Sequence learning following maternal immune activation

Maternal immune activation (MIA) is a risk factor for schizophrenia. Since memory for sequence and stimulus order are disrupted in individuals with schizophrenia, we tested whether MIA animals showed deficits in a sequence learning and object-place recency memory task. In experiment one, control and MIA-challenged rats were required to nose poke five ports in a cued sequence. The sequences were presented randomly except for one structured sequence that was repetitive and initiated from the same port. Both groups were more accurate on the structured sequence and learned the task at similar rates. When a new structured sequence was presented, control animals were able to respond flexibly and take advantage of the structure, whereas the performance of MIA animals was similar for random and structured sequences. Experiment two tested MIA and control rats were evaluated in a Temporal Ordering for Spatial Locations task (TOSL). Control animals had a significant preference for the object in the least-recent location, indicating a novelty preference, while MIA animals did not, although the between-group difference failed to reach significance. Exploration patterns changed differentially over time, possibly because of variation in habituation processes. As a result, MIA animals were significantly less likely to explore the object at the least-recent location during the second half of the exploration session, compared to control animals. Collectively these studies indicate that while MIA animals are unimpaired in simple sequence learning, they display changes in behaviour compared to controls. Differences may result from habituation rate or inflexibility when responding to change.