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. 2018 Nov 7;100(3):700-714.e9.
doi: 10.1016/j.neuron.2018.08.043. Epub 2018 Sep 27.

Distinct and Dynamic ON and OFF Neural Ensembles in the Prefrontal Cortex Code Social Exploration

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Free PMC article

Distinct and Dynamic ON and OFF Neural Ensembles in the Prefrontal Cortex Code Social Exploration

Bo Liang et al. Neuron. .
Free PMC article

Abstract

The medial prefrontal cortex (mPFC) is important for social behavior, but the mechanisms by which mPFC neurons code real-time social exploration remain largely unknown. Here we utilized miniScopes to record calcium activities from hundreds of excitatory neurons in the mPFC while mice freely explored restrained social targets in the absence or presence of the psychedelic drug phencyclidine (PCP). We identified distinct and dynamic ON and OFF neural ensembles that displayed opposing activities to code real-time behavioral information. We further illustrated that ON and OFF ensembles tuned to social exploration carried information of salience and novelty for social targets. Finally, we showed that dysfunctions in these ensembles were associated with abnormal social exploration elicited by PCP. Our findings underscore the importance of mPFC ON and OFF neural ensembles for proper exploratory behavior, including social exploration, and pave the way for future studies elucidating neural circuit dysfunctions in psychiatric disorders.

Keywords: decoding; freely behaving; in vivo calcium imaging; miniature fluorescence microscope; mouse model; preference for social novelty; schizophrenia; sociability.

Conflict of interest statement

Competing Financial Interests Statement:

The authors declare no competing financial interests.

