Using functional magnetic resonance imaging, we estimated neural activity in twins to study genetic influences on the cortical response to categories of visual stimuli (faces, places, and pseudowords) that are known to elicit distinct patterns of activity in ventral visual cortex. The neural activity patterns in monozygotic twins were significantly more similar than in dizygotic twins for the face and place stimuli, but there was no effect of zygosity for pseudowords (or chairs, a control category). These results demonstrate that genetics play a significant role in determining the cortical response to faces and places, but play a significantly smaller role (if any) in the response to orthographic stimuli.
Figure legend: Patterns of estimated neural activity when viewing the four stimulus categories (axial slice). Functional activation maps were computed for the four contrasts of interest (faces, houses, pseudowords, and chairs relative to the phase-scrambled control condition), and the similarity measures (r) between these functional maps were computed for each twin pair. (Click on figure to enlarge)
The results of this study demonstrate that genetics play a significant role in determining the cortical response to faces and places. Of course, these findings do not imply that experience plays no role in determining the observed activity. To take just one example, genes that affect social behavior could potentially lead some people to look at faces and places more than other people, and the resulting difference in experience could lead to changes in the neural circuitry (we thank one of the anonymous reviewers for this example). The results simply demonstrate that genetics do play a crucial role. The results also show that genetics play a significantly smaller role in determining the cortical response to visually presented orthographic stimuli. Overall, the findings are consistent with the view that the cortical substrates of face recognition and place recognition are partially innately specified, but that the cortical response to orthographic stimuli is more dependent on experience. Face and place recognition are older than reading on an evolutionary scale, they are shared with other species, and they provide a clearer adaptive advantage. It is therefore plausible that evolution would shape the cortical response to faces and places, but not orthographic stimuli.
Wednesday, January 02, 2008
Nature versus Nurture in Ventral Visual Cortex
Polk et al. do functional magnetic resonance imaging of monozygotic and dizygotic twins to show that genetics play a significant role in determining the cortical response to faces and places, more so than to orthographic stimuli (chairs or pseudowords). Here is their abstract, a paragraph from their concluding section and one figure from the paper.