Posts Tagged Brain
Recently I watched a TED talk by Suzana Herculano-Houzel (http://www.suzanaherculanohouzel.com/lab) entitled, “What is so special about the human brain?” (http://www.ted.com/talks/suzana_herculano_houzel_what_is_so_special_about_the_human_brain.html). In this presentation she makes the intriguing assertion that our brain is as large as it is, at least in part, because we cook our food.
Size, as in brain size, is not as important as neuron number when it comes to intelligence. Although the elephant brain is three times as large as the human brain it contains 23 billion neurons, compared with 86 billion in the human brain (http://en.wikipedia.org/wiki/List_of_animals_by_number_of_neurons).
Unfortunately the human brain is incredibly expensive to run, 25% of the energy consumed daily goes to fuel the brain. It costs around 6 kCal to run one billion neurons per day. Despite great apes being physically larger than us, their brains are smaller. Herculano-Houzel proposes that this is because they cannot consume enough calories on a daily basis to run a bigger brain. They do have a fairly low energy diet consisting predominantly of high fibre plant material with a few fruits and, in the chimpanzee’s case, some meat. This may be why the chimpanzee can afford to run 5.5 to 6.2 billion cerebral cortical neurons compared with the gorilla’s 4.3 billion.
However, humans maintain between 19 and 23 billion cerebral cortical neurons. Herculano-Houzel believes we can feed this number because of cooking, which effectively predigests our food releasing more energy and allowing us to more completely absorb our food. She depicts a graph, which correlates the increase in brain size of our ancestors with the invention of cooking.
Paradoxically we are now moving away from cooking and processing back to a more unprocessed diet because we appear to have overdone it, consuming too many calories and becoming extremely obese in the process. If we could only divert all those extra calories to our brains instead of our bodies imagine how incredibly intelligent we could become.
Dr. F. Bunny
Now that we know all vertebrates and probably the majority of invertebrates feel pain what about young animals? Until an animal (or human) reaches a certain stage of development its brain is presumably not sufficiently mature enough to recognise and register that a painful event is occurring. This does not mean painful events do not occur or that the body does not respond to them in some way. It just means that the brain is not able to consciously register the event. This happens during surgery when an animal (or human) is anaesthetised. The surgical event is still painful but the part of the brain that recognises and responds to this fact has been switched off by virtue of the anaesthetic. Extrapolating from this a foetus is effectively unconscious and unaware of painful stimuli until its brain has become complex enough to develop consciousness.
The electrical activity in the brain can be measured via an electroencephalogram (EEG). Very early on in development the EEG is absent i.e. there is no detectable brain activity. As the animal develops EEG activity begins to appear. The time when this occurs relative to an animal’s birth depends on how mature it is after it is born. Lambs are born fairly well developed and are able to stand and walk shortly after birth. They develop EEG readings and therefore conscious perception after about 80% of the pregnancy has elapsed (similar to humans) and are born more or less fully conscious, although their EEG shows significant continued maturation during the first week of life. Lamb EEG responses to castration are not as great at one to two days after birth as they after one week post birth.
Rats are reasonably immature when born and have no detectable EEG. EEG signals don’t appear until 12 to 18 days after birth. Rats whose tails are clamped five to seven days after birth do not respond, while those clamped after 12 days do.
Marsupials are an interesting case because they are born at a very immature stage and crawl into their mother’s pouch where they complete most of their development. Interestingly they are able to complete that task even though their brain consists of only two layers of cells. In the tammar wallaby EEG activity does not appear until after 120 days of pouch life (total pouch time is approximately 250 days). Earlier than this and there is no response to toe clamping (Diesch et al 2007).
The main assumption here is that EEG activity correlates with consciousness. While this seems valid it is impossible to be certain and, even if the young animal does not consciously experience pain, the body can still react to painful stimuli by releasing stress hormones, withdrawal reflexes and changes in brain blood flow. There is some suggestion that while the animal cannot consciously perceive the pain it becomes sensitised to it such that it develops an increased perception of pain after birth that could become permanent (http://www.daff.gov.au/__data/assets/pdf_file/0019/1046431/25-craig-johnson.pdf). As always it seems prudent to err on the side of caution and avoid causing pain wherever possible.
Dr. F. Bunny
Diesch, T.J., D.J. Mellor, C.B. Johnson, and R.G. Lentle. 2007. Responsiveness to painful stimuli in anaesthetised newborn and young animals of varying neurological maturity (wallaby joeys, rat pups and lambs). Proceedings of the 6th World Congress on Alternatives and Animal Use in the Life Sciences, Tokyo. Pp. 549-552.
