title: Memory signals from the thalamus: early thalamocortical phase synchronization entrains gamma oscillations during long-term memory retrieval.
abstract: The thalamus is believed to be a key node in human memory networks, however, very little is known about its real-time functional role. Here we examined the dynamics of thalamocortical communication during long-term episodic memory retrieval in two experiments. In experiment 1, intrathalamic and surface EEG was recorded in an epileptic patient implanted with depth electrodes for brain stimulation therapy. In a recognition memory test, early (300-500 ms) stimulus-linked oscillatory synchrony between mediodorsal thalamic and frontal surface electrodes at beta frequency (20 Hz) was enhanced for correctly remembered old compared to correctly rejected new items. Directionality measures (Granger causality) indicated that the thalamus was the sender, and the neocortex the receiver, of this beta signal, which also modulated the power of neocortical gamma (55-80 Hz) oscillations (cross-frequency coupling). Experiment 2 validated the cross-frequency coupling effects in a healthy participant sample. Confirming the findings from experiment 1, significantly increased cross-frequency coupling was found over frontal scalp electrodes during successful recognition. Extending anatomical knowledge on thalamic connectivity with frontal neocortex, these results suggest that the thalamus sends an early memory signal to frontal regions, triggering further memory search processes.
authors.affiliation: Department of Psychology, University of Konstanz, Postfach ZPR, 78457 Konstanz, Germany. tobias.staudigl@uni-konstanz.de
authors.forename: Tobias
authors.initials: T
authors.lastname: Staudigl
authors.forename: Tino
authors.initials: T
authors.lastname: Zaehle
authors.forename: Jürgen
authors.initials: J
authors.lastname: Voges
authors.forename: Simon
authors.initials: S
authors.lastname: Hanslmayr
authors.forename: Christine
authors.initials: C
authors.lastname: Esslinger
authors.forename: Hermann
authors.initials: H
authors.lastname: Hinrichs
authors.forename: Friedhelm C
authors.initials: FC
authors.lastname: Schmitt
authors.forename: Hans-Jochen
authors.initials: HJ
authors.lastname: Heinze
authors.forename: Alan
authors.initials: A
authors.lastname: Richardson-Klavehn
mesh_terms: D000328:Adult; D001931:Brain Mapping; D003344:Cortical Synchronization / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D057567:Memory, Long-Term / Q000502:physiology*; D021641:Recognition, Psychology; D013788:Thalamus / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult