90% of brain growth is achieved by the –
**Core Concept**
Brain growth and development occur in a well-defined sequence, with significant periods of rapid growth and maturation. The first two years of life are crucial for brain development, with a remarkable increase in brain mass and complexity. This period is characterized by significant synaptogenesis, myelination, and the formation of neural circuits.
**Why the Correct Answer is Right**
The correct answer is **C. Infancy (0-2 years)**. During this period, the brain undergoes a rapid proliferation of neurons, followed by a period of intense synaptogenesis, where new synapses are formed between neurons. This process is essential for the development of neural circuits and the establishment of brain function. The rapid growth and development of the brain during infancy are critical for the formation of cognitive, motor, and sensory functions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is vague and does not specify a particular period of brain growth. While childhood is indeed a critical period for brain development, it is not the period when 90% of brain growth occurs.
**Option B:** This option is incorrect because fetal development is a critical period for brain growth, but it is not the period when 90% of brain growth occurs. The fetal brain grows rapidly, but the majority of brain growth occurs after birth.
**Option D:** This option is incorrect because adolescence is a period of significant brain development, but it is not the period when 90% of brain growth occurs.
**Clinical Pearl / High-Yield Fact**
The first two years of life are a critical period for brain development, and any disruptions or insults to the developing brain during this period can have long-lasting effects on cognitive, motor, and sensory functions.
**Correct Answer: C. Infancy (0-2 years)**