In a recent study mice reacted more strongly to painful stimuli when they saw another mouse suffering, suggesting that they «share» the pain of their cage mates. (scientificamerican.com)
Perhaps we can summarize the difference between pleasure and pain thus — while painful stimuli demand our attention and thus inhibit supplemental phases, pleasurable stimuli are feelings which invite further complex feeling. (religion-online.org)
They knew earlier research had found that painful stimuli also create two signals: one immediate and one that reaches the brain a couple of seconds later. (discovermagazine.com)