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Abstract #1133

Saturation of Visually Evoked BOLD Response During Carbogen Inhalation

Claudine J. Gauthier1,2, Ccile Madjar2, Richard D. Hoge1,2

1Physiology/Biomedical Engineering, Universit de Montral, Montral, Quebec, Canada; 2CRIUGM, Montreal, Quebec, Canada

Oxidative metabolism can be estimated from the BOLD signal following a calibration manipulation to determine a factor M. M is the maximum possible BOLD signal change. Carbogen inhalation was used here with intense visual stimulation to test whether an asymptote in BOLD signal could be reached. Results show a convergence of percent BOLD changes around 9% in visual cortex for 10% carbogen alone, and 5-10% carbogen breathing plus visual stimulation. The diminishing incremental response from visual stimulation at high carbogen concentrations suggests that these manipulations approach BOLD levels close to the saturation plateau.