Date of Award

Spring 5-14-2016

Degree Type


Degree Name

MS Experimental Psychology




Michael Vigorito, Ph.D

Committee Member

Amy Joh, Ph.D

Committee Member

Amy Hunter, Ph.D


neurogenesis hypothesis, lipopolysaccharide, memory, infantile amnesia, CPFE


The inability to remember events experienced very early in life is referred to as Infantile Amnesia (IA) and has been observed in both humans and animals. Over the years interest in the phenomenon waned, but has recently increased with the discovery of new neurobiological methods to study brain function (e.g., Callaghan, Li & Richardson, 2014). The neurobiological mechanism behind IA has yet to be determined, but several innovative theories have been developed with these new research methods. The neurogenesis hypothesis theorizes that increased neurogenesis during early development disrupts previously established memories. The hippocampus, an area that mediates both the memory of a fearful experience and the memory of a context is an area that undergoes neurogenesis lifelong but especially early in development. The increased amount of neurogenesis in the hippocampus early in life may disrupt the memory of fearful contexts in young rats. The current study examined the effect of lipopolysaccharide (LPS), on the memory for a context paired with foot shock in developing rats using the context preexposure facilitation effect (CPFE) procedure. LPS is an endotoxin that activates the immune system and reduces neurogenesis in the process. Rats exposed to a context at 24 days of age and shocked, after a 22 day retention interval showed less freezing the next day than those tested after a 2 day retention interval, suggesting they forgot the context cues over time, a trait suggestive of IA. Rats injected with LPS showed significantly lower rates of freezing compared to saline-treated rats at both retention intervals, thus showing overall poorer performance rather than reduced forgetting at the longer retention interval. The results from the current study fail to support the neurogenesis hypothesis. Implications of using LPS for a test of the neurogenesis hypothesis are discussed.