PSY260 - 3. Habituation/Sensitization Flashcards
Role of the single cell in learning and memory
Change probability that neuron will fire (short term)
Role of the single cell in learning and memory
Change connectivity with other cells (longterm)
Synaptic transmission
provides means of modifying strength of signal as it travels along neuronal path
likelihood of a post-synaptic response depends on
of activated synapses in close proximity (spatial summation)
likelihood of a post-synaptic response depends on
# of signals arriving in close succession (temporal summation)
likelihood of a post-synaptic response depends on
Synaptic strength
Action Potentials in Synapse
graph of synapse
Synapses
1) carry signals rapidly from cell to cell
specialized cell-cell contact point
Synapses
2) electrical/chemical connections betw neurons/neuron + an effector (muscle, gland)
[changes in ion permeability are central to chemical synapse function]
Synapses
3) excitatory/inhibitory
Chemical synapses:
1) complex action
2) slower
Chemical synapses:
3) has delay of 0.3 to 3 ms
4) excitatory or inhibitory
Chemical synapses:
5) can amplify current flow
6) unidirectional (presynaptic -> postsynaptic cell)
Chemical synapses:
7)can modify properties based on recent history (have plasticity + can be strengthened with use + weakened by disuse)
Electrical synapses:
1) simple action
2) faster, no delay
Electrical synapses:
3) mostly excitatory
4) cannot amplify current flow/modify properties
Electrical synapses:
5) Bidirectional
6) Can summate over multiple cells
Action potential translation
Action potential reaches synapse Ca enters terminal Vesicles move to membrane + fuse Neurotransmitter is released Reuptake of transmitter + recycling of membrane
Variety of receptor types
GPCR
G Protein
Effector
Two modes of action in chemical synapses:
A) Inotropic actions:
- fast
- ligand-gated channels
- affects membrane potential
- act by changing membrane potential
Two modes of action in chemical synapses:
B) Metabotropic actions:
- slower
- G protein-coupled receptors
- act by changing intracellular biochemistry
Synaptic strength
=Synaptic modification: (Plasticity)
Habituation/Sensitization Facilitation/Potentiation
aplysia
we can produce/modify behaviours because of simple nervous system
few behaviours: daytime it moves + eats
protective behaviour: no moving
Habituation in Aplysia gill withdrawal
initially withdraw its gills when something comes in contact with siphon/mantle shelf
after contact proceeds for many minutes ⇒ decrease withdrawal behavior
Sensitization in Aplysia gill withdrawal
receives shock to the head ⇒ once again retract its gills in response to stimulation by siphon
Facilitation
making it easier to get signal across the synapse (more transmitter released)
Depression
making it harder (less transmitter release)
Potentiation: making the post-synaptic response larger
(larger response for the same amount of transmitter)
Induction and maintenance of LTP in the hippocampus
1) NMDA receptor opens only when both pre and post synaptic neurons are firing; after tetanic stimulation
2) Spine head enlarges, and more Glu receptors are added
Facilitation vs.potentiation
-
Long term potientiation (LTP)
-
Long term depression
-
Synaptic transmission can be altered in many ways
-
LONGER TERM CHANGES
Changes in receptor senstivity/number
• Changes in gene transcription
• Changes in synapse number/neuron shape
Facilitation
releasable neurotransmitter pool is increased
Habituation (synaptic depression)
neurotransmitter pool is depleted
Potentiation
high-frequency stimulation cause a lasting change in responding ⇒ hippocampal neurons respond to subsequent weak stimulation
Long-term potentiation [LTP]
synaptic transmission more effective as result of recent activity
postsynaptic neurons changed to become more responsive to subsequent inputs: heightened sensitivity to neurotransmitter
changes to presynaptic neurons
way to strengthen neuronal connections
need a process that can decrease strength of less useful synapses
Long-term depression [LTD]
synaptic transmission becomes less effective as result of recent activity
Connections betw neurons that don’t fire together weaken
Sensitization
- Experiences with arousing stimulus ⇒ stronger responses to later stimulus
- Seen in a wide range of species
- Not stimulus specific
- Exposure to sensitizing stimulus can amplify startle response to any stimulus that comes later
Sensitization
Larger neurotransmitter pool is replaced
Dual process theory
- Repeated events always lead to processes underlying both sensitization and habituation
- Both sensitization + habituation processes occur in response to every stimulus + summed combo of independent processes that determine strength of responding
- Actual outcome – strength of the response – depends on – how often stimulus has been repeated + how intense in recent was sensitizing event
Dual process theory
•Can depend on whether other stimuli have activated state system
•Both processes change over time so it’s the largest effects of repetition always occur in early exposures
