Charcon (L5+) Flashcards
What causes post-synaptic potentials?
The activation of the post-synaptic receptors via binding of neurotrasmitters (glutamate for ex)
What does Hebb’s postulate state?
Neurons that fire together, wire together
When axon of cell A excites cell B repeatedly, some growth process/metabolic changes take place in one or both cells such that A’s efficiency as one of the cells firing B is increased
What is Hebbian plasticity vs non-hebbian plasticity?
All synaptic connections are plastic!!
Some obey Hebb’s postulate → correlations between pre and post-synaptic activities underlie plasticity
Some don’t obber Hebb’s postulate
What protocol is commonly used to induce in the Scaffer collaterals synapsing onto CA1 cells in the hippocampus?
- Stimulate Scaffer collaterals (axons of CA3) and record from CA1 cells
- Give test pulses (1-2/min) for ~15min → measure EPSP amplitude in CA1 and normalize to 100%
- Give x Hz tetanus for ~D=15mins
- Go back to test pulses and measure EPSP
*Keep in mind that these stimuli are highly artificial
How is the tetanus measured?
T = 1/f = Hz
What is seen in CA1 cells in the case of 3Hz, 10Hz, 50Hz tetanus stimulation of the Schaffer collaterals with an electrode?
1Hz → LTD
10 Hz → No Long Term net change
50 Hz → LTP
*EPSP slope/magnitude/current can be measured
What are the main characteristics of NMDA receptors?
At rest, NMDAr blocked by Mg2+
When AP, Glutamate is released into the synaptic cleft → binds AMPAr and NMDAr
Depolarization initiated by AMPAr allowign entry of Na+ → postsynaptic depolarization → removal Mg2+ → entre of Na+/Ca2+ through NMDA receptors
NMDAr are (unlike AMPAr):
1) Voltage dependent
2) Ca permeable
Which experiment was done to prove that plasticity requires NMDA receptors?
- Block NMDAr with different concentrations of APV
- Apply tetanus protocol (1sec @ 100Hz, 3 times) → look at Long Term Plasticity
Results:
0 APV → LTP
15uM APV → LTD
50-100 uM APV → No net change (no long term potentiation) high enough concentration
*All these effects were reversible when media with APV was replaced by media without
Conclusion → NMDA receptors are required for plasticity induction
What experiment was done to prove that plasticity requires calcium?
Induction of Long Term Potentiation (protocol) in cells with different concentrations of EGTA
*EGTA is a Ca2+ chelator → binds to Ca2+ and prevents it to interact with other proteins inside the cells
Results:
0.5mM EGTA → LTP (Similar to standard conditions)
10mM EGTA → LTD
20mM EGTA → No LT plasticity
Conclusion → Calcium in the cell is required for plasticity induction
What are the cellular mechanism allowing for induction of Long Term Depression?
Moderate Ca entry in postsynaptic terminal → Ca interaction with high affinity Protein Phosphatase → Dephosphorylaiton of AMPAr → higher removal of AMPAr from the postsynaptic membrane → smaller EPSP
What cellular mechanism allows for induction of Long Term Potentiation?
Large amounts of Ca entry through NMDA receptors → interaction between Ca and Protein Kinase C and with Calmodulin kinase II → Substrate phosphorylation → Increased insertion of AMPAr in membrane → higher EPSP
*This mechanism over powers the Protein phosphatase/AMPAr removal mechanism at high Ca concentration, but does not have high enough affinity to be seen at lower Ca concentrations
What explains the equilibrium point at which no net change in long term palsticity is seen?
At a specific Ca concentration in the postsynaptic terminal, the rate removal of AMPAr by Protein Phosphatase is the same as the insertion by Kinase C/Calmodulin kinase II which does not change the # AMPAr → same Depolarization of the membrane (EPSP amplitude)
In summary, what is required for LTD vs LTP?
*IN ASSOCIATIVE PLASTICITY
Both require Calcium entry via the NMDA receptor
LTD requires moderate NMDA activation/moderate calcium entry
LTP requires strong NMDA activation/high calcium elevation
How are place fields affected by the presence/absence of LTP?
