This project investigates the neural mechanisms that subserve the monkey's ability to detect innocuous cutaneous stimuli (air puffs) delivered to the face. The magnitude of sensations produced by small increases in air puff stimuli was studied with use of a reaction time paradigm. The monkey initiated a trial by pressing an illuminated button. Subsequently air puff stimuli (AP1) of identical intensity were delivered to the face at the rate of one per second. After a variable time period between 4 and 10 seconds, an air puff of higher intensity (AP2) was presented. The subject was required to release the button as soon as the larger air puff stimulus was detected. Detection latency was defined as the time interval between the onset of the large air puff and the release of the button. The monkey's detection latencies to stimuli presented on the face were dependent on the intensity of the AP2. The psychophysical functions obtained from the monkey's face were monotonically related to the intensity of AP2. As the intensity of AP2 increased, the monkey's detection latencies shortened. Neuronal recordings were made from the medullary dorsal horn (MDH) as the monkey performed the psychophysical task. Responses produced by air puff stimuli were examined in low threshold mechanosensitive (LTM) and wide-dynamic-range (WDR) neurons. A subpopulation of WDR neurons was found that encoded the intensity of AP2 stimuli. In addition, a significant correlation was found between the peak neuronal discharge and the monkeys' detection speeds to air puff stimuli for a subpopulation of WDR neurons. Similarly, LTM neurons also encoded the intensity of AP2 stimuli and the magnitude of their discharge was correlated with the monkeys' detection speed. We concluded that the discharge of a subpopulation of WDR and LTM neurons can account for the monkeys' ability to detect innocuous air puff stimulation.
