Grant: Operating Grant

Attention can be defined as the filtering and modulation of information processing in the brain. It protects sensory systems from signal overload determining the organism's performance in many tasks. Disorders of attention affect 4-8% of school age children and are a main cause of learning disabilities. The neural mechanisms underlying attention are poorly understood, hindering our search for the cause and treatment of attentional disorders. Over the last years, we have recorded the activity of single neurons in extrastriate visual cortex of macaques. We have found that when two stimuli fall inside a cell's receptive field instructing the animal to attend to one of them causes the cell's response to selectively represent the features of that stimulus, as if the receptive field contracted around it excluding the distracter. This filtering effect became weaker as the contrast of attended and distracter stimuli increased. In the experiments proposed here we will test the hypothesis that attentional filtering by extrastriate neurons results from a modulation in the activity of different populations of striate (V1) units with small receptive fields including attended and unattended stimuli and projecting toward a recipient extrastriate cell. We will further test whether this modulation occurs through competitive interactions between populations of V1 units with different selectivities for stimulus features and receptive field locations, and whether such interactions are triggered by changes in activation strength within one population. We will finally test whether prefrontal neurons encoding the stimuli spatial location competitively interact to produce trigger signals during attention. We will record the activity of neurons within a given brain area in macaques performing attentional tasks and measure changes in the units' activation as well as interactions between them. Our results will provide new and important insights into the brain mechanisms underlying attention.