By: Matthew A. Wilson & Bruce L. McNaughton

GROUP A2:Anna LozaElyse RosaBritni Rowe

Caroline OlsenVedran Dzebic

Kris Clark

IntroductionIntroductionVery Brief Overview of Experiment: Three rats (results used from only 2) Implanted with electrodes Trained to forage for chocolate in one half of

box (Box A) Later allowed to venture into other half (Box B) Compared the readings from electrodes

Kris Clark

IntroductionIntroductionLonger term exposure to novel environments:

Rats exposed to a novel environment twice, over two days

Rapid changes on first and second days Even after the representation stabilized, the

animals' behavior remained different in the novel places

Kris Clark

IntroductionIntroduction

This suggested that other brain regions continued to distinguish novel from familiar locations

These results show that the hippocampus can form new spatial representations quickly but that stable hippocampal representations are not sufficient for a place to be treated as familiar.

Kris Clark

IntroductionIntroductionContext sensitivity of Hippocampus:

It has been indicated that hippocampal neurons are sensitive to subtle changes in task demands, even in an unchanging environment

Learning to differentiate two such contexts was associated with the development of highly context-specific neuronal firing patterns

Kris Clark

IntroductionIntroductionOverall:

This study implicated the hippocampus in spatial representation, how it is sensitive to novel environments, further elucidating the role of the hippocampus in learning

Kris Clark

Design CritiqueDesign Critique Made inferences based on extrapolation

“By extrapolation, 1-cm accuracy over 1s would require about 130 cells.” ○Extrapolation is based on trends, which

could lead researchers to the correct conclusion

○Although these results were likely based on calculations, they should have explained it better in the research paper.

Elyse Rosa

Design CritiqueDesign Critique Number of animals used:

• The number of rats used in this study initially 3

• One of the rats didn’t perform like the others so was dismissed

• … The remaining conclusions of the experiment were based on 2 rats

• More rats would provide slightly more accurate results

Elyse Rosa

Design CritiqueDesign CritiqueError: 5cm for rat 1 and 2; 2cm for rat 3EXPERIMENTAL PHASES: Phase 1: interval in box A before

partition removal Phase 2: the first 10min with the

partition between boxes A and B removed

Phase 3: the second 10min interval of this condition

Phase 4: the final time in box A

Elyse Rosa

Procedure Procedure CritiqueCritique

Rat Exploration in the boxes: Rat 1: moved freely between the two regions,

for 10min phases Rat 2: explored box B briefly then paused in

A for over an hour before resuming exploration

Rat 3: 10 min A (open) 5 min hesitate, 12 min explore, partition close after 20 minutes, 10 min A 6 min phases!

Anna Loza

Procedure Procedure CritiqueCritique

TIMING:Lack of constant time constraints:

RAT #1:○ Phase 1 = 10 minutes○ Phase 2 = 10 minutes○ Phase 3 = 10 minutes○ Phase 4 = 10 minutes

RAT #2:○ Phase 1 = 10 minutes○ Phase 2 = 6 minutes○ Phase 3 = 6 minutes○ Phase 4 = 10 minutes

Anna Loza

Procedure Procedure CritiqueCritique

TIMING:

Rat 2 paused for over an hour – but experiment takes 40 minutes…?

Rat 2 data was excluded because of this pause; but “consistent elsewhere”

Anna Loza

Procedure Procedure CritiqueCritique

PHASES:

Phases assigned totally arbitrarily – they let the rat decide the timeframe (and then said they explored for 20 mins)

“The accuracy of reconstruction reflects the consistency of spatial firing over the phase”

Anna Loza

Procedure Procedure CritiqueCritique

DIRECTION: Place cells are directional when an animal

takes limited paths, but non-directional when wondering randomly on an open field (McNaughton,Barnes,and O’Keefe 1983)

It may help if rats had a “purpose” in their exploration for directional recordings to be made

Anna Loza

Procedure Procedure CritiqueCritique

TEST:

The test seems to have been performed only once?

