Brain Advance Access originally published online on October 18, 2008
Brain 2008 131(11):2904-2912; doi:10.1093/brain/awn232
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Idiopathic normal pressure hydrocephalus: increased supplementary motor activity accounts for improvement after CSF drainage
1Department of Clinical Neuroscience, 2Centre for Biomedical Engineering and Physics, 3Department of Radiation Sciences, 4Department of Integrative Medical Biology and 5Department of Biomedical Engineering and Informatics, Umeå University, Umeå, Sweden
Correspondence to: Niklas Lenfeldt, Department of Clinical Neuroscience, Umeå University, S-901 85 Umeå, Sweden E-mail: niklas.lenfeldt{at}neuro.umu.se
In patients with idiopathic normal pressure hydrocephalus (INPH), the changes in brain function that take place in conjunction with improved behavioural performance after CSF drainage is still unknown. In this study, we use functional MRI (fMRI) to investigate the changes in cortical activity that accompany improved motor and cognitive performance after long-term external lumbar drainage (ELD) of CSF in patients with INPH. Eighteen INPH patients were initially included together with age- and sex-matched controls. Data from 11 INPH patients were analysed both before and after ELD. The average drain volume for these 11 patients was 400 ml/3 days. Brain activation was investigated by fMRI before and after the procedure on a 1.5T Philips scanner using protocols taxing motor performance (finger tapping and reaction time) and cognitive functioning (memory and attention). Behavioural data were compared using non-parametric tests at a significance level of 0.05, whereas fMRI data were analysed by statistical parametric mapping including conjunction analysis of areas with enhanced activity after drainage in patients and areas activated in controls (P < 0.005, uncorrected). Improved regions were defined as areas in the INPH brain that increased in activity after ELD with the requirement that the same areas were activated in control subjects. Following ELD, right-hand finger tapping improved from 104 ± 38 to 117 ± 25 (mean ± SD) (P = 0.02). Left-hand finger tapping showed a tendency to improve, the number of keystrokes increasing from 91 ± 40 to 105 ± 20 (P = 0.12). Right-hand reaction time improved from 1630 ± 566 ms to 1409 ± 442 ms, whereas left-hand reaction time improved from 1760 ± 600 ms to 1467 ± 420 ms (both P-values = 0.01). Significant improvements in motor performance were accompanied by bilateral increased activation in the supplementary motor area. No improvement was found in cognitive functioning. The results suggest that motor function recovery in INPH patients after CSF removal is related to enhanced activity in medial parts of frontal motor areas considered crucial for motor planning; a finding consistent with INPH being a syndrome related to a reversible suppression of frontal periventricular cortico-basal ganglia-thalamo-cortical pathways.
Key Words: SMA; lumbar drainage; fMRI; brain activity; motor areas
Abbreviations: ELD, external lumbar drainage; fMRI, functional MRI; GLM, general linear model; INPH, idiopathic normal pressure hydrocephalus; SMA, supplementary motor area
Received January 9, 2008. Revised July 28, 2008. Accepted August 29, 2008.
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