Thyroid hormone is required for normal prenatal brain development.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Role of Thyroid Hormones**: Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), are crucial for various physiological processes, including growth and development. They are secreted by the thyroid gland, which is shaped like a butterfly and located in the neck.

2. **Importance in Prenatal Development**: During pregnancy, the developing fetus relies on the mother’s thyroid hormones for proper brain development. These hormones play a significant role in the differentiation and maturation of brain cells.

3. **Oligodendrocytes and Myelin Production**: One of the key functions of thyroid hormones is to promote the differentiation of oligodendrocytes. Oligodendrocytes are specialized glial cells in the central nervous system that produce myelin, an insulating layer that surrounds nerve fibers.

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