Brain mapping of attention and neglect after stroke

The psychology of attention: “Selective attention” broadly refers to a set of mechanisms that allow people to perceive and respond to events that are behaviorally relevant. Selection is important to maintain behavioral coherence in the face of multiple stimuli and thoughts that may call for contradictory actions, and to address the limited processing capacity of the brain. Spatial attention, the most commonly investigated form of attention, is defined as the ability to select information from one or multiple locations in the environment. Selection is based on internal knowledge (top-down or goal-driven) as well as salient sensory information (bottom-up or stimulus-driven), which may be integrated in a common “saliency” map. Selection of environmental stimuli amplifies the neural responses to those stimuli and suppresses neural responses to stimuli in unattended regions. Hence lesions in the brain can disrupt selective processing of stimuli by affecting associative regions that direct spatial attention and/or by affecting sensory regions in which selection modulates neural activity. Once sensory stimuli are selected, they must be linked with the appropriate motor action (e.g. looking or reaching). As multiple motor responses are potentially available, the process of “stimulus–response mapping” is also selective. Visual stimuli are coded in visual cortex based on their retinal location, while movements are coded in motor cortex in directional coordinates, such as centered on the arm. This is the well-known problem of frames of reference in sensory-to-motor transformations.