Gamma-Band Activation Predicts Both Associative Memory and Cortical Plasticity

Drew B. Headley and Norman M . WeinbergerCenter for the Neurobiology of Learning and Memory, Department of Neurobiology and Behavior, University

of California, Irvine, California 92697-3800

The Journal of Neuroscience, September 7, 2011 • 31(36):12748–12758

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Introduction

• Oscillations linked to behavioral performance and physiological functioning (Buzsaki, 2006)

• Oscillations in the gamma band (40–120Hz) possible role in memory and neural plasticity.

• Strength at the time of the stimulus coding predicts its subsequent retrieval-----Enhanced mnemonic processing.

• Modulate plasticity in vitro

• Whether gamma affects in vivo experience-dependent plasticity linking to memory?

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Objective

• To determine whether gamma activation in primary auditory cortex modulates both the associative memory for an auditory stimulus during classical conditioning and its accompanying specific receptive field plasticity.

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Experiment design

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Behavioral in training•An example of conditioned bradycardia from a single subject on the second day of conditioning.

•Condition Response(CR) : the percentage difference between the mean heart rate for each of period

•Subjects learned the tone/shock contingency within a single day of training, displaying asymptotic performance by the second day of training.

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•CS+ induced gamma during the first conditioning session predicted the magnitude of the conditioned response 24 h later

•Gamma ceased to predict the next day’s performance for subsequent training sessions

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• The temporal dynamics of gamma’s prediction of behavior paralleled the time course of learning the tone/shock association.

• The concordance of timeframes suggests that gamma’s influence on mnemonic processing is restricted to the acquisition of associations.

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• animals often encounter similar situations, each slightly different from past experience, it should be established whether the mechanisms that facilitate initial learning can return during new learning.

• the classical conditioning phase was followed with discrimination training.

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• The onset of discrimination training did not induced gamma modulation of thenext session’s behavioral response to the previously learned CS+

• Neither did gamma predict themagnitude of conditioned bradycardia during the subsequent discrimination sessions

• The addition of a new trainingcondition, introducing the CS, did not lead to CS+-induced gamma modulating subsequent performance.

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• CS-induced gamma on the first discrimination session did predict the strength of bradycardia to the CSduring the second discrimination session.

• Discriminability was measured as the difference in bradycardia between the CS+ and CS

• gamma predicts behavior to the CS only during learning of the new tone contingency

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• Gamma plays a similar role for the CS+ and CS- during initial encoding, specifically, the learning of new information,but not its maintenance.

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•The mean RF obtained across all conditioning day increases at the CS evidently.

•RF plasticity specific to CS+

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• Given that gamma predicts behavioral learning, does it also predict the plasticity induced during that learning?

• To address this issue, the strength of gamma with the magnitude of the RF’s percentage change at the CS+ frequency on the following session was compared.

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•Recording sites with greater absolute relative gamma had weaker plasticity

• This relationship between gamma and plasticity at the CS+ was only present between relative gammaduring the first conditioning session and RF plasticity detected on the subsequent day.

• a high degree of specificity for gamma modulation of RF plasticity

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• Octave distance of the baseline BF from the CS+ was not related to the normalized gamma strength

•Gamma strength before normalization had a significant positive correlation with relative gamma strength

•Gamma bandwidth increased with relative gamma power indicating that stronger relative gamma may lack the synchrony necessary to effectively induce plasticity.

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Conclusion

• The predictive relationship between gamma and specific plasticity in A1 was not a byproduct of a recording site’s octave distance from the CS frequency or the calculation of relative gamma.

• Gamma significantly predicts both long-term memory and experience-dependent specific plasticity during initial learning.

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Thank you for your attention!