Brain Development and Plasticity Flashcards
What are the seven stages of brain development?
- Cell birth (neurogenesis; gliogenesis)
- Cell migration
- Cell differentiation
- Cell maturation (dendrite and axon growth)
- Synaptogenesis (formation of synapses)
- Cell death and synaptic pruning
- Myelogenesis (formation of myelin)
What is the neural tube?
-Rolled up sheet of cells that will form the brain and spinal cord
What are the approaches to studying development of the brain?
- Correlate nervous system development with development of specific behaviours
- Look at behaviour and make inferences about brain development
- Examine factors that influence both brain development and behavioural development
Where does neuron generation begin?
- Neural stem cells grow out of neural tube. These produce neuroblasts and glioblasts
- The ventricular zone is also lined with neural stem cells
Explain migration and differentiation
- Migration occurs up until end of first 8 months of life; brain is more sensitive to trauma during this time. Radial glial cells extend from ventricular zone to the cortex, neurons migrate by travelling along cells. Develop layers from the inside out
- Differentiation - neuroblasts become specific types of neurons (complete at birth)
What are the components of neural maturation?
- Development of the dendrites (dendritic arborization, growth of dendritic spines; slow, continues after birth)
- Development of axons (reach specific targets, grow away from cell body, some follow chemical/electrical signals)
- Neural pathways (axons) can be blocked by ingestion of toxic chemicals, damage to axon’s target, genetic abnormalities. Incorrect pathway formation can lead to athetosis (slow, involuntary writhing movements of extremities) and dystonia (sustained muscle contractions)
How are synapses formed? What are the five steps?
- Genes, cues, and signals guide formation of synapses
- Phase 1 and 2: Generated independently of experience (occurs between conception and birth)
- Phase 3: Rapid growth (at birth)
- Phase 4: Plateau and rapid elimination through puberty
- Phase 5: Plateau through middle age and steady decline with age
Which phases of synapse formation are experience expectant? What does this mean?
- Development depends on presence of sensory experiences
- Phases 3 and 4
What phases of synapse formation are experience dependant? What does this mean?
- Generation of synapses that are unique to individual
- Phases 3, 4, 5
What have imaging studies shown us about gray matter in the brain?
- MRI scans show that gray matter begins to decrease around age 6-7 beginning in the dorsal parietal and sensorimotor regions and spreading. Decline continues until around 60 years of age
- Differences in gray matter are noted between those with disorders (Wiliams syndrome, ADHD, FAS) and normal controls
- Poorer performance on vocab subtests correlates with cortical thickness
What are the four stages of cognitive development?
- Sensorimotor (object permanence)
- Preoperational (can represent things with words and drawings)
- Concrete operations (conservation)
- Formal operations (abstract reasoning)
- Brain growth spurts (increase in synapses and glial cells) coincides with stages of cognitive development
What tests show development of the forebrain?
- Forebrain is involved in learning and memory
- Nonmatching to sample task (assess temporal lobe function, children can solve around 18 months of age)
- Concurrent discrimination (assess basal ganglia function, children can solve around 12 months of age)
What is the Kennard Principle?
-Functions are spared when injury occurs during infancy
What three things do the effects of brain injury depend on?
- Behaviour affected
- Extent and location of damage
- Precise age of injury
What are the effects of age on brain injury?
- Before 1 year of age: Greater impairments
- Between 1 and 5: Some reorganization, language can be rescued
- After 5: Little to no recovery of function
How does age at language acquisition affect its representation in the brain?
- When two languages are acquired in childhood, they share Broca’s area
- When two languages are acquired in adulthood, they are separated in Broca’s area
What happens to language after early left hemisphere and right hemisphere injury?
- Language survives after early left hemisphere injury (attributable to appropriation of a potential language zone in the right hemisphere)
- Early lesions in right hemisphere - deficits similar to lesions in adults
What do left and right hemisphere lesions depress in the WAIS test?
- Left hemisphere lesions depress verbal and performance scores
- Right hemisphere lesions depress performance scores
What occurs when lesions invade both Broca’s and Wernicke’s areas?
- Left ear advantage on dichotic listening test
- After right-hemisphere sodium amobarbital injection: Mute for naming objects and series repetition (naming days of the week)
What occurs with large posterior lesions at two and a half years of age?
- Left-ear advantage for both digits and melodies
- Sodium amobarbital: Naming was disturbed by both left- and right-hemisphere injections; series repetition was performed well after left, but not right, hemisphere was injected
- Speech functions of posterior zone shifted to the right
- Anterior zone still retained speech function
What was found in patients with left-hemisphere damage early in life? (General findings)
- Left hemisphere speech, bilateral speech, and right hemisphere speech
- Representation of speech was dependent on damage
When are injuries to the brain most and least devastating? (When can and can’t the brain recover?)
- Complete recovery of function if injury recovers during neurogenesis
- Injury during migration and differentiation is devastating
- After migration and differentiation, the brain can recover
What are the plastic changes in the brain that support recovery? (Generally)
- Intact circuits of the brain reorganize
- New circuitry is generated
- Neurons and glial cells are generated to replace lost neurons
What are the effects of brain lesions on brain structure later in life?
- Damage causes brain to be smaller in adulthood
- Neuronal morphology - lesions at different ages produce differential effects on the neurons (lesions at day of birth = less extensive dendritic branching; lesions at 10 days = increased dendritic branching)
