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 3 Normal

Reference Memory Cue 1 Cue 2 Cue 3 F-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

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 SquaresdfMean SquareFp day day * group Error(day) group Error(group)

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 )  Spatial memory in Radial Maze (pg )  Memory mechanisms (pg ) Chapter 12  Memory in food storing birds (pg )

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.