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Different mechanisms of ripple‐like oscillations in the human epileptic subiculum
Author(s) -
AlvaradoRojas Catalina,
Huberfeld Gilles,
Baulac Michel,
Clemenceau Stéphane,
Charpier Stéphane,
Miles Richard,
Prida Liset Menendez,
Quyen Michel
Publication year - 2015
Publication title -
annals of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.764
H-Index - 296
eISSN - 1531-8249
pISSN - 0364-5134
DOI - 10.1002/ana.24324
Subject(s) - ictal , subiculum , neuroscience , hippocampal formation , epilepsy , bursting , hippocampus , population , neocortex , electroencephalography , temporal lobe , psychology , medicine , dentate gyrus , environmental health
Objective Transient high‐frequency oscillations (HFOs; 150–600Hz) in local field potentials generated by human hippocampal and parahippocampal areas have been related to both physiological and pathological processes. The cellular basis and effects of normal and abnormal forms of HFOs have been controversial. This lack of agreement is clinically significant, because HFOs may be good markers of epileptogenic areas. Better defining the neuronal correlate of specific HFO frequency bands could improve electroencephalographic analyses made before epilepsy surgery. Methods Here, we recorded HFOs in slices of the subiculum prepared from human hippocampal tissue resected for treatment of pharmacoresistant epilepsy. With combined intra‐ or juxtacellular and extracellular recordings, we examined the cellular correlates of interictal and ictal HFO events. Results HFOs occurred spontaneously in extracellular field potentials during interictal discharges (IIDs) and also during pharmacologically induced preictal discharges (PIDs) preceding ictal‐like events. Many of these events included frequencies >250Hz and so might be considered pathological, but a significant proportion were spectrally similar to physiological ripples (150–250Hz). We found that IID ripples were associated with rhythmic γ‐aminobutyric acidergic and glutamatergic synaptic potentials with moderate neuronal firing. In contrast, PID ripples were associated with depolarizing synaptic inputs frequently reaching the threshold for bursting in most pyramidal cells. Interpretation Our data suggest that IID and PID ripple‐like oscillations (150–250Hz) in human epileptic hippocampus are associated with 2 distinct population activities that rely on different cellular and synaptic mechanisms. Thus, the ripple band could not help to disambiguate the underlying cellular processes. Ann Neurol 2015;77:281–290.