Brain size matters

This may sound like a joke, yet it is very serious. The size of your brain can change the way you think in strange and surprising ways. Nobody truly understands why, but there are many interesting research results. More reading here, here, here, and here.

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Key idea

The structure of the brain and the relative proportions matter more than its size. A healthy lifestyle ensures a healthy brain. This article is full of interesting facts and puzzling numbers, so I sincerely recommend reading it to train your memory and shine in the office trivia.

Neanderthal brain

Human brains are among the largest in the animal kingdom compared with the body size. Clearly, whales have the largest absolute brain size in the animal kingdom. We are not sure how they use them. Elephants also have huge brains and these brains store a lifetime of memories very accurately. As primates, our brains are organized somewhat differently with a focus on visual processing and social interactions.

Europeans have some neanderthal genes. Neanderthals had huge brains. On average, this value was about 1410 cm3 (~6 cups) for Neanderthals and 1350 cm3 (5.7 cups) for recent humans. The brain burns a lot of energy, maybe 20% or more of the energy consumption while it is only 2% of the body mass. The Neanderthal brain required a high-calory diet. The brain growth was also very slow. A skill in Spain shows that Neanderthals reached 87% of their brain growth when a human child of the same age reached 95% and we have probably and by far the longest childhoods in the animal kingdom.

Also, Neanderthals had a proportionally much larger cerebellum. This means the Neanderthals were much better at acquiring procedural skills like using the tools, and much worse in declarative skills required for socialization and creativity. Basically, they were very skilled. But they needed more energy and were less creative getting this energy. So they parished.

Men and women

Human brain structures are sexually dimorphic. The male brain is 10% (7%-13%) larger than the female brain, only the brain organization is different. The male brain has much larger visual processing areas with many glial cells acting like accelerators. The female brain has a larger area dealing with emotions and language. Gray matter volume increases for males tend to be on the left side of systems, while females generally see greater volume in the right hemisphere. Partially due to larger brain size males mature more slowly.

However, there are additional differences. For example, amygdala size is different. Males tend to have stronger reactions to threatening stimuli and males react with more physical violence.

Males probably have a slightly better memory. Hippocampus atrophy is associated with a variety of psychiatric disorders that have a higher prevalence in females. Additionally, there are differences in memory skills between males and females which may suggest a difference in the hippocampal volume (HCV).

These differences are probably induced by hormones. Studies of brains in transgender humans show very confusing results, possibly linked to hormonal therapies.

Brain on sex hormones

Teenagers make impulsive and risky decisions, often ignoring common sense. Pregnant women have a strange memory loss – possibly facilitating dealing with postnatal traumas. Definitely, the human brain on hormones is different, but how? I do not really know this subject, so I quote from different sources.

Small amounts of estrogen facilitate learning. Estrogens increase synaptic and dendritic spine density in the hippocampus, Too much estrogen can have negative effects by weakening the performance of learned tasks as well as hindering the performance of memory tasks.  Menopause cause fluctuating and decreased estrogen levels in women. This in turn can “attenuate the effects” of endogenous opioid peptides. Opioid peptides are known to play a role in emotion and motivation.

Progesterone is a steroid hormone synthesized in both male and female brains. As a female sex hormone, progesterone is more significant in females than in males. several clinical research studies have shown that progesterone may even have protective qualities in the brain—a characteristic known as “neuroprotection” and increased neuroplasticity. In men, increased progesterone has been linked to adolescents with suicidal ideation.

Testosterone is a masculinizing, hormone that is synthesized in both the male testes and female ovaries, at a rate of about 14,000 μg/day and 600 μg/day, respectively. Testosterone helps regulate cortisol levels. Cortisol is commonly known as the “stress hormone,” and it’s responsible for the fight or flight mode.  Testosterone exerts organizational effects on the developing brain. Men with low testosterone commonly experience cognitive issues, often described as “brain fog.” For example, you might realize that it’s difficult to focus or think clearly, or you might have a harder time remembering things. In fact, many studies show that men with low testosterone perform lower than average on cognitive tests for verbal fluency, visual-spatial processing, memory, attention, and executive function.

