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Research at the CSLB

The ageing brain and cognition

Introduction

Cognitive ageing is a developmental process involving the interaction of lifelong cognitive experience and gradual neural change, resulting in a varied landscape of age-related cognitive declines and age-related adaptations that help preserve cognitive function. Research on cognitive ageing at the CSLB focuses on language comprehension and production and addresses the complex interaction of factors affecting performance. This involves examining how neural structure relates to neural function, how age affects the way networks of regions interact with each other, and how age differentially affects the components of a complex task. Our research uses neuroimaging data to highlight the dynamic nature of cognitive ageing, and counters the perception of cognitive ageing as a monolithic process of universal decline.

Age related structural decline. Yellow and white areas of the brain show a more rapid decline in grey matter with age compared to red regions. From Shafto, M. A. et al. (2007). Journal of Cognitive Neuroscience, 19, 2060-2070.

Ageing and neural connectivity

This research focuses on the effects of healthy ageing on structural and dynamic brain connectivity, and in turn how this impacts on cognitive functions such as language and vision. This involves a combination of noninvasive imaging and electrophysiological methods (particularly diffusion MRI and magnetoencephalography), as well as drawing on tools from computational and systems neuroscience.

Language production across the lifespan

Specific aspects of language production are affected by normal ageing, including word finding and syntactic aspects of sentence production. Word finding failures are a common source of complaint and concern for older adults because of their association with "forgetfulness" and senility. However, our ongoing research examines the specific cognitive and neural underpinnings of word retrieval problems associated with normal ageing; this includes identifying what aspects of language production are affected, the relationship between word finding and neural structure and function, and what characterises older adults with better and worse performance.

Ageing and language comprehension

We study how the neural system develops across the adult life-span to support preservation of language comprehension as response to neural atrophy. Although regions related to language comprehension, such as areas of frontal and temporal cortex, are among the most vulnerable to atrophy, most aspects of language comprehension are well preserved throughout the lifespan. We use neuroimaging methods to understand the relationship between preserved function and neural change in normal healthy ageing.

Brain activity during a language comprehension task that engages syntax in healthy young (top) and mature (bottom) volunteers. The matures recruit activity in right inferior frontal gyrus that is absent in the young. Activity in the right inferior frontal gyrus depends upon the amount of grey matter decline in the homologous region on the left. From Tyler et al. (2010) Cerebral Cortex, 20(2), 352-364.

Performing a task during language comprehension: implications for aging studies

It is widely assumed that cognitive functions decline with age and that these decrements are associated with age-related changes in patterns of functional activity. However, these studies typically use tasks which may not be orthogonal to the cognitive function being investigated, raising the possibility that the observed age-related functional changes may be due to increased responsiveness to task demands and not to core cognitive functions themselves. One project in our lab sought to test this hypothesis by scanning healthy subjects [aged 19-76] in 2 studies using the same language stimuli (ambiguous or unambiguous sentences), but different behavioural contexts (passive listening versus on-line evaluation). In one, subjects passively listened to spoken sentences [no-task condition] while in the other they performed an acceptability judgment task [task condition].

We observed consistent activation of the language network (MTG, LIFG) in both task and no-task studies, which was similarly sensitive to syntactic ambiguity in both studies, suggesting that it persists regardless of additional task demands. In addition, we found an additional 3 task-related networks in the task study that were not present in the no-task study. Furthermore, the language network showed an age-related reduction only during the task, but not in the no-task variant. Increases in functional connectivity between task-related networks dissociated correct and incorrect responses in older but not younger adults, suggesting an age-related shift in processing to regions outside the language network when a task is involved.

Our findings suggest that the language network remains consistently activated regardless of cognitive demands. Furthermore, age-related differences only emerged when a task not essential to core language function was introduced, suggesting that we may be under-estimating the extent to which cognitive functions remain stable across the adult life-span.

Ageing and novel word learning

How does the ability of integrating new words into the exiting lexicon change with ageing? What role does sleep play in this process? Word learning ability has recently been found to be enhanced by sleep. According to the complementary learning systems (CLS) model, there are two learning systems: the initial process is the acquisition of new information into short-term memory which is relatively fast, whereas later consolidation occurs much more slowly by "reinstating" the new information into long-term memory through increasing the activity of neocortical traces; this secondary consolidation process can be influenced by sleep . Older adults experience sleep disturbances, raising the possibility that sleep disturbances may influence novel word learning in older adults. To study the role of age-related changes in sleep in novel word learning, we asked young and mature participants to learn novel words and get tested before and after sleep.

Cam-CAN project

As the population gets older an important issue for research is how to support healthy cognitive ageing. Although much research on cognition and ageing focuses on declines in neural integrity and cognitive ability, the recent burgeoning of functional neuroimaging studies has pointed to evidence for neural and cognitive flexibility across the lifespan. The Cambridge Centre for Ageing and Neuroscience (Cam-CAN) builds on this research to examine lifelong cognitive development by integrating measures of cognition with measures of neural structure and function. Language tasks developed at CSLB contribute to the range of cognitive measures currently being assessed. More information about the project can be found at www.cam-can.org.

Further reading

	Tyler, L.K., Shafto, M.A., Randall, B., Wright, P., Marslen-Wilson, W.D., Stamatakis, E.A. (2010). Preserving Syntactic Processing across the Adult Life Span: The Modulation of the Frontotemporal Language System in the Context of Age-Related Atrophy. Cerebral Cortex, 20(2), 352-364.
	Shafto, M.A., Stamatakis, E.A., Tam, P.P., & Tyler, L.K. (2010). Word retrieval failures in old age: The relationship between structure and function. Journal of Cognitive Neuroscience, 22(7), 1530-1540.
	Stamatakis, E.A., Shafto, M.A., Williams, G., Tam, P., & Tyler, L.K. (2011). White Matter Changes and Word Finding Failures with Increasing Age. PLoS ONE, 6(1), e14496.