Figures

Figure 1:
Figure 1:. In vivo calcium imaging of mouse mPFC during social behavior test.
(A) Left panel: schematic diagram of experimental setup. Right panel: mouse coronal brain slice showing the anatomical position for GCamp6f expression and GRIN lens implantation. Scale bar: 1 mm. (B) Top left panel: experimental timeline. Top right panel: social behavioral test apparatus. Bottom panels: schematic paradigm for social behavior test: habituation (H), sociability (SB) and social novelty (SN). E1 and E2: empty containers; S1 and S2: stranger1 and stranger 2, respectively. (C) Left panels: raster plots for percentage of time (per 20 second bin) spent on direct-exploration of individual mouse toward different targets during each testing stage. Range indicators: 0–60%. Right histogram: statistical results, n = 18 mice. (D) Left panel: total numbers of neurons detected from individual mice. Right panel: percentage of active neurons at each testing stage. (E) Left panel: representative maximum projection fluorescent image of mPFC excitatory neurons labeled with GCamp6f, scale bar: 100 µm. Right panels: representative calcium traces from twenty regions of interest (color matched) during each testing stage. (F) Left panel: pie chart shows the percentage of neurons displaying increased, decreased or unchanged activity at the SB or the SN stages, compared to the H stage. Right histogram: the averaged calcium activities of neural groups exhibiting different activity changes at each stage. Data were represented as mean ± SEM. See also Figure S1, Movie S1, Movie S2, and Table S1.
Figure 2:
Figure 2:. Identification of behaviorally tuned ON and OFF neural ensembles in the mPFC.
(A) Raster plots of individual neural calcium activities and calcium traces of the averaged group activity of Direct-ON and Direct-OFF neurons (Dir-ON and Dir-OFF) from a representative mouse, H: habituation; SB: sociability; SN: social novelty. Red traces: Dir-ON; Blue traces: Dir-OFF. Vertical gray shadows: individual direct-exploration behavior epochs. (B) Spatial distributions of Dir-ON and Dir-OFF neurons from the same representative mouse at different stages, scale bar: 100 μm. (C) Top panel: engagement of Direct-ON neurons from a representative mouse at one testing stage; Green: “engaged” epochs; white: “not engaged “ epochs. Bottom left panel: percentage of engaged epochs for ON and OFF neurons across all behavior epochs indicated by the horizontal red box shown in top panel. Bottom right panel: percentage of engaged ON and OFF neurons at each individual behavior epoch indicated by the vertical red box shown in top panel. Box plots indicate Median and the 25–75th percentile with whiskers for maximal and minimal values. n = 9 mice. (D) Top panels: raster plot of the averaged calcium activity of individual Direct-ON and Direct-OFF neurons at the onset of direct-exploration (4 second before and 4 second after), sorted by the time of maximal activities (ON neurons) or minimal activities (OFF neurons). Bottom panels: distribution of Direct-ON neurons displaying maximal activity and Direct-OFF neurons displaying minimal activity at different time around the behavior onset. n = 9 mice. (E) Calcium-behavior correlation coefficients for Direct-ON and Direct-OFF neurons at different stages, n = 18 mice. (F) Sizes of behaviorally tuned ON and OFF neural ensembles in percentage of all imaged neurons at each testing stage, n = 18 mice. Data were represented as mean ± SEM. See also Figure S2, Figure S3 and Table S1.
Figure 3:
Figure 3:. ON and OFF neural ensembles carry real-time behavioral information.
(A) Decoding analyses for each annotated behavior using calcium activity from different groups of neurons, n = 54 decoding cases from 18 mice. ALL: all imaged neurons; ON + OFF: ON and OFF neurons together; ON + rOFF: ON and shuffled OFF neurons; rON + OFF: OFF and shuffled ON neurons; rON + rOFF: shuffled ON and OFF neurons. Each dot represents one decoding result from one mouse for one behavior at one testing stage. Bars represent group averages. (B) Pairwise correlation coefficient of neural calcium activities within and between ensembles, n = 40 ~ 108 correlation analyses from 18 mice. ON: within ON ensembles; OFF: within OFF ensembles; ON-OFF: between ON and OFF ensembles; ON/OFF-Others: between ON or OFF neurons with other neurons not tuned to the three annotated behaviors; Others: among other neurons. Each dot represents one correlation analysis from one mouse for one behavior at one testing stage. Bars represent group averages. Direct: direct-exploration; Self: self-directed activities; Irrelevant: irrelevant-exploration. Data were represented as mean ± SEM. See also Table S1.
Figure 4:
Figure 4:. Across-stage overlap analyses between ensembles identified during different stages of one social behavior test.
(A) Left panel: a matrix illustrates definitions for ON-ON intra-behavior (red circles) and ON-ON inter-behavior (blue squares) overlaps. OFF-OFF intra-behavior and OFF-OFF inter-behavior overlaps follow the same principle. H, habituation; SB, sociability; SN, social novelty. Dir, direct-exploration; Self, self-directed activities; Irr, irrelevant exploration. Right panel: Statistical results showing across-stage ON-ON and OFF-OFF intra- and inter-behavior overlaps and those predicted by chance based on random selection (Rand), n = 18 mice. (B) Left panel: illustrations showing the definition for ON-OFF intra-behavior overlap (triangles) for each annotated behavior. Right panel: Statistical results showing across-stage ON-OFF intra-behavior overlap and those predicted by chance based on random selection (Rand), n = 18 mice. (C) Comparisons of Direct-ON and Direct-OFF neural ensembles identified from the two 5-minute halves of the same stage (n = 18 mice). (D) Comparisons of Direct-ON and Direct-OFF neural ensemble identified from a full-length 10-minute period versus the union ensemble of the two 5-minute halves, n = 18 mice. Data were represented as mean ± SEM. See also Figure S3 and Table S1.
Figure 5:
Figure 5:. Across-test overlap analyses between ensembles identified during different social behavior tests.
(A) Top left panel: schematic illustration of the two social behavior tests performed at different days with strangers presented at the same locations. Bottom left panels: illustrations for ON-ON intra- and inter-behavior overlap, OFF-OFF intra- and inter-behavior overlap, and ON-OFF intra-behavior overlap for each annotated behavior as indicated by colored circles. Middle panel: across-test ON-ON and OFF-OFF intra- and inter-behavior overlaps and those predicted by chance based on random selection, n = 9 mice. Right panel: across-test ON-OFF intra-behavior overlap and those predicted by chance based on random selection, n = 9 mice. (B) Overlap analysis for two social behavior tests performed at different days with strangers presented at different locations, n = 6 mice. (C) Overlap analysis for two social behavior tests performed on the same day with strangers presented at different locations, n = 9 mice. Data were represented as mean ± SEM. See also Figure S4, Figure S5 and Table S1.
Figure 6:
Figure 6:. Dynamic population coding model.
(A) Schematic illustration for dynamic population coding model. Red circle: ON neurons; Blue circle: OFF neurons. “Engaged subset 1” and “Engaged subset 2” represent two subs ets of neurons engaged in behaviore coding at different points in time. (B) Schematic illustration of different ON and OFF neural ensembles coding for three annotated behaviors. Each oval represents a neural ensemble tuned to one annotated behavior. See also Figure S5F.
Figure 7.
Figure 7.. Acute PCP administration elicited deficits in social exploration and ensemble reorganization in the mPFC.
(A) Schematic illustration for social behavior tests performed in the absence and presence of PCP. H: habituation; SB: sociability; SN: social novelty. (B) Left panels: Raster plots for percentage of time (per 20 second bin) spent on direct-exploration toward different targets for individual mouse under acute PCP. Right panel shows the statistical results, n = 18 mice. (C) Ensemble overlap analyses between two social behavior tests performed in the absence and presence of PCP. Left panels: illustrations for ON-ON intra- and inter-behavior overlap (filled and unfilled red circles, respectively), OFF-OFF intra- and inter-behavior overlap (filled and unfilled blue circles, respectively), and ON-OFF intra-behavior overlap for each annotated behavior as indicated by colored circles. Middle panel: statistical results showing across-test ON-ON and OFF-OFF intra- and inter-behavior overlaps and those predicted by chance based on random selection, n = 18 mice. Right panel: statistical results showing across-test ON-OFF intra-behavior overlap and those predicted by chance based on random selection, n = 18 mice. Data were represented as mean ± SEM. See also Figure S6, Figure S7 and Table S1.
Figure 8:
Figure 8:. PCP disrupted information coding of social salience and novelty by Direct-ON and Direct-OFF ensembles.
(A) Top panels: schematic diagrams of the social behavior test performed in the absence of PCP. H, habituation; SB, sociability; SN, social novelty. E1 and E2 refer to empty containers; S1 and S2 refer to stranger1 and stranger 2, respectively. Middle and bottom panels: calcium activities of Direct-ON (middle panels) and Direct-OFF (bottom panels) ensembles responding to the two explorative targets at the H, SB and SN stages, n = 18 mice. (B) Top panels: schematic diagrams indicating the social behavior test under acute PCP influence. Middle and bottom panels: calcium activities of Direct-ON (middle) and Direct-OFF (bottom) ensembles responding to the two explorative targets at the H, SB and SN stages, n = 14 ~ 18 mice. Data were represented as mean ± SEM. See also Figure S8, Table S1.

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