Lecture 2 Flashcards
CORTICAL REORGANIZATION
The brain reorganizes its inputs and local circuits through out the course of learning.
Vision Puppy Test
Visual system in dogs test-
Covered eyes of young puppies- when sensory input of eyes eliminated, the cortex changed
Spines not as desne, less synaptic connections, - saw that brain was reacting
It was believed that changes could occur only during critical peroids after birth- not true- now we know that local circuits can be altered and remodeleld in the adultu brain
Can be naturally occurins, rxn to injury, and as a result of experiences
Plasticity in Individual Neurons Detected Through
Increase in neuronal excitability
Dendritic arborization
Increase in spine density
Increase in synapses
How to create long lasting synaptic connections
Repetition of a task
Initial use of lots of cortex
Eventual use of less cortex to execute task
Long-term Potentiation
Silent receptors lack glutamate receptors
Stimulation of glutamate-NMDA receptors causes slient glutamate-AMPA receptors to bind with the membrane, making them available for binding
Shape of spines changes
Gene expression increases with increased Ca++
Motor Evoked Potentials
- stimulate brain and see what parts of body move
Mereznich’s Cortical Map
Electrophysiological mapping-
Put in hundreds of electro into sensory cortex of monkey brain
Stimulate body part- and expect to see evoked potential in a particular area of brain
Neural Plasticity
“Brain Plasticity” is the brain’s ability to adaptively revise its processing machinery through out life.
Brain change underlies perceptual, cognitive and motor skill learning - and unlearning.
Who developed concept of brain plasticity
Micheal Mereznich
Negative Plasticity
Negative plasticity as a contribution to age-related cognitive and motor decline and its impact on the decline of function in ageing
- focal dystonia
Mereznich’s Digital Amputation
Amputated 3rd finger of monkey
62 days later mapped monkey and saw reorganization
Cortical area for 2 and 4 expanded bc of no 3rd finger
Mereznich’s Digital Syndactly
Sewed 3 and 4 finger together in a monkey
3-4 months of fuse- darkened area
Because they no longer had these clear boundaries
Brain change in response to a lack of input
Brain is changing due to dsorder
Mereznich Differential Stimulation Training Task
Rotation disc- monkey had to keep finger on
If he didn’t put enough force the would not get food
Did it for 5 months
Dramatic expansion in cortical area devoted to receiving stimulating
Area increased in side since it has a lot
Mereznich Differential Stimulation Training Task Results and Findings
- There was about a three-fold increase in the cortical representation of the distal parts of these digits.
- These were adult monkeys
- The plasticity and reorganization is associated with activity and training
Timing and Neuroplasticity
Not only do we make memory traces of the spatial aspects of stimulatory inputs – but we also make traces of the timing of the tactile stimuli.
Inputs that engage cortical neurons nearly simultaneously are integrated in cortical neuronal representations.
Inputs that are active synchronously are represented together
Mereznich Finger tap
Stimulate monkey all together on every finger, distally and proximally
For 4-6 weeks 300x a day
Contorlled timing of stimuli
Now represented by two large zones
Red proximal
Orange distal
Structure of representation change
The neurons now had receptive fields that spanned the stimulated surfaces – more than one finger - no longer distinct columns
In other words the spatial properties of the neuronal receptive fields came to reflect the temporal patterning of the stimulation during training.
Focal Dystonia
of negative plasticity- focal dystonia- of negative plasticity- focal dystonia- piano players, music – when they have to move fingers repetitively – because of changes in neuronal based on constant stimulation
Nudo Monkey Digit Training/ Pronation
Randy Nudo and Jeff Klein- had a device with openings the monkey had to reach through- openings would get smaller and smaller cups so they had to develop skill
Trained three monkeys on a digit training task or task that required pronation and supination
Digit Training- increased cortical area for digigts and decrease in wrist
Pronation Supination- increased wrist, decreased fingers
Outcome:Motor cortex area M1 is alterable by use
There is a use-dependent reorganization of the motor system
Acquired motor skills are reflected in the topography of the neurophysiological maps in the motor cortex.
Nudo Digit Study Outcome
Motor cortex area M1 is alterable by use
There is a use-dependent reorganization of the motor system
Acquired motor skills are reflected in the topography of the neurophysiological maps in the motor cortex.
Nature Rehab- non skilled?
Non-skilled repetitive tasks do not result in brain map changes
fMRI
changes in blood flow and blood oxygenation in the brain are closely linked to neural activity. When neurons become active, local blood flow to those brain regions
PET
- A radiotracer is injected into the body, where it travels to cells that use glucose for energy.
The more energy a group of cells needs, the more the radiotracer will build up in that location
Active areas are bright on a PET scan, and show up as “hot spots
Transcranial Magnetic Stimulation
Mark where youa re stimulated and can see which part of body is moving
Can stimulate specific tract and see if that area responds
Ankle Immobilization Study
Liepert used transcutaneous magnetic stimulation to study cortical plasticity in 22 patients
That had unilateral immobilization of the ankle joint without a peripheral nerve lesion.
Cortical area responding to stimulating the Anterior Tibialis of the casted leg was reduced when compared to the non-casted leg.
Reduction correlated with duration of immobilization
Further support for the concept of Use-dependent reorganization of the motor system
Implicit and Explicit Knowledge
Pasqual Leone
Test group (shown orderly sequence of numbers) showed progressively
shorter reaction times
and
Significant increases in the maps of
cortical output to the involved muscles
Maps of the cortical outputs enlarged to the
point in which the subject achieved explicit
knowledge of the task
Then the maps went back to their baseline topography
Neuroplasticity Findings from studies by Merzenich, Nudo and Kliem
Adult brain can be functionally and architecturally remodeled.
The structure of the cortical maps or brain representations is dynamic.
Dosing is important
This remodeling can have positive or negative consequences.
Plasticity occurs in many areas:
Neuronal level - primary motor and sensory cortices
Axonal level - intracortical pathway
Cellular level - spine density, branching, synapses
