#044 Thimblerig

The Ageing Brain

We have all seen the confidence tricksters on street corners. They have three walnut shells and a pea. The pea goes under one shell, the shells are shuffled and all you have to do is bet on where the pea ends up. Sometimes called the three cup game it has been found in the literature of ancient Greece. It was called Thimblerig in eighteenth century England when it was played with thimbles. 

A group of researchers at the Harvard were investigating visual short term memory. Short term memory is cache used to store “work in progress”. Their version of the Thimblerig was more complex. They started with two cups and a blue and red ball. They shuffled the cups once and respondents had to find the red ball. They started again and shuffled the cups twice. Then three times and finally four times. They then increased to three cups and a blue, a red and a yellow ball. Again they made the task more difficult by shuffling up to four times. Finally they added a fourth cup and a green ball . The most difficult task was finding the red with four balls and four shuffles.

The competition was between three groups of contestants. There were twenty one undergraduate students from Harvard College. They beat twenty one “six to eight year olds” from the Boston area at every level. The third contestant won all but two contests. It was Griffin, an African Grey Parrot. It beat or equalled the children in every case. It only lost to the undergraduates on the two most difficult tests. They won on the four balls with three and four shuffles.

The researchers point out that the brain of a parrot is only the size of a walnut. This tended to upset the undergraduates! It mitigation, it is so tightly packed with neurons that it has a density comparable to a human. They suggest that we may have a common ancestor that possessed this ability. The only common ancestors between humans and a parrot were the dinosaurs. Size of brain is not necessarily everything. 

Griffin and One of the Researchers (Source Harvard Gazette)¹

Is the physical shrinkage of the brain related to its performance?

I found the story of the all-conquering parrot whilst investigating this question. The evidence said that the human brain was the most developed amongst primates. When researchers started to scan the brains of different species they noticed differences. Species with large brains, had a greater proportion of the brain devoted to the cerebral cortex. This is  the part of the brain related to higher level reasoning. The cerebral cortex accounts for eighty percent of the brain in humans.  By comparison in a mouse it is only forty percent. It is the high number of neurons in the cerebral cortex and their degree of interconnectedness that makes human brains so special. 

The problem for evolution was comparable to those designing modern computer chips. The more functions you place on a chip the more difficult it is to  interconnect them. The human brain is typical of two evolutionary solutions to this problem. The first is the folded nature of its outer surfaces.  The folded cerebral cortex can pack more neurons in to a smaller volume. It  also reduces the length of the connections. 

The second solution is the creation of specialized compartments. Each is  focused on a different task. Processing speeds within the compartments are improved. Then the “results” travel to other parts of the brain.  The human brain is the supreme example of this. Rodents have forty compartments. Small primates can have one hundred compartments. Humans have three hundred and sixty compartments. 

Some compartments  process the signals from the different senses. These are  the primary sensory cortexes: the visual, olfactory (smell), gustatory (taste), the auditory and somatosensory (touch) cortexes. Some compartments deal with the motor skills. These control everything from the twitch of an eyebrow to the hand eye co-ordination needed to drive. 

The Super Agers

With age we know from brain scans that the human brain shrinks (Newsletter #030). It does not shrink evenly and the biggest loses are in the cerebral cortex. The link between that decline and mental ability is by no means clear.  I had concluded that there was insufficient evidence yet to draw a direct connection. Another Harvard Team, this time from the Medical School, have made me wonder. 

They were investigate a rare group of older people. These people have retained the mental ability of a twenty year old. The neuroscientists started by MRI scanning the brains of the “super-agers”. They found that they had a cerebral cortex whose size was comparable to a young person. The super-agers hippocampus had not shrunk. It was larger that that found in a comparable older person who was not a “super- ager”. The hippocampus manages the memory. 

There were big differences as well in the visual cortex (hence the link with Griffin the Parrot). Younger people have neurons within the cortex that are specialized. For example, some can register faces , others scenery. That allows for very fast recognition. It probably evolved when we were hunters.  It also seems to help imprint memory. As people age that specialization  fades. All neurons then register all images. That is except for the “super-agers”. They have retained the differentiation amongst neurons.

A lot of the shrinkage of the brain comes from the white matter. These are the inter- neuron connections. Network connectivity seems to fade with age. That is again except for the “super agers”. Their network connectivity is that of a younger person.

How do I become a Super-Ager?

Unfortunately the team at the Harvard Medical School have not gone that far. Previous older groups of researchers have looked at “super agers”. Without the benefit of scans they have tried to identify what makes a super-ager. The early “ emeritus professor” studies found that continuing use of the brain helps (Newsletter #010). Their early samples were retired professors who had continued to work. The work on the Puget Sound data suggests that we should “use it or lose it” (Newsletter #030). They showed that part of mental ability could be recovered through training. Their hypothesis was that at least part of mental decline was because of lack of use. If we do not use some capability it starts to decline.

In the meantime we should all assume we are super-agers and get on with life!

1. “Age and Species Comparison of Visual Mental Manipulation Ability as evidence for its Development and Evolution”, Pailian et al, Scientific Reports May 2020