Neurophysiology of the Central Nervous System
The broad aim of my research is to understand the neural basis for tactile perception. Specifically, how are spatial forms, textures, complex vibrations and three dimensional objects (stereognosis) represented and transformed in the neural pathways leading to tactile perception. Presently, my research is aimed at determining the neural mechanisms underlying 3-D form perception and determining the specificity and role that selective attention plays in the somatosensory system. Three dimensional object recognition must involve the integration of cutaneous information from the skin from different digits on the same and opposite hands and position information from joint and proprioceptive sensors. Studies on tactile attention are based on two different hypothesis. One is that attention is broadly tuned and nonspecific. If this is the case, then attention may function as a kind of neural "spotlight" that simply directs the animals efforts within the somatosensory system from one location on the body to another. The most likely role that attention plays under these circumstances is to modify the gain of neurons and to enhance the responses of neurons that fall within the "spotlight" and suppress the responses of other neurons. Another more likely possibility is that attention is highly specific and functions to tailor the neural responses in a way that allows the animal to achieve a specific perceptual goal. For example, if the animal is performing an orientation discrimination task then only those neurons that are orientation selective will show attention modulated responses and other neurons that lie near those neurons but are not critical for performing the task will not be affected. To test these alternative hypothesis and to understand the role that attention plays in tactile processing in primary (SI) and secondary (SII) cortex, we are presently performing experiments on monkeys trained to perform a variety of attention tasks. The first series of studies employ animals trained to switch their focus of attention back and forth between different sensory systems (vision, touch and audition), between different skin sites (digits on the same or opposite hands), between different submodalities at a single skin site (form, and vibration) and between different sensory capacities subserved by a single submodality (form and texture). The somatosensory stimuli employed in these studies vary in form, texture or vibratory frequency and are repeatedly presented to multiple digits on the same or opposite hand while the animal performs a discrimination or detection task on the cued digit. In the second series of experiments animals are trained to discriminate the three dimensional shape of objects that are passively presented or actively grasped by the animal.