Stability of place fields requires plasticity
In an envrionment in which there are no changes, place fields remain stable, but in the absence of LTP, they do not
Which experiment allows us to state that NMDAreceptors are required for spatial memory?
Setup:
Put mouse in a pond of water with a plateform underwater so the animal can’t see it, but has a cue card as external visual cue. remove the plateform and measure how much time the animal spends in each quadrant of that pond.
Ctrl animal spends significantly more time in the quadrant with the plateform
AP5 animal (AP5 blocks NMDA receptors) spends equal amount of time in all quadrants (no spatial memory)
What is the effect of selective KO of LTP on the formation of place fields?
Selective KO of LTPlasticity does NOT prevent the formation of place fields
Selective KO of LTO does prevent place field retention
→The relationship between plasticity and place fields if complex!
Explain the plasticity induced pairing protocol that allow to study Spike Timing Dependent Plasticity.
- Stimulating electrode in the axons of the Schaffer collaterals = Presynaptic signal
- Recording electrode in the CA1 pyramidal cell can inject current to depolarize the membrane to simulate postsynaptic signal
According to Hebb’s postulate:
Pre spike before post → Strengthening (LTP)
Post spike before pre → Weakening (LTD)
*This relationship is time dependent/spike timing dependent → if the 2 spiking actvities are farther appart, the effect on plasticity decreases
How can Spike Timind Dependent Plasticity (STDP) explain the elongation/shift of the place fields in the experiment with the rat running in a straight line 15x?
Neurons situated before the CA1 fire before the CA1 (post) → potentiation
*Further spikes longer before, so less potentiation than just before
Neurons after CA1 fire after → depression
*These cells would still fire, but the spiking is so weak that it might no be enough to generate AP in the CA1 cell
What are the different requirement for plasticity and memory retention in CA1 pyramidal cells?
Plasticity in CA1 requires NMDA receptor + Ca2+
Memory retention requires NMDA receptors (Shown by plateform in a pawn exp. with ctrl and AP5mice)
What animal model did Kendel use for its studies on learning and plasticity? Why?
Aplysia Californica
→ Simple invertebrate, slow moving gastropod mollusk
→ Very few neurons ~20,000 (compared to avg person ~ 10^11 neurons)
Has reproducible behaviour in response to unitary stimuli → Gill withdrawal reflex, you don’t have to train the animal
When you touch the Siphon, the animal will withdraw its gill
What happens in aplysia when Siphon is repeatidly touched?
What happens when we then give a tail shock?
Over multiple stimulation of the siphon, Gill movement amplitude decreases → habituation
After tail shock, when we stimulate the siphon, Gill movement comes back to original amplitude of withdrawal and even more (dishabituation / potentiation)
Conclusions:
1. A. Californica habituates to repeated harmless stimuli
2. Harmful stimuli negates this habituation
→ Nice 1:1 relationship between habituation and change in behaviour
What is the neural anatomy of Aplysia like?
From head → tail:
1. Buccal ganglion (mouth)
2. Cerebral ganglion (brain)
3. Pleural ganglion
4. Pedal ganglion (involved in motor control)
5. Abdominal ganglion (Gill withdrawal, LE sensory neuron + L7)
*Pedal ganglion can be dissected and put in a dish for spiking and recording
What neural circuit is recorded from in Aplysia?
Ganglions have huge cells (~1mm diameter sooma) which allows to label and record from specific cells/same cells from animal to animal
Spiphon → LE (sensory neuron/pre) → L7 (motor neuron/post) → Gill
*Reproducible with different animals
Tail has sensory neuron in it too → modulatory interneuron → presynaptic terminal of the siphon’s sensory neurons (not onto motor neuron directly)
How can we see the habituation behaviour as neural activity?
With repeated Sensory neuron AP → reduction in motor neuron EPSP (mV)
Also see dishabituation after tail shock
How can plasticity in aplysia be qualified?
Non-associative / Non-hebbian
→ there is no association between pre and post activity
What occurs are the cellular level when habituation is seen in aplysia, in response to repeated siphon stimulus?
