The stability of the blood oxygenation level-dependent functional MRI response to motor tasks is altered in patients with chronic ischemic stroke.
OBJECTIVE
Functional MRI is a powerful tool to investigate recovery of brain function in patients with stroke. An inherent assumption in functional MRI data analysis is that the blood oxygenation level-dependent (BOLD) signal is stable over the course of the examination. In this study, we evaluated the validity of such assumption in patients with chronic stroke.


METHODS
Fifteen patients performed a simple motor task with repeated epochs using the paretic and the unaffected hand in separate runs. The corresponding BOLD signal time courses were extracted from the primary and supplementary motor areas of both hemispheres. Statistical maps were obtained by the conventional General Linear Model and by a parametric General Linear Model.


RESULTS
Stable BOLD amplitude was observed when the task was executed with the unaffected hand. Conversely, the BOLD signal amplitude in both primary and supplementary motor areas was progressively attenuated in every patient when the task was executed with the paretic hand. The conventional General Linear Model analysis failed to detect brain activation during movement of the paretic hand. However, the proposed parametric General Linear Model corrected the misdetection problem and showed robust activation in both primary and supplementary motor areas.


CONCLUSIONS
The use of data analysis tools that are built on the premise of a stable BOLD signal may lead to misdetection of functional regions and underestimation of brain activity in patients with stroke. The present data urge the use of caution when relying on the BOLD response as a marker of brain reorganization in patients with stroke.
Mazzetto-Betti
Kelley C
KC
Department of Neuroscience and Behavoral Sciences, FMRP, University of Sao Paulo, Ribeirao Preto, Brazil.
Leoni
Renata F
RF
Pontes-Neto
Octavio M
OM
Santos
Antonio C
AC
Leite
Joao P
JP
Silva
Afonso C
AC
de Araujo
Draulio B
DB
D000328:Adult; D000368:Aged; D001921:Brain / Q000503:physiopathology*; D002545:Brain Ischemia / Q000150:complications / Q000503:physiopathology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D010291:Paresis / Q000209:etiology / Q000503:physiopathology*; D020127:Recovery of Function / Q000502:physiology; D020521:Stroke / Q000150:complications / Q000503:physiopathology*