How the maze’s arms were orientated in different directions

How directionality
influences place cells

Place cells are
driven by local external cues (Spiers et al., 2015). CA1 place fields didn’t
repeat across a T-maze or radial-arm maze, despite similar environments and
spatial cues being present in the maze arms. However, the maze’s arms were
orientated in different directions (O’Keefe and Conway, 1978). Battaglia et al.
(2004) however, demonstrated that some place cells fired when rats traversed in
opposite directions along a track. However, the track had different cues along
it, so the environments may not have been visually similar in both directions.

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Derdikman et al.
(2009) showed hippocampal place cells had similar firing fields in visually
similar parallel alleyways of a hairpin maze. Fuhs et al. (2005) further showed
place field repetition in identically orientated boxes connected by a corridor.
Putting the boxes at 180 degrees to one another caused place field remapping.
Spiers et al. (2015) observed CA1 place cell place fields repeat across four
identical parallel boxes. However, when the compartments were arranged
radially, place fields didn’t repeat (Figure 4) (Grieves et al., 2016).
Evidence therefore suggests directional information can gate place cell firing.


Figure 4: In Sham
rats, place cells repeat their place fields across visually similar
parallel-maze compartments, but not radial-maze compartments. Each row in the
Sham or LMN lesion section is the heat map indicating place cell firing from
one place cell in the parallel-maze (left) or radial-maze (right). Place cells
repeat their place fields in the radial compartments following LMN lesions.
Place cells may thus be driven by local environmental cues only and not
directional information following LMN lesions. However, not all animals showed
place field repetition. This may be because the LMN-lesion size varied across
rats (Harland et al., 2017). The odour-location discrimination task (in which
rats can only discriminate between the odours to retrieve a reward if they knew
which compartment they were in) was conducted in the same apparatus as the
electrophysiology experiments, just with the addition of the odour pots
(Grieves et al., 2016). Figure sourced from Harland et al. (2017). 


In the
odour-location discrimination task (Figure 4), rats acquired the task in the
radial-maze, but were severely impaired in acquiring it in the parallel-maze.
Environment disambiguation may therefore be constrained by place field
repetition (Grieves et al., 2016). However, the rats that performed the
behaviour weren’t the rats used in the electrophysiology study. Therefore, it
cannot be concluded that the link between place field repetition and spatial
discrimination is causative.