Paul Dudchenko (Stirling) The neural encoding of destination and direction. (Brambell Translational Neuroscience Seminar Series, 19/4/2012).
Unfortunately I had to leave this early, so I missed most of the speakers own recent work, what I did hear was partly review and partly older work, which was still all new to me.
Rats are known to have direction cells, a given direction cell has a tuning curve and fires when the rat’s head is pointed in a specific direction. If the experimental arena has a visual cue that seems to be what the rat uses to orient itself, so if the area is circular with only one cue and rat is removed from the arena and the cue moved, the direction cell tuning curve is moved by the same amount. If there are no visual cues, the rat will develop a tuning curve anyway, but if a visual cue is introduced, the rat will incorporate this into its sense of orientation, so if more than eight minutes after the cue is introduced, the cue is moved, the direction tuning curve moves by the same amount.
Now, rats also use path integration to determine direction, if a rat is allowed to move from one box to another through a door, the tuning curve in the second box will be close in orientation to the one in the first, in fact, there is a precession of about 20 degrees. One interesting experiment compared visual cues and path integration. The rat spends time in one box (a), it was then moved to another (c) but only after being moved around enough the lab a bit in a box. The direction tuning curve was different in each box. Now, four boxes were linked by doors, the two boxes the rat had been in before, a and c, and two novel boxes, b and d, with b between a and c and d after c. The rat was allow to spend time in each box before a door opened allowing the rat to move into the next box. the door then closed. Path integration meant that the tuning curve in b was almost the same as in a, the question is, would c be like b, as dictated by path integration, or as it was before, as dictated by visual cues. The answer was the latter and when the rat moved into d its direction tuning curve there was similar to the one for c. Hence, memory of visual cues beats path integration!