Download Intrinsic and Extrinsic Factors

Neuroplasticity (Neural Plasticity)
• Brain circuits are changed by experiences
• Occurs across the lifespan although more impact
during early development
• Changes structure
– Number of neurons
– Density of synapses
– Density of dendritic spines which can change shape in
seconds.
• For Example
– In rats, social isolation leads to changes in the brain.
– A brain region involved with processing odors, the
posterodorsal amygdala, is affected by play. (fig 1.4)
The Role of Play in Brain Development
Experience Is an Important Influence on Brain Development
• Visual deprivation during sensitive period can lead to
blindness.
• Amblyopia—impairment of vision in one eye with inability to
see clear forms
• The sensitive period of development is when experience or
treatment can make permanent alterations.
• Monocular deprivation during this period causes the deprived eye to
not respond in adulthood.
• Binocular deprivation—no light to both eyes–produces changes in
neurons in the visual cortex.
Brain Development in the Visual Cortex of Cats
Ocular Dominance Histograms
Which Line Is More Slanted?
The Plasticity of Somatosensory Representations
Normal and Reorganized Somatosensory Cortex
Inversion goggles
• Some preliminary experiments on vision without inversion of the
retinal image Stratton 1896
• Erismann and Kohler: Inversion goggle 1950
– https://www.youtube.com/watch?v=jKUVpBJalNQ
• Experiments with goggles, Kohler, Ivo. Scientific American, Vol
206(5), 1962, 62-86.
Neurogenesis in Adult Brain
• Fred Gage is given credit for discovering adult neurogenesis in
mammalian nervous system. Although Michael S. Kaplan found
evidence in the 1970’s but had difficulty publishing and
convincing other neuroscientists.
• neurogenesis in intact adult brain occurs in:
– Hippocampus (related to memory and behavior)
– cells lining the ventricles and the spinal canal, then migrating to olfactory
bulb (OB)
• Trauma to nervous system leads to increased neurogenesis
– Ischemia
– High levels of stress
– Toxins
• Enriched environment and exercise may also induce increased
neurogenesis
Neurogenesis in Adult Brain
• Important for replacing lost neurons
– Olfactory bulb
– Hippocampus
• Process of forming memory
– immature neurons are more excitable
• function as pattern integrators of temporally adjacent events
• enhancing pattern separation for events separated in time
– mature neurons
• contribute to pattern separation by being more amenable to learning
new information
• so there are groups of granule cells that respond to experienced
environments.
Role of Genes in Guiding Brain Development
• Genes can also have an effect on many behaviors.
• A mutation is a change in genetic structure.
• Animals with mutations may have an altered behavioral phenotype and are
useful to study.
• One group of mouse mutants includes different single-gene mutations that
affect development of the cerebellum.
• See fig. 7.19
Animals with mutations are important in researching development:
• Site-directed mutagenesis changes the sequence of a nucleotide in
a gene.
• A knockout organism has a gene disabled.
• A transgenic animal has a new or altered gene introduced.
Cerebellar Mutants among Mice
Role of Genes in Guiding Brain Development
Down syndrome is a chromosomal abnormality—the inheritance
of an extra chromosome 21.
Fragile X syndrome results from inheriting extra trinucleotide
repeats, repetitions of nucleotides, in the same gene.
Phenylketonuria (PKU) is a disorder of protein metabolism.
The defect is the absence of an enzyme that metabolizes
phenylalanine.
If not corrected by diet, high levels of phenylalanine will cause
intellectual disability.
Genes Influence on Brain Development
• Clones are genetically identical animals, yet neurons in clones can
show differences in neural connections.
• Epigenetics is the study of factors that affect gene expression,
without changing the nucleotide sequence of the genes.
– An important epigenetic factor that affects brain development is mothering.
– Poor maternal care induces methylation of a stress-response gene, causing a
lifelong heightened response to stress.
– Methylation modifies DNA and makes it less likely to be expressed.
Epigenetic Effects on Mouse Behavior
Epigenetics Definition
• Epigenetics
– epi- (Greek: επί- over, above, outer) –genetics
– is the study of heritable changes in gene expression
– caused by mechanisms other than changes in the underlying
DNA sequence
• Wikipedia, http://en.wikipedia.org/wiki/Epigenetics
• Transgenerational epigenetic inheritance
– paternal grandsons of Swedish men who were exposed during
preadolescence to famine in the 19th century
– less likely to die of cardiovascular disease
– if food was plentiful then diabetes mortality in the
grandchildren increased
Epigenetic mechanisms