Abstract
Maternal immune activation (MIA) is a risk factor for the development of schizophrenia in
the offspring. If a mother’s immune system is activated during sensitive periods of
development it can interrupt delicate brain organisation. There is some evidence that
sequence learning is disrupted in people with schizophrenia. The MIA risk factor can be
induced in laboratory animal models. The following studies used MIA and control rats to
examine whether sequence learning capacity and temporal order recognition was impacted in
MIA animals.
The aim of study 1 was to find out whether MIA rats showed a deficit in a sequence
learning task in comparison to control rats. Rats were required to learn a five-item sequence
task in which they needed to nose-poke lit ports to receive a food reward. The order in which
the five-item sequence progressed was always random except for one structured sequence.
The hypothesis was that the control rats would show a decreased reaction time on the
structured sequence compared to the random sequences, whereas MIA rats would show no
significant difference between reaction time for the structured sequence and the random
sequences. The results did not support the hypothesis and instead suggested that MIA animals
were significantly faster than controls on the structured sequence. Overall, the animals did
not appear to learn the sequence as they were faster at the structured sequence compared to
random sequences right from the start of the procedure.
The aim of study 2 was to discover if the MIA model would impact the ability of the
animals to recognise the temporal order of previous exposure to objects. Each rat was given
the opportunity for free exploration in an open field containing an object placed in different
locations, for five minutes across three familiarisation sessions. There was a three minute
break between each familiarisation session where the rat was removed from the open field
3 and the object was moved to a set location which the rat had not yet seen it in. Rats were
removed from the open field for 30 minutes before a five minute test phase during which two
identical objects were placed in the most-recent (session three) and least-recent (session one)
locations. The results showed that control animals had a significant preference for the least recent object, while MIA animals did not although there was no significant difference
between the two groups. When the five minute test phase was analysed in three time blocks.
There was a significant interaction between group and time block where MIA animals
explored the least-recent object more in the first time block, and the most-recent object more
in the third time block while control animals showed an initial preference for the most-recent
object in the first time block before exploring the least-recent object more in the third time
block. These studies have shed new light on the behaviours of MIA animals. The sequence
learning study indicates MIA animals may not have sequence learning difficulties, nor any
motivational deficits. The temporal order and novelty recognition study may suggest that
MIA animals are more anxious than controls and have a tendency to hyperfixate.