Since the time the first IQ test was developed in 1904 by Alfred Binet, there has been a continuous search for a way to predict and quantify human intelligence. The methods have ranged from measuring the diameter or volume of the head to more complex methods of today using imaging methods such as fMRI. The two brain based biomarkers that have had the most work accomplished have been the concentration of a brain chemical called N-acetyl aspartate and the second has been brain volume measurement by MRI.
The term used to refer to intelligence is called “fluid intelligence” and measures the capacity to think logically through problems and arrive at solutions without any a priori knowledge about the problem. It has been referred to as the capacity to reason and learn new things. This is different from “crystallized intelligence” which is the ability to remember and use past learning and experiences to solve problems. This is usually based on accumulation of knowledge.
An example of fluid intelligence might be a puzzle that the subject has not seen before but through reasoning determines the best way to solve the puzzle.
One feature of intelligence has been the connectivity between individual entities in the brain. The smallest entity may be a cell (neuron, glia or other type of cell) and the connectivity between them has been referred to as a “micro” connectome. These neurons assemble into larger tracts and their connectivity pattern has been called “macro” connectome.
Both the connectomes are in the process of analysis and the human connectome project has all the data available to be mined
Rather than go into the history of the test of human intelligence there is one publication that was published in 2015 (Finn et al, Nat. Neurosci 18, 1664) that analyzed data from the Human connectome project that were fMRI scans from healthy individuals and showed that it was possible to identify profiles of connectivity in the brain that correlated with fluid intelligence. By corollary, the connectivity pattern was also specific to an individual and it may be possible to identify individuals with their specific pattern.
Does the connectome change and what is the change through life? Unknow – but based on what we know about synapse formation, it is possible that some changes in connectivity may be possible.
Another question has been the cause and effect. The few biomarkers that have been studied have showed correlation but not a cause and effect. For example, if an ability to change connectome existed – would changing the connectome affect the “intelligence” level?
These are unanswered questions and more research is required.