Serhiy Dekhtyar

Reserve and resilience in cognitive and brain aging

Aging is associated with structural shrinkage, molecular alterations and functional disruptions affecting most parts of the brain. In turn, these brain changes have been linked with decline in several cognitive domains, including working memory, episodic memory, processing speed, and executive function. However, inter-individual variability in cognitive performance is often too vast to be accounted for by the brain pathology markers alone. Instead, the processes of neural decline which include brain atrophy, synaptic loss, and white matter degradation are widely believed to be counteracted by the processes of neural enhancement that involve preservation, repair, or replenishment of neural resources.

The model of cognitive reserve (CR) is one of the most well-known theories of compensatory mechanisms restricting the impact of brain damage on cognitive outcomes. CR is assumed to manifest through two mechanistic functions: neural reserve, the efficiency or capacity of pre-existing functional brain networks; and neural compensation: the ability to enlist compensatory strategies to withstand interruption in the face of damage. Despite much previous research on CR, considerable questions about its role in cognitive aging remain unanswered. These can be summarized across three key areas:

1. Reserve operationalization approaches;
2. Selection of brain pathology markers supposedly modified by reserve;
3. Consideration of changes in reserve during aging.

The work conducted by our group aims to contributes to adressing all of these pressing questions.

Extending the model of reserve to physical resilience

Physical resilience describes an individual’s ability to withstand decline or recover function in the face of age-related losses or diseases. It is believed to be shaped by the individuals’ intrinsic biological resources, but also by the social and psychosocial environments they inhabit. It is thought to manifest through two complementary processes: resistance (outright avoidance of negative perturbations) and recovery (restoration of homeostasis following a disturbance). And since resilience has been defined as a whole-person level characteristic that cuts across organ systems, enhancing it may have the potential to improve multiple outcomes facing a variety of stressors.

While its theoretical premise is largely well described and its promise well recognized, considerable questions remain about: 

1. How resilience should be measured
2. What are the biological and psychosocial signatures of resilient older adults
3. What are the consequences of resilience for older adults’ long-term outcomes, including disability trajectories, healthcare utilization, and mortality.

Recently, we began addressing these questions using the model of preserved walking speed for a given clinico-psychosocial profile. We are also exploring using SuperAgers as another model of exceptional functional preservation.

Depression in old age

Depression in late life demands urgent attention, due to its severe consequences for the individuals, their families, and the healthcare systems. It is a multifactorial disorder that likely occurs as a result of an interplay between social and biological factors unfolding throughout the entire life-course. In our group with provide key insight into:

• how old-age depression can be prevented,
• how its ill-health consequences can be mitigated
• how healthcare for people with this debilitating condition can be optimized.

We do so by exploring life course determinants of old-age depression, with a particular focus on somatic disease burden, but also psychosocial and lifestyle characteristics. We assess these associations longitudinally, across time, and with special emphasis on important moderating effects from modifiable factors. 

Furthermore, we are particularly interested at understanding the longitudinal course of depression, with a particular emphasis on transitions involving not just clinical diagnoses, but also specific symptom profiles, and subsyndromal entities. Here, we seek to understand not just the determinants of specific transition patterns across the depressive symptom continuum, but also to evaluate their consequences in terms of clinical and functional outcomes. An important part of this project involves the understanding of healthcare utilization in people with old-age depression, with a focuson complex and avoidable transitions across care settings.

Specifically, we intend to answer if healthcare use in older adults with depression is characterized by a higher rate of unplanned episodes and more complex transitions across care settings as well as identify which individual and structural factors (e.g., presence of comorbid diseases, availability of informal care) precipitate inadequate care use in older adults with depression.

Our work is primarily based on longitudinal population-based data from the SNAC-K study and the NEAR infrastructure. We collaborate extensively in international consortia, including SHARED and COSMIC

All research described above is supported by funds from the Swedish Research Council for Health, Working Life and Welfare (FORTE), and Stiftelsen 1759.

I have taught at all levels of education at KI, and have accumulated aver 150 teaching hours. Course summary can be found below:

2023-2026: Aging and age-related disorders from a biological, epidemiological and clinical perspective. Master’s course. Aging Research Center, KI. 

2018-2025: Geriatric epidemiology. Health assessments in old ages. Master’s course. Aging Research Center, NVS (KI).

2018; 2021; 2023: Application of epidemiological methods in aging research. PhD course. Doctoral program in Epidemiology, Department of Environmental Medicine, KI. Course held at ARC, KI. 

2018; 2020: Epidemiology in family medicine. Doctoral School in Family Medicine. Division of Family Medicine and Primary Care, NVS.

2014-2018: Cognitive processes (Statistics module): Undergraduate course. Dept. of Clinical Neuroscience, Section of Psychology, KI.

2016-2017: Writing and presenting successful grant applications and communicating science. PhD student course. Swedish Interdisciplinary Graduate School in Register-based Research.

2014-2016: Study designs in register-based studies: PhD student course. Swedish Interdisciplinary Graduate School in Register-based Research.

2011-2012: Consequences of demographic change: Master’s course. Centre for Economic Demography and Dept. of Economic History, Lund University.