Figure 2.

Methods for studying the various functions of PPC in rodents. (A) Two examples of PPC cells coding sequential trajectories during unrestrained foraging in the open field. Cell A fired when right turns were followed by sustained turning to the left; the motion sequence coded by the cell is illustrated to right (traced from open field data). Cell B fired bursts at the start of right-left-right-right movement sequences lasting more than 1 s. (B) Different levels of behavioral control for studying PPC in rodents. In the top example animals were freely foraging or performing stereotypical running sequences in the same open arena; the advantage to the lack of behavioral constraints here is the ability compare the coding properties of PPC neurons across very different modes of behavior. In example (2) the animal is confined to a behavior box with nose ports which afford the animal a means to trigger the delivery of stimuli and to provide a behavioral report. This type of apparatus is commonly used to study sensory decision making as well as motor planning, and offers the advantage of precise temporal control for cue presentation and behavioral assessment. The final example (3) shows a mouse in a virtual reality apparatus. This approach offers perhaps the highest degree of control by the experimenter, as the animals perform tasks while they are head-fixed and running on a track ball. One can therefore monitor precisely running speed and direction through any virtual environment.