Visual Cortical Neurons Depolarize after Hippocampal Ripples

Abstract

Objective: When memory is consolidated, the hippocampus emits brief high-frequency oscillations called ripples, which often occur simultaneously with slow waves in the neocortex. Long-term visual memory consolidation requires neuronal coordination between the hippocampus and the primary visual cortex (V1). However, little is known about the dynamics of the membrane potentials of neocortical neurons during hippocampal ripples. The aim of this study is to reveal the subthreshold activity in individual V1 neurons during hippocampal ripples. Methods: We patch-clamped V1 layer 2/3 pyramidal cells and monitored their membrane potentials while also recording local field potentials from the hippocampal CA1 region in anesthetized mice. Results: Approximately 20% of V1 neurons were transiently depolarized 18–45 ms after the onset of ripples that occurred in neocortical UP states. The depolarization magnitudes were not correlated with the durations, frequencies, or powers of ripples. Conclusions: Hippocampal ripples are associated with the subthreshold dynamics of V1 neurons, despite the lack of direct synaptic connections between the hippocampus and the V1.