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Abstract
Epidemiological research suggests that early life stress contributes to the risk of developing an anxiety disorder. One factor that has been implicated in the pathogenesis of anxiety is generalisation, yet generalisation has never been explored in the context of early life stress. Hence, in this thesis, I examined the link between early life stress and generalisation. To do this, I used maternal separation, a rodent model for early life stress, where pups are separated from the dam for 3 hours a day from postnatal day 2 to 14.
In Chapter 2, I examined whether early life stress increased cue generalisation. I found that maternal separation had no effect on generalisation when the conditioned and generalisation stimuli were relatively similar (i.e., 2 tones). However, in contrast to my predictions, it was found that early life stress reduced the generalisation of cue conditioning in both male and female rats when stimuli were less similar (i.e., a tone and a white noise).
The second series of experiments (i.e., Chapter 3) investigated whether early life adversity decreased the generalisation of fear inhibition, as reductions in fear inhibition might contribute to anxiety. There was no effect of maternal separation on the generalisation of extinction when the stimuli were relatively similar (i.e., two tones). However, in line with my predictions, early life stress reduced the generalisation of extinction when cues were less similar (i.e., a tone and a white noise).
In Chapter 4, I explored whether early life adversity increased the generalisation of context fear. I found that early life stress resulted in a faster rate of context generalisation. Moreover, treatments that typically reduce generalisation in standard reared animals were not helpful for maternally separated animals.
Taken together, these experiments contribute to our understanding of how early life stress affects fear generalisation, and suggests a possible pathway by which adversity might contribute to the emergence of psychopathology. In addition, these studies highlight the differences between context and cue generalisation. Potential reasons for these disparities are discussed in the final Chapter, as well as possible avenues for future research.