Spike-Field Coherence and Firing Rate Profiles of CA1 Interneurons During an Associative Memory Task

Flexible, dynamic activity in the brain is essential to information processing. Neurons in the hippocampus are capable of conveying information about the continually evolving world through changes in their spiking activity. This information can be expressed through changes in firing rate and through the reorganization of spike timing in unique rhythmic profiles. Locally projecting interneurons of the hippocampus are in an ideal position to coordinate task-relevant changes in the spiking activity of the network, as their inhibitory influence allows them to constrain communication between neurons to rhythmic, optimal windows and facilitates selective responses to afferent input. During a context-guided odor–reward association task, interneurons and principal cells in the CA1 subregion of the rat hippocampus demonstrate distinct oscillatory profiles that correspond to correct and incorrect performance, despite similar firing rates during correct and incorrect trials (Rangel et al., eLife 5:e09849, 2016). Principal cells additionally contained information in their firing rates about task dimensions, reflective of highly selective responses to features such as single positions and odors. It remains to be determined whether interneurons also contain information about task dimensions in their firing rates. To address this question, we evaluated the information content for task dimensions in the firing rates of inhibitory neurons. Interneurons contained low, but significant information for task dimensions in their firing rates, with increases in information over the course of a trial that reflected the evolving availability of task dimensions. These results suggest that interneurons are capable of manifesting distinct rhythmic profiles and changes in firing rate that reflect task-relevant processing.