People can find objects in a visual scene fast and effortlessly. It is thought that this may be accomplished by creating a map of the outside world that incorporates bottom-up sensory and top-down cognitive inputs—a priority map. Eye movements are made toward the location represented by the highest activity on the priority map. We hypothesized that the lateral intraparietal area (LIP) of posterior parietal cortex acts as such a map. To test this, we performed low current microstimulation on animals trained to perform a foraging task and asked whether we could bias the animals to make a saccade to a particular stimulus, by creating an artificial peak of activity at the location representing that stimulus on the map. We found that microstimulation slightly biased the animals to make saccades to visual stimuli at the stimulated location, without actively generating saccades. The magnitude of this effect was small, but it appeared to be similar for all visual stimuli. We interpret these results to mean that microstimulation slightly biased saccade goal selection to the object represented at the stimulated location in LIP.
Top-Down and Bottom-Up Attention to Memory Are Dissociated in Posterior Parietal Cortex: Neuroimagingand and Neuropsychological Evidence