Suppression of Extinction with TMS in Humans: From Healthy Controls to Patients

Oliveri, Massimiliano; Caltagirone, Carlo · 2006 · Crossref

DOI: 10.1155/2006/393924

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Summary

This review article examines the application of transcranial magnetic stimulation (TMS) in studying spatial attention and sensory extinction, a condition where a sensory stimulus fails to reach consciousness when presented simultaneously with a stimulus on the opposite side. The authors focus on how TMS can disrupt cortical activity in healthy controls to create "virtual lesions" and modulate cortical excitability in patients with unilateral brain damage to alleviate extinction deficits. The research is motivated by the hypothesis that sensory extinction results from a pathological imbalance in interhemispheric competition, specifically the disinhibition of the intact hemisphere following damage to the contralateral side. The review synthesizes findings from studies utilizing both single-pulse and paired-pulse TMS protocols. In healthy subjects, single-pulse TMS applied to parietal and frontal cortices transiently disrupted the detection of contralateral tactile and visual stimuli, effectively reproducing extinction. Paired-pulse TMS, which involves a conditioning stimulus followed by a test stimulus, was used to modulate cortical excitability based on the inter-stimulus interval (ISI). Short ISIs (1–5 ms) induced inhibition via GABAergic interneurons, while longer ISIs (8–15 ms) induced facilitation via glutamatergic circuits. In patients with right brain damage (RBD), TMS was applied to the unaffected left hemisphere to test whether disrupting its activity could restore attention to the contralesional side. Key findings demonstrate that single-pulse TMS of the left frontal or parietal cortex in RBD patients significantly reduced contralesional tactile extinction rates during bimanual stimulation, supporting the hemispheric imbalance model. Paired-pulse TMS yielded more specific results: inhibitory protocols (1 ms ISI) applied to the left parietal cortex improved extinction more effectively than single-pulse TMS, whereas facilitatory protocols (10 ms ISI) reversed these benefits. Furthermore, chronometric analysis revealed that parietal cortex contributions to attention occur earlier (20–30 ms post-stimulus) than frontal contributions (40 ms). Studies also indicated that RBD patients exhibit altered intracortical inhibition patterns in the unaffected hemisphere compared to healthy controls, particularly during bimanual tasks. The significance of these findings lies in establishing TMS as a dual-purpose tool for both cognitive neuroscience research and clinical intervention. By providing high temporal resolution, TMS allows for the precise mapping of neural circuits involved in spatial attention. Clinically, the ability to transiently suppress the hyperactive intact hemisphere offers a potential mechanism for rehabilitating sensory extinction deficits. The authors conclude that modulating cortical excitability through TMS could support the treatment of neurological disorders involving attentional biases, bridging the gap between understanding neural mechanisms and therapeutic application.

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• multisensory crossmodal