Development and Plasticity

Barbara Arrowsmith Young training principles (1 and 2)

she forced herself to use and strengthen the affected areas of her brain


1. repetition of stimulation
2. regional and functional specificity

mechanisms of neuroplasticity

* synaptic plasticity by adding/removing channel-receptors at the synapse
* adding/removing synapses during development and in adulthood
* axonal sprouting
* new neurons born in adulthood

describe progression of brain development

starts small and smooth at 29 days, no wrinkles at 11 week fetus, more wrinkles progressing from childhood to teenagehood to adulthood

why does the brain continue to grow after birth?

the size of a human head is limited by the size of the birth canal, so humans evolved to continue growing their brains after birth; this is also why an infant’s head is so fragile

evolution of cranal capacity

500 cm3 to 1500 cm3

describe human evolution as it relates to the birth canal

ability to stand and have arms free to carry children was beneficial for early ancestors; those who lived in savannah’s could see farther away to spot predators; hip bone size limited to walk efficiently; hip bones form birth canal

neoteny or heterochromy

timing of development can be modified

what happens to the number of neurons and synapses as the brain matures?

decreases

pruning

reductions of neurons and synapses; normal process during development

approximately __% of neurons and synapses we have as newborns are eliminated by adulthood

50

when does the number of neurons and synapses increase?

prenatally and until shortly after birth; peaks around 2-3 weeks

when does the number of neurons and synapses decrease?

into adolescence; peaks at 8 months or 1 year

synapses maturation

strengthening and refining

gray matter

neuronal somas and dendrites

white matter

axons covered by myelin

myelination

occurs during development and changes with age

white matter density

myelination; indicates the number of axons covered in myelin

describe the number of myelinated axons over time

increases for two decades then plateaus

Mark Rosenzweig

* studied effects of environmental enrichment on the brain
* contradicted fixed brain theory by demonstrating that learning/experience can change the brain

Mark Rosenzweig rat enrichment experiment

* rats in playful, social, engaging environments had a heavier cortex than rats in insolating, boring, barren environments
* enriched environments led to an increased number of neurons and synapses and an increased amount of neurotransmitters and myelination

Santiago Ramon y Cajal

* father of neuroscience
* neuroanatomist
* suggested mechanism underlying learning did not require formation of new neurons
* rather, memories could be formed by strengthening connections between existing neurons
* activity dependent changes in synaptic transmission can alter normal circuitry and thus behavioral response

synaptic plasticity

activity dependent changes in synaptic strength

Donald O. Hebb’s Hebbian principles of experience-based neuroplasticity

1. use it or lose it
2. use it to improve it (repetition and intensity of stimulation)


1. regional and functional specificity

LTP

long-term potentiation; occurs after high synaptic activity; insert additional AMPA receptors

LTD

long-term depression; occurs after low synaptic activity; internalization of AMPA receptors

NDMA receptor

glutamate which allows influx of Ca+2

* increased Ca+2 in post-synaptic dendrites produces LTP
* Ca+2 produces protein phosphate products LTD

critical periods of learning

temporal window during development in which environmental factors influence formation of synaptic connection and circuit function

plasticity as it relates to drugs

cocaine induces plasticity of dendrites; increased plasticity may be part of basis for addiction

X-ray

shows bone not brain

brain imaging

technology that allows us to see the brain

Computed (Axial) Tomography Scanner

CAT or CT scan; resolution: several mm

(functional) Magnetic Resonance Imaging Scanner

fMRI or MRI; resolution:

neuromodulation

transdisciplinary field focused on treating nervous system disorders with technological interventions at an appropriate neural interface that provides a therapeutic response

deep brain stimulation (DBS)

used for Parkinson’s disease, essential tremor, dystonia

transcranial magnetic stimulation(TMS)

noninvasive procedure that uses magnetic fields to stimulate nerve cells

optogenetics

light-sensitive channels