Water-diffusion slowdown in the human visual cortex on visual stimulation precedes vascular responses.
We used magnetic resonance imaging (MRI) to investigate the temporal dynamics of changes in water diffusion and blood oxygenation level-dependent (BOLD) responses in the brain cortex of eight subjects undergoing visual stimulation, and compared them with changes of the vascular hemoglobin content (oxygenated, deoxygenated, and total hemoglobin) acquired simultaneously from intrinsic optical recordings (near infrared spectroscopy). The group average rise time for the diffusion MRI signal was statistically significantly shorter than those of the BOLD signal and total hemoglobin content optical signal, which is assumed to be the fastest observable vascular signal. In addition, the group average decay time for the diffusion MRI also was shortest. The overall time courses of the BOLD and optical signals were strongly correlated, but the covariance was weaker with the diffusion MRI response. These results suggest that the observed decrease in water diffusion reflects early events that precede the vascular responses, which could originate from changes in the extravascular tissue.
Kohno
Satoru
S
Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Sawamoto
Nobukatsu
N
Urayama
Shin-Ichi
S
Aso
Toshihiko
T
Aso
Kenji
K
Seiyama
Akitoshi
A
Fukuyama
Hidenao
H
Le Bihan
Denis
D
D004058:Diffusion; D006801:Humans; D010775:Photic Stimulation; D013997:Time Factors; D014793:Visual Cortex / Q000098:blood supply* / Q000502:physiology*; D014867:Water
D014867:Water