Figure 4. LHb responses to shock cues are encoded in two distinct subpopulations.

(A) Schematic of recording from the LHb while inactivating ipsilateral rEPN with GABA agonists. (B) Schematic of inactivation behavioral paradigm in which reward and shock were delivered at 100% probability. (C) Ipsilateral rEPN inactivaiton did not affect behavioral response (food tray approach) in reward trials. (D) A majority of LHb neurons are inhibited by reward cue and activated by shock and shock cues. (E) Responses to shock cues were positively correlated with individual neuron’s responses to footshocks. Solid circles indicate neurons significantly excited by both shock cues and footshocks. (F) LHb neurons on average showed inhibition to reward cues and excitation to shock cues during 0–500 ms post-stimulus window, suggesting a valence encoding pattern. (G) Excitation to shock cues contained two phases: an ‘earlier’ phase from 10 to 30 ms post-stimulus and a ‘later’ phase from 40 to 100 ms post-stimulus (brown and gray shaded bars, respectively). (H) Rasterplots and histograms of representative early- and late-responsive LHb neurons. (I) Histogram of all shock cue-activated LHb neurons shows bimodal distribution of ratio late to early response components. (J) Early-responsive neurons do not differentiate between shock cues and neutral cues. (K) In contrast, late-responsive neurons exhibited greater responses to shock cues compared to neutral cues and reward cues. Shaded bar indiactes analysis windows for ajacent panels. (L) Late shock cue-responsive showed strongly inhibitions to reward cues than early shock cue-responsive neurons.