Gamma-Band Activation Predicts Both Associative Memory and Cortical Plasticity Drew B. Headley and Norman M. Weinberger Center for the Neurobiology of Learning and Memory, Department of Neurobiology and Behavior, University of California, Irvine, California The Journal of Neuroscience, September 7, (36):12748–12758

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? 2

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. 3

Experiment design 4

Behavioral in training 5 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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7 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

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. 8

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. 9

10 The onset of discrimination training did not induced gamma modulation of the next session’s behavioral response to the previously learned CS+ Neither did gamma predict the magnitude of conditioned bradycardia during the subsequent discrimination sessions The addition of a new training condition, introducing the CS, did not lead to CS+-induced gamma modulating subsequent performance.

11 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

Gamma plays a similar role for the CS+ and CS- during initial encoding, specifically, the learning of new information,but not its maintenance. 12

13 The mean RF obtained across all conditioning day increases at the CS evidently. RF plasticity specific to CS+

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. 14

15 Recording sites with greater absolute relative gamma had weaker plasticity This relationship between gamma and plasticity at the CS+ was only present between relative gamma during the first conditioning session and RF plasticity detected on the subsequent day. a high degree of specificity for gamma modulation of RF plasticity

16 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.

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. 17

Thank you for your attention! 18