Faculty Bibliography

Goal-directed behavior is characterized by flexible stimulus-action mappings. The lateral intraparietal area (area LIP) contains a representation of extra-personal space that is used to guide goal-directed behavior. To examine further how area LIP contributes to these flexible stimulus-action mappings, we recorded LIP activity while rhesus monkeys participated in two different cueing tasks. In the first task, the color of a central light indicated the location of a monkey's saccadic endpoint in the absence of any other visual stimuli. In the second task, the color of a central light indicated which of two visual targets was the saccadic goal. In both tasks, LIP activity was modulated by these non-spatial cues. These observations further suggest a role for area LIP in mediating endogenous associations that link stimuli with actions.

In various aspects of linguistic analysis and human cognition, some forms of observed variation are ignored in the service of handling more abstract categories. In the absence of training, rhesus discriminate between different types of vocalizations based on the information conveyed as opposed to their acoustic morphologies. We hypothesized that neurons in the ventrolateral prefrontal cortex (vPFC), an area involved in auditory-object processing, might be involved in this spontaneous categorization. To test this hypothesis, we recorded vPFC activity while rhesus listened to vocalizations conveying information about food and non-food events. Results showed between, but not within category discrimination. That is, vPFC neurons discriminated between vocalizations associated with food versus non-food events but not within the class of food calls associated with differences in quality. These results indicate that the vPFC plays a significant role in spontaneously processing abstract categorical information.

Goal-directed behavior can be characterized as a dynamic link between a sensory stimulus and a motor act. Neural correlates of many of the intermediate events of goal-directed behavior are found in the posterior parietal cortex. Although the parietal cortex's role in guiding visual behaviors has received considerable attention, relatively little is known about its role in mediating auditory behaviors. Here, the authors review recent studies that have focused on how neurons in the lateral intraparietal area (area LIP) differentially process auditory and visual stimuli. These studies suggest that area LIP contains a modality-dependent representation that is highly dependent on behavioral context.

Though each foot is controlled primarily by the contralateral hemisphere, the event-related brain potentials preceding an overt foot movement are largest over the ipsilateral side of the head. Because such "paradoxical lateralization" results from the spatial organization of the motor homunculus, it can provide a sign of motor-cortex activation. We report paradoxical lateralization in the potentials accompanying imagined foot movements, thereby demonstrating a contribution of cortical areas directly involved in movement execution.

Spatial and nonspatial auditory processing is hypothesized to occur in parallel dorsal and ventral pathways, respectively. In this study, we tested the spatial and nonspatial sensitivity of auditory neurons in the ventrolateral prefrontal cortex (vPFC), a cortical area in the hypothetical nonspatial pathway. We found that vPFC neurons were modulated significantly by both the spatial and nonspatial attributes of an auditory stimulus. When comparing these responses with those in anterolateral belt region of the auditory cortex, which is hypothesized to be specialized for processing the nonspatial attributes of auditory stimuli, we found that the nonspatial sensitivity of vPFC neurons was poorer, whereas the spatial selectivity was better than anterolateral neurons. Also, the spatial and nonspatial sensitivity of vPFC neurons was comparable with that seen in the lateral intraparietal area, a cortical area that is a part of the dorsal pathway. These data suggest that substantial spatial and nonspatial processing occurs in both the dorsal and ventral pathways.