PSYC2410 – Chapter 9
What causes neurons to die?
Competition for target-supplied neurotrophins. Nerve growth factor (NGF): the first neurotrophin to be isolated (Levi-Montalcini,
1952). From targets of sympathetic neurons. When short of neurotrophins, they die.
Nerve Growth Factor (NGF)
Brain derived neurotrophic factor (BDNF)
Glial cell-line derived neurotrophic factor (GDNF)
Neurotrophin 3 (NT-3)
Neurotrophin 4/5 (NT-4/5)
Ciliary Neurotrophic Factor (CNTF)
Fibroblast growth factor (bFGF)
Multiple Functions of Neurotrophins:
1 – they promote neuronal growth
2 – they promote neuronal survival
3 – they can function as axon guidance molecules
4 – they can stimulate synaptogenesis
5 – their absence can actively trigger apoptosis
Postnatal Development of the CNS
Mostly synaptogenesis, myelination, dendritic branching, axonal growth and connections. Also neurogenesis, new neurons being
Phases of growth alternated with phases of regression of that growth. Initially a big growth of synapses and myelination of those
axons etc. which is followed by regression, pruning, where there is loss of some synapses. Only those that are used and are
important are kept, others that aren’t used die and disappear, this fine tunes the system.
Postnatal Development of the Prefrontal Cortex
1. Working memory (temporary memory used while a task is being performed)
2. Planning and carrying out sequences of action
3. Following rules for behaviour
4. Context dependent inhibition of inappropriate responses (eg. Error perseveration in 7-12 mths old infants)
o Piaget’s test: have a toy like they, take toy and hide it behind one screen and tell them to go get the toy and they
will go get it. Now you take the toy and you hide it behind a different screen, and when you ask them to get to toy,
they go to the first screen.
Experience and Neurodevelopment
Type of experience:
Effect of Timing:
Critical period: periods during which certain types of experiences must happen or else development of a certain thing/part
won’t happen. Many, hard to study. PSYC2410 – Chapter 9
Sensitive period: when certain experiences happen they allow for an ideal development of function. Beyond these periods,
they can still develop these functions but not perfectly so. Ex: learning of language.
In brief: neurons and synapses that are not activated by experience do not usually survive. Studies on early sensory
Animals reared in the dark
Rats reared in the enriched environment: bred in enriched environment rats have more neurons and more synapses, in
particular areas for emotions and learning, hippocampus
Experience and Neurodevelopment can compete
Blindfold both eyes: cortical degeneration, few neurons and few synapses
Blindfold one eye: accelerated cortical degeneration from the blindfolded eye, because the other eye that can see takes
over, and that input accelerates the loss of activity with the blindfolded eye.
Study with ferrets: retinal ganglion axons medial (auditory) geniculate nucleus. So then the medial geniculate then gets
visual information and becomes organized like the lateral geniculate nucleus (visual)
Study with barn owls: nocturnal birds of prey. Use eyes and ears to locate prey. Raised with vision displacing (eg. By 23 )
prisms on their eyes. All the visual input becomes bent and distorted, their entire visual cortex becomes rotated by 23 , and
event he auditory cortex is also affected.
Another study with ferrets: allowed scientists to understand the spontaneous activity. Baby ferrets born with eyes closed,
neonatal optic nerve activity disturbed before eye opening.
MRI study with humans: early music training expands the area of the auditory cortex for complex tones, more active
auditory cortex. Early exposure to music, and music lessons.
Experience effects on Neurodevelopment
Direct gene regulation: that promote growth or regression of certain neurons or synapses
Neurotrophins release regulation:
Regulation of Spontaneously Active Neural Circuits
Neuroplasticity in Adults
Adult brains retain a high degree of plasticity
o Neurogenesis: new neurons are formed. Demonstrated in humans. Tracers injected into the brains of researchers
that were near death, and their brains were studied after.
o Experience-induced cortical reorganization
Neurogenesis in Adults. Majority of new neurons are not used and enter apoptosis and die.
o New neurons form in the Ventricular zone where there are new stem cells and migrate via glia-mediated
Hippocampus (2000 new neurons formed an hour): what are those neurons for?: learning and memory?
o Neurons formed in the subgranular zone new stem cell migrate into the denate gyrus granula cells where
they may or may not become integrated into the function of the hippocampus
Experience-induced cortical reorganization: PSYC2410 – Chapter 9
Adulthood experience: reorganization of sensory and motor maps. Musicians: Usually have a right auditory cortex more
developed, and the brain section responsible for hand movement, left hand movement, is more developed. Cab drivers in
London had larger hippocampi. They have lots of years of driving experience and memorizing the streets and maps of
London, and as their years of learning went by, it got larger. The training itself drove the development of the growth of the
area needed for that job.
Experience-induced cortical reorganization – 2 (A controlled EEG study by Braun et al, 2000) the electrodes measured the
response of the cerebral cortex from the hand, which match the mapping of the hand.
o Human volunteers: 20 hours of tactile stimulation (1 h a day or 20 days), training. Close their eyes and only touch
o Group 1: passive stimulation of little finger and thumb. Chatting, doing other things at the same time.
o Group 2: active stimulation (while being stimulated they were asked to identify the stimuli), like using a pin or a
brush etc, so they concentrate and think about the stimulation.
o Result 1: in group 1 the cortical somatosensory areas for thumb and little finger moved closer together. After this,
the points that represent the little finger and thumb came closer together, shrinking the areas for the other fingers
o Result 2: in group 2 the cortical somatosensory areas for thumb and little finger moved farther apart, as the cortex