Neuroplasticity History

Neuroplasticity Definition

some kind of change in the nervous system in response to intrinsic or extrinsic stimuli

50 year ago beliefs about brain

adult brain “hardens” permanently into a fixed structure that cannot be changed, born with all brain cells

Organisms with neuroplasticity

all organisms with a nervous system

What causes neuroplasticity

everything we do and experience, adapting to our environements

Timing of neuroplasticity studies

began over 200 years age, but viewed as a new discovery

First scientists to talk about the brain changing

Charles Bonnet and Michele Vincenzo Malacarne

Cofounders of Cell theory

Matthias Schleiden and Theodore Schwann

Cell theory

all living organisms are composed of cell(s) and arise from pre-existing cells

Limitations of cell theory regarding neuroplasticity

microscopes at the time were not powerful enough to see nervous tissue

Neuronists

believed the nervous system was composed of cells

Reticularists

believed nervous system was composed of continuous sheets of tissue

Santigo Ramon Y Cajal

compared nervous tissue under a microscope, saw they were made of cells. said plasticity occurs at synapses

First to use “plasticityy”

William James

Habit formation

strengthening synapses and/or forming new connections

Charles Sherrington

First to introduce “synapse”, and that they were the site of learning

Cajal’s dissonance

originally disputed that the brain was stagnant, but changed his mind 10 years later

Formal central dogma of neuroscience

Brain is stagnant and not materially affected by learning/training

David Hubel & Torsten Wiesel

Nobel prize for discoveries about sensory experiences impacting the brain

Tim Bliss and Terje Lomo

discovered long term potentiation strengthens synapses

Most convincing evidence of neuroplasticity

discovery of neural stem cells in adult brain

Benefits of current technologies for studying neuroplasticity

visualize the brain in great detail, can manipulate neuronal activity with great precision

Neuroplasticity on varying levels of NS

found on every level (molecular, structural/functional, cell populations, neural networks, brain systems)

Functional neuroplasticity

changes in some physiological aspect of nerve cell function

Changes occurring for functional neuroplasticity

modifying the number of neurons, or the frequency of AP

Structural Neuroplasticity

volumetric changes in discrete brain regions

Changes occurring for structural neuroplasticity

formation of new neural pathways via rerouting or sprouting

Rerouting

pruning extra pathways when the same thing can be done with less (3 to 2 paths)

Sprouting

one neuron will branch to a new post-synaptic neuron when the pre-synaptic neuron failed, only for incomplete SCI since something must be left

Timeline to modify synapses

milliseconds

Timeline to create or destroy synapses and branches

hours

Timeline to create or kill cells

days

Timing of heightened plasticity

most sensitive from late childhood to early adulthood

Impacts of losing an external sense

gradual changes from weeks to years

Positive feedback loop examples

long term potentiation and depression

Spike-timing dependent plasticity

special type of LTP where timing between pre-synaptic input and post-synaptic firing dictates synaptic strength
AKA neurons that fire together wire together

Example of neuroplasticity being bad

may hid the onset of a neurodegenerative disease since brain compensates, new onset epilepsy, autonomic dysreflexia after SCI