1. Brain development Nature and nurture From The University of Western Ontario Department of Psychology Psychology 240B Developmental Psychology http://www.ssc.uwo.ca/psychology/undergraduate/psyc h240b-2/

2. Outline Part 1: Brain development: A macroscopic perspective Part 2: The development of the cerebral cortex Part 3: Nature and nurture

3. Part I Brain development: A macroscopic perspective

4. 3-4 Weeks

5. Neural Groove

6. 3-4 Weeks Neural Groove Neural Tube

7. 3-4 Weeks Neural Groove Neural Tube Neuroepitheliu m

8. Neural Groove Neural Tube 3-4 Weeks Brain Spinal Chord Neuroepitheliu m

9. 5 to 6 Weeks Nervous system begins to function Hind-, mid-, and forebrain are now distinguishable

10. 5 to 6 Weeks

12. Forebrain

13. 5 to 6 Weeks Forebrain Telencephalon

14. 5 to 6 Weeks Forebrain Telencephalon Diencephalon

15. 5 to 6 Weeks Forebrain

16. 5 to 6 Weeks Forebrain Midbrain

17. 5 to 6 Weeks Forebrain Midbrain Hindbrain

18. 7 Weeks Neurons forming rapidly 1000’s per minute

19. 7 Weeks 14 Weeks Division of the halves of the brain visible

20. 7 Weeks 14 Weeks 6 Months Nerve cell generation complete Cortex beginning to wrinkle Myelinization

21. 7 Weeks 14 Weeks 5 Months 9 Months

22. 7 Weeks 14 Weeks 5 Months 9 Months Telencephalon: C-shaped growth Cortex: Folding

23. 7 Weeks 14 Weeks 5 Months 9 Months Telencephalon: C-shaped growth Cortex: Folding

24. 9 Months

26. Medulla Hindbrain Pons Cerebellum

27. 9 Months Medulla Hindbrain Pons Cerebellum

28. 9 Months Medulla Hindbrain Pons Cerebellum

29. 9 Months Medulla Hindbrain Pons Cerebellum

30. 9 Months Medulla Hindbrain Pons Cerebellum Controls respiration, digestion, circulation, & fine motor control

31. 9 Months Midbrain

32. 9 Months Midbrain Basic auditory and visual processing

33. 9 Months Thalamus Hypothalamus Diencephalon

34. 9 Months Thalamus Hypothalamus Sensory relay station Intersection of CNS and hormone system Diencephalon

35. 9 Months Telencephalon  2 Cerebral hemispheres Forms a “cap” over inner brain structures

36. 9 Months Cross-sectional view

37. 9 Months Cross-sectional view Cerebral Hemispheres

38. 9 Months Cross-sectional view Cerebral Hemispheres Thalamus Hypothalamus

39. 9 Months Cross-sectional view As the telencephalon develops, it connects both with itself, and with the diencephalon

40. 9 Months Cross-sectional view As the telencephalon develops, it connects both with itself, and with the diencephalon Corpus Callosum Internal Capsule

41. 9 Months Hippocampus Telencephalon

42. 9 Months Hippocampus Telencephalon Formation of long-term memory

43. 9 Months Hippocampus Cortex Telencephalon Thin layer of cells covering both hemispheres

44. Cortex High-level visual processing Visual Cortex

45. Auditory & visual processing Receptive language Visual Cortex Temporal Cortex Cortex

46. Sensory integration Visual-motor processing Visual Cortex Temporal Cortex Parietal Cortex Cortex

47. Higher-level cognition Motor control Expressive language Visual Cortex Temporal Cortex Parietal Cortex Frontal Cortex Cortex

