title: Decrease in gamma-band activity tracks sequence learning.
abstract: Learning novel sequences constitutes an example of declarative memory formation, involving conscious recall of temporal events. Performance in sequence learning tasks improves with repetition and involves forming temporal associations over scales of seconds to minutes. To further understand the neural circuits underlying declarative sequence learning over trials, we tracked changes in intracranial field potentials (IFPs) recorded from 1142 electrodes implanted throughout temporal and frontal cortical areas in 14 human subjects, while they learned the temporal-order of multiple sequences of images over trials through repeated recall. We observed an increase in power in the gamma frequency band (30-100 Hz) in the recall phase, particularly in areas within the temporal lobe including the parahippocampal gyrus. The degree of this gamma power enhancement decreased over trials with improved sequence recall. Modulation of gamma power was directly correlated with the improvement in recall performance. When presenting new sequences, gamma power was reset to high values and decreased again after learning. These observations suggest that signals in the gamma frequency band may play a more prominent role during the early steps of the learning process rather than during the maintenance of memory traces.
authors: Boston Children's Hospital, Harvard Medical School Boston, MA, USA.
authors: Radhika
authors: R
authors: Madhavan
authors: Program in Neuroscience, Harvard University Cambridge, MA, USA.
authors: Daniel
authors: D
authors: Millman
authors: Program in Biophysics, Harvard University Cambridge, MA, USA.
authors: Hanlin
authors: H
authors: Tang
authors: Department of Neurology, Johns Hopkins School of Medicine Baltimore, MD, USA.
authors: Nathan E
authors: NE
authors: Crone
authors: Department of Neurosurgery, Johns Hopkins School of Medicine Baltimore, MD, USA.
authors: Fredrick A
authors: FA
authors: Lenz
authors: Department of Neurosurgery, Brigham and Women's Hospital Boston, MA, USA.
authors: Travis S
authors: TS
authors: Tierney
authors: Department of Neurosurgery, Boston Children's Hospital, Harvard Medical School Boston, MA, USA.
authors: Joseph R
authors: JR
authors: Madsen
authors: Boston Children's Hospital, Harvard Medical School Boston, MA, USA ; Program in Neuroscience, Harvard University Cambridge, MA, USA ; Program in Biophysics, Harvard University Cambridge, MA, USA.
authors: Gabriel
authors: G
authors: Kreiman
authors: Department of Neurosurgery, Johns Hopkins School of Medicine Baltimore, MD, USA.
authors: William S
authors: WS
authors: Anderson
keywords: field potentials; gamma frequency oscillations; human neurophysiology; intracranial recordings; memory; sequence learning
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