The Hemispheric Distribution of α-Band EEG Activity During Orienting of Attention in Patients with Reduced Awareness of the Left Side of Space (Spatial Neglect).

EEG studies in healthy humans have highlighted that alpha-band activity is relatively reduced over the occipital-parietal areas of the hemisphere contralateral to the direction of spatial attention. Here, we investigated the hemispheric distribution of alpha during orienting of attention in male and female right brain-damaged patients with left spatial neglect. Temporal spectral evolution showed that in patients with neglect alpha oscillations over the damaged hemisphere were pathologically enhanced both during the baseline-fixation period that preceded cued orienting (capturing tonic alpha changes) and during orienting with leftward, rightward, or neutral-bilateral spatial cues (reflecting phasic alpha changes). Patients without neglect showed a similar though significantly less enhanced hemispheric asymmetry. Healthy control subjects displayed a conventional decrease of alpha activity over the hemisphere contralateral to the direction of orienting. In right-brain-damaged patients, neglect severity in the line bisection task was significantly correlated both with tonic alpha asymmetry during the baseline period and with phasic asymmetries during orienting of attention with neutral-bilateral and leftward cues. Asymmetries with neutral-bilateral and leftward cues were correlated with lesion of white matter tracts linking frontal with parietal-occipital areas. These findings show that disruption of rostrocaudal white matter connectivity in the right hemisphere interferes with the maintenance of optimal baseline tonic levels of alpha and the phasic modulation of alpha activity during shifts of attention. The hemispheric distribution of alpha activity can be used as a diagnostic tool for acquired pathological biases of spatial attention due to unilateral brain damage.