TimePlace Association in Rats

1
Time-Place Association in Rats

• Susan Szczerbicki
• Under the guidance of
• Dr. David Widman
• Juniata College

2
What is Time-Place Association?

• Animals allowed reinforcement at either a
  morning location or an afternoon location
• Need to use a timing mechanism to tell which
  location to go to

3
Two Timing Mechanisms

• Ordinal timers
• Animals anticipate events that occur in an order
• Less energy to use
• Phase timers
• Cyclic events or events that occur reliably at a
  certain time
• Circadian timer
• More energy to use

4
Timing Mechanism Controversy

• Carr and Wilkie showed ordinal timing
• Go to early bar first, independent of time of day
• Use an interval timer to time until the next
  location

• Mistlberger et al. showed circadian timing
• Select the correct location of bar pressing by
  the time of day

5
What Caused this Difference?

• Carr and Wilkie
• Ratio Difference
• Animals merely waited (4-40 seconds) until the
  VR15 was activated
• Apparatus Difference
• Four feeding stations

• Mistlberger et al.
• Ratio Difference
• Animals needed to satisfy a FR35 before
  activating the VR10
• Apparatus Difference
• Only two feeding stations

6
Cost Relationship

• More required bar presses in the Mistlberger et
  al. experiment
• An average of 45 presses vs. 15 presses
• More of a memory load in the Carr and Wilkie
  experiment due to apparatus
• Would need to remember the correct one out of
  four stations
• Widman et al. experiment showed cost affecting
  time-place association
• Time-place distinction when a higher cost
• No time-place distinction when low cost

7
This Experiment

• Test the effect the number of responses has on
  the choice of timing mechanism
• Hypothesis
• Since a circadian timer requires more energy,
  would only use this type when there is a high
  cost
• Would use an ordinal timer if there is a low cost

8
Materials and Methods

• Eight male Sprague-Dawley Rats
• Deprived to 80 of their natural weight
• Allowed 20 grams of maintenance food
• Allowed water ad-lib

9
Apparatus

• Skinner boxes
• Two bars
• Two lights
• Four rats run at the same time

FR light
VR light
Two bars
10
Materials and Methods

• Rats split into two groups
• FR30
• FR3
• Then rats had to fulfill a VR12 to obtain food
• Training was done for 25 days
• Testing occurred when the morning session was
  skipped
• Six sessions

11
Training Results
Animal
Morning
Afternoon
12
Results for FR30 Rats
Animal
Training
Testing
13
Results for FR3 Rats
Animal
Training
Testing
14
Discussion

• Previously hypothesized that the animals on the
  FR30 would use a circadian timer and the FR3
  group would use an ordinal timer
• However, the FR30 group used a mixed group of
  timing mechanisms
• Interestingly, the FR3 group all used circadian
  timing mechanisms

15
What this means

• Since the group with the lower cost of responding
  used circadian timing, cost may not be the
  deciding factor
• Instead, may be the memory load

16
Future Research

• Research using different memory loads
• Two different boxes
• Two bars
• Four bars
• Hypothesis
• Rats in the four bar box will use an ordinal
  timing mechanism due to the high amount of memory
  load with remembering the correct bar
• Rats in the two bar box will use a circadian
  timer because they have the mental space

17
References

• Carr, Jason A.R., and Donald M. Wilkie. Rats
  Use an Ordinal Timer in a Daily Time-Place
  Learning Task. Journal of Experimental
  Psychology 23.2 (1997) 232-247.
• Mistlberger, Ralph E. et al. Discrimination of
  Circadian Phase in Intact and Suprachiasmatic
  Nuclei-Ablated Rats. Brain Research (1996)
  12-18.
• Widman, David R., Douglas Gordon, and William
  Timberlake. Response Cost and Time-Place
  Discrimination by Rats in Maze Tasks. Animal
  Learning and Behavior 28.3 (2000) 298-309.

18
Questions??