Everything happens in the presynaptic side (non-associative memory)
Repated stimulation leads to weaker post-synaptic responses in motor neurons (post)
- Lower number of available synaptic vesicles underlies short-term habituation
- Lower number of synaptic connections between sensory and motor neurons underliers long-term habituation
How is short-term vs long-term sensitization done in aplysia?
Few tail shocks → short-term sensitization (ex: 1 single tail shock → sensitization ~ 150% for 1h)
Many tail shocks → long-term sensitization (ex: multiple trains over multiple days → increase au 900% over 7 days)
What general neural mechanism underlies sensitization in aplysia in the context of a tail shock?
Interneuron from tail releases serotonin onto presynaptic terminal of the siphon sensory neuron → increase in the motor neuron EPSP (post, but due to a change in pre only)
Sensitization is governed by synaptic facilitation mediated by serotonin (5HT)
Explain the neural mechanism underlying short-term facilitation by serotonin.
*PRESEYNAPTIC MECHANISM
1. Facilitatory interneuron releases serotonin onto the presynaptic terminal of a sensory neuron
2. Serotonin binds to G-protein coupled Serotonin receptor (metabotropic = activates signaling pathways, doesn’t change ion entry) → activates G protein
3. Active G protein → cAMP production by adenylyl cyclase
4. cAMP activated Protein kinase A → different effects (catalytic and regulatory subunits)
- Allows opening of K+ channel → K+ ions flow out of the cell → greater depolarization of the presynaptic terminal by Na+??
- Increeased probability of opening of Ca2+ channels for Ca2+ entry
- More Ca2+ in the presynaptic terminal increases the probability of exocytosis of the glutamate vesicles into the synaptic cleft
→ more glutamate can bind to the postsynpatic motor neuron receptors
Explain the neural mechanism underlying long-term facilitation by serotonin.
- Facilitatory interneurons release glutamate onto the presynaptic terminal of the siphon sensory neuron
… - cAMP signaling goes back to the nucleus
- Increses expression of Ubiquitin hydrolase
- Causes increase in # of new synapses/synaptic connections + increase # of presynaptic vesicles (pool of vesicles)
*All plasticity in aplysia is due to a change in the amount of glutamate being released by presymaptic side
What are some differences and similarities between plasticity in aplysia and in the mammalian hippocampus?
Similarities:
- Both require intracellular signaling pathways for plasticity
- Neuromodulators act via G-protein coupled receptors
- Ca entry is required for plasticity
Differences:
- Aplysia = all presynaptic // Human = pre and post synaptic plasticity
- Neuromodulator differs → aplysia = serotonin // human = dopamine
*Kendel won his Nobel prize because of the consequences of his work with aplysia on understanding human plasticity, not just aplysia
What cellular changes underlie pre vs post-synaptic plasticity?
Pre → Increase/decrease in vesicle pool
Post → Insertion/deletion of AMPAreceptors, number of synaptic boutons
*If only pre → non-associative
What are the main characteristics of human speech?
- It develops spontaneously (ex: sign language)
- Exposur to vocalization early in development is critical for vocal learning
- Period of practice gradually leading to match between model and imitation
- After learning, loss of feedback → graduak deterioration
- Social interactions influence development of vocal learning (the language you are most exposed to, you will be biased to learn)
- Highly structured
- Can be represented as spectrograph
*Humans are the only animal species that learn language under natural conditions
What tool is used to strudy the structure of language?
A Spectrograph → allows to see the differences frequences of differences sounds in time
*Shows how human speech is highly structured
Which 2 songbirds are used for studies?
White-Crowned Sparrow (WCS)
Zebra Finch (ZF)
What are the characteristics of bird songs/learning?
- Are NOT language → Used by the male bird to attract the female, not really to communicate
- Highly structured → can be visualized on a spectrograph
- Has to be learned by the bird (through a tutor’s singing, usually their dad)
- Songs develop spontaneously
- “Normal” song requires social interaction
- “Normal” song requires auditory feedback
*Song learning is also creative, meaning that the song will change over long periods of time (just as accents)
*Region specific song motifs are seen in WSCs from different regions (in spectrographs)
→ Lots of similarities between song learning and language in humans
What are the stages of song learning for a bird?
