Stress, memory, navigation

Created by

h.s

Cards (19)

Basics of memory
once information is learned, it must be stored in the brain; memory
there are many diff kinds of memory
we devise a hierarchy
this is not how the brain does it
From episodic to semantic
episodic memories are autobiographical
yesterday I saw the sunset
semantic memories are rules abt the world
the sun sets in the evening
always derived from personal experience
how are episodic memories turned into semantic memories?
involves hippocampus
involves repeated exposures to relevant events
Basic process of memory
events happen in the world and are perceived
the brain does some processing
the info is stored (in working memory)
the memory id consolidated into reference memory and stored there
when using it, it must be retrieved
Where in the brain? 
where does learning happen?
diff types of learning happen in diff places
cerebellum is important for some types of simple association
where is memory stored?
the memory trace itself is called an engram
hard to locate
memories are stored all over cortex
Important brain areas 
-Basal ganglia
important for habit formation, implicit learning
learning a new skill
-anterior temporal lobe
important for semantic memory
knowing facts abt the world
prefrontal cortex
lots of things; value, complex concepts
amygdala
emotional memories, memory consolidation
hippocampus
episodic, spatial, consolidation, relational learning
The hippocampus
very important for memory
precise function is debated
involved in;
turning working memories into reference memories
acquiring relational memories
where the important feature of the learning is a relationship between two or more objects
episodic memories
turning episodic memories into semantic memories
learning spatial things (which tend to be rational)
other (olfactory memory)
Damage to hippocampus
patient HM had both his hippocampi removed
had severe memory deficits, including:
anterograde amnesia
not able to form new long-term memories
retrograde amnesia; loss of previous memories
loss of episodic memory and conversion to semantic
never learned to recognize Milner
intact working memory
good implicit learning
Basics of learning
animals learn to associate events that reliably happen after each other with each other
every time u hear cookie, u get cookie
one neutral event (the word) and one innately positive/negative event (cookies)
animals begin to respond to the neutral event (the conditional stimulus) not jus the innately positive one (unconditioned stimulus)
u start salivating when u hear the word
the conditioned response doesn't have to be same as the unconditioned response
Hebbian synapses
brain is made of neurons
memories have to consist in long term changes to neuron
changes happen in synapse
Donald Hebb proposed;
neurons that fire tg, wire tg
everytime the two connected neurons fir tg, the synapses between them gets stronger
learning consists of strengthing and weakening synapse
associations are strong (easily excitable) synapses
Long-term potentiation
after repeated bursts of stimulation, synapses become easier to excite
mostly occur in glutamate synapses (excitatory)
2 types of glutamate receptors
AMPA; ionotropic, allows Na+ in
NMDA; ionotropic, allows Na+, Ca+ in, blocked by Mg+
step 1;
glutamate released
AMPA-R open, Na+ enters
NMDA-R blocked
LTP induction
Step 2:
strong stimulation (from 2 neurons)
lots of glutamate
AMPA-R opens, Na+ enters
Na+ depolarizes cells
depolarization removes Mg+ from NMDA-R
NMDA-R opens, Ca+ (and more Na+) enters
Ca+ works inside cells
step 3:
Ca+ activates CaMKll
CaMKll activated CREB
CREB regulates gene expression
LTP maintenance
Step 4:
CREB changes the expression of genes which:
increase the number of NMDA and AMPA receptors at that dendrite
AMPA receptors become easy to open
more dendrites form onto the same axon branch
postsynaptic cell will receive more EPSPs from the same presynaptic neuron
retrograde messages change the presynaptic terminal
cell is more likely to fire
release more transmitter (glutamate) per event
Inhibition
If Synapses jus had the LTP, they would all get stronger and stronger
need a way to also inhibit firing
long-term depression (LTD)
involves excitatory glutamate receptors (AMPA, NMDA)
Occurs in hippocampus and cerebellum
results from low-frequency repeated stimulation
cell reduces density of AMPA-R and phosphorylates them
Navigation
animals and humans need to find their way to food, work, back home...
need a cognitive map
the map must allow:
navigation between any two points (shortcuts)
using diff landmarks
the map needs to be:
unified; all the info in one representation
allocentric; not dependent on where I am
flexible; allowing calculation of vectors between points
spatial info is relational
my house in 3 blocks north of the church
the map is in the hippocampus
Hippocampus connection
sensory cortex -> entorhinal cortex
entorhinal cortex -> dentate gyrus
dentate gyrus -> CA3
CA3 -> CA1
CA1 -> subiculum
Cells of HF
Cells in HF represent aspects of the environment
place cells (CA1); always firing at the same place
head direction cell (EC); fire when facing a direction
boundary cells (EC & Sub.); fire when close to walls
Grid cells (EC); fire on grid
Remapping
when in a new space, need new map
cells can remap when the space changes
completely, partially, not at all, rate, stop firing
new places, grid alignment
Coordination
events in the brain need to be coordinated
firing of cells related to CS and US
brain has global rhythms of subthreshold stimulation
generated by trisynaptic circuit
abt 3-10 Hz
rhythm raises and lowers membrane potential
like an EPSP for all cells at once
makes it easier or harder to fire
causes firing to synchronize
Summary
all diff cells, coordinated, create a representation of the world
places, directions, object, time
can also focus on task (leaving, returning)
we use this representation
to navigate
to remember
to learn