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Tracing broken wiring in stroke patients

March 15, 2007

Researchers have used a technique to trace the functional disruption in brain circuitry that causes stroke patients to show a lack of awareness or response to the side of the body opposite to the side of the stroke lesion in the brain. The researchers said their findings shed new light on the neurological details of this "spatial neglect." Their findings also demonstrate the value of the magnetic resonance imaging (MRI) technique for studying how disruption in brain circuitry produces behavioral symptoms.

Maurizio Corbetta and colleagues reported their findings in the March 15, 2007 issue of the journal Neuron, published by Cell Press.

The researchers used "functional connectivity" MRI (FC MRI) to examine connections between active regions of the brain. MRI is a widely used analytical technique, in which harmless radio waves and magnetic fields are used to map oxygen levels in brain regions. By performing FC MRI in patients with spatial neglect, the authors identified regions of the brain where there was a disruption of normal functional brain circuitry.

In their experiments, the researchers used FC MRI to study the brains of 11 stroke patients with neglect, both at one month and at more than six months after their strokes. While the patients' brains were being scanned, the researchers asked them to perform a simple task to determine their ability to perceive the left and right visual fields. Specifically, the patients were asked to indicate whether they could see an asterisk presented on the right or left side of a computer screen. As a control, the researchers also conducted similar tests on healthy volunteers.

The study revealed new details about how functional connectivity within and between different regions of the "attention networks" in the parietal cortex of the brain was disrupted in the brains of the stroke patients. The study also enabled new insights into how this disruption contributes to spatial neglect.

Particularly important was that the FC MRI studies showed that the lower the functional connectivity of these regions, the more impaired the patients were in perceiving the neglected region of their visual field, said the researchers.

Such findings, they commented, show that "FC MRI is a promising new tool for the investigation of brain-behavior relationships in patient populations. It makes no demands on the subject other than holding still and possibly maintaining fixation and therefore can be acquired even in patients that cannot perform a task"¦ This significantly widens the range of patients that can participate in functional brain-imaging protocols."

Cell Press