An fMRI investigation of a memory guided vergence task: Insights to the parahippocampal area

This investigation sought to systematic study the parahippocampal area using three types of vergence eye movement tasks that utilized different demands on visual memory. The percent volume change of the functional activity in the posterior parahippocampal area (PPHA) was quantified for three different experimental paradigms that stimulated vergence eye movements: random tracking versus fixation; predictable tracking versus random tracking; and memory-guided task. A general linear model (GLM) was used to determine functional activity for each of the three vergence experiments. The average signal percent change for both the PPHA and frontal eye fields (FEF) was compared for each vergence task. Significant percent change in the average signal from the voxels in the PPHA was observed for all experiments (p < 0.005), whereas no such significant change was observed for the FEF (p > 0.06). Lastly, percent volume change was also quantified for the PPHA among experiments. Percent volume change in the PPHA was greater for the memory-guided vergence task and the change was significant across all the experiments, (p<0.02). This suggests that when utilization of working memory is required, the PPHA functions as one of the regions for a vergence eye movement dependent memory task.