Differently-shaped walled boxes placed in sam e position in curtained

environm ent

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Black curtain

Figure 6b Laboratory layout for experiments 1 and 2.

HP = holding platform. X marks the centre o f the curtained environment. Either a Square- walled box, or a circular-walled box, is placed in the curtained environment, centred on X. The cam era viewing area is kept constant.

Rat is always brought into the curtained environment through the lab-South Point o f entry, head facing lab-North, and placed at X before being released.

Laboratory layouts and testing procedures - general

Precise details, with further Figures, o f the environments and procedures used in each experiment are given in chapters 7, 8, and 9. Here, the general laboratory layout is shown for experiments 1 and 2 in Figure 6b. (The pilot study was conducted in a different laboratory). In each experiment, recording took place in differently-shaped walled boxes: one square-walled, one circular walled.

Trial timing, sequence and alternation - general comments

Trials always alternated between circle and square shapes, except in the training phase o f experiment IB described in chapter 8. Trials were always recorded for 8 minutes in the given square, and 10 minutes in the given circle (these times being proportional to the different surface areas o f the two shapes). In some probe trials, an extra minute or so was added to the trial length to allow the rat to “adjust” to the new environment. In the main experiments, the intertrial interval (ITI) was rigorously maintained between 20-25 minutes. Very few ITIs were longer or shorter than this. The ITI on

transfer/probe/further manipulation days was sometimes longer than 25 minutes. Generally, recording began within 0-15 seconds o f placing the rat in the environment, and ended about 5-20 seconds before the rat was taken out o f the environment. In other words, recording was perform ed fo r almost the entire duration o f the anim al’s experience in the environments. Each rat was tested at approximately the same time o f day, though this time could differ for each o f the rats within the same experimental series.

Procedures for bringing each rat in and out of the environments (Exps. 1 & 2) Rats were brought in and out o f the laboratory and the environments according to standard procedures. As mentioned, ITIs were strictly controlled. At the beginning o f each day, the experimental rat was brought into the laboratory as follows. It was always brought around the outside o f the o f the black curtains (on the room East side - See Figure 6b), which were always drawn so that the rat could not see inside; then it was placed on the holding platform (HP in Figure 6b). The time spent on the holding platform before trials began did vary, but was always at least 20 minutes. The rat was placed into the given walled box after being carried through an opening in the south side o f the black curtains (Point o f Entry in Figure 6b), and over the south side o f the box. The rat was always placed into the box with its head facing laboratory north, and it was always placed at the centre o f the box, give or take a few centimetres. The only exceptions to this occurred in probe trials specifically examining direction sense. The animal was always on the holding platform between trials.

These procedures are in addition to the use o f cue cards to polarise the environments (described fully in chapters 8 and 9 for experiments 1 and 2 respectively.) No attempt was made to mask sounds or other cues which could, in principle, help stabilise the head-direction system o f the rat.

It should be noted that these procedures, designed to create stability in the head- direction system, are very different from those generally employed in the Muller laboratory (eg. Bostock et al, 1991; Fenton and Muller, 2000) where animals are taken out o f the room between trials, and rats are introduced into the testing environment pseudo-randomly from four entry points in the curtains spaced 90 degrees apart.

There is no mention o f these procedures in Quirk et al, 1992, but we assume they were similar to others in the Muller laboratory. Clearly, the procedures in the Muller laboratory are designed to create ideal directional control over the place cell firing by the intramaze cues. It is possible that the rats have less chance to appreciate the essential similarity o f the position o f the testing environments in the Muller-type set up.

Environments - the “morph box”

Recording took place in differently-shaped walled boxes. In all cases, the standard testing situation compared firing in square-walled vs circular-walled boxes. In the pilot study, and in experiments 1A and IB, this was achieved using a “morph box”, presently described, from which several shapes could be constructed. In experiment 2, the morph box was used as a transfer-testing environment.

In order to create environments whose shape could be changed, without affecting other modalities such as olfaction, texture, colour (or shade), “morph boxes” were constructed (See Figure 6c). Each morph box consisted o f 32 pieces o f interlocking plastic tubing. To hide the joints, a layer o f plastic wrapping tape was stuck to the inner surface o f the walls, and then another layer o f masking tape was stuck onto the plastic wrapping tape. (By itself, the plastic wrapping tape causes static problems). Two such m orph boxes were constructed. For ease o f reference, the morph box configured with circular walls is hereafter referred to as the morph circle, and the morph box configured with square walls is hereafter referred to as the morph square.