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.

• See figure in Add Neurons Subtract Anxiety Scientific American July 2014

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.

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.

Atypical Chromosomes Have Widespread Effects

A. Down syndrome is a chromosomal abnormality–the inheritance of an extra chromosome 21

B. Fragile X syndrome results from inheriting extra trinucleotide repeats, repetitions of nucleotides, in the same gene

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