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What is a Stimulus?

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What is a Stimulus?

This is any input light, sound, touch taste gravity movement

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What is processing give an example?

What the brain does with the information

ex. simple: touching a hot pan

complex: taking an exam

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What is a behaviour, give examples?

anything you do in response

  • removing your hand for the hot pan

  • filling in the circle for answer A

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What are. the step necessary for the brain to do work?

  1. Stimulus

  2. Processing

  3. Behaviour

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What is action potential?

an electrochemical wave driven by the movement of ions along their electrical and concentration gradients

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What are Neurons?

  • cells, containing the same complement of organelles: (cytoskeleton, DNA) etc as other cells

  • They also have features that make them distinct, dendrites, axon, synapse

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What are Dendrites?

  • processes near the cell body

  • receive input form other neurons

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What is an axon?

  • the main conducting unit of the neuron

  • connects one cell to the next

  • conveys information by propagating en electrical signal (the action potential)

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What is a synapse?

  • used to communicate signals from one neuron to another

  • the action potential is converted into a chemical signal

  • the chemical connections of the axon (pre-synaptic) of one neuron to the dendrites (post-synaptic) of another

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What is a concentration gradient?

  • molecules move from area of high concentration to areas of low concentration, until they are evenly distributed

  • you can have diffusion in a wide open space

  • you can also have diffusion if there is a barrier with a hole in it ex. cell membrane

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How may concentration gradient be affect by a channel

  • if you have a channel in a membrane, the molecules will be able to move from high concentration to low concentration but they will do so more slowly

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Concentration gradient in neurons

  • HIGH concentration of sodium (Na+) outside the cell

  • Low concentration of Na+ on the inside of the cell

  • concentration gradient for Na+ goes into the cell

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What is an ion

a molecule that carries a positive charge

, ex. sodium

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What is voltage and what does it look like in relation to particles?

  • it is a force that moves oppositely charged particles toward each other

  • it also moves similarly charged particles away from each other

  • Charged particles can be either positive or negative

  • Being charged means that they experience a force when they are around other changed particles

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How is voltage created?

  • you need to separate opposite charges

  • separating charges creates voltage or “potential energy” or “potential difference”

  • voltage is a force so that if you release the charges they will move toward one another

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What is a current?

the electricity or flow of charge that happens when there’s a voltage

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Describe the electrical gradient within a neuron

  • there are positively charge ions outside of the cell and negatively charged anion inside the cell, with a membrane separating them, which creates voltage

  • adding a channel to the membrane allows charged particles to flow through

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What negatively charged particles are inside the cell and what is the voltage?

  • proteins and ions

  • voltage around -70mV

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Why are channels important for the function of a neuron?

  • they are a key part to how neurons work

  • they open at different times in response to different changed in the cell, ex. some way open when the cell is more positive or when the cell is more negative

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Ion channels

  • some channels just for Na+ ( nothing else can flow through them

  • they only let Na+ go one way: IN

  • specific for particular ions and directions

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Na+ channel

  • normally closed at a very low voltage, when its very negative inside

  • -70mV inside = closed

  • though bringing the voltage up channels will open (above -70mV)

  • once the channel opens Na+ will rush in being pushed by both the concentration gradient and electrical gradient

  • the charge on the inside will increase

  • once the voltage gets really high (eg. +40mV) the Na+ channels close, this is know as the refractory period

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Channels and voltage

  • wether a channel is open or close can depend on voltage

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What is the refractory period

  • when the voltage on the inside of the cell gets really high the channel will shut

  • these channels go “offline” for a little while because they need to reset

  • during this time you cannot get them open

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Is K+ inside or outside of the neuron?

  • it is set up the opposite way from Na+

  • Lot of K+ inside

  • concentration gradient for K+ goes out

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How does K+ flow out?

  • the concentration gradient

  • less voltage holding K+ in

  • the K+ channel may open due to a lower voltage than that of Na+

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Steps of the diffusion for K+ and Na+

  1. Na+ channels open, Na+ begins to enter the cell

  2. K+ channels open, K+ begins to leave the cell

  3. Na+ channels become refractory, no more Na+ enters cell

  4. K+ continues to leave cell causes membrane potential to return to resting level

  5. K+ channels close, Na+ channels reset

  6. Extra K+ outside diffuses away

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What is a sodium potassium pump?

