Neuroplasticity

nature vs nurture debate

• nature (genetics)- general layout of the nervous system

• nurture (environment and experience); various connections are adjusted to meet demands of environemnt; aka neuroplasticity

when is neuroplasticity most prominent

during critical period of develpment and then is reduced

what are critical periods

early development

ongoing adjustments of neuroplasticity

learning and memory; constraint-induced movement therapy etc

neuroplasticity defined

ability of the brain to change its own structure and function through activity and thought

neurons and their connections adjust to match the nervous system to their environment ex

body (sea legs) and environement (london cabbie)

neurogenesis

creating new neurons

what disproves the idea that you don’t create new neurons

the existence of neuronal stem cells

neuronal stem cells

cells that can produce new CNS neurons or glial cells

where are neuronal stem cells found

1. walls of the ventricles

2. hipposcampus

3. subventricular zone of lateral ventricles that migrate to olfactory bulb

significance of subventricular zone of lateral ventricles

can move these to replace damaged parts of brain

re-wiring

creating neew neuronal pathways (path in the snow while sledding)

unmasking

uncovering existing, but rarely used neuronal pathways

cortical re-organization

reassigning cortical “realestate” to new functions (braille proof reader on vacation)

changes in synaptic efficiency

strengthening or weakending the connections between neurons

how are neuronal pathways created?

by signals (neurotransmitters) passing from one neuron to the next at synapses (spaces between neurons)

synapse

space between neurons

actions we take to change synaptic efficiency

the things we do or think can either strengthen or weaken the connections between neurons and therefore influence synaptic efficiency (occurs through actual structural changes at synapse)

potentiation

an increase in synaptic eficiency

• the more we do or think something, the more efficient the synapses become and the easier it is to do or remember something

Hebb’s principle potentiation

neurons that fire together wire togehter- the more we do something, the more frequently neurons communicate in a particular order (fire together) and the more efficient the synapses become (wire together)

depression

a decrease in synaptic efficiency

• the less we do or think something, the less efficient the synapses become abd the harder it is to do or remember something

Hebb’s principle: depression

neurons that fire apart wire apart

• the less we do something, the less frequently neurons communicate and the less efficient the synapses become

short term potentiation or depression (3)

• lasts a few minutes

• general consequence of an activity

• ex; pt. able to tie shoes in therapy but not at home

long term potentiation of depression (3)

• produces lasting changes (hours to years)

• basis of learning and memory AND what we hope to affect in neurorehab

• ex. pt able to tie shoes anytime, anywhere

what increase the number of neuronal stem cells

environments that include novelty and physical exercise increase the # of stem cells in hippocami and prolong the life of the cells there

intensity/redundnacy

use dependent plasticity

• the more you do something, the more likely your brain will change.

• use-dependent refers to the neuronal pathways being made more efficient (long term potentiation) bc you use them over and over

4 ways to enhance neuroplasticity

1. enhanced environemtns (real kitchen in OT clinics)

2. individualized saliency (importance of meaningfulness)

3. active use of body part needed

4. goal driven tasks

individualized saliency

if it’s not important to you, it’s not important to your brain and your brain won’t rewire to help you learn

neural connections during the prenatal and early postnatal period

produced in excess

• infants must thenmatch neuronal connections to their body and external environemtn through a matching process (hitting mobile)

what does the matching process include

dying off of surplus neurons and retracting inappropriate connections

how do humans make sure the right neuronal connections survive?

1. neurotropic factors cease to be essential for survival of neurons later in development, but continue to help determine which dendrites and axon branches flourish and which wither and retract

2. immature neurons receive inputs and make synaptic connections much more easily than adult neurons

3. as time goes by, connections that contribute more effecitvely and efficiently to function last and those that do not are pruned away

what occurs during critical periods

plasticity is maximal and synapses made during critical periods are more or less permanent

critical periods length

vary in length for different parts of the brain and different skills (refinement of synapses in multimodal areas takes the longest)

what do critical periods allow

acquisition of complex skills such as language and visual discrimination

• why young children learn language more easily than adults

critical period for language

• very young infants can discriminate among speech sounds of all human languages

• at 6 months, they get better at detecting sounds heard most often, and lose the ability to detect sounds from other languages

how does the brain lay the basic wiring of neuronal networks

neurodevelopmental processes and processes during critical periods complete the basic wiring of neuronal networks

what is the adjustment of synaptic connections contingent on

synaptic efffiency (potentiation, depression)

what type of memory is used in occupations

combination of forms

two main types of long-term memory

declarative and non declarative

declarative memory

memory of facts, events, concepts, places

nondeclarative memory

how-to memory

3 primary stages of declarative memory

1. immediate memory

2. working memory

3. long term memory

immediate memory

• lasts up to 3 seconds

• snapshot of sensory input

what part of the brian processes immediate memory

primary sensory and sensory assoication areas of brain and is encoded for the next stage

working memory (3)

