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Correlation Between the Amplitude of Cortical Activation and Reaction Time: A Functional MRI Study

¹ The Russell H. Morgan Department of Radiology and Radiological Sciences, Division of Neuroradiology, Johns Hopkins Hospital, 600 N Wolfe St., Phipps B-112, Baltimore, MD 21287.
² Olin Neuropsychiatry Research Center, Institute of Living, 200 Retreat Ave., Hartford, CT 06106.
³ Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510.
⁴ The Russell H. Morgan Department of Radiology and Radiological Sciences, Division of Psychiatric Neuroimaging, Johns Hopkins Hospital, Baltimore, MD 21287.

Abstract

OBJECTIVE. We sought to examine the correlation between reaction time and the amplitude of cortical activation during the performance of a visuomotor response-time task in a functional MRI (fMRI) experiment. We hypothesized that the fMRI blood oxygenation level-dependent (BOLD) amplitude may have a negative correlation with a subject's reaction time: the lower the amplitude within the cortical areas along the visuomotor pathway, the slower the response. A larger amplitude of the fMRI signal would reflect faster response times.

SUBJECTS AND METHODS. During a single-event fMRI experiment, the reaction times (in milliseconds) of 32 right-handed subjects responding to a visual cue were recorded. Analysis of the single-event paradigm using Statistical Parametric Mapping (SPM99) was performed, activation maps were produced for each subject, and then a random effects group analysis was performed. The maximum amplitudes of cortical activation (percent signal change) in four activated cortical regions were estimated and tabulated. The regions of interest included were the right and left occipital visual cortices, the supplementary motor area, and the left sensorimotor area. Simple and multiple regressions were performed between the mean reaction times of the subjects and the BOLD amplitudes in each region of interest and for the composite region of interest.

RESULTS. The results showed significant negative associations between the reaction times and maximum amplitudes in the right occipital, left occipital, and left sensorimotor area cortical regions (p < 0.05). However, no significant association was found between reaction times and the amplitude within the supplementary motor area. When the effects of age and sex on these associations were analyzed, we found that age had an impact on the results for individual regions of interest in the left occipital and left sensorimotor areas, but the composite amplitude of activation remained significantly correlated with reaction times.

CONCLUSION. The degree of signal change in BOLD fMRI response of the right occipital, left occipital, and left sensorimotor areas reflects the speed of performance during the visuomotor response time task by the subject. Thus, the amplitude of activation can be used as one parameter to assess change in function.

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