Blood Oxygen Level Dependent (BOLD) Signal
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Transcript of 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.11.05.20.(Fri)
Computational Modeling of IntelligenceSummarized by Joon Shik Kim
Blood Oxygen Level Dependent (BOLD) Signal
• Amount of oxygen molecules bound to hemoglobin.
• If a specific task is performed, re-lated brain regions are activated and the need for more oxygen leads to BOLD signal increase.
Task• In a control task, subjects viewed a
series of 14 letters with an interstim-ulus 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.
Generation of fMRI time se-ries
Brain Activation Maps
Structural Equation Modeling (SEM) (Bullmore et al., 2000)
1( )I K
1( ) ( ) ( )T TI K I K
where q denotes the number of path coefficients to be estimated and C denotes the sample covariance.
Model by Automated Search
Path Coefficient
Significant Path CoefficientRight Left
Discussion (1/3)• Manipulation of cognitive demand in
a verbal working memory task is as-sociated with concomitant changes in corticocortical connections.
• Under both 1-back and 2-back condi-tions, there was a significant connec-tions from the left inferior frontal gyrus to the left posterior parietal cortex.
Discussion (2/3)• The projection from the left inferior frontal
gyrus to the left posterior parietal cortex may be important in mediating articula-tory rehearsal.
• Increasing n from 1 to 2 increases the load on articulatory rehearsal. This ma-nipulation was associated with the emer-gence of a second significant connection between the inferior frontal gyrus and posterior parietal cortex via SMA.
Discussion (3/3)• Our model did not provide a good fit to
the 3-back data.• The change in functional integration in-
duced by an increase in load from 2- to 3-back may require qualitative reconstruc-tion of the path diagram.
• Enhanced prefrontoprefrontal connectivity under the 2-back condition may reflect greater demand for executive process.