Design of the human brain has evolved over thousands of generations by the process of natural selection in a gradual manner1. It is not developed on a preconceived plan or a blue-print.
Such development has enabled it to transit from running on lower amount of resources for processing information in earlier generations to higher amount of resources in succeeding generations, an ability it has retained which helps it optimize its operations.
In detail: According an estimate, our brain can store 1 petabyte of information. A computer with the same amount of information would require 1 gigawatt of power to process it, which our brain does with just 20 watts of power. Such optimization is based on the optimizing aspect of the evolutionary process2.
One of the many methods it uses to optimize its operations is by controlling what we call the “degree of attention”, in which the conscious part of the brain (VP3) controls the amount of resources that are required to process its ongoing interactions.
How Degree of Attention Works: The conscious part of the brain, with the help of non-conscious part (LB4), evaluates how significant each ongoing interaction is to its goals, proportional to which, it allots the amount of resources that are required to process it – higher the significance, higher the amount of processing resources it allots to it and vice versa. In other words,when you pay more attention to something, your brain allots and uses higher amount of resources to process it and vice versa.
An example of the same is when you hear a news item; the conscious part (with help from non-conscious part of your brain) evaluates it. If it is significant for you, e.g. a road accident very close to your house, your brain evaluates it as significant (as it may involve someone close to you) and allots higher amount of resources to process it. This way, higher degree of attention offers better processing and thus, better capability to interact with something significant.
Note: This post sufficiently explains the mechanism of degree of attention and the logic behind fidgeting behaviour like shaking legs, biting nails, tapping feet, etc. Please follow the links given below only when you want to dig deeper into these subjects.
(Source – Mechanisms of the Mind by Parag Jasani)
1 more under title Optimizing Aspect of the Evolutionary Process – page 3
2 more under title Optimizing Aspect of the Evolutionary Process – page 3
3 more under title Virtual Person (VP) – page 20
4 more under title Logical Brain (LB) – page 19