Contralesional rTMS relieves visual extinction in chronic stroke

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neurology

Background:

• Right parietal lobe lesions often cause severe attention deficits, particularly in the left visual field, a condition known as visual extinction.
• This deficit may stem from hyperactivity in the undamaged left hemisphere, leading to excessive inhibition of the damaged right hemisphere.
• Previous research lacked direct physiological evidence for this inter-hemispheric inhibition hypothesis.

Purpose of the Study:

• To test the hypothesis that reducing left hemisphere hyperactivity can alleviate inter-hemispheric inhibition and improve attention in patients with right parietal lesions.
• To investigate the potential of repetitive transcranial magnetic stimulation (rTMS) as a therapeutic intervention for post-stroke attentional deficits.

Main Methods:

• Six patients with visual extinction due to right parietal stroke participated in a counterbalanced study.
• Participants received either low-frequency rTMS over the left parietal lobe or sham stimulation in separate sessions.
• Performance was assessed using an attentional tracking task focusing on visual fields.

Main Results:

• Patients showed significant improvement in attentional tracking in the contralesional (left) visual field immediately after rTMS targeting the left hemisphere.
• No significant improvement was observed after sham stimulation.
• Performance in the ipsilesional (right) visual field remained unchanged in both conditions.

Conclusions:

• rTMS applied to the healthy left hemisphere can temporarily reduce its hyperactivity.
• This reduction appears to alleviate excessive cross-hemispheric inhibition, thereby disinhibiting the damaged right hemisphere.
• These findings suggest a potential therapeutic strategy for cognitive recovery in patients with right parietal lesions and associated attentional deficits.