Fragile X syndrome (FXS) is the most common inherited form of mental retardation, occurring in roughly 1/4000 males and 1/8000 females. An abnormal expansion of a trinucleotide CGG repeat sequence in the fmr1 gene results in transcriptional silencing of this gene, which codes for the Fragile X Mental Retardation Protein (FMRP). The loss of FMRP, directly and/or indirectly, gives rise to the FXS phenotype, which includes a characteristic set of anatomic and cognitive/behavioral features. The present studies were designed to test the hallmark areas of dysfunction (i.e. attention, inhibitory control, hyperarousal, and emotional regulation) seen in human FXS and further characterize spared and impaired functions in fmr1 KO mice. The performance of F1 hybrid fmr1 KO mice (a C57BL/6J x FVB/NJ cross) and wild-type (WT) littermate controls were evaluated on a series of tasks designed to assess inhibitory control and various aspects of attention, Reversal Learning Task, and Associate Learning Task. Regulation of arousal and emotion, two domains affected in FXS, was also evaluated in these tasks by examining the animals' reaction to the unexpected presentation of potent olfactory distractors (in the Distraction task), as well as their reaction to committing an error on the previous trial.The present studies provided the first evidence that the hallmark deficits in human FXS --impaired attention, inhibitory control, and arousal regulation -are also impaired in the fmr1 mouse model of FXS. In addition, these findings demonstrate that attentional dysfunction and impaired inhibitory control are most prominent when task contingencies change and when the animal has just committed an errorsituations that arouse or disturb the mice. Analysis of videotapes further demonstrates that arousal regulation is impaired in the fmr1 KO mice. Additionally, the fmr1 KO mice were not impaired in associative learning, transfer of learning, or reversal Jisook's stidies in New Generation stimulated her desire for a deeper and moe systematic understanding of the neural mechanisms of human brain. She was accepted into the Department of Psychology at Yonsei University, which is considered one of the best programs in Korea. This allowed her the unique combination of being able to study at Yonsei University and to work part time for New Generation C&C. Working and studying at the same time allowed her many opportunities to apply academic knowledge to real-world situations.To the end, Jisook assisted Dr. Kang in her lab, the Cognitive Neuroscience and Medical Physics Lab at the Seoul National University Hospital. There, she conducted studies on memory and learning in normal human conditions, as well as abnormal states of perception such as epilepsy and dementia. Through cutting-edge imaging methods (i.e. fMRI, PET, and MRI) coupled with some behavioral tests, she furthered her knowledge of functional and structural workings of the human brain iv during learning, memorizing, and recognizing. She also ganed insight into how the activity of the brain dif...