5: Development and plasticity of the brain

Myelin sheath; muscle

A crushed axon can regenerate, by following its ___ ___ back to the original target; a cut motor axon may reattach to the wrong ___

¹⁴C

A radioactive isotope of carbon. By measuring the concentration in various body parts, it is possible to determine how often the cells turn over. Found that cells in the cerebral cortex correspond to year of birth, therefore no new cortical cells formed throughout life.

Ischemia

A restriction in blood supply to tissues, causing a shortage of oxygen and glucose needed for cellular metabolism (to keep tissue alive). Generally caused by problems with blood vessels, with resultant damage to or dysfunction of tissue.

Closed head injury

A sharp blow to the head resulting from accident or assault that does not puncture the brain.

Hemorrhagic stroke

A type of stroke that involves arteries or other blood vessels rupturing and spilling blood into the brain tissue and surrounding area. Damage directly occurs from effects of blood and excess oxygen, calcium, and other waste products. (Nearly always fatal)

Ischemic stroke

A type of stroke that involves obstruction, blood clot, or temporary narrowing of blood vessels causing blood supply to be closed off, with damage caused by loss of oxygen and glucose

Cerebrovascular accident

AKA for stroke

Dendritic spines

About 6% of ___ ___ appear or disappear within a month, representing the process of learning. In addition, dendritic branches can expand or retract.

Quick; peer pressure

Adolescents are able to make reasonable mature decisions when they have plenty of time to think them through, but are impulsive when making ___ decisions in the face of ___ ___.

Earlier (in fact, in the first few days after damage, therefore assessment and recovery treatment should start asap)

After stroke, the brain has most plasticity earlier/later following the damage

Retrieval

Brain damage impairs memory ___, but does not destroy the memory trace, making relearning easier

Tonal

Certain brain areas are up to 30% larger in professional musicians, which enables them to recognise and learn the meanings of the rises and falls in ___ languages faster than non-musicians

Neurotrophins

Chemicals that promote the survival and activity of neurons, of which Nerve Growth Factor (NGF) is one

Result; cause

Does musical training cause brain changes, or do people with certain types of brains seek out musical training? Scans before and after commencement of musical training have indicated that the associated brain changes are the ___ of musical training, rather than the ___.

Neural darwinism

During embryological development, long before first exposure to light, repeated waves of spontaneous activity sweep over the retina from one side to the other; consequently, axons from adjacent areas of the retina send almost simultaneous messages to the thalamus. Each thalamic neuron selects a group of axons that are simultaneously active. In this way, it finds receptors from adjacent regions of the retina, then rejecting synapses from other locations. This is an example of ___ ___.

Chemical gradients

During pathfinding, axons aim to their correct location through ___ ___, where it follows a path of cell-surface molecules, attracted by some chemicals and repelled by others, with relevant brain areas having higher and lower concentrations of corresponding chemicals. Example: TOPdv in the amphibian brain - 30 times more concentrated in the axons of the dorsal retina and 10 times more concentrated in the ventral tectum. Axons with highest concentration connect with brain areas with highest concentration, and axons with lowest concentration connect with brain areas with lowest concentration.

Apoptosis

Foetal Alchohol Syndrome occurs when alcohol suppresses glutamate release (the main excitatory neurotransmitter), and enhances GABA activity (the main inhibitory neurotransmitter). Thus, developing neurons receive less excitation and less neurotrophin exposure, leading to widespread ___.

Synaptogenesis

Formation of synapses. This is the last step in neural development and continues throughout life.

Myelination

Glia cells produce myelin sheaths around axons which allow for rapid transmission. In humans, myelin forms first in the spinal cord before forming in the brain. ___ begins in the prenatal period and continues into adulthood.

Occipital

In blind people, non-visual stimuli such as touch or audition produce activity measured on fMRI and PET scans in the ___ lobe of the brain. This indicates that unused brain areas are taken over by other functions.

Temporal cortex

In older people over 60, the thickness of the ___ ___ shrinks by around 0.5% per year, leading to gradual memory impairment

Prefrontal cortex

In the context of impulse control, adolescents demonstrate less activity in the ___ ___ area of the brain

Neural darwinism

In the development of the nervous system we start with more neurons and synapses than we can keep. Synapses form with only approximate accuracy, and then a selection process called ___ ___ keeps some and rejects others, with the most successful axons and combinations surviving.