48. Cortical Development Begins prenatally Continues into late adolescence

49. II: The development of the cerebral cortex A microscopic view

50. Development of the Cortex 2 types of cells: Neurons Glial cells

51. Development of the Cortex 2 types of cells: Neurons Glial cells

52. Development of the Cortex 2 types of cells: Neurons Glial cells Dendrite

53. Development of the Cortex 2 types of cells: Neurons Glial cells Dendrite Cell body

54. Development of the Cortex 2 types of cells: Neurons Glial cells Dendrite Cell body Axon

55. Development of the Cortex 2 types of cells: Neurons Glial cells Dendrite Cell body Axon Synapse

56. Development of the Cortex 2 types of cells: Neurons Glial cells Dendrite Cell body Axon Synapse Transmit information through the brain

57. Development of the Cortex 2 types of cells: Neurons Glial cells Outnumber neurons 10:1 Nourish, repair, & mylenate neurons Crucial for development

58. Development of the Cortex 2 types of cells: Neurons Glial cells Outnumber neurons 10:1 Nourish, repair, & myelinate neurons Crucial for development

59. Development of the Cortex 2 types of cells: Neurons Glial cells Outnumber neurons 10:1 Nourish, repair, & myelinate neurons Crucial for development Eg. Oligodendroglia

60. Development of the Cortex 2 types of cells: Neurons Glial cells Outnumber neurons 10:1 Nourish, repair, & myelinate neurons Crucial for development

61. 8 stages of cortical development 1.Neural proliferation 2.Neural migration 3.Neural differentiation 4.Axonal growth 5.Dendritic growth 6.Synaptogenesis 7.Myelination 8.Neuronal death

62. 1. Neural proliferation Begins with neural tube closure

63. 1. Neural proliferation Begins with neural tube closure

64. 1. Neural proliferation Begins with neural tube closure New cells born in ventricular layer

65. 1. Neural proliferation Begins with neural tube closure New cells born in ventricular layer 1 mother cell produces ≈ 10,000 daughter cells

66. 1. Neural proliferation Begins with neural tube closure New cells born in ventricular layer 1 mother cell produces ≈ 10,000 daughter cells All neurons (100 billion in total) are produced pre-natally

67. 1. Neural proliferation Begins with neural tube closure New cells born in ventricular layer 1 mother cell produces ≈ 10,000 daughter cells All neurons (100 billion in total) are produced pre-natally Rate of proliferation extremely high; thousands/minute

68. 2: Cellular migration Non-dividing cells migrate from ventricular layer

69. 2: Cellular migration Non-dividing cells migrate from ventricular layer Creates a radial inside-out pattern of development

70. 2: Cellular migration Non-dividing cells migrate from ventricular layer Creates a radial inside-out pattern of development Importance of radial glial cells

71. 2: Cellular migration Non-dividing cells migrate from ventricular layer Creates a radial inside-out pattern of development Importance of radial glial cells

72. 3. Cellular differentiation Migrating cells structurally and functionally immature

73. 3. Cellular differentiation Migrating cells structurally and functionally immature Once new cells reach their destination, particular genes are turned  growth of axons, dendrites, and synapses

74. 4. Axonal growth Growth occurs at a growth cone

75. 4. Axonal growth Growth occurs at a growth cone Growth cone

76. 4. Axonal growth Growth occurs at a growth cone Axons have specific targets Targets often enormous distances away Some axons extend a distance that is 40,000 times the width of the cell body it is attached to Finding targets ?  chemical & electrical gradients, multiple branches

77. 5. Dendritic growth Usually begins after migration Slow Occurs at a growth cone Begins prenatally, but continues postnatally Overproduction of branches in development and resultant pruning Remaining dendrites continue to branch and lengthen

78. 78 Human Brain at Birth 6 Years Old 14 Years Old

79. 6. Synaptogenesis Takes place as dendrites and axons grow Involves the linking together of the billions of neurons of the brain

80. 6. Synaptogenesis Takes place as dendrites and axons grow Involves the linking together of the billions of neurons of the brain 1 neuron makes up to 1000 synapses with other neurons Neurotransmitters and receptors also required

81. Overproliferation and pruning The number of synapses reaches a maximum at about 2 years of age After this, pruning begins By 16, only half of the original synapses remain

82. 7: Myelinization The process whereby glial cells wrap themselves around axons

