Human’s life as we know, goes through quite distinct stages. But these stages are not as simple as infancy, childhood, adolescence, adulthood and old age as most of us even medical fields recognize. That is why many medical studies including those in neuropsychiatry or neuropsychology plan their studies based on the above commonly known life stages. Even in many instances children including infants are mixed up with adolescents in studies or adults with elderly. As we know for example pediatrics cover the medical care of infancy, childhood and adolescents, while as we will read here with clear evidence by probing into the brain development that any of these stages are quite distinct. Here by probing into the brain development, a new classification and definition of different stages of life is presented that is vital to understand for medical, psychological and behavioural, even medical intervention of diseases and in a near future their preventions.
Psychological, behavioural and cognitive classification of life stages:
Long time ego, Freud (1) the father of psychology and psychoanalysis divided early stages of life into: 1) Oral stage in the first year of life or infancy; 2) Anal stage in the second year of life; 3) Phallic stage in the 3-5 years of life; 4) Latency stage of 6-11, and 5) sexual stage from 12 to 18 years of age. Due to the sexual nature of his psychology, Freud’s classification of life stages was based on sexual development and the pressure on ego by id and superego and all speculative and not experimental and scientific.
After Freud, Erik Erickson (2) tried to classify all stages of life from infancy up to old age as: 1) Birth-2 years (Infancy), that he believed the stage of learning Trust; 2) 2-4 years (Toddlers), when the child moves toward Autonomy; 3) 3-5 years (Preschoolers), when the child becomes Initiative; 4) 6-12 years (school age), when the child starts to become Industrious, more aware of themselves as individuals and responsible; 5) 13-19 years (Adolescents), when the teenager starts the process of Identity and role identification and self-confidence; 6) 20-40 (young adulthood), when the young adult enters Intimacy and serious and life long relationships; 7) 40-65 (middle adulthood) when the middle aged adults are at the stage of generativity vs. stagnation; 8) Late adulthood (65-death) when the individual facing integrity or despair.
Later on Jean Piaget (3) classified the stages of life from a cognitive developmental perspective into: 1) Sensorimotor Stage: Birth-2 years, when the infant perceives the world around only through his senses and discovers the surroundings by his motor movements; 2) Preoperational stage: 2-7 years, when the child masters the language, expressing himself and controls surrounding somewhat by speech without yet having any sense of abstracts, logic and no mental power to operate well enough in the environment; 3) Concrete operational stage: 7-11 years, when the child is more logical, though still in a concrete manner without understating the abstracts; 4) Formal operational stage: 11-18 years, when the teen masters the abstract logic, hypothetical and deductive reasoning. Like Freud, Piaget did not go beyond adolescence and did not cover the cognitive development beyond age 18, even into adulthood.
None of the above classifications of the stages of life that were proposed in the first half of 20th century, based on the different stages of brain development and were strictly observational, though from quite distinct perspectives. The second half of the past century and the advent of neuroimaging and neurochemical studies brought to medical specially the filed of neuroscience, that the brain goes through different stages of development and that would not stop after the stall of the growth of the brain in size by age five. The neuroscientists cruising in the field of the brain development soon discovered not increasing in the number and sizes of neurons, but increasing in the surface of the brain by folding and making the convolutions and gyries, and specification in the development of the brain for different purposes throughout the different stages of life. Here I will present some of these discoveries as we walk through different years of life in an attempt to re-define the stages of life based on the development of the brain.
The brain development during the fetal stage of life:
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