Hyperexcitability of parietal-motor functional connections in the intact left-hemisphere of patients with neglect

Giacomo Koch, Massimiliano Oliveri, Binith Cheeran, Diane Ruge, Emanuele Lo Gerfo, Silvia Salerno, Sara Torriero, Barbara Marconi, Francesco Mori, Jon Driver, John C. Rothwell, Carlo Caltagirone

Research output: Contribution to journalArticlepeer-review

Abstract

Hemispatial neglect is common after unilateral brain damage, particularly to perisylvian structures in the right-hemisphere (RH). In this disabling syndrome, behaviour and awareness are biased away from the contralesional side of space towards the ipsilesional side. Theoretical accounts of this in terms of hemispheric rivalry have speculated that the intact left-hemisphere (LH) may become hyper-excitable after a RH lesion, due to release of inhibition from the damaged hemisphere. We tested this directly using a novel twin-coil transcranial magnetic stimulation (TMS) approach to measure excitability within the intact LH of neglect patients. This involved applying a conditioning TMS pulse over left posterior parietal cortex (PPC), in order to test its effect on the amplitude of motor evoked potentials (MEPs) produced by a subsequent test pulse over left motor cortex (M1). Twelve RH stroke patients with neglect, an age-matched group of eight RH stroke patients without neglect, and 10 healthy controls were examined. We found that excitability of left PPC-M1 circuits was higher in neglect patients than the other groups, and related to the degree of neglect on clinical cancellation tests. A follow-up found that 1 Hz repetitive TMS over left PPC normalized this over-excitability, and also ameliorated visual neglect on an experimental measure with chimeric objects. Our results provide 'direct' evidence for pathological over-excitability of the LH in the neglect syndrome, as quantified by left PPC influences on left M1, with implications for possible treatment.

Original languageEnglish
Pages (from-to)3147-3155
Number of pages9
JournalBrain
Volume131
Issue number12
DOIs
Publication statusPublished - Dec 2008

Keywords

  • Connectivity
  • Cortical excitability
  • Neglect syndrome
  • Parietal cortex
  • rTMS
  • Transcranial magnetic stimulation

ASJC Scopus subject areas

  • Clinical Neurology

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