83. 7: Myelinization The process whereby glial cells wrap themselves around axons Increases the speed of neural conduction

84. 7: Myelinization The process whereby glial cells wrap themselves around axons Increases the speed of neural conduction Begins before birth in primary motor and sensory areas Continues into adolescence in certain brain regions (e.g., frontal lobes)

85. 8: Neuronal death As many as 50% of neurons created in the first 7 months of life die Structure of the brain is a product of sculpting as much as growth

86. III: Nature and nurture in brain development

87. III: Nature versus nurture The adult brain consists of approximately 1 trillion (surviving) neurons that make close to 1 quadrillion synaptic links Functionally highly organized, supporting various perceptual, cognitive and behavioural processes Perhaps the most complex living system we know

88. Question Of all the information that is required to assemble a brain, how much is stored in the genes? Nature view: argues that most of the information is stored in the genes Nurture view: brain is structurally and functionally underspecified by the genes  emerges probabilistically over the course of development

89. Nature View (1) Not much is left to chance

90. Nature View (1) Not much is left to chance (2) Brain a collection of genetically-specified modules

91. Nature View (1) Not much is left to chance (2) Brain a collection of genetically-specified modules (3) Each module processes a specific kind of information & works independently of other modules

92. Nature View (1) Not much is left to chance (2) Brain a collection of genetically-specified modules (3) Each module processes a specific kind of information & works independently of other modules (4) In evolution: modules get added to the “collection”

93. Nature View (1) Not much is left to chance (2) Brain a collection of genetically-specified modules (3) Each module processes a specific kind of information & works independently of other modules (4) In evolution: modules get added to the “collection” (5) In development: genes that code for modules are expressed and modules develop according to these instructions “The grammar genes would be stretches of DNA that code for proteins… that guide, attract, or glue neurons together into networks that… are necessary to compute the solution to some grammatical problem.”

94. The nature view: Evidence Neurogenesis Neuroblasts give rise to a limited number of daughter cells Cells have a genetically mediated memory that allows them to remember how many times they have divided

95. Genetics and migration Mutant or “knock-out” mice The nature view: Evidence

96. Genetics and migration Mutant or “knock-out” mice Cannot produce a class of proteins called cell adhesion molecules (CAM’s) Migration is disrupted because cells cannot attach to and migrate along glia The nature view: Evidence

97. Growth of dendrites and axons Undeveloped neuron needs to establish basic “polarity:” which end is which? The nature view: Evidence

98. Growth of dendrites and axons Undeveloped neuron needs to establish basic “polarity:” which end is which? Involves specific proteins The nature view: Evidence

99. Growth of dendrites and axons Undeveloped neuron needs to establish basic “polarity:” which end is which? Involves specific proteins Axons: Affords a sensitivity to chemical signals emitted by targets The nature view: Evidence

100. Growth of dendrites and axons Undeveloped neuron needs to establish basic “polarity:” which end is which? Involves specific proteins Axons: Affords a sensitivity to chemical signals emitted by targets The nature view: Evidence

101. Formation of synapses Knock-out mice

102. The nature view: Evidence Formation of synapses Knock-out mice Staggered Neurons in the cerebellum make contact, but receptor surface does not develop Thus, a single gene deletion can interfere with the formation of synapses in the cerebellum

103. The nature view: Evidence Cell death Cells seem to possess death genes When expressed, enzymes are produced that effectively cut- up the DNA, and kill the cell Similar mechanism may control the timing of neuronal death

104. Nurture view (1) Brain organization is emergent and probabilistic not pre- determined (2) Genes provide only a broad outline of the ultimate structural and functional organization of the brain (3) Organization emerges in development through over- production of structure and competition for survival

105. Nurture view (1) Brain organization is emergent and probabilistic not pre- determined (2) Genes provide only a broad outline of the ultimate structural and functional organization of the brain (3) Organization emerges in development through over- production of structure and competition for survival Gerald Edelman: Neural Darwinism Overproliferation of structures + sensory experience produce Darwinian-like selection pressures in development Structures that prove useful in development win the competition for survival The rest are cast off

106. The “nurture” view: Evidence Does experience affect developing structures and functions? Is the pruning of brain structures systematic? Do developing brain regions competitively interact?

