Cell Type-Specific Firing during Ripple Oscillations in the Hippocampal Formation of Humans

Centre National de la Recherche Scientifique, Cognitive Neuroscience and Brain Imaging Laboratory, Unité Propre de Recherche 640, Hôpital de la Pitié-Salpêtrière, 75651 Paris, France.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 07/2008; 28(24):6104-10. DOI: 10.1523/JNEUROSCI.0437-08.2008
Source: PubMed


High-frequency field ripples occur in the rodent hippocampal formation and are assumed to depend on interneuron type-specific firing patterns, structuring the activity of pyramidal cells. Ripples with similar characteristics are also present in humans, yet their underlying cellular correlates are still unknown. By in vivo recording interneurons and pyramidal cells in the human hippocampal formation, we find that cell type-specific firing patterns and phase-locking on a millisecond timescale can be distinguished during ripples. In particular, pyramidal cells fired preferentially at the highest amplitude of the ripple, but interneurons began to discharge earlier than pyramidal cells. Furthermore, a large fraction of cells were phase-locked to the ripple cycle, but the preferred phase of discharge of interneurons followed the maximum discharge probability of pyramidal neurons. These relationships between human ripples and unit activity are qualitatively similar to that observed in vivo in the rodents, suggesting that their underlying mechanisms are similar.

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Available from: Anatol Bragin
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    • "In patient studies and chronic animal models of epilepsy, there appear to be different types of HFOs with some that have properties that strongly resemble 100–200 Hz ripples in the normal nonprimate and nonhuman primate hippocampal formation (Axmacher, Elger, & Fell, 2008; Bragin, Engel, Wilson, Vizentin, & Mathern, 1999; Buzsaki, 1998; Le Van Quyen et al., 2008; Skaggs et al., 2007; Staba, Wilson, Bragin, Fried, & "
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    • "Selective elimination of ripples during postlearning results in impairment of memory performance (Girardeau et al., 2009; Jadhav et al., 2012). Despite the critical role of ripples for information transfer from the hippocampus to the neocortex and for memory consolidation, and their postulated role in epilepsy (''fast ripples''; Bragin et al., 1999; Le Van Quyen et al., 2008), the local network mechanisms underlying the generation of ripples are not well understood (Buzsá ki and Silva, 2012). Three classes of models for ripple generation have been proposed . "
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    • "In particular, the authors of those reports have shown that, like in the case of the rodent sharp-wave ripple complexes, units coordinated their firing to specific phase of ripple HFO cycle in humans, during which interneurons fired before pyramidal cells. The neuronal correlates of induced ripples and fast ripples, or cortical HFOs remain to be explored but given the evidence from human (Le Van Quyen et al., 2008, 2010) and rodent studies (Sullivan et al., 2011) they could share similar networks and mechanisms. "
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