title: Oscillation Phase Locking and Late ERP Components of Intracranial Hippocampal Recordings Correlate to Patient Performance in a Working Memory Task.
abstract: In working memory tasks, stimulus presentation induces a resetting of intracranial temporal lobe oscillations in multiple frequency bands. To further understand the functional relevance of this phenomenon, we investigated whether working memory performance depends on the phase precision of ongoing oscillations in the hippocampus. We recorded intra-hippocampal local field potentials in individuals performing a working memory task. Two types of trials were administered. For high memory trials presentation of a list of four letters ("List") was followed by a single letter memory probe ("Test"). Low memory load trials, consisting of four identical letters (AAAA) followed by a probe with the same letter (A), were interspersed. Significant phase locking of ongoing oscillations across trials, estimated by the Pairwise Phase Consistency Index (PPCI) was observed in delta (0.5-4 Hz), theta (5-7 Hz), and alpha (8-12 Hz) bands during stimulus presentation and recall but was increased in low memory load trials. Across patients however, higher delta PPCIs during recall in the left hippocampus were associated with faster reaction times. Because phase locking could also be interpreted as a consequence of a stimulus evoked potential, we performed event related potential analysis (ERP) and examined the relationship of ERP components with performance. We found that both amplitude and latency of late ERP components correlated with both reaction time and accuracy. We propose that, in the Sternberg task, phase locking of oscillations, or alternatively its ERP correlate, synchronizes networks within the hippocampus and connected structures that are involved in working memory.
authors.affiliation: Department of Neurology, University of California, San Francisco San Francisco, CA, USA.
authors.forename: Jonathan K
authors.initials: JK
authors.lastname: Kleen
authors.affiliation: Department of Neurology, Geisel School of Medicine at Dartmouth Hanover, NH, USA.
authors.forename: Markus E
authors.initials: ME
authors.lastname: Testorf
authors.affiliation: Department of Surgery, Geisel School of Medicine at Dartmouth Hanover, NH, USA.
authors.forename: David W
authors.initials: DW
authors.lastname: Roberts
authors.affiliation: Department of Neurological Sciences, University of Vermont College of MedicineBurlington, VT, USA; Department of Neurology, University College London, Institute of Child HealthLondon, UK.
authors.forename: Rod C
authors.initials: RC
authors.lastname: Scott
authors.affiliation: Department of Neurology, Geisel School of Medicine at Dartmouth Hanover, NH, USA.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Jobst
authors.affiliation: Department of Neurological Sciences, University of Vermont College of Medicine Burlington, VT, USA.
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Holmes
authors.affiliation: Department of Neurological Sciences, University of Vermont College of MedicineBurlington, VT, USA; INMED Institut National de la Santé et de la Recherche Médicale U901Marseille, France; Aix Marseille Université, INMEDMarseille, France.
authors.forename: Pierre-Pascal
authors.initials: PP
authors.lastname: Lenck-Santini
keywords: alpha; delta; phase locking; theta; working memory