Figure 6.

Proximodistal Organization of CA2 Activity in Time and Space

(A) High-density multisite silicon probes (256 channels) allowed simultaneous recordings of CA3, CA2, and CA1 unit activity from 6 rats running (RUN) in a linear maze and subsequently sleeping (REM) (Oliva et al., 2016a).

(B) Mean theta phase modulation from pyramidal cells from the 6 rats organized from proximal to distal penetrations through CA2. A total of 688 CA2 pyramidal cells were isolated: 87 from rat 2, 126 from rat 4, 88 from rat 5, 65 from rat 6, 188 from rat 7, and 134 from rat 8. The reference for theta cycles was taken at SLM of CA1, with the theta peak at zero. Data from RUN and REM episodes are shown separately.

(C) Proximodistal group difference of the preferred theta phase for RUN (F = 25.4, p < 0.0001) and REM (F = 22.5, p < 0.0001). Note the statistical differences for proximal and distal CA2. Data are from 262 pyramidal cells in CA3a, 387 pyramidal cells in proximal CA2, 301 pyramidal cells in distal CA2, and 389 pyramidal cells in proximal CA1. ^∗p < 0.05 from post hoc t test.

(D) No statistical effects were found between groups in the strength of theta modulation.

(E) Cross-correlation between pyramidal cells from proximal and distal CA2 with CA3 and with CA1. Proximal CA2 neuronal firing is more correlated with CA3 firing, whereas distal CA2 cells tend to better correlate with CA1, especially during RUN periods. Data are shown as mean ± SEM.

(F) Proximodistal differences of slow and fast gamma modulation.

(G) Representative examples of CA2 place cells recorded from the proximal and distal sectors.

(H) Proximodistal differences of spatial coding properties of CA2 place cells.