- Email: [email protected]
Hyperventilation strongly reduces bold contrast in motor, visual and auditory cortices
NeuroImage
13, Number
6, 2001, Part 2 of 2 Parts 1 D E a
[@
METHODS
Hyperventilation Navid Seraji-Bozorgzad”,
- ANALYSIS
Strongly Reduces BOLD Contrast in Motor, Visual and Auditory Cortices
Gregory Moore *, Manuel Tamer*,
Stephen Dager?, Stefan Posse*
*Dept. Psychiatry and Behavioral Neuroscience, Wayne State University, University Health Center, Detroit, MI USA *University of Washington School of Medicine, Seattle, Washington Introduction. Global changes in cerebral blood flow (CBF) due modulation in respiration can substantially change BOLD contrast. Previous studies have shown that controlled hyperventilation reduces gCBF and strongly decreases fMR1 contrast in a visual task [l]. Possible motion artifacts and shifts in attention during hyperventilation, however, may have amplified the loss of signal response. Tbis study extends our investigation to the motor system, the performance of which can be controlled, and to the auditory system, which is known to be particularly sensitive to attention shifts[2]. Reduction of motion artifacts was achieved through synchronization of breathing with data acquisition. Methods. Six healthy subjects were investigated using a clinical 1.5 T scanner. The task paradigm consisted of: 20 sec. baseline (rest), followed by 20 seconds repetitions of consecutive visual (black/white checker board alternating at a rate of 8 Hz), auditory (syllable recognition task [2]) and motor tasks (2 Hz finger tapping with controlled amplitude) in an alternating, randomized order without interleaved rest periods. (Total duration: 6min 48se.c.) Task paradigm was performed during normocapnia (end expiratory PET-CO, = 40 mmHg) and hyperventilation induced hypocapnia @ET-CO, = 20 mmHg), controlled by capnometry via nasal cannula. Whole head EPI (TR/IE: 4s/66ms, voxel size: 6x6x6.5 mm’, no. slices: 16) employed optimized gradient timing to reduce motion sensitivity. Data were analyzed using SPM99 software including: motion correction, slicetime adjustment and spatial smoothing [3]. A corrected statistical threshold of p=O.O5 was used to obtain maximum T-scores and extents of the activated regions. Results. The areas of activation associated with the motor task (contralateral primary motor area, and ipsilateral cerebellum), auditory task (Heschl’s gyms) and visual task (Calcarine fissure and adjacent visual areas) show marked decrease in extent and strength of activation (maximum T-scores) in the hypocapnic vs. the normocapnic condition consistently across the six subjects (Fig. 1 and 2). The reduction in the average area of activation was approximately 4% per mmHg (Table 1). Table
Figure 1. Normocapnia (top row) vs. Hypocapnia (bottom) for visual ctx., motor ctx., cerebel., and auditory ctx. (left to right).
Figure 2. Reduction of activation extent and strength across the subjects in four regions of the brain.
Figure 3. Trace of typical head movements, showing the minimized affect of hyperventilation on motion.
1 % Reduction
Visual CX Prim. motor Cerebellum Audit. CX.
CX
of extent
83 t 18 84t 17 742 11 87 221
% Reduction 46 52 53 59
Synchronization of breathing with data acquisition and subject training lead to nearly identical motion parameters and hypocapnia (Fig. 3). The choice of a motion insensitive EPI sequence, as well as whole brain coverage further sensitivity, and allow for post-processing motion compensation, respectively.
