1999; Parsons et al., 2006; Kwapis et al., 2011). In addition, AG-221 supplier amygdala activity in fMRI experiments has been shown to correlate with RG7800MedChemExpress RG7800 conditioned fear responses (Cheng et al., 2003; Knight et al., 2005; Cheng et al., 2006b; Cheng et al., 2007). Work from studies employing emotional visual stimuli has shown that emotional responses evoked by such images are dependent upon the normal functioning of the amygdala (Bechara et al., 1995; Glascher and ?Adolphs, 2003), and correlated with amygdala activation (Williams et al., 2001). Our results suggest indeed that response expression is one function of the amygdala. Further, our results suggest that the activity needed to produce a conditioned response occurs within the centromedial subregion of the amygdala, which is anatomically connected with the diencephalon. Although we do not have the anatomical specificity to equate the centromedial subregion defined here with the location of the central nucleus, the central nucleus likely makes up at least a portion of the centromedial region in the majority of the subjects (Sah et al., 2003; Amunts et al., 2005).Fig. 5. Theoretical model depicting information flow through the amygdala. According to our model visual input enters the amygdala through the laterobasal subregion, which processes visual features. Salient visual features are then evaluated in intrinsic processing nodes in the interspersed tissue. Finally, behavioral output is generated by the centromedial region if and only if the salient visual features predict a motivationally significant event in the environment.LimitationsAlthough the current results suggest that there are distinct subregions of the amygdala that mediate different aspects of amygdala function, these results should be considered within the context of the limitations of the study. First, by increasing the resolution of our functional images, we necessarily decreased the signal to noise ratio. Future studies at high-field should be conducted to expand upon these findings. In this study, we created single-subject masks based on the anatomical connectivity of the amygdala. One of the limitations of this approach is that these masks do not encompass the entire amygdala, and the remainder of the tissue is distributed heterogeneously across subjects, making it difficult to summarize at the group level. Although it is unclear whether this absence of connectivity reflects a limitation of our imaging procedure or a feature of the underlying anatomy, our results suggest that the amygdalar tissue not accounted for by our connectivity masks and the amgydalar tissue in our masks are playing fundamentally different roles in the psychological processes commonly identified as `amygdala-dependent’. Another limitation is that we did not use a strictly seed-based approach to identify white matter tracts. Instead, we pre-computed the white matter pathways and interactively identified those that passed through the amygdala, making it difficult to identify the origin of the fibers. However, it should be noted that the white matter pathways were similar across subjects, and our results are consistent with the known anatomical connectivity of the amygdala (Aggleton et al., 1980; Sah et al., 2003). One final limitation of this study is that we do not address the intra-amygdala connectivity of the subregions. Although intra-amygdala connectivity is an interesting question, identifying short-range connections within the grey matter of the amygdala is.1999; Parsons et al., 2006; Kwapis et al., 2011). In addition, amygdala activity in fMRI experiments has been shown to correlate with conditioned fear responses (Cheng et al., 2003; Knight et al., 2005; Cheng et al., 2006b; Cheng et al., 2007). Work from studies employing emotional visual stimuli has shown that emotional responses evoked by such images are dependent upon the normal functioning of the amygdala (Bechara et al., 1995; Glascher and ?Adolphs, 2003), and correlated with amygdala activation (Williams et al., 2001). Our results suggest indeed that response expression is one function of the amygdala. Further, our results suggest that the activity needed to produce a conditioned response occurs within the centromedial subregion of the amygdala, which is anatomically connected with the diencephalon. Although we do not have the anatomical specificity to equate the centromedial subregion defined here with the location of the central nucleus, the central nucleus likely makes up at least a portion of the centromedial region in the majority of the subjects (Sah et al., 2003; Amunts et al., 2005).Fig. 5. Theoretical model depicting information flow through the amygdala. According to our model visual input enters the amygdala through the laterobasal subregion, which processes visual features. Salient visual features are then evaluated in intrinsic processing nodes in the interspersed tissue. Finally, behavioral output is generated by the centromedial region if and only if the salient visual features predict a motivationally significant event in the environment.LimitationsAlthough the current results suggest that there are distinct subregions of the amygdala that mediate different aspects of amygdala function, these results should be considered within the context of the limitations of the study. First, by increasing the resolution of our functional images, we necessarily decreased the signal to noise ratio. Future studies at high-field should be conducted to expand upon these findings. In this study, we created single-subject masks based on the anatomical connectivity of the amygdala. One of the limitations of this approach is that these masks do not encompass the entire amygdala, and the remainder of the tissue is distributed heterogeneously across subjects, making it difficult to summarize at the group level. Although it is unclear whether this absence of connectivity reflects a limitation of our imaging procedure or a feature of the underlying anatomy, our results suggest that the amygdalar tissue not accounted for by our connectivity masks and the amgydalar tissue in our masks are playing fundamentally different roles in the psychological processes commonly identified as `amygdala-dependent’. Another limitation is that we did not use a strictly seed-based approach to identify white matter tracts. Instead, we pre-computed the white matter pathways and interactively identified those that passed through the amygdala, making it difficult to identify the origin of the fibers. However, it should be noted that the white matter pathways were similar across subjects, and our results are consistent with the known anatomical connectivity of the amygdala (Aggleton et al., 1980; Sah et al., 2003). One final limitation of this study is that we do not address the intra-amygdala connectivity of the subregions. Although intra-amygdala connectivity is an interesting question, identifying short-range connections within the grey matter of the amygdala is.
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