  • it uses energy (ATP) to move K+ in and Na+ out until everything is back to normal

  • starting the whole process over again

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Why is energy (ATP) important in with the diffusion of K+ and Na+ across the cell membrane?

  • Similarly to potential energy with gravity or a battery, you put energy in to create the separation

  • then you get movement when you release it

  • Then you need energy to create the separation again

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Do all channels open at once?


ex. like popcorn popping, at first you hear a few popcorn popping which leads to a flood of the popping popcorn

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How does action potential diffuse down the axon?

  • Na+ comes in

  • Na+ diffuses from the channel

  • Adjacent areas get more positive

  • Opens adjacent channels

  • More Na= comes in

  • Na+ diffuses from the channel

  • Adjacent area gets more positive

  • Opens adjacent channels

  • more Na+ comes in

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Can action potential travel in multiple directions?

  • on each cell action potential travel in one direction

  • from the cell body to the synapse

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Why doesn’t action potential flow backwards?

  • After Na+ flows in and makes the inside positive the Na+ channels in that patch close

  • Na+ channels won’t open again for a little while, they have to reset

  • Even though Na+ diffuses in both directions inside the cell it can only open channels that haven’t recently opened

  • it can only move forward

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How can we measure action potential?

by the voltage

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How can we manipulate action potential?

  • either by altering the chemistry or by altering the voltage

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What can alter the speed at which action potential moves?

this depends on:

  • size

  • structure

of the neuron

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What is a Loligo?

  • a large axon

  • action potentials were first studied using these

  • worked on by two scientists, (Hodgkin and Huxley)

  • who did measurements to figure out how action potential works

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Why was using a Loligo important to Hoagkin and Huxley

  • it was big and easy to work with

  • they were measuring electrodes, in order to do this they needed to put in a tiny piece of metal, the size of this axon allowed them to do so

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Do larger axon conduct action potential faster or slower then a smaller axon and why?

  • Faster

  • charge travels faster in large axons before leaking out

  • Big neurons can space channels and pumps further apart

  • recreate the action potential fewer times

  • less work for the Na+/K+ pump to do

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When would a squid use their large axon?

  • to convey signals for critical reflexes

  • where information needs to get to the muscles quickly

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What is a Schwann cell (Myelination)?

  • seen in many vertebrates

  • this wraps the axon

  • this insulates the axon, preventing Na+ and K+ from leaking out or in

  • enables the cell to hold the charge for longer

  • i.e the positive charge from the influx of Na+ can travel farther down the axon

  • used as a “solution”(instead of) bigger axons

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Does the Myelin (Schwann cell) wrap the entire axon in one piece?

  • No

  • Rather there are many Schwann cells that wrap the axon

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What are the “Nodes of Ranvier”

in between Schwann cells

  • At these nodes there are lots and lots of channels and pumps

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How does Myelination increase the rate of action potential along the axon?

  • instead of having to open channels along every single cm of the axon

  • the action potential can “skip” rapidly from one node to the next, regenerating just at he nodes instead of at all the areas in between

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Multiple Sclerosis

  • an autoimmune disease that results in damage to and breakdown of the myelin

  • patience show impaired movement and other deficits because signals are no longer travelling quickly or efficiently

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Does the action potential regenerate at different strengths"?

  • no

  • “all or none”

  • you either have one or you don’t

  • “0s and 1s”

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How does action potential change at the synapse?

The all-or-nothing action potential gets turned into a graded more complex response

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Pre-synaptic vs post

before the synapse (axon terminal), after the synapse (dendrites)

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Describe how the synapse works

  • action potential leads to the release of neurotransmitter from the terminal of the pre-synaptic cell

  • It travels across the space between the pre-synaptic cell and the post-synaptic cell

  • Its binds to receptors on the post-synaptic cell

  • binding to receptors leas to all kinds of things

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What will the neurotransmitters control

They modulate the cell’s activity

  • probability and timing of action potentials

  • how much input will be needed to fire

  • when the cell will fire relative to that input

  • how many action potentials will be produced and so on

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Are all receptors the same?

No, there are different receptors for all of different kinds of substances

  • different receptors do different things

  • some are just channels

  • some activate second messenger systems, they aren’t channels though they activate many “down stream pathways”, ex dopamine

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What are second messenger systems?

