Psychophysiological Study of Pain Perception in Depressed Patients With Suicidal Risk

Joiner's interpersonal theory of suicide postulates that the wish of death comes from feelings of perceived burdensomeness and thwarted belongingness. But, only people who have acquired the capability to kill themselves will attempt suicide. The acquired capability refers to a reduction of fear to death, and a higher pain tolerance. Indeed, to commit suicide involves to endure pain during the act. Thus, higher pain tolerance seems to be a necessary feature for suicidal act. Past studies have shown higher pain threshold and tolerance in suicidal patients, whatever the stimulus was (electric, thermic or mechanical), compared to patients without suicide history. Moreover, Caceda and colleagues demonstrated higher pain threshold in recent suicide attempters (suicidal act within 72h) compared with depressed patients. Five days after the initial evaluation, pain threshold of recent suicide attempters decreased to be similar to depressed patients with suicidal ideation. Therefore, it may exist a specific state during which the pain tolerance is increased. During this "hypoalgesic state" patients with suicidal ideation could attempt suicide to get relief from suffering. However, little is known about the specific mechanisms that are responsible for the higher pain threshold and tolerance in suicide attempters. Pain is a dynamic system that results from excitatory and inhibitory messages. The modification of one of these mechanisms could explain the higher tolerance in recent suicide attempters. Three of them are of particular interest: 1. The conditioned pain modulation (CPM) is a modulatory pain mechanism. CPM works through descending pathway that reaches the spinal cord and modulates pain processing from the first nociceptive synapse.In recent suicidal patients, an increase of the CPM could explain higher pain tolerance. 2. The "wind-up" mechanism is defined as the highest excitability of the second order nerve. Even if the stimulus remains stable, pain continuously ra