Proximodistal organization of CA2
The proximodistal axis is considered a major organizational principle of the hippocampus. The CA2 region apparently breaks this rule. We discovered that CA2 is organized around the limit of the mossy fibers (Fernandez-Lamo et al., Cell reports 2019). We found a characteristic molecular gradient within CA2 in the rat and marked proximodistal trends of synaptic activity and phase-locked theta and gamma firing. Our data suggest that the structure and function of CA2 are distributed along the proximodistal hippocampal axis.
Sublayer organization of CA1 replay
Recently, we discovered that deep and superficial CA1 pyramidal cells participate differentially during sharp-wave ripples (Valero et al Nat Neu 2015). Using unsupervised clustering of ripple events, we next disclosed a mechanism determining firing selectivity and its distorsion in the epileptic hippocampus (Valero et al. Neuron 2017). Our data support the idea of a strong regionalization of hippocampal function during basic processes underlying memory consolidation, which is a major research line today in our lab.
Mechanisms of epileptic fast ripples
Fast ripples are high-frequency oscillations (HFOs) >250 Hz recorded in epileptogenic hippocampal regions. In 2007, we proposed a mechanism by which fast ripples emerge from the pathological desynchronization of neuronal firing (Foffani et al. Neuron 2007). Later in 2010, we developed the out-of-phase firing hypothesis which is now accepted as a major mechanism of pathological HFOs (Ibarz et al. JNeurosc 2010). More recently, using unsupervised learning we disclosed synaptic mechanisms underlying firing selectivity collapse during fast ripples (Valero et al. Neuron 2017).