In this study, we sought to clarify prior, sometimes conflicting, findings regarding the presence or absence of an FFA and a PPA in school-aged children. Additionally, we sought to provide a first investigation of the EBA in children. To do this, we conducted an fMRI study to examine the developmental trajectories of these three social and nonsocial category-selective extrastriate visual regions in terms of their localization and specificity of responses in 7- to 11-year-old children. We also studied a sample of adults in order to provide an anchoring assessment of the mature state of these category-selective regions.
We identified a face-selective region of the right fusiform gyrus in 7- to 11-year-old children and adults. The right FFA was localized similarly in adults and children and the selectivity of this region did not vary as a function of age. These findings contrast with two prior fMRI studies that failed to identify the FFA in a group of children within this age range (Aylward et al., 2005
; Scherf et al., 2007
), but are consistent with three other studies that have demonstrated the existence of an FFA in school-age children (e.g., Passarotti et al., 2003
; Gathers et al., 2004
; Golarai et al., 2007
). A prior report described a potential shift in the localization of the FFA in children versus adolescents and adults. Scherf et al. (2007
) reported that children exhibited a more posterior and lateral face-sensitive region of the right fusiform gyrus; however, with a more generous contrast, they instead reported two different regions that were more dorsal and medial to the adult FFA. In contrast, we found that the FFA in children was slightly more anterior and medial to the adult FFA. It is difficult to evaluate the importance of the reported shifts in localization. In both fMRI studies, normalization of the fMRI data was used to allow direct comparisons of participants of various ages. However, different normalization algorithms were employed between the two studies. Within either study, the differences in localization could be attributable to the normalization process. Further research is necessary to determine whether these reported shifts are indeed meaningful.
It does appear potentially important that the child FFA was only found in the right hemisphere, whereas the adult participants displayed an FFA in both hemispheres. Similar right-lateralization of the FFA in children followed by bilateral adult activity has been reported by other researchers (Gathers et al., 2004
; Aylward et al., 2005
). Future research should address the behavioral consequences of the emergence of a left FFA during childhood. Behavioral studies have reported a variety of developmental changes in different aspects of face processing across the 7- to 11-year period, including a shift from more feature-based to configuration-based strategies (e.g., Carey and Diamond, 1977
; Diamond and Carey, 1977
; Carey, 1992
), improvements in emotion discrimination (Camras and Allison, 1985
; Gnepp, 1989
; Felleman et al., 1993
), the emergence of an inversion effect (e.g., Carey and Diamond, 1977
; Carey, 1992
), and improvements in recognition abilities (Baenninger, 1994
; Chung and Thomson, 1995
; Brace et al., 2001
; Taylor et al., 2004
; for review, see Passarotti et al., 2007
). It could be that the neurofunctional change observed here would be related to these behavioral changes.
Notably, we did not observe any change in the response properties (defined here as the specificity of the response for the preferred stimulus class compared to another category of stimuli) of the right FFA across this age range. This finding supports the conclusion that the right FFA is already “adult-like” by age 7
years in terms of differentiating faces and objects. This finding is consistent with the results of comparisons of functional characteristics of the FFA in 9- to 11-year-old children reported by Gathers et al. (2004
). However, this finding differs from the findings of Aylward et al. (2005
) that suggested that children lack a face-selective region in the fusiform gyrus.
This study is the first to localize the EBA in children. This region was identified bilaterally with very similar coordinates in children and adults. In both groups, the coordinates were similar to those reported in prior studies of adults (Downing et al., 2001
; Astafiev et al., 2004
; Taylor et al., 2007
). The selectivity for images of bodies did not differ between children and adults, and there was no correlation between age and specificity in the children. These findings demonstrate, for the first time, the presence of the EBA in children. Furthermore, they illustrate that the EBA is already adult-like in terms of localization and specificity by 7
years of age.