Physical activity

It has been found that ___ ___ accounts for a large part of the increased rat brain mass and intelligence found in the enriched condition experiment, thanks to angiogenesis in cortex and better oxygen utilisation

Cannabinoids (marijuana)

It has been found that, if administered within the first few hours after a stroke, ___ can have a marked improvement on cell loss, due to suppression of glutamate (since glutamate causes excitotoxicity)

Nicotine; cocaine

Mothers who use ___ and/or ___ during pregnancy tend to have children with higher incidences of ADD and behavioural deficits. However, this is based on correlational studies, and thus the effect may be less than suggested, due to the operation of third variables such as socioeconomic status.

Migration

Movement of primitive neurons and glia toward their final destination in the brain. Chemicals known as immunoglobins and chemokines guide the new cells to their eventual destination in the brain

Neuronal Stem Cells

Neurons do not divide during development; instead the body has a population of ___ ___ ___ which are able to form into neurons or glial cells

Excitotoxicity

Process following stroke whereby the sodium-potassium pump in neurons is damaged, leading to an accumulation of sodium, and release of glutamate which overstimulates neurons, eventually leading to cell death and penumbra

Differentiation

Process whereby neurons develop an axon and dendrites (this distinguishes neurons from other cells in the body); the axon grows before the dendrites, while the neuron is migrating toward its destination

Collateral sprouting

Process whereby, following deafferentation and associated loss/degeneration of previous axons, nearby axons fill in the cortical space/vacant synapses; accounts for neuroplasticity

Proliferation

Production of new cells; early in development, cells along the ventricles of the brain divide to become neurons and glia

Apoptosis

Programmed neuronal cell death; the developing nervous system produces far more neurons than will survive into adulthood; natural part of neural development AKA "Neural Darwinism" - the neurons that aren't able to integrate into functional networks die. The suicide program all neurons are born with.

Chemokines

Promote axonal pathfinding during migration; ensure axons are integrated into the right networks etc.

Deteriorate

Recoveries in functioning after stroke or brain damage deteriorate/stay stable in old age

Nerve Growth Factor (NGF)

Released by muscles; determines whether or not neurons die or survive; neurons that become part of a neural network receive this chemical from the other neurons in the network, and survive; neurons that are not integrated into a network fail to receive the chemical from other neurons, and die. Originally discovered in snake venom by Rita Levi-Montalcini.

Chemical pathfinding

Sperry, 1943: Experiment to prove ___ ___ by axons. Cut the optic nerves of newts, and rotated the eyeball. Showed that axons grew back to the original positions, and not to the positions corresponding to the new position of the eyeball.

Antisaccade task

Test to measure level of impulseness, whereby an 'attention getter' like a face or wiggling finger is presented on one side of visual field, and person's ability to turn eyes/head in opposite direction is measured. Children and adolescents have reduced ability compared to adults. ADHD children have more difficulty.

Edema

The accumulation of fluid, increasing pressure on the brain - a common side-effect of stroke

Penumbra

The area surrounding an ischemic brain area, which dies off or is adversely affected by the ischemia, through the process of excitotoxicity

Postcentral gyrus of the right hemisphere

The brain area that shows expanded representation of the left hand in people who began practicing stringed instruments in childhood: ___ ___ of the ___ ___ [write "of the" in answer]

Diaschisis

The decreased activity of surviving neurons after damage to other neurons. Increased stimulation, for example thalamic stimulation, can help, e.g. with stimulant drugs. Recovery from stroke depends largely on increasing activity for the opposite side of the brain, since it can atrophy in the absence of input from the damaged side. (not penumbra)

Brain damage

The exception to the rule that the cortical brain areas do not form new neurons in adulthood is that new cortical neurons can and do form after ___ ___

Enriched condition

The famous ___ ___ experiment involved rats being put in cages alone, cages with a few other rats, or cages with lots of rats and toys and opportunities for physical activity, with the latter rats showing increased cortical acetylcholine, and a heavier, thicker cortex due to: larger cell bodies, increased number of dendritic spines, more dendritic branching, and larger synapses

a. Proliferation; b. Migration; c. Differentiation; d. Myelination; e. Synaptogenesis

The five steps of neural development (a through e)

Adult neurogenesis

The process whereby stem cells differentiate into new olfactory bulb and hippocampus neurons in adults

Far transfer

The proposed phenomenon whereby practice on one type of task should yield improvement on other unrelated tasks e.g. doing crossword puzzles might improve memory etc. Has not been shown to have much applicability.

