Spatio-temporal Analysis of Auditory Cortex
Activation as Detected with Silent Event-Related fMRI
October 14, 2005, 3:00 pm in 131 DLSB
ABSTRACT
Functional magnetic resonance imaging (fMRI) allows neuroscientists to assess brain function by evaluating hemodynamic activity (blood flow) when a stimulus is present or absent. In clinical practice, the hearing levels of individuals are determined using an audiometer that allows presentation of a pure-tone of specific intensity and frequency. Functional images of the auditory nervous system have been obtained using stimuli such as pure-tone, speech, noise, etc. However, the observed activation evoked by the stimulus is confounded with the neuronal response evoked by scanner noise generated during imaging. Silent event related fMRI is a recently reported fMRI technique diminishing the confounding effects of background scanner noise. A drawback of sfMRI is that it requires long acquisition times (30 to 40 min) to achieve statistically significant activation. An additional complication associated with all fMRI data is that measurements obtained at consecutive times tend to exhibit substantial temporal correlation. Temporal dependence within each voxel’s measurements is modeled, and a regional measurement-error-free kriging predictor is used to combine information from neighboring voxels when assessing voxel activation. Instead of simply applying a post hoc smoothing to the voxelwise test statistics (e.g., t statistics), we attempt to make optimal use of information in the locality of each voxel when estimating the voxel’s mean, variance, and temporal dependence parameters. The primary advantage to this spatial modeling approach is that the degree to which voxel parameters are smoothed is driven by the data. The resulting voxel activation maps exhibit substantially more spatial continuity than other currently-used approaches, while exhibiting desirable inferential properties including a lower false-positive rate and high power for detection of activated regions.