Neuroplasticity Flashcards
What is Localisation of Function [LOF]?
Certain functions of the brain are completed in specific areas
ideas of homunculus in motor, somatosensory, cerebellar and other areas consist with LOF model
Phenomenon of Wallerian degeneration fits well with model.
Wallerian degeneration
is a process that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. farther from the neuron’s cell body) degenerates. This is also known as anterograde or orthograde degeneration.
Founders of Localisation of Function: Rene Descartes [1576-1650]
The brain is the centre and nerves are ‘tubes’ running from brain to limbs and back
Reflexes are phenomenon where info travels in fluid to brain and back down
Body therefore has parts - mechanical
Founders of Localisation of Function: Paul Broca & Carl Wernicke
Paul Broca - surgeon
Stroke patient lost ability to speak - one word
Post-mortem exam - damage to left frontal lobe
Found other with same issue: Broca’s area
Carl Wernicke - surgeon
Connected left parietal area with inability to understand/comprehend language: Wernicke’s area
Fits well with LOF model.
Founders of Localisation of Function: Wilder Penfield
1930’s surgeon
Operated on conscious cancer and eplilepsy patients
Used electrical probe whilst ‘awake’ during brain surgery
Touch area and recorded what was felt [sensory] or moved [motor]
Normally done to ensure healthy tissue kept safe
But gave homunculus fine detail.
Founders of Localisation of Function: Changing times
Some evidence from 1800’s localisation may not be perfectly correct
Jules Cotard [1868] - children with loss of left hemisphere learned to speak
Otto Soltmann [1876] - removed motor cortex from infant dogs/rabbits, still learned to move
Shepherd Ivory Franz [1915] - stroke patients with paralysis made recovery with exercise!
Founders of Localisation of Function: Donald Hebb
1947 - rats raised as pets better at solving problems than rats in cage: Environmental enrichment influences brain growth [and capacity]
Neurones that fire together, and close in time, more likely to fire together again
Neurones that fire out of time unlikely to fire together
“Neurones that fire together, wire together”
Already suggested by others, including Sigmund Freud, but now called “Hebburn Theory” or Hebb’s Rule”
Changing Brain Maps [homunculi]: Hubel & Torsten [1960’s]
Hubel & Torsten [1960’s] - closed right eye of kittens, used electrodes to monitor brain activity
Permanently lost sight if eye closed between 3-8 weeks, partly recovered if opened, but no recovery in adult cats.
Nobel Prize: “critical period”
Critical periods of learning observed for many functions, e.g. Language, pattern recognition
NB - Changing Brain Maps [homunculi]: Michael Merzenich (1960’s - Present] - NB
Crossed nerves in adult monkey and remapped months later
Expected to see, e.g. Touch on finger = felt on thumb if ‘crossed’
Found normal brain map, must recognise!
Plasticity a competitive process now accepted
Changing Brain Maps [homunculi]:What did Merzenich’s research show?
It showed ‘competition’:
- learned maps takes over form unused areas [useful to remove unwanted processes]
- need some practice to retain map in competitive process
- more/better practice: less brain map required for task, therefore room for other maps
- learn early (child) then map takes foothold, harder to remove
- adult brain capable of learning/relearning
“Use it or loose it”
Neuroplasticity - Hebbian Theory = NB!!!
Experiences/situations that stimulate sensory and/or motor pathways lead to strengthening of synapses - LONG TERM POTENTIATION (LTP)
Neurones that fire together wire together
Therefore, neural networks adapt and alter
Changes to motor/sensory homunculus - cortical reorganisation
Disuse can weaken synapses - LONG TERM POTENTIATION (LTP)
This promotes maladaptive plasticity and impedes recovery [but good if want to ‘unlearn’]
Occurs if stroke survivor preferentially use only non-paretic limb in functional activity
Therefore ‘movement’ within 24hrs of stoke essential, ambulation if possible but only by trained personnel with medical clearance.
Neuroplasticity - Mark Rosenzweig [1960/70’s]
Name some findings that their research found:
Took Hebb’s research further to study changes in brain function, mass [cerebral cortex mass], neurotransmitters, etc.
Put rats in places with toys, ladders, wheels, etc. mental and physical stimulation
Rosenzweig & Bennet (1972) - enriched environment lead to heavier thicker cortices, more glial cells, larger cell bodies and nuclei, more dendritic spines, larger synaptic junctions, more protein synthesis, etc
But still about ‘development’ rather than ‘change’
Multitasking Brain Areas: Paul Back-y-Rita [1960’s]
Recorded from cat visual cortex with electrodes
Visual stimulus caused response
But so did touch and sound
Therefore visual cortex must process other senses
Not ‘learning’ but already present
Idea of single location for single function [LOF] incorrect?
Multitasking Brain Areas: Paul Back-y-Rita [1960’s] - History
Paul Bach-y-Rita’s Father suffered a stroke [1959]
Brother used progressive learning [crawling, washing dishes, etc.] and father recovered
Post mortem indicated massive brain damage [97% of tracts], but largely recovered!
Indicated ability for change, other areas take over task, in area where not thought possible
1969 [nature] - vibrators on backs of visually impaired replays 2D of video, people learned to ‘see’
Multitasking Brain Areas: Paul Back-y-Rita [1960’s] - Exercise
He also developed exercise plans for stroke:
- realised that patients improved, plateaued, improved, and so on
- normal rehab stopped at first plateau
- probably because plasticity-based learning = cyclic learning and consolidation