• dependent on attention

• lasts 3-30 seconds

• information we keep in mind- manipulate and rehearse

long term memory

• lasts greater than 30 seconds

• relatively permanent sotrage

consolidation

conversion of working memory to long term memory

how is long term memory stored

cerebral cortex stores thius info in diffuse neuronal networks, interconnected by snapses

what is the primary structure associated with declarative memory

hippocampus

hippocampus location in brain

cuved area of the cortex that lies in the limbic lobe, submerged in the parahippocampus gyrus

Famous Case of HM

1. HM underwent bilateral removal of his medial temporal lobes bc he had frequent, severe epileptic seizures

2. epilepsy improved, but had memory loss

   • 1 year retrograde memory loss

   • anterograde memory loss (but could remember non-declarative)

retrograde amnesia

loss of memeories from a period prior to the brain injury

anterograde amnesia

inability to form new memories

brain map memory

anterograde amnesia

deficit in forming new memories

HM showed what about the hippocampus

process memories from short term to long term, but memories aren’t stored in the hippocampus

three general types of nondeclarative memory

1. skills and habits

2. emotional associations

3. conditioned reflexes

non declarative memroy in basal ganglia, cerebellum, neocortex

skills and habits

non declarative memory amygdala

emotional associations

nondelarative memory cerebellum

conditioned reflexes

nondeclarative memory consciousness

doesn’t require full awarness, and can do with little attention paid to task

what is needed to sotre procedural memories

practice (motor learning)

• perfect practice makes perfect

three stages involved in motor learning

1. cognitive

2. associative

3. autonomous

cognitive motor learning

verballly guide motor task; requires much attention

associative motor learning

movement is refined and made more efficient

autonomous motor learning

movements are practically automatic; requires very little conscious attention

therapeutic use of nondeclarative memory in alzheimers

• people with alzheimers have problems with declarative memories because the hippocampus is affected

• work with their basal ganglia

• go through the motions with them rather than listing out steps

common diagnoses involved in memory loss (6)

1. Traumatic Brain injuries (cerebral contusions)

2. stroke and anoxia

3. korsakoff’s psychosis

4. alzheimer’s disease

5. psychogenic amnesia

6. normal memory loss

areas commonly affected by TBI

• areas commonly affected are anteromedial temporal lobes and basal orbitofrontal cortex

type of memory most affected by TBI

anterograde

retrograde amnesia in TBI

may be present for a short time prior to brain injury, but often more remote memories come back first, with memories of events just prior to injury coming back last or not at all

stroke and anoxia memory

hippocampus is especially vulnerable for memory loss bc it has poor blood supply

korsakoff’s psychosis cause

seen in people with alchoholism and people with B12 deficiency

what anatomical part does korsakoff’s psychosis affect

mammillary bodies (responsible for formation of episodic memories)

what characterizes korsakoff’s psychosis

anterograde amnesia and lack of awareness of deficits

confabulation

filling in memory gaps by fabrication

what part of the memory is effected in the early stages of alzheimers

memory loss of recent events

what brain structures does alzheimers disease mostly affect

bilateral, hippocampal, temporal, and basal forebrain structures

psychogenic amnesia

dissociation, repression, functional neurologic disorder, and malingering

PNS neuronal repair

PNS nerve fibers can re-grow after injury; typical rate of axonal regeneration is 1 inch per month

what type of PNS injury is the best for neuronal repair

crush injuries bc the pipes are laid on where to guide axons on where to grow

PNS nerve recovery in complete transections

the axon grows randomly, with no guidance, and complete recovery is rare

neuronal repair in CNS

CNS neurons do not typically regenerate

why do neurons not recovery in CNS (3)

1. Glial cells lay down scar tissue and produce molecules that impede neuronal growth

2. axons do not reestablish connections and parent cell bodies atrophy

3. if damage is to the cell body the whole neuron may die