has redefined concepts of how the human brain is organised and operates, Dr. Corbetta noted. Neuroscience now recognises that the whole of the brain is far larger than the sum of its constituent neurons. Functional magnetic resonance imaging (fMRI) studies have shown that the brain is one of the most metabolically active organs in the body. More detailed studies have found that most of the energy used by the brain is devoted to internal signalling.

Signalling is not restricted to times and areas of active sensory input or motor output, Dr. Corbetta continued. About 90% of the cerebral cortex is active and signalling at all times, he explained. This steady state of background signalling, sometimes dismissed as background noise, has become recognised as resting state network, or RSN, activity.

"This RSN signal is resilient and independent of behavioural state," Dr. Corbetta continued. "You see it during wakefulness, anaesthesia, even during deep coma."

RSN signalling is not random, he continued. The strength of connectivity within the brain varies by a person's functional skills. Differences in cognitive and motor skills are reflected in these spontaneous RSNs. The more traffic a particular network has supported in the past, the more activity it shows during the resting state.

More importantly, Dr. Corbetta noted, it is not necessary to have active participation by the patient in order to measure RSN activity. Network activity can be assessed if the patient is too young to respond coherently, physically incapable of coherent response because of injury or disease, or if the patient is unconscious. That makes Functional magnetic resonance imaging (fMRI) particularly valuable as a diagnostic tool for stroke, multiple sclerosis, and other conditions that produce cerebral lesions.

Stroke inhibits RSN activity between the 2 hemispheres of the brain, he explained. The degree of RSN inhibition appears to correlate with behavioural deficits in both movement and attention, even in the absence of apparent structural damage. RSN measurement by Functional magnetic resonance imaging (fMRI) immediately after stroke shows systematic disruptions that reflect observed physical symptoms. Follow up fMRI at 37 weeks post stroke restoration of RSN activity that also reflect the current state of physical symptoms.

"We can obtain this kind of diagnostic data in the emergency room," Dr. Corbetta said. "Observed RSN connectivity is reflected in physical activity and predicts recovery."

Source: DG news