Download The Brain for Not-So

Week 2 – Normal Brain Dynamics
Overview:
Physical Development – growing a brain.
“Fine Tuning” the brain – part of development that
continues throughout life
Aging – Maturation followed by (different degrees of)
degeneration.
Response to injury – restoration of function, or disorder.
Timeline of neuron birth & death in brain development
Neurulation
Failure to close the neural plate results in “neural tube defects” (NTDs)
spina bifida, encephalocele, anencephaly
Folate reduces the incidence of NTDs, but MUST BE ON BOARD FOR 1st TRIMESTER!
Apoptosis – “programmed cell death”
- An “orderly” death and removal of a cell
- As opposed to “necrotic” or injury-induced cell death
(“messy”)
- Important for proper neural tube formation
- Also matches neuronal population to available targets
- Eliminates neurons with erroneous or inadequate
projections
Myelination – adding “insulation” to axons
Unmyelinated axon
Myelinated axon
Enables faster & more efficient propagation of the Action Potential
Neurogenesis does not stop at birth
 Occurs in normal adult brain
 Adds neurons in hippocampus
 “
“
striatum
 Maybe also in cerebral cortex
 Neurogenesis is enhanced/supported by exercise
 Seems to be increased by antidepressant drugs
Synapse “Pruning”
Synapse Proliferation and Pruning in Human Brain
Summary of Grey Matter Changes in Developing Brain
A Reminder of how much humans can differ
Ok , so we built a brain…what’s it do now?!
The brain is “tuned” to its experience
For certain functions/areas there is a “critical period” for “tuning”
Imprinting
 Studied how newborns bond with parents
 He was first creature seen by newly-hatched
geese
 They became “imprinted” with/by his
appearance.
 Reason for naming of “baby duck syndrome”
by computer software developers
Konrad Lorenz
The “Westermarck Effect”
 “Reverse Sexual Imprinting”
 Seen among non-related populations raised together
 E.g. Kibbutz System
 Out of the nearly 3,000 marriages that occurred across the
kibbutz system, only fourteen were between children from
the same peer group. Of those fourteen, none had been
reared together during the first six years of life.
 Evolutionary advantage of reducing in-breeding
Edvard Westermarck
Harry Harlow – Maternal Bonding
 Investigated factors influencing newborn bonding to
mother
 Experiment with infants growing up with 2 “surrogate
mothers”
 One provided food, but was cold and hard (wire)
 The provided no nourishment, but was soft and warm
 Infants greatly preferred the “cloth mother”
 Retreated to the soft mother when anxious
 Were more outgoing, adventurous, able to meet new
monkeys in presence of “cloth mother”
 Touch (e.g., “skin to skin”) now an important part of
premature infant care.
Effect of environment on synapse pruning & stabilization
Development involves fine-tuning circuits ready for input
NORMAL
BIRTH
2 WEEKS
4 WEEKS
6 WEEKS
VISUAL CORTEX
LATERAL GENICULATE
(THALAMUS)
IF ONE EYE IS CLOSED
The developing brain “tunes” to its environment
Visual input alone is not sufficient – must coordinate with movement
Passive exposure does not yield appropriate motor reponses
Passive kittens do not learn:
- Paw placement
- How to recognize a “cliff”
- Blink reflex
“If you use it, your brain glues it” (?)
Standard Cage
Enrichced Cage
Effects of Environmental Enrichment on the Brain
SC
IC
Neuron Branching
Standard
Enriched
Dendrite Structure
EC
“Enriched” environment = “Enriched” brain structure and function
Use-Dependent Reorganization in Human Auditory Cortex