Summary: Scene-selective cortical regions show greater age-related sensitivity than face-selective regions in both perception and memory.
Source: UT Dallas
Healthy brains generally become less efficient with age, but this decline is neither uniform across tasks nor across brain regions. Mapping these differences helps clarify how the brain supports perception and memory throughout life.
Researchers at The University of Texas at Dallas examined how specific visual-processing regions of the cortex respond differently across the lifespan. Their new study focuses on neural dedifferentiation: the reduction in functional selectivity of cortical areas that are normally specialized for particular kinds of visual input.
A team from the Center for Vital Longevity (CVL) used functional MRI (fMRI) to measure how selectively different parts of the visual cortex responded to faces and scenes, and how that selectivity related to subsequent memory for those visual contexts.
“Not all brain regions age in the same way,” said CVL director Dr. Michael Rugg, professor in the School of Behavioral and Brain Sciences and the study’s corresponding author. “Our data indicate that regions specialized for processing visual scenes are particularly vulnerable to age-related reductions in selectivity.”
Prior work has established that the cerebral cortex contains category-selective regions—areas that are tuned to particular classes of visual input such as faces, objects, or scenes. This division of labor, known as differentiation, supports efficient perception and memory.
As people grow older, differentiation can decline. Dedifferentiation refers to a pattern in which cortical responses become less distinct across stimulus categories, so that formerly specialized regions respond more broadly.
“On average, older adults show less distinct neural activity when processing different visual categories,” Rugg explained. “Using fMRI, we can quantify how selective a region is for its preferred stimulus type, and we find substantial individual differences in that selectivity.”
The study tested 48 healthy adults: 24 young adults (ages 18–28) and 24 older adults (ages 65–75). Participants studied words presented with images that were either faces or scenes while undergoing fMRI. During encoding, participants were instructed to imagine the object named by each word and how that object would interact with the accompanying face or scene image.
After the study phase, participants rated how vividly they could imagine the word paired with the face or scene. Later memory testing probed whether they could recall the category (face or scene) that had been paired with each word.
Analyses focused on two scene-selective regions—the parahippocampal place area (PPA) and retrosplenial cortex (RSC)—and two face-selective regions—the fusiform face area (FFA) and occipital face area (OFA). The team measured neural selectivity using both a univariate differentiation index and multivoxel pattern similarity, two complementary fMRI analysis techniques.
Both analytic approaches converged on the same result: scene-selective cortical regions exhibited clear age-related reductions in neural differentiation, whereas face-selective regions did not. In other words, the PPA and RSC became less selective for scenes in older adults, but the FFA and OFA retained their selectivity for faces.
Lead author Sabina Srokova, a cognition and neuroscience doctoral student at UT Dallas, emphasized the functional significance of this finding. “Scene-selective areas support spatial processing—situating objects within an environment and navigating surroundings. If older adults encode scene information less efficiently, that could explain dedifferentiation in these regions,” she said.
The reasons for the differential vulnerability of scene versus face regions are not yet settled. The authors propose that accumulated life experience may play a role: by later life, people have extensive familiarity with scenes and well-formed expectations about them, which could reduce neural novelty and apparent selectivity. Faces, by contrast, are stimuli for which humans develop expertise early in life, possibly stabilizing face-selective responses.
Importantly, the researchers found that stronger neural differentiation in scene-sensitive areas predicted better memory performance across both age groups. “Whether you are 25 or 75, greater scene selectivity in these regions correlated with better subsequent memory for the associated image category,” Rugg said. This age-invariant relationship suggests that differentiation in scene areas supports memory performance independent of chronological age.
Other contributors to the study included Dr. Paul Hill (postdoctoral research associate), Dr. Danielle R. King (former research associate), and Dr. Joshua Koen (University of Notre Dame), who previously trained in Rugg’s lab.
Funding: This research was supported by the National Science Foundation (grant 1633873) and the National Institutes of Health via the National Institute on Aging (grant 2RF1AG039103-06A1).
Abstract
Neural Differentiation is Moderated by Age in Scene-Selective, But Not Face-Selective, Cortical Regions
The aging brain often shows neural dedifferentiation, a decline in the functional specificity of category-selective cortex. Although dedifferentiation has been proposed to contribute to cognitive aging, recent work indicates it is not uniform across stimulus categories, and the link between neural differentiation and cognition may be independent of age. In this experiment, younger and older adults viewed words paired with scene or face images while undergoing fMRI and later completed a memory test. Neural selectivity was measured in two scene-selective regions (parahippocampal place area and retrosplenial cortex) and two face-selective regions (fusiform face area and occipital face area) using both a univariate differentiation index and multivoxel pattern similarity analysis. Both methods yielded consistent results: age-related reductions in selectivity emerged in scene-selective but not face-selective regions. Additionally, differentiation in the parahippocampal place area positively predicted subsequent source memory for image category, and this relationship did not vary with age. These findings indicate that age-related neural dedifferentiation is selective rather than universal, and that scene-specific neural responses are predictive of memory performance regardless of age.
Original Research: Open access — “Neural Differentiation is Moderated by Age in Scene-Selective, But Not Face-Selective, Cortical Regions” by Sabina Srokova, Paul F. Hill, Joshua D. Koen, Danielle R. King, and Michael D. Rugg. eNeuro. DOI: 10.1523/ENEURO.0142-20.2020