Deafferentation

The sensory-motor cortical homunculus associated with e.g. a hand digit will experience re-wiring following ___ (i.e. removal of the digit), whereby the areas for the surrounding digits will invade the cortical space occupied previously by the removed digit; accounts for phantom limb syndrome

Cooling (to between 34-35 degrees celsius)

The severity of penumbra cell death after stroke can be reduced by ___ the brain for three days after stroke

Thicker (because proper apoptosis / cell pruning does not occur due to absence of the relevant neural networks forming, so they end up with an overabundance of remaining neurons in this brain area)

The visual cortex in blind people is ___

More

To compensate for old age decline, some adults use ___ brain areas to compensate for reduced functioning

True

True/false: Following death to a brain area caused by stroke, the corresponding brain area on the other (contralateral) hemisphere will experience compensatory growth, providing some potential amelioration of brain damage

False

True/false: It is not possible to use a deafferented limb; once the sensory input is gone, the motor functions also cease

True

True/false: Some neurons do not complete migration to their final location until adulthood

False (think foetal alcohol syndrome etc)

True/false: The developing brain is more robust to toxins and other exposures than the brains of adults

False (when transplanted early, changes to match the new location; when transplanted later, partially changes, but retains some original characteristics)

True/false: When a very immature neuron is transplanted from one brain area to another, it retains the properties of the original location. When it is transplanted at a later developmental stage, it changes to completely match the new location.

Stress

When a mother rat (and similarly, a mother human) is exposed to ___, she tends to spend less time grooming her offspring, becomes more fearful, and her offspring become permanently more fearful in a variety of situations.

Collateral sprouting

Whether ___ ___ is helpful or harmful depends on whether the new replacement axonal branches serve a similar function to before (helpful, behaviour maintained), or serve a different function (unhelpful, behaviour impeded)

Immunoglobulins & chemokines

___ & ___. Chemicals that guide neuron migration; deficit in these chemicals leads to impaired migration, decreased brain size, decreased axon growth, and mental retardation.

Tissue Plasminogen Activator (tPA)

___ ___ ___: A protein given to ischemic stroke victims, which breaks up blood clots, and can be administered up to three hours after stroke, reducing cell death in the penumbra. Worsens hemorrhagic stroke symptoms, causing death, but administered anyway, since these people will die anyway, and it takes too long to distinguish ischemic from hemorrhagic strokes.

Focal hand dystonia (aka musician's cramp, or writer's cramp)

___ ___ ___: Process that occurs when, due to large amounts of musical practice, the somatosensory cortical representation of all fingers grows from side to side without spreading out, so that representation of each finger overlaps that of its neighbour. Representation of the middle fingers expands, overlapping and displacing representation of the index and little fingers, with one or more fingers going into constant contraction. Possible treatment via focusing carefully on bursts of vibration stimuli.

New neurons

___ ___ form in an area of the songbird brain necessary for singing; this area loses neurons in fall and winter and regains them the next spring (mating season)

Stem cells

___ ___ in the nose remain immature throughout life, with periodic division involving one cell remaining immature while the other differentiates to replace a dying olfactory receptor.

Phantom limbs

___ ___ only develop if the relevant portion of the somatosensory cortex reorganises and becomes responsive to alternative inputs e.g. from the face. In this case, a facial sensation is experienced as well as a simultaneous sensation in the amputated body part.

Denervation supersensitivity

___ ___: The long-term process whereby, following neural damage, the dendrites in dopamine synapses of remaining neurons become more responsive and more easily stimulated. Helps compensate for decreased input, sometimes enabling continued functioning, but can also lead to chronic pain.

Brain-Derived Neurotrophic Factor (BDNF)

___-___ ___ ___: Most abundant neurotrophin in cortex