My lab is interested in the role that neuronal firing patterns play in the encoding, storage, transfer and retrieval of information by the brain. To study this question, we focus on in-vivo extracellular recordings and computational analyses of spike trains from up to 100 neurons from the hippocampus and cortex during activity and sleep, combined with optogenetic and chemogenetic manipulations. In this talk, I will discuss the distinct patterns that we see in these spike trains on multiple timescales and how they change during and across different brain network states. Because these activities are found in the hippocampus, I will discuss their relationship to memory. Finally, I will describe current efforts to evaluate the temporal structure in neuronal spike trains using unsupervised machine learning by hidden Markov models.