Small-world brain efficiency, brain fitness & IQ
The human cerebral cortex – the more recently evolved portion of the brain that is used for thinking and our conscious experience – is a complex network of functionally specialized regions interconnected by neuron fibers. As Dr. Alex Fornito from the Melbourne Neuropsychiatry Centre at the University of Melbourne puts it:
The brain is an extraordinarily complex network of billions of nerve cells interconnected by trillions of fibres.
How is the brain organized?
The organizational principles for the brain’s neural networks remain largely unknown. However, it’s becoming clear that the brain is organized like many other networks in nature:
Complex networks, from ecosystems to metabolic pathways, occur in diverse fields of biological science. Nervous systems are complex networks at multiple scales of time and space. It has been shown that …brain networks have characteristically small-world properties of dense or clustered local connectivity with relatively few long-range connections. (Reference)
What is called ‘small-world’ topology (spatial arrangement) is an attractive model for brain network organization because it supports:
- Segregated and parallel information processing
- Gives resilience against pathological attack
- Minimizes wiring costs in the network’s communication.
Small world networks solve the economic problem of maximising information processing or communication efficiency while minimising costs, i.e. the amount of ‘wiring’ (and metabolism) needed to make the connections useful for communication purposes. The better networks solve this trade-off problem, the more ‘cost-efficient’ they are.
Here are some small world networks in our lives, that are designed – or evolved - for greater c0st-efficiency:
The brain’s network is small-world optimized
From the point of view of evolution, small-world cost-efficient brain networks have been naturally selected over the course of evolution. Cost-efficiency is one way of defining ‘brain fitness’.
The brain tries to maximize its bang-for-buck by striking a balance between making more connections to promote efficient communication and minimising the “cost” or amount of wiring required to make these connections. Dr. Alex Fornito
Here is a diagram showing the small world architecture of the human brain:
Recent study demonstrates that brain network cost-efficiency is largely genetically based
In a study published recently in the international publication The Journal of Neuroscience led by Dr Fornito, a cost-efficiency index of the overall brain network was measured using fMRI brain-imaging – with both identical (monozygotic) twins (16 pairs) and non-identical (dizygotic) (13 pairs) twins. Differences in cost-efficiency between individuals was dramatic, and the study found that genetics accounted for a full 60% of the brain’s overall efficiency.
Our findings indicate that -a brain’s ‘cost-efficiency’ has a strong genetic basis. …Ultimately, this research may help us uncover which specific genes are important in explaining differences in cognitive abilities.” Dr Alex Fornito
Some of the strongest effects showing genetic contribution were observed for regions of the prefrontal cortex which play a vital role in different aspects of intelligence: problem solving, planning, decision-making and memory.
Link with IQ
Previous work has shown that people with more efficient brain connections score higher on tests of intelligence (more on this later), and that brain network cost-efficiency is reduced in the elderly as well as people with schizophrenia, particularly in the prefrontal cortex.
Thus optimization of network ‘cost-efficiency’ represents an important principle for the brain’s functional organization, and this organization – to a large extent – may account for differences in intelligence.
Implications for i3 working memory training?
It is known that working memory training (such as the dual-n back of i3 mindware software) results in pre-frontal changes in synaptic connections. An interesting question is whether this kind of brain training may result in increased ‘cost-efficiency’ in critical brain networks.