Working & Reference Memory Following Fimbra-Fornix Lesions

Purpose

To determine the role of the septo-hippocampal system in working and reference memory

Predictions

Lesions of the fimbria-fornix will produce deficits in spatial working and reference memories

Subjects

6 female Long-Evans rats, housed at NIU Approximately 6 months in age 3 subjects receive F-F lesions 3 unoperated control

Fimbria-fornix lesion Rats will be anesthetized with a mixture of isofluorane and

oxygen during the surgery. Lesions will be made using standard stereotaxic techniques with

the aid of a surgical microscope. Prior to making the incision, the hair will be shaved and the

surrounding area will be scrubbed with Betadine. There will be two lesion sites per hemisphere, using coordinates

with respect to bregma and the surface of the dura: -1.3mm posterior, 1.5mm lateral, and –3.6 mm ventral; -1.5mm posterior, 0.5mm lateral, and 3.3 mm ventral.

Fimbria-fornix lesions will be produced by passing 1.5mAmp current for 40 seconds.

Following lesion incision will be sutured General appearance and weight will be monitored every day for

the duration of behavioral testing

Working Memory Prior to training with baited arms, rats will be given two

habituation sessions (15 min) in which the rats will be free to explore the radial eight-arm maze

Rats will receive five training sessions in which each arm of the radial eight-arm maze will be baited with one half of a fruit loop

placed into the center of the maze and the arms visited will be recorded

After all of the arms have been visited or 15 minutes has elapsed the rats will be removed from the apparatus

maze will be cleaned with Windex prior to running the next rat

Working Memory

Cue 1

Cue 3

Cue 2

Working Memory

Cue 1

Cue 3

Cue 2

Normal

Working Memory

Cue 1

Cue 3

Cue 2

F-F Lesioned

Reference Memory

Subsequent to completion of working memory training sessions

Rats will receive five training sessions in which only four of the eight arms will be baited

After all of the arms with bait have been visited or 15 minutes has elapsed, the rats will be removed from the apparatus

Reference Memory

Cue 1

Cue 2

Cue 3

Reference Memory

Cue 1

Cue 2

Cue 3Normal

Reference Memory

Cue 1

Cue 2

Cue 3F-F Lesioned

Measures

Several measures will be used to characterize the rat’s performance: number of repeat visits to an arm (errors) time to visit all arms

Number of Errors

0

5

10

15

20

D1 D2 D3 D4 D5

Ave

rage

Num

ber o

f Err

ors

F-F

C

Main effect of day F(4,16)=30, p<.05 Main effect of group F(1,4)=697.69, p<.05 Significant dayXgroup interaction F(4,16)=18, p<.05

  Sum of Squares df Mean Square F p

day 72 4 18 30 0

day * group 43.2 4 10.8 18 0

Error(day) 9.6 16 0.6  

group 1116.3 1 1116.3 697.6875 0

Error(group) 6.4 4 1.6    

Time to Visit All Arms

0

2

4

6

8

10

12

14

16

D1 D2 D3 D4 D5

Tim

e (M

in)

F-F

C

Conclusions

F-F lesions distrupt working and reference memory

Discuss literature that supports this and contradicts this Packard M Hirsh R White N (1989) Differential effects of fornix and caudate

nucleus lesions on two radial maze tasks: evidence for multiple memory systems.

Future work (recovery, model for memory impairments, Alzheimer's disease)

Things to consider

How are the rats solving these two tasks? Is reference memory the same as place

learning? What do these studies imply in terms of the

role of the hippocampus in memory?

References

Chapter 11 Working memory & Reference memory (pg. 319-

20) Spatial memory in Radial Maze (pg. 326-29) Memory mechanisms (pg.332-43)

Chapter 12 Memory in food storing birds (pg. 354-58)

References pubmed.org psycinfo Terms

Working memory & reference memory Hippocampus & fimbria-fornix Place learning Spatial memory Morris water maze

Important People David Olton Larry Squire Eric Kandel Ian Whishaw

Remember

Think conceptually when reading the literature, don’t just describe methods of study.