An FMRI Study On Retrieval Success In Short-term Memory

In this study two recognition experiments were designed to explore how different factors affected retrieval success in short-term memory by using Chinese words as materials. Further we employed Blood Oxygenation-Level dependent functional MRI (fMRI) to index neural activity in cerebra cortex according to different condition of retrieval success in order to discuss neural mechanism of human memory.The first experiment tested the effectiveness of recognition density on retrieval success during retrieve stage and the second one tested the effect of learning density on retrieval success during code stage. The main findings of behavioral results were as follows: both recognition density and learning density showed a significant effect on retrieval success. The differences of retrieval success made by learning density were more remarkable.The main findings of functional neuro-imaging results were as follows: retrieval process of Chinese words was associated with increased activity in prefrontal cortex, medial temporal lobe, anterior cingular cortex, precuneus, parahippocampal cortex, insula, superior temporal cortex and so on.In experiment 1, results revealed similar pattern of activation across varying levels of retrieval success. Retrieval success-associated activation were as follows: left and right inferior prefrontal cortex (BA47), left superior prefrontal cortex (BA9), left and right middle prefrontal cortex (BA46), left ventro-prefrontal cortex (BA45), left medial prefrontal cortex (BA8), left and right medial temporal lobe (BA19), left and right precuneus (BA31), left and right Parahippocampal cortex (BA36), left Anterior Cingular Cortex (BA32), left precentral cortex (BA6) and left Insula (BA13).Relative to the low density condition, to a lesser extent, high-density recognition was associated with left and right superior medial temporal cortex (BA22), right superior prefrontal cortex (BA9), right precentral cortex (BA6) and right medial temporal lobe (BA8).In experiment 2, activation across multiple levels of retrieval success were demonstrated as follows: left and right inferior prefrontal cortex (BA47), left and rightsuperior prefrontal cortex (BA9), left and right middle prefrontal cortex (BA46), right superior prefrontal cortex (BA10), left medial prefrontal cortex (BA8), left ventro-prefrontal cortex (BA45), right medial temporal lobe (BA19), left and right precuneus (BA31), left and right parahippocampal cortex (BA36), left anterior cingular cortex (BA32), left precentral cortex (BA6), left and right insula (BA13) and right superior temporal cortex (BA22).The activation of left superior prefrontal cortex (BA10), right medial prefrontal cortex (BA8) and right ventro-prefrontal cortex (BA45) could reflect processes associated with high retrieval success compared by low retrieval success. Contrarily left superior temporal cortex (BA22) and left precentral cortex (BA6) reflected greater activity in low retrieval success.It was suggested left and right prefrontal cortex reflected retrieval process of Chinese words. The findings were consistent with the proposal that activation of right prefrontal cortex played an important role in retrieval success, especially its anterior and dorsolateral cortex were more sensitive to retrieval success.