What protocol does your doctor have for increasing your cortical thickness? Not having one is grounds for calling the hospital president and asking about the competence of the stroke department. What are the departments goals and objectives? Hopefully it is about getting survivors to 100% recovery, not run as a profit center.
Youthful Brains in Older Adults: Preserved Neuroanatomy in the Default Mode and Salience Networks Contributes to Youthful Memory in Superaging
Felicia W. Sun, Michael R. Stepanovic, Joseph Andreano, Lisa Feldman Barrett, Alexandra Touroutoglou and Bradford C. Dickerson
Journal of Neuroscience 14 September 2016, 36 (37) 9659-9668; DOI: https://doi.org/10.1523/JNEUROSCI.1492-16.2016
Abstract
Decline
in cognitive skills, especially in memory, is often viewed as part of
“normal” aging. Yet some individuals “age better” than others. Building
on prior research showing that cortical thickness in one brain region,
the anterior midcingulate cortex, is preserved in older adults with
memory performance abilities equal to or better than those of people
20–30 years younger (i.e., “superagers”), we examined the structural
integrity of two large-scale intrinsic brain networks in superaging: the
default mode network, typically engaged during memory encoding and
retrieval tasks, and the salience network, typically engaged during
attention, motivation, and executive function tasks. We predicted that
superagers would have preserved cortical thickness in critical nodes in
these networks. We defined superagers (60–80 years old) based on their
performance compared to young adults (18–32 years old) on the California
Verbal Learning Test Long Delay Free Recall test. We found regions
within the networks of interest where the cerebral cortex of superagers
was thicker than that of typical older adults, and where superagers were
anatomically indistinguishable from young adults; hippocampal volume
was also preserved in superagers. Within the full group of older adults,
thickness of a number of regions, including the anterior temporal
cortex, rostral medial prefrontal cortex, and anterior midcingulate
cortex, correlated with memory performance, as did the volume of the
hippocampus. These results indicate older adults with youthful memory
abilities have youthful brain regions in key paralimbic and limbic nodes
of the default mode and salience networks that support attentional,
executive, and mnemonic processes subserving memory function.
SIGNIFICANCE STATEMENT
Memory performance typically declines with age, as does cortical
structural integrity, yet some older adults maintain youthful memory. We
tested the hypothesis that superagers (older individuals with youthful
memory performance) would exhibit preserved neuroanatomy in key brain
networks subserving memory. We found that superagers not only perform
similarly to young adults on memory testing, they also do not show the
typical patterns of brain atrophy in certain regions. These regions are
contained largely within two major intrinsic brain networks: the default
mode network, implicated in memory encoding, storage, and retrieval,
and the salience network, associated with attention and executive
processes involved in encoding and retrieval. Preserved neuroanatomical
integrity in these networks is associated with better memory performance
among older adults.
Introduction
As
humans age, memory and many other cognitive functions often decline.
When a neuropsychologist evaluates an older adult, “normal” performance
is substantially lower than that of a younger adult. For example, on the
California Verbal Learning Test (CVLT), an average 25-year-old
remembers 14 words, while an average 75 year-old remembers 9 words, more
than 2 SDs lower (Delis et al., 1987).
Nevertheless, there is substantial variation in the degree of cognitive
decline with age. Some older adults—referred to by one group as
“superagers”—continue to perform at a level similar to middle-aged
adults (Harrison et al., 2012; Rogalski et al., 2013; Gefen et al., 2014; Gefen et al., 2015), and sometimes even young adults (Weintraub et al., 1994).
Investigation of the biological mechanisms associated with “youthful”
cognitive function in such individuals is crucial to understanding
“successful aging” (Depp and Jeste, 2006).
In this study, we sought to replicate and extend prior work on
superaging by testing hypotheses regarding the structural integrity of
two key brain networks that contribute to memory function.
Memory
requires that information be encoded, stored, and retrieved. To
explicitly encode information, such as a list of words, an individual
must first be motivated to attend to the relevant material, engage
working memory, and organize the information (Wolk et al., 2011).
Broadly speaking, these functions are subserved by
fronto–parietal–cingulate circuitry, variously referred to as
attentional (Corbetta and Shulman, 2002), executive (Dosenbach et al., 2006; Cole and Schneider, 2007), working memory (Koechlin et al. 1999; Gruber and Goschke 2004), and/or salience systems (Seeley et al. 2007; Touroutoglou et al., 2012).
In conjunction with circuitry supporting semantic memory, this
circuitry is engaged when new information is organized within the
context of previously existing knowledge (Simons and Spiers, 2003; Squire, 2007).
Once encoded, information is consolidated and stored as “long-term
episodic memories,” by way of the medial temporal lobe (MTL) memory
system localized in the hippocampus, medial temporal cortex, and
retrosplenial/posterior cingulate cortex (Squire et al., 2004), as well as other key nodes of the default mode network (Dickerson and Eichenbaum, 2010).
When information is subsequently retrieved (e.g., during free recall of
a word list), attentional, salience, executive, and semantic networks
are engaged in conjunction with the MTL memory system; when any of these
brain regions are lesioned, memory retrieval is impaired (Wolk et al., 2011).
Normal aging is well known to be accompanied by widespread reductions in the thickness of many of these brain regions (McGinnis et al., 2011; Bakkour et al., 2013), in parallel with age-related decline in memory function (McDaniel et al., 2008).
Age-related atrophy is particularly prominent in key frontoparietal
nodes of the working memory, executive, salience, and default mode
circuitry, such as in lateral and medial prefrontal and lateral parietal
cortices, as well as portions of the cingulate cortex and medial
temporal lobe (McGinnis et al., 2011; Bakkour et al., 2013).
Based on this summary of the processes that subserve memory function
and our knowledge of age-related cortical changes, we hypothesized that
superagers would exhibit “youthful” neuroanatomy within the networks
summarized here. We further hypothesized that, within the entire group
of cognitively normal older adults, the cortical thickness of these
brain regions would predict individual differences in memory
performance.
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