plasticity Flashcards
(28 cards)
What is plasticity?
Brain’s ability to structurally and functionally adapt to reorganise neural circuits.
Important for developing more effective rehab interventions.
What is habituation?
Component of plasticity
- process that causes an organism to become less responsive to repeated exposure to stimulus.
What is sensitsation and dishabituation?
Process that allows an animal to generalise an aversive response elicited by a noxious stimulus to a variety of other non-noxious stimuli
Dishabituation is a form of sensitisation and refers to the fast recovery of a response that has become habituated and is typically a result of the presentation of novel, strong, and sometimes noxious stimuli
What synaptic mechanisms occur for sensitisation and habituation (in sea hares)?
Activation of the serotonergic modulatory interneurons enhances release of transmitter from the sensory neurones onto the motor neurons synapses and causing the motor neurons to contract the strongly excite gill muscle more vigorously
How is the brain organised for sensory stimuli?
S1 (the primary sensory cortex) is located in the central gyrus. Contains 3 brodmann’s areas.
Within S1 is a body map think homunculus.
What makes up the sensory system?
2 major ascending pathways carry information to brain include: dorsal column which is the medial lemniscus pathway and the spinothalamic pathway
Although they different routes in the spinal cord / brain stem both synapse in the ventral thalamic nucleus and then project to the primary sensory cortex (S1). (brain not vertebra)
What sensory representations are there and what properties do they have?
Full sensory map exists in the brain in S1
Plastic e.g. 2 months post amputation of 3rd digit the map substantially changes, the area that previously corresponded to 3rd digit now re-maps and respond to digit 2 and 4 (chimps)
- e.g. following below elbow amputation in L hemisphere (right) hand representations are missing and only present in the right hemisphere. L hemisphere hand cortex remolds to respond to face and upper arm.
What functions does each ascending pathways have?
Dorsal column:
- localised fine touch sensation, vibrations, two-point discrimination and proprioception of from the skin and joints
Spinothalamic pathway:
- Crude touch, pain and temperature
How is movement organised?
Motor has similar somatic maps
By stimulating the motor cortex this evokes movement. Mapping movements reveals a somatic map of the body. Again homunculus however in M1.
What changes in motor maps have been observed in animals?
Monkeys trained in task that required dextrous movements of the digits found that as they got better they made less finger flexions. With extended training digit representations expanded whereas representations of the wrist / forearm movements contracted.
Suggested that due to level of skill required it is not just amount of training that leads to increased mapping. When rats were trained in a skilled reaching tasks vs unskilled lever pressing task the animals who were training in the skilled task had maps with larger wrist and digit representations and a decrease in the elbow / shoulder representations (Kleim, Barbay and Nudo, 1998).
How have changes in motor areas been observed in humans?
fMRI showed that activity in hand area gets larger with practice compared to unpractised sequence
When trained with a five finger tapping task timed by a metronome (2h/day) over the 5 days of training the cortical motor output maps for the long finger flexor and extensor muscles expanded in the trained hand but no change for the untrained hand
However can also occur when mentally practice a task for 5 days as cortical map size increased whether physically or mentally rehearsing a task
What is a real-life example of improved cortical representation?
during CIMT improved upper limb function is produced, this is associated with increased size of the cortical representations of both hemispheres
What differences are observed between strength and skill training?
Changes in excitability can be used to assess plastic changes in the cortex through probing cortical excitability
Jensen et al., 2005 found that the strength training group got stronger whereas the skill training group gained skills.
Cortical excitability increased with training the group that learnt the skill whereas cortical excitability decreased in the strength training group
What are experiments that have demonstrated plasticity in the adult cortex?
Somatosensory mapping
Congenitally blind people observation
Tapping task
What did the california sea hare help to discover?
In sea hares touching the siphon causes the gill to retract. However, after multiple touches the protective mechanism decreases and the sea hare becomes situated to the touch.
Allowed demonstration of sensitisation:
When paired with electrical stimulus to tail and light touch of siphon. Gill retraction returned (dishabituation)
How has habituation been shown in rats?
Used repeated loud noise which intially produces a startle, after repeated exposure the stimulus becomes habituated
What is somatosensory mapping and how has it been used in relation to plasticity?
Records the brain while the periphery is stimulated and allows for cortex mapping.
In high-res somatotopy have been able to uncover that most sensitive parts of the body (ie hand and face) have greater representation in the cortex
Individual digits each have representations however there are overlapping representations between digits. (initially found in apes but also found in humans)
How can sensory restructuring for plasticity in animals be demonstrated in experiments?
Animal maintains contact with a rotating disk for 10-15s for banana pellet. Only distal aspect of distal segment of digits contacts disk. Disk continuously rotates at 1 rev/s providing stimulation. Trained mainly with digits 2, 3 and sometimes 4. After months larger region was activated by digits used in the task and representation hence increased in size for those digits.
What is referred sensation?
Rats have barrels that correspond to whiskers, if all whiskers are cut but one the receptive field expands so that cells in other barrels respond. Found in amputees where systematic mapping was observed between the location of trigger region of the face and the location of the referred sensation on the L phantom hand
What plasticity occurs in congenitally blind people?
The cortical areas that are usually used for visual processing are used for other tasks like hearing and reading braille with fingers. Appears to relate to how long someone has been blind for.
Similar occurrence in those with anopthalmia (non-developped eyes)
Vise versa true with deaf people, area normally activated by sound is activated by visually.
How was repeated movement tested in terms of movement maps
Repeatedly stimulated thumb to move one direction. After training TMS evoked movements in the direction of training. This wore off over time and suggests that repeated use changes the motor map
What is use dependent plasticity and how has it been tested?
Increased cortical representation due to history of motor use. Tested if pairing a synchronous pulse of transcranial magentic stimulation (TMS) would enhance learning
Found a main effect of training, training improved all groups however synchronous TMS had an additional effect that the asynchronous TMS did not showing possible long term potentiation
What is rescuscitation?
Form of recovery
Involves reengaging the brain areas initially dysfunctional after injury or disease
What is recruitment?
Engaging new brain areas - form of compensation
