Regarding invertebrate sentience “we might discover that, for a unit of objective time, some invertebrate’s experience of suffering lasts subjectively longer than a human’s experience would”
Read more: https://www.animal-ethics.org/invertebrate-sentience-a-review-of-the-neuroscientific-literature/
Only mammals and birds are sentient, according to neuroscientist Nick Humphrey’s theory of consciousness, recently explained in “Sentience: The invention of consciousness”.
In 2023, Nick Humphrey published his book Sentience: The invention of consciousness (S:TIOC). In this book he proposed a theory of consciousness that implies, he says, that only mammals and birds have any kind of internal awareness.
His theory of consciousness has a lot in common with the picture of consciousness is described in recent books by two other authors, neuroscientist Antonio Damasio and consciousness researcher Anil Seth. All three agree on the importance of feelings, or proprioception, as the evolutionary and experiential base of sentience. Damasio and Seth, if I recall correctly, each put a lot of emphasis on homeostasis as a driving evolutionary force. All three agree sentience evolved as an extension of our senses–touch, sight, hearing, and so on. But S:TIOC is a bolder book which not only describes what we know about the evolutionary base of consciousness but proposes a plausible theory coming as close as can be to describing what it is short of actually solving Chalmers’ Hard Problem.
Plants are not usually thought to be very active behaviorally, but the evidence suggests otherwise. Moreover, in stressful situations, plants produce numerous chemicals that have painkilling and anesthetic properties. Finally, plants, when treated with anesthetics, cannot execute active behaviors such as touch-induced leaf movements or rapid trap closures after localizing animal prey
Only humans can report feeling pain. In contrast, pain in animals is typically inferred on the basis of nonverbal behaviour. Unfortunately, these behavioural data can be problematic when the reliability and validity of the behavioural tests are questionable. The thesis proposed here is based on the bioengineering principle that structure determines function.
Researchers find that growth-stunted farmed salmon show chronic serotonergic activity and do not respond to acute stress — a state that could be interpreted as depression.
In the vertebrate brain, serotonin mediated signaling is vital for several key physiological functions such as the body’s energy regulation, neural plasticity, behavioral and emotional control, and responses to stress. However, prolonged serotonin activation is associated with chronic stress and stress-induced pathologies in mammals. Such states include depression-like behaviors. This paper represents the first physiological data, showing that growth-stunted commercially farmed salmon have elevated serotonergic activity; what’s more, this is determined as the main characteristic of the growth-stunted phenotype. Compared to healthy fishes, these salmon are suggested to experience chronic stress. In fact, the researchers show that the fishes’ brains are not responsive to additional acute stress, representing a classic example of when regulatory mechanisms are unable to react to further challenges, indicating a depressive state.
When conducting the mirror test, scientists place a visual marking on an animal’s body, usually with scentless paints, dyes, or stickers. They then observe what happens when the marked animal is placed in front of a mirror. The researchers compare the animal’s reaction to other times when the animal saw itself in the mirror without any markings on its body.
Animals that pass the mirror test will typically adjust their positions so that they can get a better look at the new mark on their body, and may even touch it or try to remove it. They usually pay much more attention to the part of their body that bears a new marking.
Currently, nine non-human animal species pass the mirror test. Not all individuals of each species pass, but many do.
There has historically been almost no effort made to reduce the inhumaneness of fish slaughter. The majority of fish are killed without stunning, by asphyxiation either in the air or on the ice. One study found that it takes common species of fish 55-250 minutes to die via asphyxiation. Fish that aren’t asphyxiated often die by being live gutted; the same study found that live gutting can take up to 25-65 minutes to kill the fish. Fish who are stunned are typically struck on the head (percussive stunning), stunned electrically, or stunned using gas. Pre-slaughter stunning is more common in wealthier nations (like the UK, Northern Europe, Chile, Canada, and Australia) and for high-value species (like salmon and trout).