AJDRAJNR - American Journal of Neuroradiology

Published ahead of print on September 20, 2007
doi: 10.3174/ajnr.A0632
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Nonlinear Changes in Brain Activity During Continuous Word Repetition: An Event-Related Multiparametric Functional MR Imaging Study

R.E. Hagenbeeka, S.A.R.B. Romboutsb, D.J. Veltmand, J.W. Van Strienf, M.P. Witterc, P. Scheltense and F. Barkhofa

a Department of Radiology, VU University Medical Center, Amsterdam, the Netherlands
b Department of Physics and Medical Technology, VU University Medical Center, Amsterdam, the Netherlands
c Department of Anatomy and Embryology, VU University Medical Center, Amsterdam, the Netherlands
d Department of Psychiatry, VU University Medical Center, Amsterdam, the Netherlands
e Department of Neurology, VU University Medical Center, Amsterdam, the Netherlands
f Department of Psychology, Erasmus University, Rotterdam, the Netherlands


Figure 1
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  		Fig 1. Mean percentages of correct responses (bar charts) and mean RTs in milliseconds (line chart) of 15 participants to new words (identified as a new word) and repeated words (R1-R9). Error bars depict the standard error of the means.


Figure 2
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  		Fig 2. Brain areas showing positive activity for encoding (new words) versus baseline, by using fixed-effects analyses. Positive activity is found in the left inferior frontal gyrus, bilateral middle frontal gyrus, nucleus lentiformis, left motor cortex, and anterior cingulate cortex. Z-values of 3.0–4.7 correspond with changing brain activation colors from red to yellow, respectively. The right side of the brain on the image corresponds with the left hemisphere, and vice versa.


Figure 3
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  		Fig 3. Correct responses to repeated words, each occurring with the same amplitude, reveal, in a fixed-effects analysis, activation in the right inferior, middle, and superior frontal gyrus; anterior cingulate cortex; right posterior central sulcus; and left precentral sulcus. Z-values of 3.0–5.8 correspond with changing brain activation colors from red to yellow, respectively. The right side of the brain on the image corresponds with the left hemisphere, and vice versa.


Figure 4
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  		Fig 4. Brain areas showing a linear decrease in activity as a function of word recognition, by using fixed-effects analyses. Linear changes in brain activation are found in prefrontal, thalamus, anterior cingulate cortex, and parietal regions. Z-values of 3.0–5.1 correspond with changing brain activation colors from red to yellow, respectively. The right side of the brain on the image corresponds with the left hemisphere, and vice versa.


Figure 5
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  		Fig 5. A, Brain areas negatively associated with group average RT, shown in the top row, found to be the anterior cingulate cortex. Changing brain activation colors from red to yellow correspond with Z-values of 3.0–4.3, respectively. B, Both center rows reveal brain areas positively associated with group average RT. Regions involved were found to be the posterior cingulate cortex and left middle frontal gyrus. Changing brain activation colors from red to yellow correspond with Z-values of 3.0–4.3, respectively. C, The bottom row shows that the anterior cingulate cortex was also negatively associated with individual RT. Brain regions involved were calculated by using fixed-effects analysis (P < .001, uncorrected). Changing brain activation colors from red to yellow correspond with Z-values of 3.0–3.8 for the bottom row. The right side of the brain on the image corresponds with the left hemisphere, and vice versa.


Figure 6
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  		Fig 6. Plotted Z-scores for each regressor in the most significant brain areas for constant activation and activation following group RT. For the RIFG there is a significant fit to the experimental data for the model "brain activation with constant amplitude as function of word repetition." No significant fit was found for linear or nonlinear regressors. For the PCC, we found a significant fit for the model "positive nonlinear brain activation following group RT," whereas no significant fit was found for constant, linear, or nonlinear brain activation following individual RT. RIFG indicates right inferior frontal gyrus; indiv, individual.





Copyright © 2008 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X