max. T score + t k +
25 27 20 29
during normoreduces motion
Discussion. In this study we extend previous findings by demonstrating similar sensitivity to hypocapnia in extended brain regions activated in response to well controlled sensory-motor tasks. Further studies are need to improve biophysical modeling of BOLD contrast to calibrate gCBF related changes in fMR1 contrast. This study emphasizes the importance of considering the role of breathing patterns when assessing task related changes in brain activation with fMR1. References U] Weckesser et al., Magn. Reson. Med., 41(l): 213-216, 1999. 121 L. Jancke et al., Neuropsychologia 36 (9): 875-883 1998. 131 SPM web site at : http://www.fil.ion.ucl.ac.uk/spm
S243
13, Number
6, 2001, Part 2 of 2 Parts 1 D E a
[@
METHODS
Hyperventilation Navid Seraji-Bozorgzad”,
- ANALYSIS
Strongly Reduces BOLD Contrast in Motor, Visual and Auditory Cortices
Gregory Moore *, Manuel Tamer*,
Stephen Dager?, Stefan Posse*
*Dept. Psychiatry and Behavioral Neuroscience, Wayne State University, University Health Center, Detroit, MI USA *University of Washington School of Medicine, Seattle, Washington Introduction. Global changes in cerebral blood flow (CBF) due modulation in respiration can substantially change BOLD contrast. Previous studies have shown that controlled hyperventilation reduces gCBF and strongly decreases fMR1 contrast in a visual task [l]. Possible motion artifacts and shifts in attention during hyperventilation, however, may have amplified the loss of signal response. Tbis study extends our investigation to the motor system, the performance of which can be controlled, and to the auditory system, which is known to be particularly sensitive to attention shifts[2]. Reduction of motion artifacts was achieved through synchronization of breathing with data acquisition. Methods. Six healthy subjects were investigated using a clinical 1.5 T scanner. The task paradigm consisted of: 20 sec. baseline (rest), followed by 20 seconds repetitions of consecutive visual (black/white checker board alternating at a rate of 8 Hz), auditory (syllable recognition task [2]) and motor tasks (2 Hz finger tapping with controlled amplitude) in an alternating, randomized order without interleaved rest periods. (Total duration: 6min 48se.c.) Task paradigm was performed during normocapnia (end expiratory PET-CO, = 40 mmHg) and hyperventilation induced hypocapnia @ET-CO, = 20 mmHg), controlled by capnometry via nasal cannula. Whole head EPI (TR/IE: 4s/66ms, voxel size: 6x6x6.5 mm’, no. slices: 16) employed optimized gradient timing to reduce motion sensitivity. Data were analyzed using SPM99 software including: motion correction, slicetime adjustment and spatial smoothing [3]. A corrected statistical threshold of p=O.O5 was used to obtain maximum T-scores and extents of the activated regions. Results. The areas of activation associated with the motor task (contralateral primary motor area, and ipsilateral cerebellum), auditory task (Heschl’s gyms) and visual task (Calcarine fissure and adjacent visual areas) show marked decrease in extent and strength of activation (maximum T-scores) in the hypocapnic vs. the normocapnic condition consistently across the six subjects (Fig. 1 and 2). The reduction in the average area of activation was approximately 4% per mmHg (Table 1). Table
Figure 1. Normocapnia (top row) vs. Hypocapnia (bottom) for visual ctx., motor ctx., cerebel., and auditory ctx. (left to right).
Figure 2. Reduction of activation extent and strength across the subjects in four regions of the brain.
Figure 3. Trace of typical head movements, showing the minimized affect of hyperventilation on motion.
1 % Reduction
Visual CX Prim. motor Cerebellum Audit. CX.
CX
of extent
83 t 18 84t 17 742 11 87 221
% Reduction 46 52 53 59
Synchronization of breathing with data acquisition and subject training lead to nearly identical motion parameters and hypocapnia (Fig. 3). The choice of a motion insensitive EPI sequence, as well as whole brain coverage further sensitivity, and allow for post-processing motion compensation, respectively.
max. T score + t k +
25 27 20 29
during normoreduces motion
Discussion. In this study we extend previous findings by demonstrating similar sensitivity to hypocapnia in extended brain regions activated in response to well controlled sensory-motor tasks. Further studies are need to improve biophysical modeling of BOLD contrast to calibrate gCBF related changes in fMR1 contrast. This study emphasizes the importance of considering the role of breathing patterns when assessing task related changes in brain activation with fMR1. References U] Weckesser et al., Magn. Reson. Med., 41(l): 213-216, 1999. 121 L. Jancke et al., Neuropsychologia 36 (9): 875-883 1998. 131 SPM web site at : http://www.fil.ion.ucl.ac.uk/spm
S243