dynamics of the hippocampal ensemble code for space
DESCRIPTION
Dynamics of the Hippocampal Ensemble Code for Space. By: Matthew A. Wilson & Bruce L. McNaughton GROUP A2: Anna Loza Elyse Rosa Britni Rowe Caroline Olsen Vedran Dzebic Kris Clark. Introduction. Kris Clark. Very Brief Overview of Experiment: Three rats (results used from only 2) - PowerPoint PPT PresentationTRANSCRIPT
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.