Thoughts of Death Modulate Psychophysical and Cortical Responses to Threatening Stimuli

Abstract

Existential social psychology studies show that awareness of one's eventual death profoundly influences human cognition and behaviour by inducing defensive reactions against end-of-life related anxiety. Much less is known about the impact of reminders of mortality on brain activity. Therefore we explored whether reminders of mortality influence subjective ratings of intensity and threat of auditory and painful thermal stimuli and the associated electroencephalographic activity. Moreover, we explored whether personality and demographics modulate psychophysical and neural changes related to mortality salience (MS). Following MS induction, a specific increase in ratings of intensity and threat was found for both nociceptive and auditory stimuli. While MS did not have any specific effect on nociceptive and auditory evoked potentials, larger amplitude of theta oscillatory activity related to thermal nociceptive activity was found after thoughts of death were induced. MS thus exerted a top-down modulation on theta electroencephalographic oscillatory amplitude, specifically for brain activity triggered by painful thermal stimuli. This effect was higher in participants reporting higher threat perception, suggesting that inducing a death-related mind-set may have an influence on body-defence related somatosensory representations.

Visual reminders of death enhance nociceptive-related cortical responses and event-related alpha desynchronisation

“…The lack of modulation of the subjective experience of pain may seem at odds with this evidence and with our previous studies (Valentini et al, 2014;. The lack of a conditioning effect on the painful experience may be explained by a competition between visual reminders of death and painful stimuli for attentional and motivational resources.…”

“…4, right). Related to this issue, one can note that, as we previously discussed (Valentini et al, 2014), the theta oscillatory activity mostly reflects synchronised activity which only partially represents specific time-locked nociceptive evoked potentials (particularly the N2 and P2 waves).…”

“…We previously adopted a repetition suppression design and tested the mortality salience effect on the second stimulus out of each pair of stimuli without any other co-occurring sensory stimulus (Valentini et al, 2014;. Here we used a multisensory context in which single painful stimuli were coupled to each experimental visual condition.…”

“…Importantly, previous neurophysiological studies used single words or entire sentences as operational means to induce awareness of mortality in experimental volunteers (e.g., Han et al, 2010;Klackl et al, 2013;Quirin et al, 2012). At variance with these studies that did not explicitly require reflection on the idea of death, we recently provided evidence that death cognition based on classical mortality salience manipulation (Rosenblatt et al, 1989), where healthy individuals are asked to reflect on the ideas and emotions originating from thinking about their own death, is associated with higher intensity and threat ratings for nociceptive painful stimuli (Valentini et al, 2014;Valentini et al, 2015).…”

“…In the current study, we addressed whether visual cuing of death-related content (thus not requiring explicit reflection on the idea of death) could trigger effects on pain perception and brain activity recorded by means of electroencephalography (EEG) akin to those observed following explicit mortality salience induction (Valentini et al, 2014;Valentini et al, 2015). In fact, it is surprising that no study so far investigated whether images representing death-related content may induce prominent effects on brain activity compared to similar negative valence and arousing images but conveying a different meaning.…”