Biomedical Engineering Reference
In-Depth Information
Chapter 12
Resting-State Functional Connectivity in Animal Models:
Modulations by Exsanguination
Bharat B. Biswal and Sridhar S. Kannurpatti
Abstract
We studied the spatiotemporal characteristics of the resting state low frequency fluctuations in functional
MRI (fMRI), blood oxygenation level dependent (BOLD) signal in isoflurane-anesthetized rats. fMRI-
BOLD measurements at 9.4 Tesla were made during normal and exsanguinated condition previously
known to alter cerebral blood flow (CBF) fluctuations in anesthetized rats. fMRI signal time series were
low-pass filtered and studied by spectral analysis. During normal conditions, baseline mean arterial pres-
sure (MAP) was 110
10 mmHg and low-frequency fluctuations in BOLD signal were observed in the
frequency range of 0. 01
±
−
0. 125 Hz. Following blood withdrawal (exsanguination), MAP decreased to
68
7 mmHg, resulting in an increase in the amplitude of the low-frequency fluctuations in BOLD
signal time series and an increase in power at several frequencies between 0.01 and 0.125 Hz. Spa-
tially, the BOLD fluctuations were confined to the cortex and thalamus spanning both hemispheres with
sparse presence in the caudate putamen and hippocampus during both normal and exsanguinated states.
Spatial distribution of the low frequency fluctuations in BOLD signal, from cross correlation analysis,
indicate substantial inter-hemispheric synchrony similar to that observed in the conscious human brain.
The behavior of the resting state BOLD signal fluctuations similar to CBF fluctuations during exsan-
guination indicates a myogenic dependence. Also, a high inter-hemispheric synchrony combined with
different phase characteristics of the low frequency BOLD fluctuations particularly in the hippocampus
relative to the cortex emphasizes distinct functional networks.
±
Key words:
fMRI, BOLD fluctuation, CBF, resting state connectivity, brain, rat, isoflurane
1. Introduction
We first demonstrated a significant temporal correlation of
resting-state low-frequency blood oxygenation level dependent
(BOLD) signal fluctuations in functional MRI (fMRI) both
