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Cortex. 2017 Sep;94:87-99. doi: 10.1016/j.cortex.2017.06.002. Epub 2017 Jun 23.

Brain state-dependent recruitment of high-frequency oscillations in the human hippocampus.

Author information

1
División de Neurociencia, Centro de Investigación en Complejidad Social, Facultad de Gobierno - Universidad Del Desarrollo, Santiago, Chile.
2
Centro Interdisciplinario de Neurociencia y Laboratorio de Circuitos Neuronales, Departamento de Psiquiatría, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
3
Department of Psychology, Université Grenoble Alpes, CNRS, LPNC UMR 51055105, Grenoble, France.
4
CHU Grenoble, Department of Neurology, INSERM U704, Grenoble, France.
5
INSERM U1028-CNRS UMR5292, Brain Dynamics and Cognition Team, Lyon Neuroscience Research Center, Lyon-Bron, France; University Claude Bernard, Lyon, France.
6
Centro Interdisciplinario de Neurociencia y Laboratorio de Circuitos Neuronales, Departamento de Psiquiatría, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile. Electronic address: pfuentealba@uc.cl.

Abstract

Ripples are high-frequency bouts of coordinated hippocampal activity believed to be crucial for information transfer and memory formation. We used intracortical macroelectrodes to record neural activity in the human hippocampus of awake subjects undergoing surgical treatment for refractory epilepsy and distinguished two populations of ripple episodes based on their frequency spectrum. The phase-coupling of one population, slow ripples (90-110 Hz), to cortical delta oscillations was differentially modulated by cognitive task; whereas the second population, fast ripples (130-170 Hz), was not seemingly correlated to local neural activity. Furthermore, as cognitive tasks changed, the ongoing coordination of neural activity associated to slow ripples progressively augmented along the parahippocampal axis. Thus, during resting states, slow ripples were coordinated in restricted hippocampal territories; whereas during active states, such as attentionally-demanding tasks, high frequency activity emerged across the hippocampus and parahippocampal cortex, that was synchronized with slow ripples, consistent with ripples supporting information transfer and coupling anatomically distant regions. Hence, our results provide further evidence of neural diversity in hippocampal high-frequency oscillations and their association to cognitive processing in humans.

KEYWORDS:

Hippocampus; Intracortical EEG; Ripples

PMID:
28728081
DOI:
10.1016/j.cortex.2017.06.002
[Indexed for MEDLINE]

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