3 lecture 7 Flashcards
what is memory
a change in the number or strength of synaptic connections
what makes a neutron look bumpy
synapses often occur on “spines”, tiny extensions on the dendrites –Spines make the neuron look bumpy
are the spines permanent
These spines and synapses can come and go, appear and disappear, depending on their input (connections to other cells)
–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
does learning impact the number of stable spines
yes, it increases them
where does Synaptic plasticity (spine stabilizing, etc) happen
anywhere
what is stored in the hippocampus
Specifically, decades of research support the idea that episodic memories are formed and stored in the hippocampus
what is Episodic memory
A memory of autobiographical events, things that happened to you Involves What, Where and When
what is semantic memory
things you remember but didn’t experience, for example, if you remember that Eric Knudsen studied owls with goggles on or Diego Velazquez painted “las meninas” in 1656, that is semantic memory
Why do we think episodic memory is in the hippocampus
Accidental experiments (patient HM) Size of hippocampus Lesions (removal) of the hippocampus Monitor activity during learning and memory
who is patient HM
Henry Gustav Molaison or HM
Suffered severe epilepsy which was localized to his medial temporal lobe, where the hippocampus is
William Beecher Scoville, a Harvard neurosurgeon removed HM’s hippocampal region (and some neighboring structures).
This surgery cured HM of his epilepsy
but
He lost his memory of personal events that happened in the few years just prior to the surgery AND
He was subsequently unable to form new episodic memories
Thus, he was left mostly with long-term semantic knowledge of events prior to 1953
So that tells us something about the role of the hippocampus in episodic memory, but clearly there’s more that we need to know
what is the theory about the correlation between the hippocampal size and episodic memory
studied in birds;
The idea is, animals that naturally perform tasks that rely heavily on the hippocampus ought to devote more of their brain to the hippocampus
–Either through use or evolution, the hippocampus should be larger in animals that use it a lot than in animals that don’t use it as much
what is spatial memory
We call this use of geographic location and spatial cues SPATIAL MEMORY
what bird has a quit large hippocampus compared to other births
the humming bird
The function of the hippocampus has been studied a lot in food-caching in birds, how is this done
these are birds that collect food and hide it in order to eat it later
–kind of like squirrels
The parids collect small seeds or insects and hide them in the bark of trees in tiny holes that they make with their beaks
The corvids collect larger seeds, nuts and insects and hide them in holes in the ground that they dig with their beaks
This “caching ” or hiding of food potentially requires a map of the environment as well as memory of the locations where the food is cached
what is the correlation that has been found between birds and the hippocampus size
birds that store food have a larger hippocampus than those that do not store food
how do we know that the hippocampus size is experience dependent
Hippocampus size is also related to spatial ability in humans:
Work by Eleanor Maguire found that London taxi drivers have larger hippocampi than non-taxi drivers
And, the size of the hippocampus increases with time on the job –the more time they spend learning to navigate the city, the
larger their hippocampus is
So in this case, hippocampus size is experience dependent
Some of the earliest demonstrations of the role of the hippocampus in spatial memory came from studies using what
the Morris water maze
how was the the Morris water maze experiment conducted
With brief training (or after showing them the position of the platform)
–Rats can use local or room cues to navigate from any spot over to the platform –However, after training, rats with hippocampal lesions still take a long route to find the platform
In addition, Morris also removed the platform then tested to see how often rats would cross the pool and where they seemed to look
Control rats spent most of their time where the platform used to be
Lesioned rats did not
Instead, the lesioned rats searched all four quadrants for similar amounts of time
In fact, they made as many crosses of the quadrant boundaries as intact rats, they just visit all quadrants equally
The hippocampus is larger in individuals or species that tend to do more what
“spatial” tasks
Removing the hippocampus does what
impairs spatial learning and memory
How do we look at activity
EEG, PET, fMRI and electrophysiology
how is the PET scanner used for this
In 1998, Eleanor McGuire and colleagues had people go into a PET scanner and navigate around a virtual world
They found that hippocampal activity
How much it increased depended on whether they were good at navigating
people that were more accurate had more acidity than people that got lost
This result was pretty exciting, but it still leaves the question of how the hippocampus works? What exactly are those cells doing? How is a map of the world encoded in your hippocampus?
This is where we need higher resolution
what are Place cells
They discovered that certain cells are active at certain spots in the space (red dots
And other cells are active at other spots
how do place cells respond/activate
It turns out that, as a group, place cells respond to an entire environment, with each cell responding to just a tiny part
what provides the start of a code for spatial memory
pattern of activity provides the start of a code for spatial memory
what animals have this code for spatial memory
rats and bats
what do place cells prove
Our goal here isn’t to solve the code
Rather, we want to
–verify that the hippocampus is indeed one place that stores episodic memory
–get a very basic idea of how we know that memory is there and how that memory is encoded
So what we’ve covered on place cells will suffice
Place cells are for what
are part of the code for navigating and remembering the environment
What makes you remember something
what is conditioning
to associate a place and an event, then test to see if they if they remember the association
We mentioned at the beginning that it can be difficult to ask animals about their “autobiographical” memories
We can do this through a behavioral training method called CONDITIONING
Activity of cells in the hippocampus provide us with what
very detailed information on the role of the hippocampus in navigation
–there is clearly a very complex code that helps you to remember and navigate around a familiar place
how do we study “what” and “where”
using conditioning
how does conditioning work
In general conditioning works like this: Seeing food makes a dog salivate
But, hearing a bell (neutral stimulus, NS) does nothing
During conditioning, the dog learns the pairing of the bell and food (the bell predicts that food is coming)
After conditioning, just hearing the bell will make the dog salivate
But you can “condition” other things, like a place and event instead of a sound and food
what is the experiment with a mouse and conditioning
Put a mouse in a blue room, it will wander around and explore
While it’s in the blue room, let’s say you give a mild foot-shock, then return it to its home cage
.
.
. foot-shock (even if you don’t give one) .
.
Later on, when you put the mouse back into the blue room
It will behave as though it expects there to be a
That is, it will act scared
What do mice do when they’re scared? They freeze i.e. they stand very very still
This means mice can quickly learn to associate
.
a place (blue room)
with an experience (foot shock)
.
and demonstrate that they remember the experience (freezing) to the place (“where” = blue room)
Conditioning
. (“what”= foot shock) by displaying a conditioned response
.
This is known as Fear Conditioning
what can the hippocampus learn with regards to conditioning
The hippocampus can learn these sorts of associations
like conditioning and fear conditioning
in general, can you have animals generate a memory
You can also have animals generate a memory by giving them particular experiences, then look at their behavior or gene expression
how do we test “when”
In order to test whether birds have episodic-like memory, Nicki Clayton did several experiments with Western Scrub Jays
Scrub jays are a species of corvid that also includes
–ravens, crows, jays, jackdaws, nutcrackers
what are corvids
The corvids collect larger seeds, nuts and insects and hide them in holes in the ground that they dig with their beaks
how was the experiment conducted to connect Episodic memory: spatial memory and time
look back at lecture to explain experiment (lecture 18 November 23, 2017
what was the conclusion of the Episodic memory: spatial memory and time experiment
to avoid the decayed worms, birds need to remember WHAT they cached WHERE and WHEN
This means that scrub jays could remember:
“What” was cached “where” (locations of worms vs. nuts)
i.e. spatial memory
AND
“When” those items were cached (and therefore whether they would still be edible)
This has the hallmarks of episodic memory
