Effects of scopolamine, d-amphetamine, and apomorphine on alternation and position biases

The sequencing of arm entries in a symmetrical Y-maze was examined in mice treated with either scopolamine, d-amphetamine or apomorphine. These treatments could potentially alter both alternation tendencies and rotational tendencies. Therefore, a measure of spontaneous alternation was evaluated which was computed by taking an average of the right going percent alternation and the left going percent alternation. The number of arm entries was increased by amphetamine, unchanged following scopolamine and reduced by apomorphine. All three drugs reduced spontaneous alternation tendencies and increased the magnitude of a bias to turn consistently in the same direction (rotational tendency). All three drugs thus altered the sequencing of arm entries from patterns consistent with spatial alteration to patterns consistent with egocentrically defined responses. These results indicate that the measure of spontaneous alternation which was an average of the right going percent alternation and the left going percent alternation is a better index of alternation tendencies. Thus, when an animal is not able to navigate on the basis of an extrapersonal (allocentric) system as a result of drug treatment, it will revert to an egocentric system.