  • they aren’t channels though they activate many “down stream pathways”, ex dopamine

  • they activate pathways that can affect activity of proteins (like channels) gene transcription, mRNA translation and more, because of this they have more longterm effect on the neuron’s activity

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How can we change the response of a post-synaptic cell?

  • this is caused by the many different chemicals used (and therefore different receptors)

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What are inhibitory inputs?

reduce action potential

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What are excitatory inputs?

  • increased action potential

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What are modulatory inputs?

  • alter the effects of other inputs

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What inputs does a neuron typically receive?

  • excitatory inputs

  • inhibitory inputs

  • modulatory inputs

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post-synaptic cell and inputs

  • its sums up the inputs and produces a response

  • it could fire an action potential (or not)

  • It could fired one or many spikes

  • it could fire immediately or a little later

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What causing the “sprinkling of sodium” inside the cell?

  • this may be due to inputs

  • not all input will result in an act potential

  • they may just alter the potential a little bit

  • with enough of these inputs an action potential may be cause

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synapse + action potential = ?

synapse can turn action potential into a graded and complicated response

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networks of neurons

  • hundred or thousands or neurons working as a group

  • how you scale up from one cell to a network in complicated, because of how synapses work, and because of the convergence of multiple inputs

  • They are not just the passing of a signal from one cell to the next, but the signal changes in the process

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functional neuroanatomy

  • information comes in through a specialized receptor

  • then is goes through a relay station called the thalamus (for vision, it’s called lateral geniculate nucleus)

  • Then it goes to more outer brain areas like the cortes, lots of the processing happens in the cortex

  • Once the information is processed, the output of the cortex goes back down to areas that will execute

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Sensory Inputs

  • They process sensory input

  • they turn external information into action potentials

  • Information gets taken apart at the sensory receptors, then progressively assembled at high stages in the brains (the thalamus and cortex)

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Sensory input - Vision

  • Photoreceptors in your retina turn light into action potentials

  • the pattern of action in visual cortex recreates the visual scene

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Sensory input- Hearing

  • hair cells in you cochleas turn sound waves into action potentials

  • the pattern of action potentials in your auditory cortex indicates what and where a sounds is

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Sensory Inputs - Smell

  • Olfactory receptors in your nose turn odours into action potentials

    • olfactory cortex and other cortical and memory areas (hippocampus) identify smell

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How does processing work

  • Many sub-cortical (under the cortex) regions monitor your current and previous internal state (hypothalamus, preoptic area amygdala, nucleus accumbens, septum, ventral, pallidum, hippocampus)

    • Cortical regions provide top-down information on what you should or can do, decision-making

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  • refers to the outermost part of the brain

  • It is a layered structure: the cells are organized into layers and columns

  • does a lot of high-level processing

  • Integrates information from multiple sources

  • it’s where your brain recreates the sensory world

  • it’s where you brain makes decisions and plans movements

  • the cortex has lots of connections to other parts of cortex as well as to underlying structures

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Who did some of the first drawings of the cortex?

  • Santiago Ramon y Cajal

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Cortex function

  • different subdivisions, some are concerned with sensory input (figuring out what or where a stimulus is)

  • some are concerned with memory or recognition or decisions or language

  • some are concerned with determining how to respond assembling a behaviour or motor response

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What is white matter?

  • directly underneath the cortex

  • filled with axons going to and from the cortex

  • this is called white matter because the myelin on the axons make them appear white

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regulates body function

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What allows you to execute a behaviour?

  • motor cortex, basal ganglia and cerebellum are important for learning and altering movements

  • they allow you to assemble a motor plan to enable you to execute a behaviour

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electroencephalography (EEG)

  • uses electrodes to measure electrical activity along the scalp

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What are the pros and cons of electroencephalography (EEG)

Pros: Non-invasive People can move around during recording (for example, there are studies of people playing the guitar)

Cons: Electrodes are outside the brain, Means you can say when a change in activity happens, but hard to determine exactly where

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What is Positron Emission Tomography PET

  • Person eats radioactively labeled sugar (fluorodeoxyglucose or FDG)

  • Sugar gets picked up by active cells (because busy cells need energy to run the Na+/K+ pump!)