•Emotional responses to extreme events: initial phase of scary followed by rebound effect of exhilaration. After repeated experiences, initial fear responses become weaker, whereas rebound responses grow stronger
well-suited to explain short-term habituation
Opponent process theory
assumes experienced event leads to 2 independent processes: 2 emotional processes, 1 pleasurable + 1 less pleasant. Overall emotion one experiences in response to event is combined result of 2 independent processes
Perceptual learning
- Learning in which repeated experiences with set of stimuli makes stimuli easier to distinguish
- develop capacities to detect subtle differences through repeated exposures to stimuli
Mere exposure learning
- Latent learning
* Perceptual learning without explicit training
Discrimination training
- Training to respond diff to diff stimuli
- Perceptual learning shows high degree of learning specificity: learning about 1 group of stimuli doesn’t transfer automatically to other stimuli
- Perceptual learning is stimulus specific
Comparator model
changes in responses to repeated events/consequence of gradual construction of neural representations of stimuli + context in which they occur
•brain detects stimulus - forms representation of stimulus + compares it with memories of previously experienced stimuli
no match ⇒ response triggered, provoking organism to further examine stimulus
partial match ⇒ existing representation modified to include additional details
good match ⇒ orienting response supressed + no changes made to representation
better account for long-term habituation and perceptual learning
Differentiation theory
representations of stimuli initially formed rapidly + vaguely, become more precise overtime by incorporating further details as stimulus is repeated
•Assumes brain limited in how much info it can collect in single exposure
•More complete representations allow more accurate discriminatory judgments betw + recognition of stimuli
cortical plasticity
- Learns to recognize stimulus differences not noticed before, sensory neurons may change how they respond to events overtime
- Somatosensory cortex has similar homunculus that maps part of body receiving touch messages
- Sensory Cortices is our specially important for making distinctions
- Sensory Cortices is our areas of cerebral cortex that process visual stimuli, auditory stimuli, so Maddow sensory stimuli and so on
- With in each of these brain regions, individual neurons respond to different stimulus features
cortical plasticity
- Receptive Field: Range of stimuli that cause particular cortical neurons to fire
- in somatosensory cortex, receptive field is defined as patch of skin or tissue that when stimulated causes neurons to fire
- More neurons that are tuned to a particular type, source or strength of stimulus, better to organism will be able to make find distinctions related to that stimulus
- Spatial organization of somatosensory cortex reflects the fact that neurons with similar receptive fields are often found closer together and sensory Cortices
cortical plasticity
• Topographic map: Clusters organized in predictable ways, pattern of cortical organization
o Cortical neurons that are physically close together are tuned to similar stimulus features
• Neighboring cortical neurons have overlapping receptive fields
• Receptive fields of neurons and sensory cortices is changed during early development and also after various injuries and as a result of repeated experiences
• Cortical plasticity: capacity for cortical receptive fields and cortical spatial organization to change as a result of experience
• Perception may also change over time
Hebbian learning
- Neurons that fire together wired together
- Learning that involve strengthening connections between cells that work together
- Connections between coactive neurons are strengthened as a result
- Repeated collectivity has a cumulative effect, resulting in strong connections
- Repeated exposure to stimulus can strengthen connections within distinctive subset of cortical neurons
- Provides a possible neural mechanisms for representational processes proposed in comparator models and differentiation theories of perceptual learning
- And also explain how repeated exposures facilitate recognition
- Priming might then be explained as a strengthening of existing connections
Identifying places
- Place cells: neurons with such spatially two and firing patterns
- Place field: each neuron has certain preferred location to which it responds with maximal activity
- Create place cells as you need them
- Place fields should form during learning
- Place cell responses also depend heavily on visual inputs
- Importance of visual landmarks in determining when I hippocampal place cell will fire
Identifying places
- Some place cells in rats seem to be sensitive to other variables such as speed or direction in which rat is moving
- Place cells respond like sensory cortical neurons with multimodal receptive fields
- One factor affecting creation of place fields is experience
- When the rats repeatedly experience in environment, place cells become increasingly tuned to locations within that environment
- Spatial learning that occurs during expiration is correlated with changes instability and selectivity of place cells
