Week 10 Overheads

Research Questions

1. What do the birds remember?
2. How are the memories used to retrieve cached food?

Issues

1. Animal cognition consists of specialized and general purpose mechanisms.
2. Specialized cognitive mechanisms are adaptations to specific slection pressures.
3. The brain is responsive to selection for cognitive abilities.

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Black-capped chickadees

Store thousands of food pieces over the winter

Do not reuse cache sites

Recover most of the food on the same day it is cached (some cached much longer)

Black-capped chickadee experiments

(Sherry, 1997)

Octagonal cage surrounded by landmarks with feed site
Maintaining landmark formation, rotate them

• Birds orient by landmarks to find feed site

Randomize landmark formation

• Birds ignore landmarks and use unknown cues to find feed site

Sun-compass and landmarks in black-capped chickadees

(Sherry, 1997)

Use outdoor cache cage
Birds on 6 hr phase delay

• Sun compass off by 90 deg

Birds actually shift 45 deg
Compromise between sun compass and landmarks

Hippocampus

(Sherry, Jacobs, and Gaulin, 1992)

Avian hippocampus (HP) on dorsal surface of brain
Avian and mammalian HP different, but true homologues
Lesioning black-capped chickadee HP eliminates cache recovery ability

• Lesioned birds keep caching and searching, but search in wrong places

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Hippocampal Differences between Food Storing/Non-storing Birds

(Sherry, Vaccarino, Buckenham, and Herz, 1989)

Food storing birds have bigger HP

Brown Headed Cowbirds (BHC)

Brood parasites

• Lay eggs in other birds nests

• Neither RWB or G are brood parasites

• Lay egg next morning when host bird goes to feed

Female BHC have bigger HP than male BHC
Non-brood parasites, no sex difference

• Big sex difference for HP

• No sex difference for HP
• Both females and males search for host nests

• No sex difference for HP

• Both females and males cache

Pinyon jays, nutcrackers, scrub jays
Pinyon & nutcrackers: 10,000s seeds in 1,000s sites. Scrub jays: 1,000s seeds in 100s sites
Test: pick new sites only after retention interval

Environmental pressures on spatial memory performance

• Poke seed into bark, wipe beak, turn head back and forth, fly off

Spatial processing believed to decrease with age

• Lesion neocortex or hippocampus impairs Morris maze in rats

• Needed to learn new spatial information
• Cholinergic disfunction in older animals...impaired memory (especially spatial) performance
• Block cholinergic neuron function
  • Use atropine sulfate
  • Impairs Morris maze performance

Interactive effect

• Cholinergic, shifting between strategies, decreased attention, etc.

Posterior Parietal Cortex (PPC) damage in humans

1. Visuospatial deficits on visual localization tasks
2. Orientation difficulties
3. Object positioning in egocentric framework
4. Visual neglect contralateral to lesion
5. Preferential search in field ipsolateral to lesion

Protocol

1. Light at RGD on, rat presses door, gets milk, then a NGD lighted. If lighted NGD pressed, another reward. For 70 trials.
2. Distractor trials: one or both DLs flash.

Bilateral PPC lesions: less direct routes

Unilateral PPCs did not affect route

• Need only one intact side

Distinguish hippocampus (HP) from parietal cortex (PC)
14 HP, 15 APC, 14 PPC, 17 CT

Results: locomotory speed, landmarks touched

     

HP not reacting to spatial changes is consistent with other studies
PPC relevant to spatial representational memories
APC detect geometric changes, but dont acquire new spatial information (attentional processes impaired)
HP crucial in "cognitive map", but not for simple associative tasks

Morris water maze

• Dark condition: egocentric (path integration)
• Light condition: geocentric

Conclusions

• Bilateral PPC adversely affects acquisition of navigation tasks from kinesthetic information
• PPC probably involved in converting egocentric to geocentric representation