The human brain develops rapidly during prenatal development. It takes years after birth to fully mature. During the first month, the neural tube forms from the ectodermal germ layer and begins to regionalize into the brain and spinal cord. By 9 weeks, the major divisions of the brain are visible. Throughout prenatal development, the brain grows in size and complexity, with folding of the cortex and development of neural connections. Full term birth is considered 40 weeks after conception. Most abortions occur in the first trimester, before 12 weeks of gestation. Women under 25 obtain about half of all abortions in the United States.

1. PSYCH 125, Lecture 3
Functional Brain Anatomy & Prenatal
Development

2. Question for discussion in section
The human brain takes years to mature, consumes 30% of the
body’s energy, and has gotten so large that unassisted
childbirth is dangerous.
What important function(s) does the brain serve, beyond what
the spinal cord & brain stem can accomplish?

3. Review
One way to subdivide the brain is according to
anatomical features – either macroscopic ones (sulci,
gyri) or microscopic ones (appearance of cells & cell
layers under microscope)
•What’s another way to subdivide the brain?
•Which techniques can we use in humans to figure out
what a brain region does?

4. Topographic organization in primary motor &
somatosensory cortices (Penfield, 1940s-50s)

5. Primary visual cortex
Lateral View Medial View
W. W. Norton

6. Retinotopy in Primary Visual Cortex
• injected radioactive glucose into bloodstream while monkey viewed
image
• “developed” brain like a photograph
• Map of retina reproduced in brain!
Roger Tootell et al., 1988

7. Visual processing
Two processing streams (pathways):
1. “What”: object recognition (ventral stream = occipito-temporal)
2. “Where”: spatial localization (dorsal stream = occipito-parietal)
(or “How”: how to act w/r to an object)
W. W. Norton

8. Tonotopy in Primary Auditory Cortex

9. Primary, secondary, and association
cortices
Primary cortex
Secondary cortex
Association cortex
W. W. Norton

10. Frontal cortex: Goal-directed behavior

11. Quiz
A. B. C.
Which of these lobes would play the biggest role in…
•deciding which of two courses to take?
•finding your way to the classroom?
•remembering facts that you learned in class?

12. Poll
What does ‘topography’ mean, in the context of the
brain?
A) A map of the gyri and sulci of the brain
B) The spatial organization of cytoarchitectonic regions
C) The fact that frequencies of sound are represented
in a systematic way across primary auditory cortex
D) The ordered projection of a sensory surface, like the
retina or the skin, or an effector system, like the
musculature, to the brain

13. Poll: Which box represents the sense of
hearing?
B
A
C D
Primary cortex
Secondary cortex
Association cortex
W. W. Norton

14. Next up
Prenatal brain development
9 months
http://capturedbycarrie.com/

16. 200-300 million sperm deposited –
only 1 (if any) will fertilize the
egg

17. That one lucky little spermatozoid

18. Formation of the embryo

19. Early stages of embryonic development
Inner cell mass will Formation of the
reorganize into a disk 3 germ layers

20. Germ layers

21. The Ectodermal germ layer will give rise to…
• Central Nervous System
• Peripheral Nervous System
• Sensory epithelium of ear, nose, and eye
• Skin (including hair and nails)
• Pituitary, mammary and sweat glands
• Enamel of teeth
• Important gene for ectodermal development: Growth factor
BMP4 22

22. Formation of the neural tube
thebrain.mcgill.ca

23. Week 4: From neural tube to brain and
spinal cord

24. Neural tube defects
Humpath.com

25. Regionalization of the brain
Prof. Thomas Jessell, researchchannel.org

26. From 1 month after fertilization through birth
Prof. Thomas Jessell, researchchannel.org

27. Face development from 5.5 weeks to 8.5
weeks
• Facial structures fuse during the 7th week
• Cleft palate (1 in 500 births) develops from errors during this period

28. 9 weeks
• Around the size of a peanut
• Head is roughly half the length – bulging forehead reflects
extremely rapid brain growth that has been going on for
weeks

29. 11 weeks: major divisions of brain are visible

30. 16 weeks
• can tell the sex of the fetus
• kicking & some reflexes (breathing movements, grasping, sucking)

31. 18 weeks

32. 20 weeks
• sleep/wake cycles
• facial expressions (eyebrows, forehead, mouth)
• head-down position more frequent

33. 28 weeks
• eyelids flutter during REM sleep
• reacts to sounds
• brain waves similar to newborn
• brain and lungs sufficiently developed that – if born now –
could potentially survive without medical intervention.

34. The home stretch: 8th-9th month
• Red, wrinkled skin fills out with fat
(provides insulation to protect
against heat loss)
• Gains 1/2 lb. per week
• Startle reflex is present; responds
to light and sound, lifts its head
• 60 percent of adult head size
present36

35. Birth
• Considered full-term if born within 10-14 days of calculated
delivery date; if born earlier, considered pre-term
• The earlier born, the greater the risk (due to
underdevelopment)
• Correlated with prematurity is low birth weight, which
brings its own set of complications and risk
• Normal birth weight >3500 grams
• LBW <2500 grams
• VLBW <2500 grams
• ELBW <1000 grams
37

36. Milestones in prenatal development
• Zygote forms after conception
• Blastocyst embeds in uterine wall
• Germinal stage gives rise to
embryonic stage, which lasts about 8
weeks; during this time all organs,
systems, etc. form
• Fetal stage lasts 7 months (in full
term pregnancy) and is period of
elaboration and growth
• Labor and delivery culmination of all
this hard work – generally, 40 weeks
post conception
Sadler, TW (2010). Medical Embryology, Eleventh
38 38
Edition. Baltimore: Lippincott Williams & Wilkins

37. When do abortions occur?
Percentage of 2008 Reported Abortions
by Weeks of Gestation* (CDC)

38. Who is having abortions?
• At current rates, nearly one-third of American women will have an
abortion (AGI)
• 50% of U.S. women obtaining abortions are younger than 25;
women aged 20-24 obtain 33% of all U.S. abortions and teenagers
obtain 17% (AGI).
• The abortion rate of women with Medicaid coverage is three times
as high as that of other women (NAF).