At approximately day 1

Synapses increase significantly.

Reference

O’Rahilly R, Muller F. 1999. The embryonic human brain. An atlas of developmental stages. Second edition. New York: Wiley-Liss.

At approximately day 1

All structures in the brain are present by the end of the first trimester.

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 1

Layers of the cerebellum undergo cell divisions to produce the various populations of cerebellar neuroblasts.

Reference

Larsen WJ. 1997. Human Embryology. New York: Churchill Livingstone Inc.

At approximately day 1

Cerebral cortex begins to fold into lobes and gyri as the hemispheres grow.

Reference

Larsen WJ. 1997. Human Embryology. New York: Churchill Livingstone Inc.

At approximately day 1

Eye opening and eye movements.

Duration: 3 weeks

Reference

DiPietro JA. 2001. Fetal neurobehavioral assessment. In: Singer LT, Zeskind PS, eds. Biobehavioral assessment of the infant. New York: The Guilford Press. p 43-80. Citing Als, H. 1982. Toward a synactive theory of development: Promise for the assessment and support of infant individuality. Infant Mental Health J 3:229-243.