103_15_full - PSYC 103 Winter 2011 Lecture 15 Principles of...

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Unformatted text preview: PSYC 103 Winter 2011 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 Baker (1984) - 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 Air pressure Changes in altitude result in changes in air pressure. Can pigeons detect this potential source of information? 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 travel (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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