Foetal brain development from 4-9 months, illustration. Around the 4th month of pregnancy (left), the brain stem, which is above the spinal cord and to the right of the cerebral cortex, is almost entirely developed. The brain stem is involved in regulating automatic functions such as heart rate, breathing and blood pressure. From 4-6 months, the cerebellum, which is involved in motor control, develops. From the 7th month of pregnancy (centre), the brain triples in weight. The surface area of the brain increases with more gyrification (folding, second from right). These folds allow the brain to accommodate a greater number of neurons. In the eighth month of pregnancy (second from right), the brain is growing quickly. By 9 months (right) the brain appears similar to the adult brain. The brain continues to grow and develop up until 25 years old.