Effect of emotional state induced by expectation for pain on cortical neuronal activity in awake behaving monkeys

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In order to clarify the effect of emotional state induced by expectation for pain on cortical neuronal activity, single neuronal activities were recorded form the Primary somatosensory cortex (SI) or Anterior cingulated cortex (ACCx) and the correlation between behavior and neuronal responses were analyzed Monkeys were sitting quietly on the monkey chair. When the "Go light" conies on, monkeys press the button. Then the heat stimulus is applied to the facial skin through the thermal probe. We introduced three different types of detection trials for monkey's perceived intensity of heat stimulus intensity. 1) Heat detection: T1 temperature consists with 44-46℃ and T2 temperature is 0.2-0.8℃. Monkey need to try to detect the temperature change using a heat stimulus without light. 2) Light detection: When the monkey presses the button, L1 (basic light) comes on. After 4 to 8 second hold period, L2 (a small light intensity increment) is added on L1. Monkeys detect the change in L2 change and get reward. 3) Light detection with heat: When the monkeys press the button, L1 light comes on. With 44-46℃ heat. After 4- 8 second hold time, L2 comes on. Monkey need to detect the change in light intensity change. Many nociceptive neurons in SI and ACCx increased firing frequency following increase in stimulus temperature. When monkeys escaped from T1 before T2 coming, nociceptive neurons significantly increased their firing frequency in ACCx. The firing frequency of the S1 nociceptive neurons significantly correlated with detection latency, while ACCx neurons did not show any correlation.These suggest that SI neurons would be involved in sensory discriminative aspect of pain whereas, ACCx nociceptive neurons would be involved in motivational aspect of pain, and also nociceptive neuron sin both areas would be involved in attention of pain.