Happy hormones and neurotransmitters

Dopamine is an important part of your brain’s reward system, along with learning, memory, motor system function.

Serotonin helps regulate your mood as well as your sleep, appetite, digestion, learning ability, and memory.

Oxytocin is essential for childbirth, breastfeeding, and strong parent-child bonding. This hormone can also help promote trust, empathy, and bonding in relationships.

Endorphins are your body’s natural pain reliever, which your body produces in response to stress or discomfort.

Neurotransmitters regulate a lot of brain functions. If you took antibiotics that killed your gut bacteria, you might be depressed, less socially active, and with reduced memory. Something similar happens if you do not get enough sunlight, sleep, physical activity…

The brain size and morphology are just a part of the picture…

Small changes matter

Even small changes in the brain structure may have a strong aggregate effect. Consider Einstein. His brain has been studied. The brain was cut into 240 blocks and reviewed under  a microscope since 1955.

In 1985, a study revealed that two parts of Einstein’s brain contained an unusually large number of non-neuronal cells – called glia – for every neuron, or nerve-transmitting cell in the brain. Ten years after that, Einstein’s brain was found to lack a furrow normally seen in the parietal lobe. Scientists at that time said the missing furrow might have been related to Einstein’s enhanced ability to think in three dimensions, as well as to his mathematical skills. Now the most recent study, by Falk et. al., suggests that the pattern of convolutions in Einstein’s prefrontal cortex looks different from most people’s. 

These are not large changes, and yet the way Einstein thought was profoundly different. I do not know anyone who can think even remotely like Einstein…

Aging brain

A report published in 2021 stated that asymmetrical thinning of gray matter in the cerebral cortex’s left and right hemispheres is accelerated in Alzheimer’s disease patients. The report also suggests that the posterior cerebellum was affected by both healthy aging and Alzheimer’s disease and that healthy aging showed bilateral grey matter loss. This means that as we age, it becomes increasingly difficult to acquire new skills, but for Alzheimer’s, the effect is faster and focused.

Aging changes not just the structure of the brain, but also our metabolism and hormones. It may be interesting to speculate how hormonal therapy in old age may affect the brain – as I do not know any massive study of such sort.

I do know, that by increasing the immune system activity it is possible to slow or even stop Alzheimer’s. Moreover, there are indicators that normal brain deterioration also slows down.  This makes me think that 20 years from now, we will probably have some potent and affordable generic drugs for aging brains. At least I hope so.

Memory training modifies brain

Recently, a group of people was asked to remember multidigit numbers using mental palaces. The guy who executed the experiment used to be Germany’s memory champion.

“Across participants of the training study, we found increased hippocampal connectivity during rest after training with the lateral prefrontal cortex, left angular gyrus, parahippocampal regions, and the caudate nucleus that was higher the more durable memories were formed,” wrote the researchers. The follow-up analysis showed that these effects were “specific to the memory training group after training but were not present in any of the control groups.”

This hippocampal connectivity applied not just to memory champions, but even to novices doing the memory training.

It remains to be seen how long the effect of training lingers. During WWII pilots used to train with a tachistoscope. They could recognize ships very fast and from far away. This is basically one of the speedreading effects. Unfortunately, this particular effect disappeared several months after the training.

What do neural networks tell us?

When we do not really know something, we simulate it. Neural networks simulate quite well the brain’s learning activities. Distinguishing complex scenarios requires more features and hence larger networks.

We know that the larger the network, the slower it learns. Moreover, if the network is larger than it should be, some parts of the network do not actually activate or send random signals. Such networks will also be slower and use more energy. So it makes sense to train the network of just the right size.

The morphology of the network matters more as the network grows. The metaparameters of the network learning may matter more than the structure or the morphology of the network. And the training database often matters more than all other factors combined.

Does that sound familiar to the human brain as we know it? For me, it does. Yet human brain is significantly more complex than any AI I have ever trained. Who knows what we are missing!