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You are here: Home Publications CENs Bibliography Gamma Power Reductions Accompany Stimulus-Specific Representations of Dynamic Events

Hui Zhang, Juergen Fell, Bernhard P Staresina, Bernd Weber, Christian E Elger, and Nikolai Axmacher (2015)

Gamma Power Reductions Accompany Stimulus-Specific Representations of Dynamic Events

Current Biology, 25(5):635--640.

Neural representations of specific stimuli rely on activity pat- terns indistributedneuralassemblies [1–4]. According toone influential view, these assemblies are characterized by syn- chronized gamma-band activity (GBA) [5–11] that reflects stimulus-specific representations [12–14]. However, recent studies have shown that GBA is closely correlated with the overall amount of cellular activity and may be detrimental for precise representations of specific stimuli [15, 16]. Until now, the role of GBA for the formation of dynamically chang- ing representations has been unknown. Here, we applied representational similarity analysis (RSA) [17] to intracranial electroencephalogram (iEEG) data from ten presurgical epi- lepsy patients to identifystimulus-specificneural representa- tions. Patients first learned and then retrieved their paths throughvirtual houses. Dynamic representationswereidenti- fied by the rapidly changing distributions of frequency-spe- cific global (spatial) activity patterns across the brain. We found that GBA patterns during successful (but not unsuc- cessful) retrieval of one sequence were more similar to activ- ity during encodingof that same sequencecompared toother sequences. Thecontribution of individual electrodes to these global representations was correlated with local similarity in individual electrodes (i.e., with RSA across time). Moreover, time-resolved RSA values were negatively correlated with the magnitude of iEEG gamma power: RSA values were higher at time points when gamma power was reduced. Both global and local representations relied on a small pro- portion of electrodes. These results show that behaviorally relevant neural representations of specific dynamically changing stimuli can be tracked by iEEG recordings and that they are associated with reductions of gamma power.

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