Neurodevelopment 2 Flashcards
Does the brain produce new neurons in adulthood?
- Originally it was believed that no new neurons were formed after early development
- Early findings in rats were dismissed or highly criticised (Altman, 1962; Bayer, 1982; Kaplan, 1981)
Neurons in songbirds
In songbirds – there is a steady replacement (seasonal) of neurons in the ‘singing’ area (Nottebohm 70s and 80s)
“What we found…was a huge pool of labeled cells – and many of the cells were new neurons. Every bird, young or old, was producing thousands of them each day” (Specter, 2001)
New neurons were generated in the lining of the ventricles, migrated to their final destination, differentiated and then responded to auditory stimuli
Neurons in humans
- what are there few of?
- what contains cells that continuously divide to provide new olfactory sensory neurons, and replace damaged one?
- what do cells produced in the subventricular zone (SVZ) of the lateral ventricles migrate to replace?
- what is the long path of migration towards the olfactory bulb called?
- There are a few ‘neurogenic’ (we can still create new neurons in adulthood in those regions) regions in the adult human brain
- Olfactory epithelium
- interneurons in the adult olfactory bulb
- the Rostral Migratory Stream (RMS) (Altman, 1969; Curtis et al 2007)
The Rostral Migratory Stream (RMS)
- where do newborn cells from the subventricular zone (SVZ) migrate to?
- what wrap around the migrating neurons and what do they create + function of this
- occur?
- Newborn cells from the subventricular zone (SVZ) migrate to the olfactory bulb and become interneurons
- Astrocytes wrap around the migrating neurons to create a ‘pipeline’ and keep them on the right path
- This occurs throughout life
The hippocampus:
- what was the first neurogenic area to be discovered?
- what happens with new neurons?
- The granular layer of the dentate gyrus of the hippocampus, was the first neurogenic area to be discovered (Altman & Das, 1965)
- New neurons are created and added to the dentate gyrus throughout life
Cerebral cortex:
- what does there seem to be?
- what can be induced by injury but what does it depend on?
- There seem to be very few adult-born neurons in the cortex, which are created in the subventricular zone (SVZ) but still not much is known
- Neurogenesis can be induced by injury but it depends on the extent of the injury.
Recovery following injury:
1- what brains is recovery better in?
2- collateral sprouting meaning
3- what happens? (2 things)
4- when after damage is the rate of new synapses forming very fast?
1- Recovery is better in younger brains than in older brains and it is better in the periphery than it is in the brain
2- The mechanisms of recovery mainly involve new branching of axons and dendrites, a process known as collateral sprouting
3- new branches formed by non-damaged axons attach to vacant spots of dendrites and cell bodies
3- The cells secrete neurotrophins that allow collateral sprouting to occur
4- Especially in the first 2 weeks after damage, the rate of new synapses forming is very fast.
(Rearrangement of neuronal branching so we can recover some of the function- collateral sprouting- happens after injury)
Collateral Sprouting:
at first and after injury
At first:
Axon is coming and synapsing on dendrites (axon 1) and another neuron that is synapsing on (axon 2)
Injury:
If there is an injury and we lose an axon- axon 2 is eliminated- there is a big gap. Neurons detect that there is space around and they grow and branch, taking over this area. Collateral sprouting occurs, involving growing and extensions and increasing the point of contact with the neuron.
sum-
at first: axon 1 and axon 2
injury: axon injured- degenerates- loss of an axon
afterwards: collateral sprouting to fill vacant synapses
Brain adaptations occur throughout life:
- what is there in people blind since infancy?
- who have a better sense of touch and vision
- in what cases can we intervene and what does this force us to do?
- so, what happens and term
- In people blind since infancy there is enhanced tactile (finger sensitivity) and auditory ability
- People who are deaf have a better sense of touch and vision
- In cases of amblyobia or lazy eye we can intervene (i.e. wear an eye patch) and reinstate good vision. Forces to use weak eye which causes that eye to become stronger.
- So, the brain adapts according to the environmental stimuli, known as neuroplasticity (synaptic plasticity)
Reorganisation in the monkey cortex
What did scientists do and find?
Scientists recorded from the somatosensory cortex of the monkey and they were able to map out which areas of the somatosensory cortex responded to stimuli of the fingers of the monkey.
They then did a recording (D1, D2, D3, D4, D5)
Experimenters then surgically removed one of the fingers of the monkey and when the monkey after some time they repeated their recording.
They found the areas of the brain that corresponded to the missing finger were taken over by the areas of the brain that responded to the digits that are near by. They have taken over the space of the finger that is no longer used. This demonstrates there is rearrangement of the brain depending on whats going on in the environment.
Somatosensory cortex of a monkey after a finger amputation
The cortical area previously responsive to the third finder becomes responsive to the second and fourth finger and part of the palm.
Blindness (Burton et al 2002)
study and results
procedure:
Researchers asked sighted and blind people to feel Braille letters or other items and say whether they were the same or different
results:
- Blind people performed better (they have more experience/ sensitivity)
- PET and fMRI scans indicated substantial activity in the occipital cortex (back of brain) of blind people while they performed these tasks
- Auditory stimuli also produced increased responses in visual areas of the cortex
Music Training
- musicians and brain area functions?
- what do MRI scans reveal?
Musicians have larger brain areas responsible for hearing and finger control
MRI scans reveal:
- The temporal cortex of professional musicians in the right hemisphere is 30% larger than in non-musicians
- Thicker grey matter in the part of the brain responsible for hand control and vision of professional keyboard players
- Larger than normal area of the postcentral gyrus in the right hemisphere for the movements of the left hand (string control)
More vs Fewer Experiences
- Rats raised in an enriched environment develop a thicker cortex and have increased dendritic branching (Rosenzweig & Bennet 1980) (this could perhaps mean they have more synapses)
- Much of the enhancement was due to physical activity (they get to explore and move around more compared to standard cage)
- Increased dendritic branching was correlated with improved ability to learn
Broca’s Area and Language Development
- dendritic spines growing potentially due to differentiation
- 2 year old in terms of language/ experience- already has experience in linguistic environment which also helps them develop this rich brain area
