1. PART 4: BEHAVIORAL PLASTICITY #24: SPATIAL NAVIGATION IN RATS I
spatial learning
cells that code for space
synaptic plasticity in the hippocampus
experiments that are knockouts
summary

2. PART 4: BEHAVIORAL PLASTICITY #24: SPATIAL NAVIGATION IN RATS I
spatial learning
cells that code for space
synaptic plasticity in the hippocampus
experiments that are knockouts
summary

3. SPATIAL LEARNING
rats...
order Rodentia
family Muridae
subfamily Murinae... all common mice & rats
cosmopolitan
arboreal, terrestrial & even aquatic
nocturnal (generally)

4. two most common species black house rat... Rattus rattus
SPATIAL LEARNING
two most common species
black house rat... Rattus rattus
brown house rat... Rattus norvegicus
really good motor and navigation skills 

5. SPATIAL LEARNING
navigation by cues... two types, both used
 path integration
using memory of familiar environment
missing sensory cues (e.g., visual)
use internally generated ideothetic cues...
vestibular
proprioceptive
optic flow (deprived in this e.g.)
 external landmarks
learning the environment
direct sensory input (e.g. visual observation)

6. SPATIAL LEARNING – MAZE LEARNING
navigation by learning in a novel environment
how do animals learn this task?
complex problem
rat used to study
behavioral strategies
neural mechanisms
maze learning...

7. SPATIAL LEARNING – MAZE LEARNING
maze learning among earliest experiments with rats
Tolman (1930s)
cognitive maps for solving spatial problems
internal representations
for current problems
extend to novel problems
also, first guy to study inheritance of behavior

8. SPATIAL LEARNING – MAZE LEARNING
radial arm maze
reward at end of each arm
optimal foraging
how many visits until all 8 food items retrieved?
training
few days... 7/8
~ 3 weeks... ~8/8

9. SPATIAL LEARNING – MAZE LEARNING
2 types of memory in this experiment
 working memory used within single trials
which arms have yet to be visited?
experiments to test different possible strategies
visible landmarks
rules... e.g., clockwise
marking visited arms
rats establish map of
maze over time

10. SPATIAL LEARNING – MAZE LEARNING
2 types of memory in this experiment
 reference memory used between trials
memory of food items in specific arms
remember positions between trials

11. SPATIAL LEARNING – MAZE LEARNING
Morris water maze - spatial learning
must find hidden platform
relative to visible cues in room
training... trials
test reference memory
rat encodes spatial relationships
QUADRANTS

12. SPATIAL LEARNING – MAZE LEARNING
Morris water maze - spatial learning
must find hidden platform
relative to visible cues in room
training... trials
test reference memory
rat encodes spatial relationships
QUADRANTS

13. SPATIAL LEARNING – MAZE LEARNING
Morris water maze - cued learning
associates visible platform with reward (escape)
QUADRANTS

14. SPATIAL LEARNING – MAZE LEARNING
circular platform maze
~ terrestrial version of Morris water maze
rats prefer to hide rather than be exposed
1 hole  access to hidden chamber
test reference memory ~ visible cues in room

15. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
rat brain

16. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
hippocamus

17. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS

18. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
hippocampal formation = hippoc. + associated bits
hippocampus... “sea horse” (Greek)
major connections: entorhinal cortex & fornix

19. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
regular longitudinal internal circuitry (~ MB)
 pyramidal cells in single layer
similar array in dentate gyrus, associated structure
 granule cells in single layer    

20. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
3 main subdivisions: CA1, CA2 (not shown), CA3
main pathways;  = trisynaptic circuit
 perforant path: entorhinal cortex  dentate gyrus
 mossy fibers: granule  CA3 cells
 Schaffer collaterals: CA3  CA1 cells
 commissural path:
through fimbria  CA1
highly oversimplified
additional circuits
feed-back & -forward
~ rest of brain

21. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
limbic system – humans

22. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
hippocampal lesions – humans, other mammals
not all memories lost
memories of facts or events (explicit, declarative, episodic) impaired or lost
post-lesion memory impaired only
pre-lesion memory intact
procedural, implicit memories ok
important for acquisition & memory
of types of new information
spatial information in particular
LIMBIC
SYSTEM

23. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
effects of hippocampal lesions – rats, radial arm maze
cued learning (informed that arm visited) ok
spatial impaired*
perseveration *

24. SPATIAL LEARNING – ROLE OF THE HIPPOCAMPUS
effects of hippocampal lesions – rats, water maze
spatial impairment  longer circuitous routes
swimming impaired or just enjoy a good swim?
3-part experiment
 spatial task  impaired ability to find platform
 cued task  can swim, would rather not
 spatial task  still impaired... no memory!

25. CODING SPACE – HIPPOCAMPAL PLACE CELLS
extracellular recordings from hippocampus
in freely moving rats
firing of neurons ~ spatial position in chamber, e.g. B
many neurons ~ spatial position  place field maps
“complex spike cells”... CA1 & CA3 (as it turned out)

26. CODING SPACE – HIPPOCAMPAL PLACE CELLS
cues governing a place cell’s spatial preference
free moving rats, chamber, “permanent” electrodes, camera from above recording position ~ space
place field maps
differences in preference, size & shape of fields, some cells (D) do not behave like place cells (strictly)

27. CODING SPACE – HIPPOCAMPAL PLACE CELLS
pattern not innate... acquired, then ~ stable  weeks
cells can have multiple preferences
preferences shaped by contexts (e.g., rewards)
gradual drift in preference ~ changing context

28. CODING SPACE – HIPPOCAMPAL PLACE CELLS
cells fire ~ cues
move cues, cell fires ~ preferred cue new position
remove cues, cell fires ~ memory of preferred cue position... “deduced reckoning” or ideothetic cues
what are these internal ideothetic cues?
movement related... vestibular & visual
test in striped cylinder; walls & floor rotation separately
showed that animals own movement  place cell firing

29. CODING SPACE – HIPPOCAMPAL PLACE CELLS
what happens in the dark (without visual cues)?
train animal in light, turn out lights
place cell activity remains ~ 30 min after lights out
~ memory
train animal in light, remove, return to dark chamber
cell established a new place field
train animal in light, remove, return to dark chamber, turn on the lights
retains remapped field determined in dark
preference ~ real time or memory of cue preferences

30. CODING SPACE – HIPPOCAMPAL PLACE CELLS
another cool place cell experiment...
cell readings made during all parts of experiment
rats trains in 4-arm maze ~ visual cues
could find food relative to position of cues in test
next, trained in 4-arm maze ~ visual cues
cues removed before test, had to remember place
when tested correctly, cells fired as before in arm
when tested incorrectly, cells fired incorrectly
suggests that if cell firing  (processing... memory... )  behavior 

31. CODING SPACE – HIPPOCAMPAL PLACE CELLS
place cells encode more than simple space
T-maze, trained (fruit loops) to alternate L & R turns
subset of place cells showed interesting pattern
e.g., activity (sector 3) anticipating right turns only
suggests hippocampal network represents episodic memories, cells are small segments of an episode
link of cells with overlapping episodes  memories

32. CODING SPACE – HIPPOCAMPAL PLACE CELLS
spatial dreaming
large # space cells
only ~ 15% active in any 1 environ.
some silent in one environ., active in others
time- & labor-intensive to get larger picture
device to measure 150 cells at once
population or ensemble code
code predicts rat behavior in maze
many environments & codes
overlapping, not interfering
used to study plasticity...

33. CODING SPACE – HIPPOCAMPAL PLACE CELLS
spatial dreaming
plasticity
strengthening of code  learning
accompanied by reduced inhibitory activity
does code relate to consolidated (permanent) memory
trained rats in spatial task
measured code during
training
sleeping before training
sleeping after training
dreaming replay of events  memory consolidation

34. BREAK