Unlike simple reactive saccades, directing the eyes to a target most appropriate in a given situation requires substantial cognitive processing. Sensory cues present in the environment need to be evaluated in terms of symbolic meanings associated with them. These then have to be translated so that the saccade goal is chosen among alternatives available at the moment. Identifying neural underpinnings of these complex processes is essential for advancing our knowledge of how the brain makes choices and how cognitive information is utilized in oculomotor behavior. Equally important, this knowledge will provide a better understanding such abnormal behaviors as oculomotor apraxia in which reflexive visually-guided saccades are preserved while saccades prompted by verbal commands are impaired and frontal lobe dysfunction in which the inability to make choice decisions is an important feature. Both the latter disorders are of public health concern. In this project, we will collect neural data while saccades are generated as a choice response based on the pre-trained associations between color and spatial location: Animals will attend to visual stimuli of different colors delivered at the fovea and respond with an eye movement to a unique location associated with each color. Experiments are designed to achieve the following specific aims: 1) To characterize neural signals in the superior colliculus (SC) and the cortical frontal eye fields (FEF) related to saccadic choice responses by recording from single neurons. Whether these signals are indeed necessary for saccadic choice responses will be determined by making reversible chemical lesions in the 2 structures. More specifically, by selectively inactivating the foveal portion of the FEF, we will test the hypothesis that the FEF is the place where sensory cue information given at the fovea is translated into the activation of neurons representing a target in the periphery. 2) To identify the source of cue-driven signals observed in the caudal SC. Given the fact that the FEF has abundant connections to this region, we will test the hypothesis that the FEF is the source of cognitive signals recorded in the SC. Reversible lesions will be made in FEF as a SC neuron with cue-driven signals is being recorded. Changes in the activation of the SC during choice response would support this hypothesis. 3) To examine the temporal relationship between the activities in pairs of FEF cells that code for the target location and others that code for non-target locations, while a choice decision is being made. This data will help to differentiate between 2 current models that attempt to explain the neural mechanisms underlying choice response. ? ? ?