Listening phase (d30-70 after hatching) → bird listens to the song sang by its dad under natural conditions
Practice phase (d40-90 after hatching) → bird tried to imitate the song, the song is plastic at this stage, there is an overlap with the listening phase
*In the spectrographs, we can see the song changing and getting closer to the tutor’s spectrograph
Crystallization → Stereotyped song (doesn’t change anymore) ~ d90, no more change for the rest of its life
What does the spectrograph of an isolated or deafened White-Crowned Sparrow (WCS) show?
Isolated → Song development is spontaneous, the bird will sing, but the song will not resemble the tutor’s song if the bird has not been exposed to it
Deafened → Auditory feedback is required for vocalization → there will be some singing, but not nice and very inconsistent
What is required for birds to learn the song syntax?
Describe the experiment
There has to be a repeating motif between different learnt blocks
Teach in that order:
1. D-E
2. C-D
3. B-C
4. A-B
The bird will sing → A-B-C-D-E
*Can be sung backwards or forwards, but final element might be forgotten
What is the error-driven model for learning and maintaing the song in birds?
- Bridbrain stores a model of the song/template
- Syllable + Sequence - Bird sings and attempts to reproduce model
→ Sound production - Song feedback
→ Acoustic and Motor Feedback
→ Model/production comparison → vocal motor correction
*Cycle goes on and on until crystallization
What pathways are involved for song learning in the bird’s brain?
Song production:
Auditory input → HVC → RA → nXIIts → Syrinx (vocal organ)
Learning:
LMAN → RA (to modify the sing production)
Midbrain → X
DLM → LMAN → X → DLM (loop)
HVC ⭢ X area
*Comparison between the template and the motor command (feedback)
*Occurs in the Hemispheric forebrain (neocortex)
*HVC = High Vocal Center
*Area X = basal ganglia nucleus of the anterior forbrain pathway
What happens in birds when there is a lesion in the X area?
In juvenile bird, it disrupts the song learning
In adults, it has no effect because the song is known (after crystallization)
*The X area receives input from HVC and LMAN, and sends it to ⭢ DLM
Why does the song production descendent pathway in the bird go through nXIIts?
nXIIts = tracheosyringeal nucleus of the XII cranial nerve ⭢ control breathing ⭢ required for singing
How can we generate LTP in adult birds?
What characterizes the LTP?
Stimulate LMAN or HVC, depolarize and record from Area X ⭢ Pairing of the stimuli results in LTP
This LTP is synapse-specific and activity dependent
⭢ If you induce LTP of LMAN ⭢ area X, HVC ⭢ area X is not affected and inversely
Is the plasticity studied in the bird song model hebbian or not?
It is Hebbian because LTP required both pre and postsynaptic activity
- With only tetanus ⭢ no change
- Only postsynaptic depolarization ⭢ no change
- TET + Dep ⭢ LTP
What is LTP is the bird song model dependent on?
Dependent on NMDAreceptor and Ca2+
- APV ⭢ blocks NMDAreceptors ⭢ no change
- BAPTA ⭢ Calcium chelator ⭢ no change
What is the difference between plasticity in juvenile vs adult birds? What does it explain?
Induction of plasicity by pairing protocol is much greater in juvenile birds ⭢ might explain why the song can’t change in adult birds
Explain the principle of sensory reafference.
Movement can lead to sensory reafference!
Motor command ⭢ motor system + copy element
Copy element ⭢ afference/copy efferent (-) ⭢ percepetion (a copy of the motor signal goes to you visual cortex to dim the visual perception)
Motor sysem ⭢ reafference ⭢ external afference ⭢ sensory system (your visual feild receives the input of your hand moving in front of your face) ⭢ perception
Efference copy + reafference stimulus are combined ⭢ perceived stimulus
Explain the mechanical tickling experiment.
(Which is the motor command, reafference, perceived stimulus)
1 actuators that is moved/commanded by right hand of subject ⭢ connected to a computer ⭢ which controls a second actuator which moves a feather on the left hand of the subject
Subject rates how ticklish it is every time
Motor command = arm movement
Reafference = tactile stimulus
Perceived stimulus = tickling sensation
*Non-invasive experiment which gives a lot of info on the brain
What do the results of the mechanical tickling experiment show?
