Friday, May 21, 2010
Franklin Hall B Level 4 (Philadelphia Marriott Downtown)
9:00 AM
Background: Abnormalities in the structure and function of fusiform gyrus (FG) are promising biomarkers of autism spectrum disorders (ASD). There is quite a large neuroimaging literature on FG function in healthy, non-ASD participants, but nearly all samples are relatively small (< 20). Larger samples are needed to study issues such as hemispheric asymmetries and regional brain connectivity. In addition, statistical and image processing methods have greatly advanced in recent years, and past studies have often used approaches that were suboptimal. A more complete understanding of FG function and connectivity in typically developing samples is critical for the study of ASD.
Objectives: The present study tested 3 primary hypotheses. First, FG would not only show a sample-wide main effect for faces (versus a non-face condition), but would prove highly stable on a per-participant basis. Second, FG activity would be significantly right-lateralized. Third, FG would show effective connectivity with amygdala – another brain structure implicated in ASD. Exploratory analyses tested unilateral versus bilateral connectivity models between FG and amygdala.
Methods: 46 typically developing adults (22 female, Mean/SD age 23.7/3.0) completed a 5-minute fusiform “face localizer” task in which side-by-side pairs of faces and non-faces (houses) were presented. Participants were asked to indicate whether the pairs represented the same or different person or house (subordinate-level processing). Statistical analyses consisted of a) per-voxel GLMs of task effects, b) per-voxel tests of task X FG and task X amygdala effects (i.e., psychophysiological interactions), and c) dynamic causal modeling of FG-to-amygdala connectivity. In order to formally test the rightward asymmetry typically associated with FG, fMRI data were registered to a symmetrical brain template via non-linear algorithms. This symmetrical registration procedure – to our knowledge the first applied to face processing data – allowed for direct, focal (per-voxel) asymmetry tests.
Results: Support was obtained for each of the three primary hypotheses. 45 participants (98%) showed significantly increased FG activation during face perception. 43 participants (94%) also showed significantly increased amygdala activation during face perception. Group findings were remarkably robust in these and other brain areas (including the lateral occipital complex and dorsolateral prefrontal cortex), surviving Bonferroni correction. As predicted, these analyses revealed a strong rightward asymmetry within FG and adjacent temporal regions, including superior temporal sulcus (also implicated in ASD). Lastly, exploratory connectivity analyses using psychophysiological interactions and dynamic causal modeling supported a bidirectional model of FG-to-amygdala connectivity above unidirectional models (i.e., FG-to-amygdala or amygdala-to-FG).
Conclusions: Data from this study verify, and quantify, hypothesized asymmetry and connectivity models of FG function. These data underscore the relevance of FG, amygdala, and their connectivity, in the processing of facial information – a network implicated in the pathobiology of ASD. It is likely that findings on FG-amygdala connectivity differences in ASD would appear most robustly in studies using relatively brief face tasks that are widely deployed (i.e., large samples and short scan durations).
Objectives: The present study tested 3 primary hypotheses. First, FG would not only show a sample-wide main effect for faces (versus a non-face condition), but would prove highly stable on a per-participant basis. Second, FG activity would be significantly right-lateralized. Third, FG would show effective connectivity with amygdala – another brain structure implicated in ASD. Exploratory analyses tested unilateral versus bilateral connectivity models between FG and amygdala.
Methods: 46 typically developing adults (22 female, Mean/SD age 23.7/3.0) completed a 5-minute fusiform “face localizer” task in which side-by-side pairs of faces and non-faces (houses) were presented. Participants were asked to indicate whether the pairs represented the same or different person or house (subordinate-level processing). Statistical analyses consisted of a) per-voxel GLMs of task effects, b) per-voxel tests of task X FG and task X amygdala effects (i.e., psychophysiological interactions), and c) dynamic causal modeling of FG-to-amygdala connectivity. In order to formally test the rightward asymmetry typically associated with FG, fMRI data were registered to a symmetrical brain template via non-linear algorithms. This symmetrical registration procedure – to our knowledge the first applied to face processing data – allowed for direct, focal (per-voxel) asymmetry tests.
Results: Support was obtained for each of the three primary hypotheses. 45 participants (98%) showed significantly increased FG activation during face perception. 43 participants (94%) also showed significantly increased amygdala activation during face perception. Group findings were remarkably robust in these and other brain areas (including the lateral occipital complex and dorsolateral prefrontal cortex), surviving Bonferroni correction. As predicted, these analyses revealed a strong rightward asymmetry within FG and adjacent temporal regions, including superior temporal sulcus (also implicated in ASD). Lastly, exploratory connectivity analyses using psychophysiological interactions and dynamic causal modeling supported a bidirectional model of FG-to-amygdala connectivity above unidirectional models (i.e., FG-to-amygdala or amygdala-to-FG).
Conclusions: Data from this study verify, and quantify, hypothesized asymmetry and connectivity models of FG function. These data underscore the relevance of FG, amygdala, and their connectivity, in the processing of facial information – a network implicated in the pathobiology of ASD. It is likely that findings on FG-amygdala connectivity differences in ASD would appear most robustly in studies using relatively brief face tasks that are widely deployed (i.e., large samples and short scan durations).