Journal Club: Hippocampal-prefrontal theta mediating anxiety in rodents?

18th June 2015


We discussed the paper entitled “Single units in the medial prefrontal cortex with anxiety-related firing patterns are preferentially influenced by ventral hippocampal activity” by Adhikari, Topiwala, and Gordon [Neuron, 2011]. We chose to read this paper because we are interested in the role of oscillatory brain activity in psychological disorders, as well as in the consequences of anxiety for learning, memory, and attention.

The paper discussed the role of single units in the medial prefrontal cortex (mPFC) in rodents in representing anxiety-related task features. Results showed that there were subsamples of units that displayed preferential firing for either the safe or aversive features of the elevated plus maze. Moreover, those units that showed the most robust representation of the anxiety features were also those that were most phase-locked to- and temporally followed theta input from the ventral hippocampus (vHPC). Thus, mPFC single units use input from the vHPC to form representations of anxiety features of the maze; thus, the unidirectional projection from the vHPC to the mPFC is implicated in anxiety in rodents. However, an unexpected finding was that those units reflecting anxiety features were highly present in non anxious rodents, while representations in anxious mice were at chance level; one would expect that anxious rodents would possess these units to a greater extent, given that they could adaptively be used to guide avoidant behaviour.

We enjoyed reading this paper and puzzled over how it can inform us about the coding of anxiety in humans. It is always tricky to label rodents based on a psychological trait, such as anxiety. We also wondered about how these anxiety-related functions co-exist in the same circuitry with spatial encoding in working memory, as reported by the same laboratory (Spellman et al 2015 Nature 522: 309-314, doi: 10.1038/nature14445). Interesting…