A recent article discusses pain in insects. It underscores the difficulty of "knowing" what animals, especially insects, feel. A response to a stimulus does not necessarily imply that the organism experiences the stimulus in a similar way that we do (e.g., pain). Further, the lack of response due to the application of pain-killers (morphine, etc.) does not prove that pain has been suppressed -- only that the reaction is silenced.

> Bateson's (1991) seminal review on the assessment of pain has been influential in inspiring numerous researchers investigating pain in animals. Well-defined criteria were proposed and it was suggested that animals that fulfilled all criteria should be considered capable of pain. These criteria were: possession of nociceptors, receptors that detect damaging stimuli on or in the body; pathways from nociceptors to the brain; brain structures analogous to the human cerebral cortex that process pain; opioid receptors and endogenous opioid substances in a nociceptive neural system; a reduction in adverse behavioural and physiological effects after administration of analgesics or painkillers; learning to avoid potentially painful stimuli and that this learning is rapid and inelastic. 

> Animals have both physiological and behavioural responses to nociception that parallel those that accompany the experience of pain in humans and this is the basis for the argument by analogy. Some suggest animals may behave as though they are in pain, but this behaviour may reflect nociception without suffering. The opposition to the idea that animals experience pain has sparked fierce debates over the capacity of nonprimate animals for pain. However, although it cannot be proven that animals experience pain, it also cannot be proven that they do not. 

> How nociceptive information is processed within the insect central nervous system remains almost entirely unknown, although there is evidence that nociceptive information reaches higher learning centres in the insect brain. Nociception in insects can be modified using simple peripheral mechanisms, without the involvement of the central nervous system. Therefore, simply showing that nociception is modifiable (e.g. by endogenous opioids or other molecules) is not a compelling argument that insects feel pain. Plasticity in response to noxious stimuli does not necessarily indicate that an animal has the complex central nociceptive processing power required for the experience of ‘pain’.

> Moreover, recent advances in artificial intelligence (AI) have shown that robots can be programmed to express pain-like behaviour using relatively simple processing systems. The behaviour of these robots fulfils the behavioural criteria for pain. AI researchers develop such ‘emotional’ robots because they recognize that affective processes give biological entities a great deal of cognitive flexibility. These ‘emotional’ robots have no subjectively experienced emotions, but the robot's artificial emotions allow it to reprioritize its goals, modulate its behaviour and provide learning rewards. Similarly, insects, and possibly other animals, could use simple processing rules to produce pain-like behaviour, without any internal experience of pain.

Sneddon, L. U., Elwood, R. W., Adamo, S. A., & Leach, M. C. (2014). Defining and assessing animal pain. Animal Behaviour, 97, 201-212.

Related:

> Honeybee is a widely used insect model for learning and memory research. Recently, it has become a potentially good subject for evaluating the effects of addictive drugs on the nervous systems. Our previous study has found that acute morphine injection affected associative memory and locomotor activity in honeybees. In the current study, the effect of chronic morphine treatment and its cessation in honeybees were assessed.

Chen, Y., Fu, Y., Yang, H., Yao, T., Ma, Y., & Wang, J. (2014). Effects of Chronic Morphine Treatment on an Odor Conditioning Paradigm, Locomotor Activity and Sucrose Responsiveness in Honeybees (Apis mellifera). Journal of Insect Behavior, 1-13.

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