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Unformatted text preview: PSYC 103
Lecture 15 Principles of Hippocampal Function
The hippocampus is necessary for acquisition and storage
of short(er) term, but not very long term memories.
• As the time between the training and lesion increases, the
effect of the lesion decreases Hippocampus processes spatial information imbedded in
working memory and/or reference memory tasks
• If lesions precede training, acquisition of both working and
reference memory are impaired.
• Cued learning is never impaired. Hippocampal place cells
Hippocampal place cells: (discovered by John O’Keefe)
• Firing pattern of the cell increases when animal moves to
specific locations within an area.
Firing field of the cell: spatial area within which the place cell is
active. Firing pattern of a place cell as the animal navigates in the environment. Four different place cells within the same arena Preferred region What cues drive ‘place cell’ spatial preference?
The wandering rat experiments…
1. Different cells encode different regions of space.
2. The size and shape of a place field can differ.
3. A place field develops over time in novel environments, but remains
relatively constant as long as the environment does not change.
4. Visual cues are important for place cell selectivity. If visual cues are
rotated, place field will rotate as well.
5. If all external cues are removed, the place field remains intact, but
drifts. (ideothetic cues) Place cells fire regularly, and repeatedly, as a rat moves through space 6 Long range navigation Navigation: Homing, and Migration
Homing: The ability of animals to return to their home having been
taken some distance from it and released
Migration: seasonal movement Information can be derived from different cues:
1. Topographic features and other visual landmarks
2. The angle of the sun in the sky (sun-compass)
3. Geomagnetic information
4. The position of the stars
5. Olfactory information
6. Polarized light Homing
The ability of animals to return to their home having been taken some distance
from it and released The use of landmarks
Biro, Meade & Guilford (2004)
- Pigeons repeatedly released from sites 10 km from their lofts
- Route back to lofts tracked when released from novel locations
- Birds headed for a familiar route, and then followed it back
- Often following roads – birds remember a sequence of landmarks Keeton (1974)
- Released pigeons more than 50 miles from familiar territory.
- Birds still homed.
- Unlikely to be due to the use of landmarks 9 Homing
Retracing the outward route
- The route a pigeon takes from a release point back to the loft is influenced by the route taken
to the site But …. Walcott & Schmidt-Koenig (1973)
- Anesthetized pigeons on journey to release site
- They still homed 10 Navigational cues
North American migratory flyways follow topographic features and other landmarks Overwintering
Monarchs clustered in an Oyamel Fir
tree at the Sierra Chincua overwintering site
in central Mexico. Monarch Migration Navigational cues
Changes in altitude result in changes in air pressure. Can pigeons detect this potential source
Delius & Emmerton (1978)
- 10-sec change in air pressure to signal shock
- Substantial increase in heart rate to the change
- Birds may be able to detect vertical displacements of around 20 meters
-Infrasound: fluctuations in air pressure of less than 20 Hz – inaudible to humans
Yodlowski, Kreithen & Keeton (1977)
- Pavlovian conditioning with pigeons
- 0.1 Hz infrasound → shock
- Conditioning was successful Olfaction
Odours present at the release sight also present at the loft
- Wallraff & Andreae (2000): Showed the strengths of gasses varied over a 200 km
area. Birds moves to better match the current odour with the odour at the loft
- Papi, Mariotti, Foa & FIaschi (1980): Homing adversely affected by depriving
pigeons of sense of smell
19 Navigational Cues
Polarized and ultraviolet light
- Von Frisch (1950): Bees can detect both of these types of light
- Kreithen (1978): Pigeons can detect and be conditioned with ultraviolet and polarized
light. Polarized light is useful for navigation because it allows the sun to be located on a
cloudy day The map and compass hypothesis
Animals might have a “map” and “compass” that enables them to determine in
where they are and which direction to go “Sun compass”
(1) bird notes the position of the sun upon release
(2) using internal clock computes the direction it needs to
(3) extrapolates the position of the sun at e.g. midday
20 Sun-compass navigation Clock-shift experiments
• Birds maintained indoors under artificial light conditions.
Artificial light-dark cycle brought out of phase with natural light-dark cycle (by e.g. 6 h)
At 9 am, the internal clock will inform them it is 3 pm
Sun in a different location, navigation should be disrupted. Some birds use a precise internal
clock in combination with the angle of
the sun Navigational cues
Magnetic compass 23 Navigational cues Magnetic fields - Pigeon homing is less accurate when:
(a) There is a magnetic storm (Gould, 1982)
(b) When they are near anomalies in the earths’ magnetic field (Walcott, 1978)
(c) When they are carrying magnets or coils (Keeton, 1974; Walcott & Green, 1974) - Studies in conditioning chambers using magnetic cues are less clear cut
24 Turtle migration Turtle migration Migratory paths of sea turtles once they have left their nesting beaches in
Florida. The arrows indicate the flow of ocean currents (the turtle is not drawn
to scale). Turtle migration Turtles orient toward home in
simulated magnetic fields Gyre (current) -guided navigation ...
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- Spring '07