  • Cells will give off radiation that can be detected by the scanner

  • This means that active regions will give off a lot of radiation and “light-up” on the scanner

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What are the pros and cons of What is Positron Emission Tomography PET?

Pros: Better resolution than the EEG and can see deeper brain structures

Cons: the part where you have to eat radioactive sugar Also, you can’t move around much in the scanner

Lots of PET studies involve watching or listening to things

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What are Functional Magnetic Resonance Imaging fMRI?

  • Like PET, also involves a scanner, but this time it uses magnets

  • Scanner applies magnetic fields to the brain then measures the energy emitted by different brain areas as they return to their normal, unmagnetized states

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How is fMRI able to use magnets?

  • cells take up oxygen from the blood

  • blood returns to the lungs to get more oxygen

  • blood without oxygen is more magnetic than oxygenated blood

  • Areas that are more metabolically active (e.g use more oxygen) emit different signals than less active areas

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What are the pros and cones of fMRI?

pros: compare activity across the whole brain to different stimuli

no radioactive sugar

Cons: once again, participants can’t move around much

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What is Electrophysiology

  • uses electrodes to measure action potentials of neurons

  • Can measure one or hundreds at the same time

  • in humans this is often done prior to brain surgery, it can help the surgeon determine where speech and language areas are located and avoid them

  • mostly done on animals

  • high resolution: you can find out what a single cell is doing during behaviour

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What are examples of measuring the brains activity indirectly?

  • PET

  • fMRI

  • look at which area use more energy or oxygen and therefore more active

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What are examples of measuring the brains activity directly?

  • electrophysiology

  • EEG

  • directly measure action potentials

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Gene and protein expression

  • Label mRNA or proteins with radioactivity, dye or antibodies attached to fluorescent tags

  • look at the expression under the microscope

  • you can do this by making a very thin brain slice and then reconstructing it, now we can do this with the entire brain by making it clear

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What are the pros and cons of gene and protein expression?


  • can look at expression across a wide range of brain areas ( hard to do with electrophysiology)

  • Can look at expression within single neurons (can’t do with EEG, PET, or fMRI)

  • tells you abut changes or differences in particular molecules or cell types


  • you have to take the brain out to look a it

  • can’t measure the brain during behaviour

  • can only have one “treatment” pre individual, compare expression between groups

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How do you know what a brain area does?

  • Look at when its active ( EEG, PET, fMRI, etc)

  • or manipulate activity in a brain then look at behaviour

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How can we manipulate activity in the brain?

  • Increase the activity of cells: stimulate cells using electricity or lights

  • Decrease the activity of cells: lesion or kill cells or block cell activity with drugs, e.g tetrodotoxin is a poison (from puffer fish) that blocks sodium channels which means it blocks action potentials

  • modulate the activity of cells: block or stimulate receptor chemical like serotonin, dopamine, norepinephrine

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How do we increase the activity of cells:

  • stimulate cells using electricity or lights

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How do we decrease the activity of cells

  • lesion or kill cells or block cell activity with drugs, e.g tetrodotoxin is a poison (from puffer fish) that blocks sodium channels which means it blocks action potentials

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How do we modulate the activity of cells?

  • block or stimulate receptor chemical like serotonin, dopamine, norepinephrine

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a behavioural change caused by experience

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What does a memory look like in the brain?

a change in the number or strength of synaptic connections

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What leads to the formation of a memory

  • changes in the activity of neurons or circuits can lead to changes in synaptic connections

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Describe the spines the denrites. Are the spins always present?

  • tiny extensions on the dendrites

  • make neurons look bumpy

  • spines and synapses are dynamic: they comes and go, appear and disappear

  • Depends on the input (action potentials) to the synapse

  • if there’s a lot of input they might increase in size or become stable (less likely to disappear)

  • If there’s only a little or no input they might shrink or disappear

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What activity can increase the number of stable spines?


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Where in the brain should we look for memory?

  • anywhere there is synaptic plasticity (changes to spines and synapses), everywhere in the brain

  • there are part of the brain that seem to be dedicated to storing particular kinds of memories

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Where is episodic memory formed?

the hippocampus

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What are episodic memories?

  • abut autobiographical events

  • things that happened to you

  • generally tend to involve: what, where and when

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What are semantic memories?

  • things you remember but didn’t experience

  • ex. you remember that John Edmonstone taught Charles Darwin taxidermy

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