Strokes Stop Essential Brain Crosstalk

ST. LOUIS, March 14 -- Spatial neglect -- a common attention-deficit sequel to stroke -- appears to be caused by a lack of communication between two regions of the brain, according to researchers here.

The finding contradicts the traditional explanation that spatial neglect is caused by damage to a specific brain region, said Maurizio Corbetta, M.D., of Washington University.

Instead, magnetic resonance imaging showed that patients with neglect -- in which patients have difficulty paying attention to one side of their bodies or the visual field -- have disrupted connections between dorsal and ventral frontoparietal attention networks, reported Dr. Corbetta and colleagues in the March 15 issue of Neuron.

"For more than a century, we have linked neurological deficits and their recovery to the damage done to neurons directly affected by a stroke or other injury," Dr. Corbetta said in a statement.

"However, we are learning that a lesion in one part of the brain can impair the function of brain regions not directly harmed by the lesion," he said.

The finding may be useful to guide the clinical approach to patients with spatial neglect, he said.

The dorsal attention network controls the allocation of attention outside the body, while the ventral network is essential for finding targets and re-allocating attention to unexpected events.

In stroke patients with neglect, the researchers said, the ventral network is often structurally damaged, but the dorsal network is not.

For this study, the researchers used MRI to establish the functional connections between the two regions in healthy volunteers, and then conducted a longitudinal case-control study of 11 patients with right frontoparietal stroke and spatial neglect compared with 12 healthy controls.

Patients were scanned within a month of their stroke and again six months later as they performed a task in which they had to detect and respond to an asterisk appearing on a screen.

The researchers assessed three types of behavioral deficit:

• Increased misses and slowed reaction times across both visual fields, compared to controls.
• A similar comparison but for misses and reaction times in the spatial region opposite from the side of the stroke.
• How well volunteers disengaged their attention from the good visual field and reoriented it to the other field - the "disengagement deficit."

Patients had significantly more misses than controls, both at the acute and chronic stage (P=0.0002 and P=0.01, respectively.) They were also particularly impaired in the left visual field.

Patients had a significantly greater disengagement deficit compared to controls, but at the acute stage, hit rates tended to be lower (P=0.06) while reaction times were not significantly different. The pattern was reversed six months later, with the hit rates not significantly different, but reaction times significantly lower (P=0.05).

MRI scanning showed that communication between the dorsal and the ventral networks was disrupted, as was communication within regions of the dorsal area, the researchers said.

Specifically, the communication between the anterior and posterior intraparietal sulcus in the dorsal network was impaired, Dr. Corbetta and colleagues said, and the degree of impairment was significantly associated with the degree of disengagement deficit (P<0.05). The other deficits were not significantly associated with this impairment, but showed trends in the same direction.

The researchers noted that a patient with severe damage to the intraparietal sulcus - but no disruption of communication between the ventral and dorsal networks - showed no evidence of spatial neglect.

The research provided more evidence that intact functional communication across brain regions is "critical for normal brain function," the researchers concluded.