Posts Tagged Brain

Cooking With Gas

Recently I watched a TED talk by Suzana Herculano-Houzel ( entitled, “What is so special about the human brain?” ( 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 (

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


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Wake Me When It Hurts

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 ( 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.

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Happy As A Clam









Dr. F. Bunny






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