Ricerc@Sapienza

Studies with event-related potentials have highlighted deficits in the early phases of orienting to left visual targets in right-brain-damaged patients with left spatial neglect (N). However, brain responses associated with preparatory orienting of attention, with target novelty and with the detection of a match/mismatch between expected and actual targets (contextual updating), have not been explored in N. Here in a study in healthy humans and brain-damaged patients of both sexes we demonstrate that frontal activity that reflects supramodal mechanisms of atten- tional orienting (Anterior Directing Attention Negativity, ADAN) is entirely spared in N. In contrast, posterior responses that mark the early phases of cued orienting (Early Directing Attention Negativity, EDAN) and the setting up of sensory facilitation over the visual cortex (Late Directing Attention Positivity, LDAP) are suppressed in N. This uncoupling is associated with damage of parietal-frontal white matter. N also exhibit exaggerated novelty reaction to targets in the right side of space and reduced novelty reaction for those in the left side (P3a) together with impaired contextual updating (P3b) in the left space. Finally, we highlight a drop in the amplitude and latency of the P1 that over the left hemisphere signals the early blocking of sensory processing in the right space when targets occur in the left one: this identifies a new electro- physiological marker of the rightward attentional bias in N. The heterogeneous effects and spatial biases produced by localized brain damage on the different phases of attentional processing indicate relevant functional independence among their underlying neural mechanisms and improve the understanding of the spatial neglect syndrome.