Directional, locational, and rhythmic organization of firing are present during initial exploration, including adultlike directional firing.
Crucially, even when directional firing cannot be stabilized, ensembles of unstable HD cells show short-timescale (1 10 s) temporal and spatial couplings consistent with an adult-like HD network.
Following eye opening, the HD system matures rapidly, as more cells exhibit directional firing, and the quality and reliability of the directional signal improves dramatically.
Candidate shifter cells, with directional firing modulated by turning speed, have been identified in the anterior thalamus [26,79], presubiculum [80] and retrosplenial cortex [81].
The fact that cells exhibit directional firing before eye opening is consistent with data from adult animals showing that head direction cells maintain directional tuning in complete darkness even though the preferred tuning direction drifts over extended time intervals [ 13].
Figure 2C,F depict the temporal evolution of head directional firing for cumulative samples and independent time-binned samples, demonstrating head directional activity is present from the first minute of exposure to the environment (irrespective of environment shape).
Doing so abolishes the directional firing in the anterior dorsal thalamus (Goodridge & Taube, 1997; Blair et al., 1998, 1999), which in turn is necessary for normal head direction cell firing in the postsubiculum, and for both head direction and tuned grid cell activity in the medial entorhinal cortex (Winter, Clark, & Taube, 2015).
10.7554/eLife.08902.006 Figure 4. Bi-directional firing of V1 and CA1 cells on the C-shaped track.
We also analyzed whether this direction of interaction was true to those V1-CA1 cell pairs with both showing bi-directional firing.
(C, D ) Histograms of the cross-correlogram peak positions of all V1 (C ) and CA1 (D ) cells with significant bi-directional firing.
