Theta rhythms coordinate hippocampal–prefrontal interactions in a spatial memory task. Matthew W. Jones and Matthew A. Wilson show that correlated firing in the hippocampus and prefrontal cortex is enhanced during spatial working memory tasks, allowing integration of hippocampal spatial information into a decision-making network. This coordination is paralleled by increased coupling in the 4- to 12-Hz theta frequency range. Theta rhythms may thus serve as a general mechanism for controlling the timing of neural activities, enabling specialized brain structures to encode information independently and interact selectively based on behavioral demands. The study explores how phase-locking of neuronal firing to theta rhythms in the hippocampus and prefrontal cortex may underlie coordination between these structures. It finds that mPFC neurons show increased phase-locking to hippocampal theta rhythms during spatial working memory tasks, suggesting a role in integrating spatial information. The study also shows that cross-correlations between hippocampal and prefrontal spike times are enhanced during spatial working memory tasks, indicating coordinated activity between these structures. Theta rhythms are found in many mammalian brain structures, but are most prominent in the hippocampus. Hippocampal place cells fire in a phase-locked manner with respect to the local theta rhythm. This phase-locking is an example of temporal coding in the brain and may allow higher-order coding of spatial information. Phase-locking has also been described in other brain regions, including the prefrontal cortex. The study finds that mPFC neurons show increased phase-locking to hippocampal theta rhythms during spatial working memory tasks. This suggests that phase-locking may play a broader role in defining the temporal relationships between cross-structural activities. However, it remains to be established how these phase relationships influence the firing of connected neurons and how they relate to behavior or hippocampal function. The study also finds that the degree of phase-locking of mPFC neurons to the CA1 theta rhythm is enhanced during choice epochs relative to forced-turn and choice-error runs. This suggests that phase-locking may be a mechanism through which to temporally coordinate populations of neurons in these two structures. The study also finds that coherence between CA1 and mPFC LFP is enhanced during choice epochs, indicating coordinated activity between these structures. The study concludes that theta-frequency coordination between CA1 and mPFC peaks during behavioral epochs presumed to require effective communication between these two structures. This coordination may reflect the nature of cross-structural coordination at network and neuronal levels and may contribute to both the clinical diagnosis of cognitive disorders and to characterizing animal models of these diseases.Theta rhythms coordinate hippocampal–prefrontal interactions in a spatial memory task. Matthew W. Jones and Matthew A. Wilson show that correlated firing in the hippocampus and prefrontal cortex is enhanced during spatial working memory tasks, allowing integration of hippocampal spatial information into a decision-making network. This coordination is paralleled by increased coupling in the 4- to 12-Hz theta frequency range. Theta rhythms may thus serve as a general mechanism for controlling the timing of neural activities, enabling specialized brain structures to encode information independently and interact selectively based on behavioral demands. The study explores how phase-locking of neuronal firing to theta rhythms in the hippocampus and prefrontal cortex may underlie coordination between these structures. It finds that mPFC neurons show increased phase-locking to hippocampal theta rhythms during spatial working memory tasks, suggesting a role in integrating spatial information. The study also shows that cross-correlations between hippocampal and prefrontal spike times are enhanced during spatial working memory tasks, indicating coordinated activity between these structures. Theta rhythms are found in many mammalian brain structures, but are most prominent in the hippocampus. Hippocampal place cells fire in a phase-locked manner with respect to the local theta rhythm. This phase-locking is an example of temporal coding in the brain and may allow higher-order coding of spatial information. Phase-locking has also been described in other brain regions, including the prefrontal cortex. The study finds that mPFC neurons show increased phase-locking to hippocampal theta rhythms during spatial working memory tasks. This suggests that phase-locking may play a broader role in defining the temporal relationships between cross-structural activities. However, it remains to be established how these phase relationships influence the firing of connected neurons and how they relate to behavior or hippocampal function. The study also finds that the degree of phase-locking of mPFC neurons to the CA1 theta rhythm is enhanced during choice epochs relative to forced-turn and choice-error runs. This suggests that phase-locking may be a mechanism through which to temporally coordinate populations of neurons in these two structures. The study also finds that coherence between CA1 and mPFC LFP is enhanced during choice epochs, indicating coordinated activity between these structures. The study concludes that theta-frequency coordination between CA1 and mPFC peaks during behavioral epochs presumed to require effective communication between these two structures. This coordination may reflect the nature of cross-structural coordination at network and neuronal levels and may contribute to both the clinical diagnosis of cognitive disorders and to characterizing animal models of these diseases.