Need an average of rat’s behaviour:What if they are afraid of novelty? Have they ever done this before? Ideally, they should have been trained, and then

presented with another novel environment to be tested on….

Anna Loza

Discussion Discussion CritiqueCritique

Strong statements based on 2 rats:

“ Incorporation of new spatial information has little effect on previously stored information, at least within the limits of this experiment”

Britni Rowe

Discussion Discussion CritiqueCritique

Strong statements based on 2 rats (continued):

“…suggests that the synaptic modification mechanisms that are presumably involved are rapid”

Britni Rowe

ProsProsTETRODE PROCEDURE: Multiple unit spike trains from multi-unit

recordings is not always accurate Tetrode developed by Wilson and

McNaughton eliminates this problem Has the ability to identify and measure many

individual neurons Can measure the activation during many

different states and activities.

Vedran Dzebic

ProsPros Considering the small sample size, and

limitations, the results and the extrapolation are in line with what you expect

Previous attempts with single unit recordings failed to show different firing after experience in environment.

Vedran Dzebic

ProsPros The concept of looking for activation

in specific cells, as rats move through environment provides a good basis for measuring cell activation, but would be better if goal is implemented.

Demonstrates the important point of ensemble neural activity

Vedran Dzebic

Further ResearchFurther Research EFFECTS OF AGE:

Age of rats not publishedChanges in hippocampal connectivity and plasticity

impairs spatial learning in older rats○ Aged rats maintain familiar representations in novel

environments○ Delayed in anchoring new representations to external

landmarks○ New spatial representations are multi-stable across repetitive

exposures to the previously novel environment

-Wilson et al. 2004

No reports of other screening of rats e.g. vision

Caroline Olsen

Further ResearchFurther Research

Compare scavenging for reward vs. directional task

Place cells are non-directional when wandering randomly

Directional when taking limited paths

Some hippocampal CA1 cells encode location with respect to reference frames associated with the task

Gothard et al. 1996

Caroline Olsen

Further ResearchFurther Research Averaged readings from many neurons over

very wide time bin Limitations of technology at the time Frank et al. 2004 measured on millisecond time

scale and results were consistent Also found decrease in inhibitory neuron activity

in first exposure to novel environment Also reassess stability of representations of

formerly novel environment on subsequent exposure

Frank et al. 2004

Caroline Olsen

CONS PROS FURTHER RESEARCH

Use of extrapolation and estimation

Tetrode procedure highly reliable method

Wilson et al.(2004) Considered the effects of age

Very small sample size Pioneering experiment, which led to many other experiments

Gothard et al. (1996) Compared scavenging for reward vs. directional task

Lack of constant time constraint

Frank et al. (2004) Averaged readings over many neurons over wide time bin

Phases appeared to be based around performance

No purpose or direction of exploration

ReferencesReferences Frank, L. M., Stanley, G. B., & Brown, E. N. (2004). Hippocampal

plasticity across multiple days of exposure to novel environments. The Journal of Neuroscience, 24(35), 7681-7689.

Loren M. Frank, Garrett B. Stanley, and Emery N. Brown., The Journal of Neuroscience, September 1, 2004, 24(35):7681-7689

Griffin, A., Eichenbaum, H., & Hasselmo, M. (2007). The Journal of Neuroscience, 27 (9), 2416-2423.

Redish. A.D. (1999).Beyond the Cognitive Map.MIT Press Wilson, M.A., & McNaughton, B. (1993). Dynamics of the

hippocampal ensemble code for space. Science 261: 1055-1058 Wilson, I. A., McMahan, R. W., Gallagher, M., Eichenbaum, H., &

Tanila, H. (2004). Cognitive aging and the hippocampus: How old rats represent new environments. The Journal of Neuroscience, 24(15), 3870-3878.