The PPA was localized in both children and adults in the bilateral parahippocampal gyri, consistent with previous reports (Passarotti et al., 2003
; Golarai et al., 2007
; Scherf et al., 2007
). Moreover, the coordinates for the regions identified in the two groups were similar to each other and to previous reports (e.g., Epstein and Kanwisher, 1998
). Notably, we found that adults and children showed more place-sensitive voxels in the right hemisphere than in the left hemisphere, in accord with previous adult findings (Epstein and Kanwisher, 1998
; Passarotti et al., 2003
). This similarity contrasts with the findings reported by Scherf et al. (2007
) that suggested that young children showed bilateral activity, older children illustrated right-lateralized activity, and adults demonstrated more evenly bilateral activation patterns again, although they noted that there was a significantly larger proportion of active voxels in the right than the left hemisphere in all age groups. As with the EBA, no age differences were found in selectivity of this area, in contrast with other findings (Golarai et al., 2007
) that suggested that children had lower place selectivity than adults in the left hemisphere.
While we believe that this study provides a number of important findings to the growing literature on the development of category-selective regions in the human brain, the study suffers from a number of limitations that should be addressed in future work. For example, scanning younger children would likely be more informative with regard to informing competing theories of neurofunctional brain development. Moreover, our design was cross-sectional. A longitudinal design would have allowed us to examine the shape of developmental trajectories of brain functioning in the different, category-selective regions, and this would have provided more detail on the nature of differences in development pathways among these brain regions than did comparisons of different children at various ages and comparisons between children and adults. Lastly, future work should include more categories of images. In particular, the addition of classes of stimuli such as letters and numbers potentially could result in longer and/or later developmental trajectories owing to later learning and familiarity with such stimuli during childhood.
Along with these potentially later-developing categories, it would be interesting to explore in greater detail some visual categories that draw upon multiple brain regions for their processing. For example, examinations of complex facial stimuli, possibly displaying emotions, motion, or different forms of eye contact, could draw upon the FFA, the posterior superior temporal sulcus region (STS), and the amygdala. Currently, it is known that the STS has relatively mature functioning for some tasks during middle childhood, such as assessing the intentionality of eye movements (Mosconi et al., 2005
), but it is still developing for other processes, including the perception of biological motion (Carter and Pelphrey, 2006
). This could signify that different networks of regions that include the posterior STS are developing at different rates owing to different interactions, resulting in varying degrees of tuning for stimuli.
Our findings raise important questions about differences in the developmental trajectories of the PPA, EBA, and FFA. In particular, we and others have found that the PPA is the most adult-like at a young age out of the three regions examined. Why should this be so? We hypothesize that this difference in developmental trajectories can be explained by the possibility of fewer regions involved in place processing more generally, resulting in fewer interactions that need to develop and relatively complete development early in ontogeny, along with less potential for complexity inherent in these stimuli relative to faces and bodies. Faces and bodies are social entities that not only can be viewed from many different angles, but can convey identity through simple features, motion patterns, and feature configurations. They can also illustrate various emotions and other conditions without changing their identities. Moreover, all of these factors can and do change rapidly, and small nuances are important in social interactions. Also, whereas a viewer can change his or her location relative to a place and therefore change his or her viewpoint, it is highly unlikely that the location will change relative to him while he stays completely still. Individuals do not move quickly relative to places that they are viewing, resulting in lesser demands on processing speed as compared to watching other individuals who move unexpectedly and with great speed. Viewers are not in control of their perspectives on the faces and bodies of others, as other people are separate agents. All of these factors might increase the perceptual complexity of social stimuli like faces and bodies and the amount of attention that needs to be allocated to these categories of stimuli for proper processing.
Finally, our findings might offer important implications for understanding the etiology of social deficits in autism spectrum disorders. Previous reports have identified abnormalities in the localization and specificity of the FFA in adults with autism spectrum disorders (e.g., Pierce et al., 2001
; Hubl et al., 2003
; Schultz et al., 2003
; Ashwin et al., 2007
; Pelphrey et al., 2007
). Understanding the normative developmental pathway and mechanisms by which this region typically develops could provide invaluable data for understanding the causes of FFA dysfunction in individuals with autism spectrum disorders. This information could also inform our understanding of treatments for social perception deficits in autism with the goal of normalizing developmental pathways or supporting alternative, compensatory mechanisms.
In conclusion, we have identified face-, body-, and place-sensitive areas of the cortex in school-aged children that are somewhat, but not completely, similar to those of adults. Importantly, it further elucidates the developmental trajectories for these category-specific regions. This work also has import for research on autism spectrum disorders. Future work should study these regions longitudinally, along with other category-selective regions identified in adults.