“differential development of the ventral visual cortex extends through adolescence”

Golijeh Golarai et al. have a new paper in FRONTIERS IN HUMAN NEUROSCIENCE: Differential development of the ventral visual cortex extends through adolescence. The upshot: “We found that the volume of face-selective activations in the right fusiform gyrus was substantially larger in adults than in adolescents, and was positively correlated with age.” They found a similar trend in the left FFA (that’s “fusiform face area,” the region in the fusiform gyrus of the temporal lobe that responds more to faces than other things). And the size of the FFA is also correlated with interesting things like face recognition performance, as well as other quantitative measures like response amplitudes and face selectivity — so it’s at least plausible that adults are better at face recognition (and other studies establish that they are) because of development in this putative module for face recognition, rather than because of overall improvement in higher cognitive functions. (This could have been disconfirmed by a finding of no correlation, which is why “plausible” is interesting — but it’s also, as always, plausible that the expanded FFA and the improved face recognition performance in adults are both due to some third development-related variable.)

It’s a nice paper, but the things sticking in my mind are three small observations they don’t emphasize (none of which detracts from the main point of the paper):

  1. Previous studies suggest, and Golarai et al. confirm, that the size of the ventral temporal cortex is stable from adolescence into adulthood — this area of the brain is not bigger in adults. But the right FFA is still bigger. Now, the FFA isn’t an anatomically defined region, it’s just the set of voxels that respond more to faces than other things, so this isn’t paradoxical, nor does it suggest that some other part of the brain is shrinking in compensation — but it does underscore that important large-scale changes in neural connectivity and neural response properties can happen without any obvious changes in the amount of grey matter. Neural network modeling supports this intuition — by convention, you don’t add units, but as representations develop, an individual unit’s response profile tends to sharpen up. So if you’re thresholding for really strong responders and measuring FFA size via “number of strong responders,” your FFA will be “bigger” in a model that’s been trained for longer (up to some asymptote, of course).
  2. Women have smaller brains than men, but bigger right FFAs. So a substantially larger fraction of a woman’s brain (versus a man’s) responds strongly to faces. It’s tempting to read much into this, so let’s also note that right object-selective cortex (but not place-selective cortex) was also bigger in women. Which suggests that women might have more sharply differentiated neural representations of lots of objects, at least on the right side of the brain. This isn’t what you’d expect based on CW — CW says that men are more liable to make sharp distinctions, and women are more liable to see the world in shades of grey. It also isn’t strong evidence for reversal of CW. It’s just interesting — it’s a small prod to do what we’re all supposed to do when interpreting these studies, which is to think hard about what the neural measures might mean for cognition and behavior, and how they might come to mean it (i.e. how those neural measures reflect the neural structures and processes that underlie cognition and behavior).
  3. Adolescents also trend toward having larger object-selective regions than adults, although the variability is pretty large and the differences aren’t statistically significant. Not sure what to make of that — given the observations in women vs. men, there doesn’t seem to be a trade-off at work. Intuitively, it does seem to ratify certain easy stereotypes about adolescents — they’re more materialistic, less empathic — but obviously that’s a leap too far.

Anyway. Science is fun. As you were.

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