The effects of structural and functional damage to limbic structures on cognitive abilities

Functional and degenerative damage to regions of the limbic system are often associated with cognitive impairments in different aspects of memory. Neuroimaging studies in post-traumatic stress disorder (PTSD) and Alzheimer’s disease (AD) have reported selective hippocampal atrophy. Neuroimaging studies in panic disorder have also suggested reduced functional activity in the right parahippocampal gyrus. It is unclear whether this hippocampal damage is responsible for the emergence of selective neuropsychological deficits. Abnormal activity in limbic structures has also been reported in PTSD patients exposed to trauma-related stimuli. This thesis was concerned with examining the effects of structural and functional damage to the limbic system on selective cognitive abilities. The limbic structures under investigation included the hippocampus, parahippocampal gyrus, anterior cingulate cortex and amygdala. In order to investigate this issue, a series of neuropsychological and neuroimaging experiments were carried out using groups of patient populations, such as panic disorder, PTSD and AD, known to exhibit abnormalities to the limbic structures. An fMRI study, using the Color Stroop and Emotional Stroop task was also administered to PTSD patients and healthy controls.Results from the neuropsychological studies showed greater impairments in topographical/spatial memory compared to verbal memory in all groups of patients. In addition, voxel-based correlation analyses found that both PTSD and AD are associated with neuropsychological deficits in the area of visuo-spatial and topographical memory that may be explained by the regional brain atrophy in limbic structures. Abnormalities of the parahippocampal gyri and cingulate cortex and possibly the amygdalae in the fMRI study also suggested a dysregulation in limbic-cortical networks in PTSD. This thesis has demonstrated that damage to limbic structures might contribute to the cognitive abnormalities of panic disorder, PTSD and AD