The hippocampal rate code: anatomy, physiology and theory

Since the days of Cajal, the CA1 pyramidal cell has arguably received more attention than any other neuron in the mammalian brain. Hippocampal CA1 pyramidal cells fire spikes with remarkable spatial and temporal precision, giving rise to the hippocampal rate and temporal codes. However, little is known about how different inputs interact during spatial behavior to generate such robust firing patterns. Here, we review the properties of the rodent hippocampal rate code and synthesize work from several disciplines to understand the functional anatomy and excitation-inhibition balance that can produce the rate-coded outputs of the CA1 pyramidal cell. We argue that both CA3 and entorhinal inputs are crucial for the formation of sharp, sparse CA1 place fields and that precisely timed and dominant inhibition is an equally important factor.