In a new paper published in the Proceedings of the Royal Society B, scientists from the Queen Mary University of London argue that insects most likely have central nervous control of nociception (detection of painful stimuli); such control is consistent with the existence of pain experience, with implications for insect farming, conservation and their treatment in the laboratory.

Modulation of nociception allows animals to optimize chances of survival by adapting their behavior in different contexts.

In mammals, this is executed by neurons from the brain and is referred to as the descending control of nociception.

Whether insects have such control, or the neural circuits allowing it, has rarely been explored.

“Nociception is the detection of potentially or actually damaging stimuli, which is mediated by specialized receptors: nociceptors,” said Queen Mary University of London’s Professor Lars Chittka and colleagues.

“It can be accompanied by the feeling of pain, which is a negative subjective experience generated by the brain.”

“Nociception and/or pain can be inhibited or facilitated (modulated) by descending neurons from the brain (including the brainstem in vertebrates) called the descending pain controls.”

Based on behavioral, neuroscientific and molecular evidence, the authors argue that insects probably have descending controls for nociception.

“Behavioral work shows that insects can modulate nocifensive behavior,” the researchers said.

“Such modulation is at least in part controlled by the central nervous system since the information mediating such prioritization is processed by the brain.”

“Central nervous system control of nociception is further supported by neuroanatomical and neurobiological evidence showing that the insect brain can facilitate or suppress nocifensive behavior, and by molecular studies revealing pathways involved in the inhibition of nocifensive behavior both peripherally and centrally.”

The presence of descending nociception controls in insects is important and interesting for many areas of insect and human neuroscience.

The descending control of nociception in humans can also affect pain perception, so it is conceivable that a form of pain perception exists in insects, and can be similarly modulated.

“Mammalian researchers quantify pain through measuring non-reflexive, complex and long-lasting changes to the animal’s natural behavior, which are likely mediated by descending controls,” the scientists said.

“For example, in rodents, reduced feeding, locomotion and burrowing behaviors are used as pain indicators.”

“Thus, the examples of insects performing these kinds of behaviors may support the idea of pain in insects.”

“For example, insects show reduced attraction to appetitive stimuli if they have to also experience nociceptive stimuli. Further, recent evidence demonstrating sentience-linked cognitive abilities in some insects supports this idea, as well as studies indicating pain perception in other invertebrates.”

“This is important morally, as insects are often subjected to potentially painful stimuli in research and farming,” they said.

“The possibility of pain sensations in insects is also an important consideration for modeling human pain disorders.”

“The fruit fly Drosophila melanogaster is currently used as a model organism for human pain research, because of similarities in the genetics and behavioral responses to human nociception.”

“The abnormal and persistent pain states in humans seem to occur due to dysfunction of descending pain controls, so, if insects have descending nociception controls, they could potentially be viable models for human pain disorders.”

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