Impact of signal-to-noise on functional MRI of the human amygdala

The impact of signal-to-noise (SNR) on fMRI of the amygdala was investigate d during a picture encoding task. The SNR value required to observe reliabl e activation was determined by computer simulations. Blood oxygen level-dep endent (BOLD) sensitivity maps were generated to indicate brain regions wit h sufficient SNR to test the statistical hypotheses. The results showed tha t the medial aspect of the amygdala had insufficient SNR to detect a 1% pea k BOLD signal change for a t-test comparison in a majority of subjects. Non e of these subjects showed activation in regions with unacceptable SNR valu es, indicating a low false positive rate. Furthermore, hemispheric asymmetr ies in the BOLD sensitivity maps mirrored asymmetries in the activation pat terns. Impoverished SNR was also found in the basal forebrain and orbitofro ntal cortex. These findings emphasize the importance of considering SNR whe n interpreting fMRI results in the limbic forebrain. (C) 2001 Lippincott Wi lliams & Wilkins.