The predicted sensory stimulus (efference copy) is compared to the actual stimulus
⭢ If discrepancy, then the subject perceives the stimulus as causing tickling sensation
⭢ Efference copy contains both temporal and spatial information about the reafferent stimulus (tactile stimulus)
Had 2 controls: 0ms/0˚ delay and an 100% external stimulus with no motor command
As the delay in time of degrees increased compared to motor command increased, the tickling sensation increased ⭢ as 300ms or 90, no significant difference with external stimulus
*Cerebellum
What part of the brain is required for timing of movements?
Cerebellum
Explain the experiment that allows to show that timing of movements require the cerebellum.
2 paired stimuli: Loudspeaker + Air jet in the rabbit’s eye with always the same time delay between both
Normal rabbit learns to anticipate and starts closing its eye a bit before the air jet
Cerebellum lesion subject doesn’t show anticipation
What cognitive activities is the cerebellum involved in?
- Balance
- Coordination movement
- Timing of movements
- Timing of discontinuous movements
- Motor learning ⭢ acquiring and maintaining
*The cerebellum is present in all vertebrates and is one of the most anatomically conserved structures throughout evolution (similar in fish an in primates)
What does cerebellar anatomy look like?
Deeper ⭢ Surface:
White matter ⭢ Granule cell layer ⭢ Purkinje cell layer (receive synapse from parallel fibers) ⭢ Molecular layer (composed of parallel fibers)
*Climbing fibers go up all layers and wrap around the purkinje cells
*Mossy fibers input onto granule cells
What protocol allows to induce cerebellar plasticity? (where do we stimulate/record from)
What do we get?
Climbing Fiber Stimulus + Parallel Fiber stimulus
Record from Purkinje cell
Co-activation of parallel and climbing fibers input ⭢ LTD on Purkinje cells ⭢ NON HEBBIAN
*In cerebellum
In motor learning, what is the cerebellum required for?
Sensorimotor coordination does NOT require the cerebellum
ADAPTATION to novel conditions does require cerebellar function ⭢ error driven process (like bird song)
A subject that puts glasses on that shift the glaze can adapt, but not patients with cerebellar lesions
⭢ For patients that have adapted, they need to relearn when they take glasses off, but the ones with lesions don’t
What is the electric fish a good study model for? Why?
- Electric fish are good model system to study cancellation of referent input → emits eletric fields through an electric organ in their tail
- Similar cerebellar anatomy to us (very developped) → cerebellar anatomy is conserved across vertebrates
- Electric fish have simple anatomy and behaviours
Electric fish uses perturbations of their generated electric field (tail) to interact with their envrionment
→ Pulses generated by the animal can activate their own electrosensory system
*What mechanism allows sensory neurons to ignore the reafferent stimuli?
What is the anatomy of the eletric fish brain like?
Cerebellar-like anatomy:
Input from a sensory surface (sensory input layer) → Principal cell layer → Molecular layer → Granule layer
In electric fish, changes in the reafferent stimulus cause changes in the efference copy. What mechanisms underlie these changes?
Negative image input matches the afferent input to cancel it out (plasticity in the fibers)
Exp1: Pairing the EOD command with an excitatory stimulus (amplify the EOD) → the negative image is amplified → when the excitatory stimulus is removed, the EOD command/efference copy is decreased
Exp2: Pairing the EOD command with an inhibitory stimulus (reduce the EOD) → opposit
How can the plasticity in electric fish be qualified?
ANTI-HEBBIAN plasticity
Record from a parallel fiber and stimulate from granule cell → spike timing dependent plasticity
- Pre before post → depression
- Post before pre → potentiation
*More time between them = less plasticity
IMPORTANT → Anti-hebbian STDP underlies the adaptative cancellation of reafferent input
During sensory processing of internal vs external stimuli, what acts as a predictor ?
Efference copy = predictor
It is compared to the actual of the sensory stimulus
If they don’t match/time delayed → perceived as external
What 2 informations are contained in the efference copy?
efference copy = copy of the voluntary mouvement signal
Temporal and spatial information about the reafferent stimulus
What is homeostasis?
