Cognitive Neuroscience David Eagleman Jonathan Downar Chapter Outline The Brain Dynamically Reorganizes to Match Its Inputs The Brain Distributes Resources Based on Relevance The Brain Uses the Available Tissue ID: 565298
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4: Neuroplasticity
Cognitive Neuroscience
David Eagleman
Jonathan
DownarSlide2
Chapter Outline
The Brain Dynamically Reorganizes to Match Its Inputs
The Brain Distributes Resources Based on Relevance
The Brain Uses the Available TissueA Sensitive Period for Plastic ChangesHardwiring versus World ExperienceThe Mechanisms of ReorganizationChanging the Input Channels
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The Brain Dynamically Reorganizes to Match Its Inputs
Changes to the Body Plan
Changes to Sensory Input
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Changes in the Body Plan
The brain is constantly changing, reorganizing with each new experience.
Plasticity is the ability to change and to retain that new structure.
Plastic changes must be relevant.Some systems have a sensitive period early in life when they have greater plasticity.4Slide5
Changes in the Body Plan
The homunculus is the map of the body within the sensory and motor cortices.
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Changes in the Body Plan
Changes to the body, such as losing a limb, can result in changes to the representation of the body in the brain.
Sensory areas that responded to the damaged part of the body are taken over by adjacent sensory areas.
Phantom limb pain is pain that seems to come from the missing body part.6Slide7
Changes in the Body Plan
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Changes to Sensory Input
Removing or altering sensory input, even on a temporary basis, can cause a remapping of the brain.
The speed of this remapping suggests that there are existing connections that can be unmasked.
Such reorganization has been observed in auditory and visual systems.8Slide9
Changes to Sensory Input
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The Brain Distributes Resources Based on Relevance
The Role of Behavior
The Role of Relevance: Gating Plasticity with Neuromodulation
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The Role of Behavior
The brain uses adaptive coding, altering the amount of resources assigned to a function depending on how important it is.
Sensory and motor representations will reorganize based on the particular skills and needs of the person.
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The Role of Behavior
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The Role of Relevance: Gating Plasticity with Neuromodulation
The behavior must be relevant to the organism to result in plasticity.
Plasticity can be turned on or turned off (gated) in particular places at particular times.
Neuromodulators, such as acetylcholine, control this gating.13Slide14
The Role of Relevance: Gating Plasticity with Neuromodulation
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The Brain Uses the Available Tissue
Maps Adjust Themselves to the Available Brain Tissue
Cortical Reorganization after Brain Damage
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Maps Adjust Themselves to the Available Brain Tissue
Maps will make use of the available amount of brain tissue.
Research with the visual system of tadpoles found that the input makes use of the available brain area, whether there is less brain area or more input.
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Maps Adjust Themselves to the Available Brain Tissue
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Cortical Reorganization after Brain Damage
Following injury to the central nervous system, some function tends to be recovered as swelling decreases.
Cortical reorganization can occur over a longer period of time to allow further recovery of function.
The language problems of aphasia tend to decline as the right hemisphere takes over.18Slide19
A Sensitive Period for Plastic Changes
A Window of Time to Make Changes
The Sensitive Period in Language
Neuromodulation in Young Brains19Slide20
A Window of Time to Make Changes
Plasticity is greatest during periods of development known as sensitive periods.
After the sensitive period has passed, plasticity is still possible, but not as easy.
The success of treatment for strabismus (lazy eye) early in life is an example of these sensitive periods.20Slide21
The Sensitive Period in Language
Acquisition of a second language supports the idea of sensitive periods.
If you are exposed to a second language before age 7, you will be as fluent as a native speaker.
If exposed between 8 – 10 years, it will be harder to achieve fluency.If exposed after age 17, fluency will be low.
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The Sensitive Period in Language
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Neuromodulation in Young Brains
In humans, young people have greater brain plasticity.
There is a tradeoff between plasticity and efficiency, and, as your brain gets better at some tasks, it becomes less able to perform other tasks.
Young animals show widespread plasticity without needing attentional focus.23Slide24
Hardwiring versus World Experience
Aspects of the Brain Are Preprogrammed
Experience Changes the Brain
Brains Rely on Experience to Unpack Their Programs Correctly24Slide25
Aspects of the Brain Are Preprogrammed
We are born with certain reflexes, such as grasping and sucking.
Sperry conducted studies of the newt visual system and developed the
chemoaffinity hypothesis.Connections within the visual system are preprogrammed to follow chemical cues to reach their target.Chemical cues can be attractive or repulsive.
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Aspects of the Brain Are Preprogrammed
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Experience Changes the Brain
The environment alters the brain and affects the brain’s ability to learn.
Rats in an enriched environment have more extensive dendrites.
Neurons in the language area known as Wernicke’s Area have more elaborate dendrites in college-educated individuals.27Slide28
Experience Changes the Brain
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Brains Rely of Experience to Unpack Their Programs Correctly
The environment not only influences brain development, but is necessary for development.
The encoding discussed previously is only at a general level.
Experience is required to refine the connections.29Slide30
Brains Rely of Experience to Unpack Their Programs Correctly
Kittens raised with strabismus do not develop binocular vision because they do not get appropriate input from both eyes.
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Brains Rely of Experience to Unpack Their Programs Correctly
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The Mechanisms of Reorganization
Neurons Compete for Limited Space
Competition for
NeurotrophinsRapid Changes: Unmasking Existing ConnectionsSlow Changes: Growth of New Connections
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Neurons Compete for Limited Space
Neurons, axons, and dendrites need to compete for resources to survive.
The initial connections to the muscles and the visual system are refined over time by activity-depended plasticity.
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Neurons Compete for Limited Space
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Neurons Compete for Limited Space
Pruning is the process of removing neurons and processes that are not needed.
Apoptosis is a form of cell death that is normal in development and enables the cells to die without affecting adjacent neurons.
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Competition for Neurotrophins
Neurotrophins
are chemicals that help to sustain the neurons.
Generally, they are secreted by the target to promote survival in the neurons that reach the target.They allow the cell to differentiate.In young cells, they prevent apoptosis in cells that make appropriate connections.
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Competition for Neurotrophins
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Rapid Changes: Unmasking Existing Connections
Many existing connections are masked by activity within the nervous system.
Other connections predominate and inhibit the weaker connections that exist.
Following damage or loss of input, this inhibition is lost, unmasking these connections.38Slide39
Rapid Changes: Unmasking Existing Connections
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Slow Changes: Growth of New Connections
Longer-term changes, over weeks or months, are likely due to the growth of new connections.
If the short-term changes are advantageous, then growth of new connections will follow.
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Slow Changes: Growth of New Connections
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Changing the Input Channels
The plasticity of the brain enables new forms of input.
For example, the brain can learn to interpret input from a retinal implant.
The BrainPort enables different sensations to be delivered tactilely to the tongue.42Slide43
Changing the Input Channels
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