The functional properties of neurons in the superficial layers of the somatosensory cortex have received considerably less attention than those occupying the middle or deeper layers. A recent investigation focusing on the upper layers of the first somatosensory area (S-I) in cat described a class of neurons that had previously been ignored or overlooked. The proposed project will 1) examine in greater detail than has been accomplished to date, the response properties of superficial S-I neurons of the cat, and 2) determine which spinal tracts provide the various types of input to these neurons. In the first phase of the project, I will test the responsiveness of superficial S-I neurons to a wide battery of cutaneous stimuli -- mechanical and thermal, innocuous and noxious -- using both extracellular and intracellular recording techniques. Ethical considerations require that noxious stimuli only be used in the presence of a general anesthetic. For scientific validity, the agent used to produce anesthesia must not greatly alter the responsivity of the neurons under study. Thus, an initial step in the first phase of this project will be to identify anesthetic agents which would allow the study of a qualitatively unaltered neuronal population in the superficial S-I cortex. The second phase of this project involves determining the relative contributions of the various spinal tracts to the behavior of superficial S-I neurons. If an anesthetic is found that will allow investigation of the functional properties of the upper layer S-I neurons, the influences of the different input pathways will be assessed by electrically stimulating the spinal tracts while recording the responses of superficial S-I neurons. If such an anesthetic is not found, electrophysiological recordings will be made in the S-I cortex after the cat has recovered from a spinal tract lesion. Either method can indicate the spinal pathways providing input to the various types of superficial S-I neurons, and reveal the relative contributions of each pathway. The data gathered in this project could complement neuroanatomical data which indicate that the superficial layers of the somatosensory cortex have different afferent and efferent connectivity than the middle or deeper layers, as well as the more recent histochemical data showing a preferential distribution of certain neuropeptides in the superficial layers of the cerebral cortex. Elucidation of the functional properties of these neurons will extend current views of the S-I somatosensory cerebral cortex as an initial stage in the processing of inputs leading to somatic sensations.