107. Hubel & Weisel Raised kittens but deprived them of visual stimulation to both eyes (binocular deprivation) No abnormality in the retina or thalamus Gross abnormality in visual cortex Disrupted protein production caused fewer and shorter dendrite to develop, as well as 70% fewer synapses Effects only occur early in development, but persist into adulthood Example: Surgery on congenital cataracts in adult humans The “nurture” view: Evidence

108. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired Hubel & Weisel The “nurture” view: Evidence

109. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired One effect: Monocular deprivation disrupted the establishment of ocular dominance columns Hubel & Weisel The “nurture” view: Evidence

110. Development of mammalian visual system Eyes/Retinas Thalamus Cortex Adult structure

111. The “nurture” view: Evidence Development of mammalian visual system Adult structure Eyes/Retinas Thalamus Cortex

112. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired Sensory input competes for available cortex With input from one eye eliminated, no competition Therefore, input from uncovered eye assumes control of available visual cortex and disrupts the establishment of ocular dominance columns Hubel & Weisel The “nurture” view: Evidence

113. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired Sensory input competes for available cortex With input from one eye eliminated, no competition Therefore, input from uncovered eye assumes control of available visual cortex and disrupts the establishment of ocular dominance columns Hubel & Weisel The “nurture” view: Evidence Findings point to the importance of stimulation from the environment

114. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired Kratz, Spear, & Smith The “nurture” view: Evidence

115. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired A second effect: Residual function of the deprived eye competitively inhibited by strong eye Kratz, Spear, & Smith The “nurture” view: Evidence

116. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired A second effect: Residual function of the deprived eye competitively inhibited by strong eye Deprived one of experience and then removed strong eye Kratz, Spear, & Smith The “nurture” view: Evidence

117. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired A second effect: Residual function of the deprived eye competitively inhibited by strong eye Deprived one of experience and then removed strong eye Prior to surgery, stimulation of deprived eye elicited activity in only 6% of cortical neurons Kratz, Spear, & Smith The “nurture” view: Evidence

118. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired A second effect: Residual function of the deprived eye competitively inhibited by strong eye Deprived one of experience and then removed strong eye Prior to surgery, stimulation of deprived eye elicited activity in only 6% of cortical neurons: After surgery  31% Kratz, Spear, & Smith The “nurture” view: Evidence

119. Early monocular deprivation After restoring stimulation, vision in this eye is severely impaired A second effect: Residual function of the deprived eye competitively inhibited by normal eye Deprived one of experience and then removed normal eye Prior to surgery, stimulation of deprived eye elicited activity in only 6% of cortical neurons: After surgery  31% Kratz, Spear, & Smith The “nurture” view: Evidence Findings point to the importance of competitive interaction between developing brain regions

120. Impoverished Environments The “nurture” view: Evidence Animal raised in impoverished environments have brains that are 10 to 20% smaller than animal raised in normal environments. Why?

121. Impoverished Environments The “nurture” view: Evidence Animal raised in impoverished environments have brains that are 10 to 20% smaller than animal raised in normal environments. Why? Decreased glial cell density Fewer dendritic spines Fewer synapses Smaller synapses

122. Cortical surgery Severed connection between optic nerve and the occipital cortex as well as the connection between auditory nerve and auditory cortex Reconnected optic nerve to auditory cortex Animals developed functionally adequate vision The “nurture” view: Evidence Sor

123. The “nurture” view: Evidence Daphnia: A crustacean; easily cloned Simple nervous system consisting of several hundred neurons Connection patterns can be studied directly Genetically identical individuals show different patterns of neuronal connectivity

124. Nurture view: Summary Order in the brain is not highly specified by the genes Instead, structures and functions emerge probabilistically in development through the combined influence of initial over- production of structure, neural competition, and experience