Lecture 26- refinement of synaptic connections I Flashcards
Are our brains complex?
-yes -85 billion synaptic connections
How does the number of prefrontal synapses change throughout life?
- number of excitatory synapses in the brain increases rapidly after fertlization
- the increase lasts until 5 years of age
- after 5 years of age the number of prefrontal excitatory synapses starts decreasing
- at the age of 15 the number of prefrontal inhibitory synapses starts increasing and continues for a while
What is the role of synapse elimination?
-During brain development there is an explosion of synapses, the connections that allow neurons to send and receive signals. - During childhood and adolescence, the brain prunes synapses, limiting their number so different brain areas can develop specialised functions. -Brain plasticity is the crucial thing for this!
What does plasticity mean?
-Plastic is derived from the Latin word plasticus and the Greek word plastikos, both meaning able to be moulded, pertaining to moulding
What is required for refinement of synaptic connections?
-Experience
Why is it important to understand how experience shapes brain development?
-if we could understand this maybe it would help with treating the disorders of the synapse such as autism and schizophrenia
What is the problem in autism?
- autism is an excess of synaptic connections
- at about 2 years of age something goes wrong
What are the symptoms of Schizophrenia in terms of brain development?
- myelination is reduced (deficient myelination)
- decrease in interneuron activity
- excessive excitatory pruning
- decrease in inhibitory neuron activity
- schizophrenia differences are visible later in development, around 20 years of age usually
What is the evidence for refinement of synaptic connections needing experience?
-experiments with deaf cats where the cats that were deaf (lack of experience) have different synaptic connections
What are the critical periods of development?
-Specific times in early life when the brain is actively shaped by environmental input: heightened brain plasticity -Understanding the triggers for critical periods will allow us to re-open them in adulthood, re‐open them in adulthood, thus re-awakening a brain’s youth‐like plasticity. -Critical period plasticity in local cortical circuits. -Such research has implications for brain injury repair, sensory recovery, and neurodevelopmental disorder treatment. -sensitive periods= another way of saying critical period -first sensory, motor and then higher cognition
What is often used as an experimental model of critical period plasticity?
-the visual system
What does the visual system need during development and how has it been discovered?
-Need visual stimulation during development -Deprivation of certain experiences at an early age compromises brain development and function. -Limited success corrective surgery for children with cataracts -‐-‐ a condition - No improvement in children older than 8 but success in infants. -The differences in patient outcomes suggested receiving sensory information early in life was important to healthy visual development. -there is a critical period in the visual system -if you don’t have the visual experience then your visual system will not develop normally
What are the occular dominance columns?
- Ocular dominance columns are stripes of neurons in the visual cortex of certain mammals that respond preferentially to input from one eye or the other
- this is what develops when normal development occurs
What is the Hubel and Wiesel experiment?
-demonstrated importance of experience for correct cortical development:
A) gradation of where the input is coming from, stimulate the eye and some neurons only respond to stimulation in one or the other eye and some from both
B) close the eye for a little period of time just after birth= completely changed the response, only one eye active
C) here close it in an adult, the change wasn’t big, both eyes respond,
What is the mouse barrel cortex?
- Topographic maps occur when the physical organisation of a part of the brain reflects the organisation of the world outside the brain
- topographically mapped -for every whisker is one barrel shaped cell in the cortex= the barrel cortex
- Mouse sensory homonculus includes whiskers (barrel fields) -Each whisker separately mapped
- Mutant with extra whisker have extra representation in cortex -this is easy to stain histologically
- each whisker maps onto the cortex -so you only trim a whisker
- or add more whiskers (mutant) hen get extra barrels = so plastic part of the cortex
- if you trim it during development= then the barrel doesn’t form
What happens when you remove a whisker in a mouse?
-it removes its representation in the cortex
What happens when two whiskers are tied together in a mouse?
-Tying two whiskers together leads to their separate representations fusing
What happens when you remove all the whiskers bar one in a mice?
-Remove all whiskers bar one and cortical representation for remaining whisker increases
What happens when you stimulate one whisker a lot?
-Stimulate one whisker and representation decreases
What did Wilder Penfield do?
- Epilepsy surgeon at Montreal Neurological Institute
- he would take out bits of the brains that were responsible for seizures
- before taking them out he stimulated them and see what is experienced= developed the map the homuluncus from his surgeries
- e.g.: 1. Tingling in the left thumb
2. Protrusion of the tongue
3. Hears specific orchestral music
