Aging affects test-taking, not language, study shows.
The ability to understand language could be much better preserved into old age than previously thought, according to researchers from the University of Cambridge, who found older adults struggle more with test conditions than language processing.
Scientists from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) scanned participants during testing and found that the areas of the brain responsible for language performed just as well in older adults as in younger ones.
The research, published in the Journal of Neuroscience, suggests that increased neural activation in the frontal brain regions of older adults reflects differences in the way they respond to the demands of the task compared with younger adults, rather than any difference in language processing itself.
“These findings suggest our ability to understand language is remarkably preserved well into old age, and it’s not through some trick of the mind, or reorganisation of the brain,” says co-author Professor Lorraine Tyler, who leads Cam-CAN. “Instead, it’s through the continued functioning of a well-used language processing machine common to all humans.”
Professor Tyler says cognitive neuroscientists attempting to explain how the mind and brain work typically approach the question with tasks designed to measure particular cognitive abilities, such as memory or language. However, it’s rarely as simple as that, she says, and tasks never end up measuring only one thing.
“Scientists claim that they are studying language, when really they are studying language plus your motivation to do well, plus your understanding of the instructions, plus your ability to focus, and so on,” says lead author Dr Karen Campbell, now based at Harvard University. “These poorly defined tasks become even more problematic when it comes to studying the older brain, because older adults sometimes show increased neural activation in frontal brain regions, which is thought to reflect a change in how older brains carry out a given cognitive function. However, this extra activation may simply reflect differences in how young and older adults respond to the demands of the task.”
Campbell and her Cam-CAN colleagues tried to isolate the effect of the testing by scanning 111 participants aged 22-87 using functional magnetic resonance imaging (fMRI) while they either passively listened to sentences or decided if the sentences were grammatical or not.
The researchers found that simply listening to and comprehending language, as we do in everyday life, “lights up” brain networks responsible for hearing and language, whereas performing a cognitive task with the same sentences leads to the additional activation of several task-related networks.
Age had no effect on the language network itself, but it did affect this network’s ability to “talk with” other task-related networks.
Funding: The Cambridge Centre for Ageing and Neuroscience is funded by the Biotechnology and Biological Sciences Research Council and is jointly based at the University of Cambridge and the Medical Research Council Cognition and Brain Sciences Unit.
Source: Craig Brierley – University of Cambridge
Image Source: The image is credited to Pedro Ribeiro Simões and is adapted from the University of Cambridge press release.
Original Research: Abstract for “Robust Resilience of the Frontotemporal Syntax System to Aging” by Karen L. Campbell, Dávid Samu, Simon W. Davis, Linda Geerligs, Abdur Mustafa, Lorraine K. Tyler, and for Cambridge Centre for Aging and Neuroscience in Journal of Neuroscience. Published online May 11 2016 doi:10.1523/JNEUROSCI.4561-15.2016
Abstract
Robust Resilience of the Frontotemporal Syntax System to Aging
Brain function is thought to become less specialized with age. However, this view is largely based on findings of increased activation during tasks that fail to separate task-related processes (e.g., attention, decision making) from the cognitive process under examination. Here we take a systems-level approach to separate processes specific to language comprehension from those related to general task demands and to examine age differences in functional connectivity both within and between those systems. A large population-based sample (N = 111; 22–87 years) from the Cambridge Centre for Aging and Neuroscience (Cam-CAN) was scanned using functional MRI during two versions of an experiment: a natural listening version in which participants simply listened to spoken sentences and an explicit task version in which they rated the acceptability of the same sentences. Independent components analysis across the combined data from both versions showed that although task-free language comprehension activates only the auditory and frontotemporal (FTN) syntax networks, performing a simple task with the same sentences recruits several additional networks. Remarkably, functionality of the critical FTN is maintained across age groups, showing no difference in within-network connectivity or responsivity to syntactic processing demands despite gray matter loss and reduced connectivity to task-related networks. We found no evidence for reduced specialization or compensation with age. Overt task performance was maintained across the lifespan and performance in older, but not younger, adults related to crystallized knowledge, suggesting that decreased between-network connectivity may be compensated for by older adults’ richer knowledge base.
SIGNIFICANCE STATEMENT Understanding spoken language requires the rapid integration of information at many different levels of analysis. Given the complexity and speed of this process, it is remarkably well preserved with age. Although previous work claims that this preserved functionality is due to compensatory activation of regions outside the frontotemporal language network, we use a novel systems-level approach to show that these “compensatory” activations simply reflect age differences in response to experimental task demands. Natural, task-free language comprehension solely recruits auditory and frontotemporal networks, the latter of which is similarly responsive to language-processing demands across the lifespan. These findings challenge the conventional approach to neurocognitive aging by showing that the neural underpinnings of a given cognitive function depend on how you test it.
“Robust Resilience of the Frontotemporal Syntax System to Aging” by Karen L. Campbell, Dávid Samu, Simon W. Davis, Linda Geerligs, Abdur Mustafa, Lorraine K. Tyler, and for Cambridge Centre for Aging and Neuroscience in Journal of Neuroscience. Published online May 11 2016 doi:10.1523/JNEUROSCI.4561-15.2016
