First We Grow

Our brains begin to develop during the third week of gestation. During the period of brain formation, our brains add as many as 250,000 neurons per minute. By the time we’re born, we have almost all the neurons we will ever have. In fact, by the age of two, the brain is approximately 80 percent of its adult size.1 By the age of six, it is 90 percent of its adult size.2 

The biggest impact on brain development at this fetal stage is the mother’s health. Risk factors to consider include:

  • Diet – During pregnancy, the fetus is completely dependent on its mother for adequate nutrition. The same is true for infants that are exclusively breastfed. If the mother fails to get certain nutrients in her diet, the fetus or nursing infant may ultimately fail to get that nutrient as well.
  • Stress – Stress, whether brought on by the pregnancy itself or by external factors, results in a number of physiological changes in the mother that can have a negative impact on the child’s brain development.3 Maternal stress during pregnancy is associated with smaller birth weights, premature pregnancy and increased risk of miscarriage. It is also associated with increased fussiness and temperamental problems in infants and problems with attention, attention control and lower scores on mental development tests. In the child’s later years, maternal stress during pregnancy has lead to increased hyperactivity in boys, emotional problems in boys and girls and conduct problems in girls.4,5
  • Alcohol Consumption – Since babies in effect consume whatever their mothers consume, it’s not surprising that drinking alcohol affects the development of the brain, particularly if the child is exposed during critical periods of growth and differentiation of cells into different organs and biological systems. Alcohol exposure during those times can negatively affect cognition and behavior. The severity of these effects depends on the amount of alcohol and the duration and timing of the exposure. At the extreme end, maternal alcohol consumption leads to the disorder known as Fetal Alcohol Syndrome (FAS).6 Children with FAS can have severe cognitive and behavioral disabilities
  • Smoking – Numerous studies have shown that smoking while pregnant can cause many physical and mental impairments, including Attention Deficit Disorder with Hyperactivity (ADHD), behavioral problems and mood disorders.7
  • Diabetes – Diabetes prior to or during pregnancy (known as pre-gestational and gestational diabetes, respectively) has been shown to negatively impact the attention span and motor functions of the offspring. The effects are dependent upon how well the mother controls her blood sugar during the pregnancy.8

What happens as we age? 

It’s normal: we can’t remember where we left our keys, we forget someone’s name or lose a word for a moment. These are the normal declines in brain health that happen with age. In some cases, this can progress to mild cognitive impairment (MCI) or worse, dementia from Alzheimer’s disease or other neurological conditions.

What’s the difference between normal cognitive decline and MCI? Patients with MCI experience the following: 

  • Forgetting things more often
  • Forgetting important events such as appointments or social engagements
  • Losing their train of thought or the thread of conversations, books or movies
  • Feeling increasingly overwhelmed by making decisions, planning steps to accomplish a task or interpreting instructions
  • Having trouble finding their way around familiar environments
  • Becoming more impulsive or show increasingly poor judgment
  • Feelings of depression, irritability and aggression, anxiety and/or apathy9


1 Neuroscience for Kids, University of Washington
2 Neuropsychol Rev. Dec 2010; 20(4): 327–348.
3 J Child Psychol Psychiatry. Feb 2013; 54(2): 115–130.
4 Current Directions in Psychological Science, 13(2), 71-74.
5 Psychiatric Quarterly, 72(4), 347-357
6 Alcohol Res. 2013;35(1):37-46
7 Crit Rev Toxicol. 2012 Apr;42(4):279-303.
8 Pediatr Endocrinol Rev. 2005 Dec;3(2):104-13.
9 Mayo Clinic