Attentional influences on noxious and innocuous cutaneous heat detection in humans and monkeys

This study examines whether selective attention can influence sensory-discriminative aspects of nociception in humans and monkeys trained to detect innocuous and noxious thermal stimuli. Human subjects had two contact thermodes positioned bilaterally above the upper lip. Upon trial initiation both thermodes heated to either 39 degrees C, an innocuous warm temperature, or 45 degrees C, a slightly noxious temperature. After 4 to 9 sec, the temperature of one thermode increased an additional step of less than 1 degree C. Subjects released a button when they detected this second temperature increase (T2). Three types of trials were presented in order to assess the effects of spatially selective attention on thermal detection. On 40% of the trials a light correctly signaled the location of the thermode on which T2 would occur. On 10% of trials a light incorrectly signaled the location of T2. No signal was presented on the remaining trials. From the 45 degrees C base line, detection latencies were shortest in the correct signal condition, longest in the incorrect signal condition, and intermediate in the unsignaled condition. The percent of undetected T2s was greatest in the incorrect signal condition and least in the correct signal condition. From the 39 degree C base line, the detection latency in the incorrect signal condition was greater than in the unsignaled condition, but the latter latency was not different from the correct signal latency. In addition, the percent of undetected T2s was the same on all three types of trials.(ABSTRACT TRUNCATED AT 250 WORDS)