Object location memory after TBI

Abstract

Object location memory (OLM) is important in completing many daily tasks and relies on brain regions including the inferior and medial temporal lobes, posterior parietal lobes, and frontal lobes. TBI often results in frontal lobe dysfunction, which can adversely impact memory and working memory. The purposes of the current study were to investigate the neural substrates of working memory and OLM after TBI. 17 Males (12 Healthy control (HC); 5 individuals with TBI) completed two types of tasks in the fMRI scanner: (1) OLM encoding task during which they were presented with Novel stimuli and Repeated (control) stimuli, and (2) spatial and verbal n-back tasks (0-back and 2-back). Participants completed the OLM retrieval task outside of the scanner. They also completed a neuropsychological screen and memory questionnaires. Between-group analyses were performed on 5 TBI (moderate-severe) and 5 matched HC participants. There were no significant between-group differences in performance on the n-back and OLM tasks, but medium to large effect sizes were present for both tasks. Regarding neural activation during working memory tasks (2-back>0-back contrast), the TBI group demonstrated widespread increases in activation in working memory regions (e.g., dorsolateral prefrontal cortex, inferior parietal lobule) compared to the HC group. During the OLM encoding task (Novel>Repeated) the HC group demonstrated widespread increases in activation in regions associated with OLM (e.g., ventral and dorsal visual processing streams, prefrontal cortex). This unexpected finding was due to unexpected activity during Repeated trials in the TBI group. Implications are discussed in terms of possible lack of expected repetition suppression. Overlay activation maps of the n-back and OLM tasks demonstrated several shared regions of activation in fronto-parietal regions that are part of a working memory network. The present study supported previous findings that patients with TBI demonstrate increased activation during memory and working memory tasks compared to the HC. Given the overlap of activation between task types and the lack of medial temporal lobe activation between groups on the OLM task, differences in encoding OLM after TBI are due to disruptions within a fronto-parietal network. These findings have implications on developing memory strategies for individuals with TBI.%%%%Ph.D., Clinical Psychology – Drexel University, 2012