The relationship between pupil dilation response to noxious stimulation and defense response

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The pupil dilates markedly in response to increasing noxious stimulation in humans. However, a central unresolved issue is whether this pupil dilation response (PDR) is a spinal sympathetic reflex or not. Our previous reports indicate that the PDR could be a brain-mediated response such as a defense response, and examined two experiments as follows :Experiment 1 : We examined whether PDR amplitude is increased by unexpected stimuli(B,C,D) compared to expected stimuli(A)Result : The amplitude of PDR to D significantly increased compared to that to A.Experiment 2 : We examined whether the amplitude in PDR,SEP are decreased during propofol sedation(0.3,0.6,0.9μg/ml=0.3P、0.6P、0.9P)Result :1. The amplitude of SEP to noxious stimulation during 0.6P,0.9P significantly decreased compared to that to control.2. The amplitude of PDR to strong stimulation during 0.9P significantly decreased compared to that to control.3. The VAS during 0.9P significantly decreased compared to that to control.4. BIS value were positively related to PDR,SEP and VAS with strong stimulation.We concluded that PDR to noxious stimulation(1) increases the amplitude with increasing anxiety.(2) is an objective parameter for pain.(3) is an objective parameter for sedation level.(4) is a more complex brain response.