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Blood Oxygen Level Dependent (BOLD) Signal

Effects of Verbal Working Memory Load on Corticocorical Connectivity Modeled by Path Analysis of Functional Magnetic Resonance Imaging Data ( Honey et al ., Neuroimage , 2002) 12.04.19.(Thu) Summarized by Joon Shik Kim Computational Models of Intelligence.

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Blood Oxygen Level Dependent (BOLD) Signal

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  1. Effects of Verbal Working Memory Load on Corticocorical Connectivity Modeled by Path Analysis of Functional Magnetic Resonance Imaging Data(Honey et al., Neuroimage, 2002)12.04.19.(Thu)Summarized by Joon Shik KimComputational Models of Intelligence

  2. Blood Oxygen Level Dependent (BOLD) Signal • Amount of oxygen molecules bound to hemoglobin. • If a specific task is performed, related brain regions are activated and the need for more oxygen leads to BOLD signal increase.

  3. Task • In a control task, subjects viewed a series of 14 letters with an interstimulus interval of 2 s. • Subjects pressed the mouse button if the currently presented letter was the same as that presented n trials previously. If n=1, we call the task as 1 back task. If n=2, 2 back task and if n=3, 3 back task.

  4. Generation of fMRI time series

  5. Brain Activation Maps

  6. Structural Equation Modeling (SEM) (Bullmore et al., 2000) where q denotes the number of path coefficients to be estimated and C denotes the sample covariance.

  7. Model by Automated Search

  8. Path Coefficient

  9. Significant Path Coefficient Right Left

  10. Discussion (1/3) • Manipulation of cognitive demand in a verbal working memory task is associated with concomitant changes in corticocortical connections. • Under both 1-back and 2-back conditions, there was a significant connections from the left inferior frontal gyrus to the left posterior parietal cortex.

  11. Discussion (2/3) • The projection from the left inferior frontal gyrus to the left posterior parietal cortex may be important in mediating articulatory rehearsal. • Increasing n from 1 to 2 increases the load on articulatory rehearsal. This manipulation was associated with the emergence of a second significant connection between the inferior frontal gyrus and posterior parietal cortex via SMA.

  12. Discussion (3/3) • Our model did not provide a good fit to the 3-back data. • The change in functional integration induced by an increase in load from 2- to 3-back may require qualitative reconstruction of the path diagram. • Enhanced prefrontoprefrontal connectivity under the 2-back condition may reflect greater demand for executive process.

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