Piaget believed that cognitive development occurs concurrently with physical development. Although this makes sense, it was not until more recently that psychologists have been able to observe these changes.

Research on neuroplasticity also taught us that each brain has "its own path" to development.  Although there are definite patterns of development, our brain development is a combination of genetic and environmental factors. Negative environmental stimuli can interfere with brain development and have a negative effect on cognitive development.

Early research on brain development was predominantly done on animals, as there were no ethical means available for such research before we had brain imaging technology.  One of the most famous studies was done by Rosenzweig, Bennet & Diamond (1972). This study showed that positive environmental stimulation led to more neural connections in the frontal lobe which is important for learning. Of course, in order to measure the level of brain development, the rats had to be killed.

The studies below look at the use of brain imaging technology to understand the developing brain.  Please note that the first study uses a PET scan, whereas the second uses an MRI.  Remember that PET scans measure brain activity/function; MRIs measure structure.

Chugani (1999) carried out an analysis of his own and others’ research into the brain development of infants and young children.  Chugani and others used PET scans to determine areas of brain activity, by measuring glucose metabolism in different brain regions.  They used a cross-sectional research design, comparing infants and toddlers of different ages.

Several important findings came out of this research:

• A baby’s brain develops neuronal connections (white matter) from the back to the front, with the frontal cortex that is responsible for higher-level processing developing last.
• Glucose metabolism in the brain of a newborn baby is 30% lower than that of adults.
• But by the age of three years, and until about 10 years old, the glucose metabolism, and therefore the activity and neuronal growth, is more than twice the level of that in adults.  This period is characterized by maximum neuroplasticity and is a critical period for learning.  Chugani calls it a ‘window of opportunity.’
• With adolescence, glucose metabolic rates decrease to adult levels by about age 16-18 years.

Giedd (2004) performed MRI scans on healthy children using a longitudinal research design. The sample consisted of 95 males and 66 females. Scans were conducted approximately every two years on children between 6 years and 20 years of age.  This corresponds to a repeated measures design.

He found that 95% of the brain structure is formed when the child is around five or six years old, but areas in the prefrontal cortex (PFC) start growing again in adolescence. The PFC is the last part of the brain to mature. It is responsible for cognitive processes such as planning, impulse control, the direction of attention, and decision making. He also found that the dorsal lateral prefrontal cortex, which is important for controlling impulses, does not mature until the early 20s.

The research above reflects the findings in animal research.

Although there is clear evidence of change in the brain from infancy to adulthood, it is not currently possible to establish a cause and effect relationship between these changes and specific aspects of cognitive development.

As Chugani's research was cross-sectional, it had a large sample size. As it was an independent samples design, the participants may differ in unknown ways as a result of their personal history and environment. Participant variability may affect the reliability of the results. As it was not a longitudinal study, change over time was not observed in any one individual.

Giedd's research was longitudinal repeated measures design. This means that change in brain structure was measured over time in specific individuals.  This rules out the problems of participant variability seen in Chugani's study. 

As the study is biological in nature, there is not a concern about the generalizability of the sample. The brains of people from different cultures should not have different developmental patterns. However, it should be noted that these studies were done on "healthy" children.  This is appropriate for the study because the researchers are trying to determine what the normal trajectory of development would be.