Exactly how happy are clams? Not very, according to Mark Miller of the Huffington Post (http://www.huffingtonpost.com/mark-c-miller/happy-as-a-clam_b_901054.html), who cites Dr. Patra Gupta of the Kerala Institute of Undersea Study. Dr. Gupta states that “the clams’ liquid secretions are identical in DNA structure to human tears. Clams also have less mobility than almost any other living creature, one of the sure signs of depression. They don’t fight back, don’t react to pain, take no interest in their appearance, don’t play or communicate. I’ve seen suicidal individuals with more zest for life, coma patients with a greater level of activity. These clams have less than zero interest in living; we might as well eat them.”
Gupta’s team attempted to generate some degree of happiness or life in the clams, introducing them to the far peppier shrimp, scallops, crab, lobster, even angel fish. But nothing. “Those clams couldn’t have cared less; they scarcely peered out of their shells. It was quite rude, actually. We’re getting in touch with a fish therapist to see if counselling might help, but quite honestly, I’m not holding out a lot of hope for it. I think we’re just going to have to face the fact that clams as a species are severely depressed.”
Maybe they were depressed because they were examined at low tide because the complete expression is, “happy as a clam at high water” (http://www.phrases.org.uk/meanings/as-happy-as-a-clam.html). High tide is when clams are much less likely to be predated, a good reason for happiness. Apparently the phrase originated from the US in the early nineteenth century.
The idea of happiness implies some kind of functioning nervous system, which makes me wonder, not about the clam’s state of mind but, carrying on from the previous post, can clams feel pain? Lobsters and crabs do have what can be termed a brain and, despite what our lobster eating friends would have us believe, do appear to feel pain and don’t appreciate being boiled. In a 2008 study a noxious stimulus was applied to the antenna of prawns. The prawns immediately began grooming the treated antenna and rubbed it against the side of the tank. This activity did not occur if the prawns were treated with benzocaine, a local anaesthetic (Barr et al 2008). In a much earlier study lobsters tossed into boiling water took up to seven minutes to die, all the time writhing, thrashing and convulsing (Baker 1975) (http://www.shellfishnetwork.org.uk/facts/fact4.htm).
While this appears extremely disturbing it is important to determine if these movements are the result of an organism in pain or merely a reflex to a noxious stimulus without a conscious perception of pain. While this may seem counter intuitive the brain of so called lower life forms is not as all important as it is for higher life forms. Many tasks are delegated to the spinal cord or other clusters of neurones. This can even be seen in higher vertebrates. Many years ago, while necropsying a freshly dead horse, I cut through a nerve in the groin region and promptly received an impressive kick for my trouble. The horse was well and truly dead, could feel no pain and yet reacted to the stimulus. A similar event occurred during a lizard necropsy. The lizard had a severed spine and, at the conclusion of the procedure, I was left with the lizard’s tail, back legs and pelvis. When I pinched a toe the leg and tail both wriggled, even though they were no longer attached to the top half of the body. (As a digression freshly dead reptiles often still have beating hearts when they are opened up. They are, however, definitely dead. If the heart is removed from the body it will continue to beat, lying on the table by itself, for up to an hour. It certainly creeps the students out and can make it somewhat tricky to confirm death in a reptile.)
It can be difficult to differentiate reflex from pain response in a live animal of limited reactions. I feel that, if the animal responds to pain killers by not reacting to the noxious stimulus, like the prawns and the fish in the previous post, then it is probably experiencing pain. The implication here is that the animal has pain receptors that can be chemically blocked. Pain and opioid receptors have been identified in snails, nematodes, crustaceans and insects (http://en.wikipedia.org/wiki/Pain_in_invertebrates).
But the clincher, for me at least, is the phenomenon of avoidance learning. To demonstrate this effect a light was shone on a crayfish. Ten seconds later the crayfish received an electrical shock. The crayfish learned that the light was associated with the shock and rapidly moved away when the light came on, thus avoiding the shock. A similar phenomenon was reported for Drosophila flies. In this case the electrical shock was paired with an odour. The flies quickly learned to fly away from the odour whenever they detected it (Elwood 2011). This cannot just be reflex. These animals are displaying a learned response and acting peremptorily to avoid a painful stimulus.
Which brings us back to clams. As far as I can tell clams do not have a brain as such but do have clusters of nerve cells called ganglia, which allow them to respond to certain stimuli. Pain receptors have been identified in their snail relatives and presumably exist in clams. Given that the avoidance of pain is universally beneficial to all forms of animal life and most clams are capable of movement, at least some of the time, I am prepared to give them the benefit of the doubt and say that they can feel pain. I hope that, at least, makes them happy.
Dr. F. Bunny
Baker, J.R. 1975. Experiments on the humane killing of lobsters (Homarus vulgaris) and crabs (Cancer pagarus). Part 1. The killing of lobsters by gradual heating. Scientific papers of the Humane Education Centre 1: 1-10.
Barr, S., P.R. Laming, J.T.A. Dick and R.W. Elwood. 2008. Nociception or pain in a decapod crustacean? Animal Behaviour 75: 745-751.
Elwood, R.W. 2011. Pain and suffering in invertebrates? Institute for Laboratory Animal Research 52: 175-184.