The ability of the body/cell to seek and maintain a condition of equilibrium or sability within its internal environment when dealing with external changes
→ Internal compensation for external changes
What can we see when putting neurons in culture?
If we add TTX/CNQX?
If we add bicuculline?
- Spikin activity develops spontaneously in cortical cultures (neurons will spontaneously make connections)
TTX = Na channel antagonist → restricts spiking activity → increase excitability (seen when TTX is washed after 2 days)
Bicuculine= GABAa antagonist → promotes spiking activity → decreases excitability (seen when washed after 2 days)
How can we confirm that the changes in excitability seen in neurons when restricting/promoting spiking activity (TTX/GABAa) are proportional?
What is the name of that concept?
Synaptic scaling:
reduced activity → increase in current (mEPSC)
increased activity → decrease in current (mEPSC)
When normalizing the %mEPSC, we see that the current stays constant
In the study of culture neurons (TTX and GABAa), what changes underlie plasticity?
Changes in AMPA receptor trafficking underlie plasticity
Increased activity (GAGAantagonist) → some synapses will get depressed
Reduced activity (TTX) → all synapses will get potentiated (more AMPA receptors go to the membrane to be able to cover for the lack of activity)
What is the STG?
Lobster Somatogastric Ganglion
It coordinates the movement of teeth in the stomach for proper chewing of the food → muscles that move the pylorus and the gastric mill (teeth) in a highly periodic manner (every neuron individually too)
Composed of big neurons ~ 200um → can plate in a dish
→ These neuron are highly periodic
Why is the STG a good study system for neural homeostatic activity?
- It has 2 rhythms → pyloris and gastric mill
- The rythms see in vitro are similar to those observed in vivo
- Individual neurons can be identified reliably across animals → few neurons in the cricuits but connected in complex manners (complex relationship between spiking activities)
- Multi-unit intracellular and extracellular recordings can be done
What experiment was done to study homeostatic plasticity in the STG?
Day 1 → Whole STG has constant rhythm (intact)
Day 1 after cutting part of the circuit off → decentralization → loss of rhythm
Day 5 post-decentralization → new rhythm is set (not the same, but the found a new homeostasis/equilibrium)
What happens when a single cell from the STG is pharmacologically isolated? (AB cell)
Isolation alters neural activity in the short term
Recovery of the activity (firing) occurs spontaneously over long term (3 days)
Day 1 of isolation → no firing
Day 2 → High firing rate
Day 3 → cell finds a new rhythm
What are the underlying mechanisms responsible for the fact that an isolated STG cell spontaneously finds a new rhythm post-isolation?
Changes in intrinsic conductances (Na and Ca channels) of neurons regulate excitability of the neuron and its ability to fire → co-regulation of membrane conductances
In bursting activity, Ca is more dominant
In tonic activity, Na is more important
What characterizes membrane currents/conductances in bursting neurons?
Bursting neurons displayed lower outward currents and larger inward currents
How can the pyloric neuronal network in the STG achieve homeostasis in modeling conditions?
Describe the experiment briefly.
Different sets of parameter values can give rise to similar outputs (firing patterns)
→ When 1 parameter is changed, no need to undo that change to get the same firing rate, can change another parameter to find the homeostatic state again
It has been shown that the same firing pattern in the pyloric network can be obtained with 2 very different membrane and synapse conductance setups through the different neurons (the solutions are not unique)
→ Mechanism of HOMEOSTASIS
What is neuron plasticity? (as opposed to synapse plasticity)
It is a change in the expressed channels allowing for changes in outward/inward currents/conductances to restore the baseline rhythm
→ One cell on its own, not in relationship with another cell
What 2 mechanisms allow to maintain homeostasis together when there is sensory or activity deprivation?
Synaptic hemoestasis → more or less receptors or channels (same proportion)
Intrinsic homeostasis → change the ratio of inward vs outward current
What type of plasticity is seen in the weak electric fish?
Anti-hebbian STDP → underlies adaptative cancellation of the reafferent input
