Cognition and Aging
COGS 2120
Methodologies
• There are two main types of experiments on age effects on cognition
• Cross-sectional studies examine different people of different ages at
one point in time
• E.g., three groups of participants (60 year olds, 65 year olds, 70 year olds)
complete the same experiment
• Longitudinal studies examine the same people as they age
• E.g., the same participants complete similar experiments at 60 years old, 65
years old, 70 years old
Methodological concerns
• Cross-sectional studies are subject to cohort effects – generational
differences
• Differences in behavioral results could be due to aging or a completely independent
group difference
• E.g., a study comparing millennials to Gen-Z would have an age difference but also all
kinds of other differences
• Longitudinal studies require repeated exposure to the cognitive test
• Practice-related and experience-related performance gains/differences
• Indeed, results from cross-sectional and longitudinal studies often differ
• A better way: quasi-longitudinal studies, which tests different people from
the same cohort longitudinally
Perspectives on cognitive aging
• Micro vs. Macro – should researchers investigate individual processes
to see how they change over time (micro) or several variables
simultaneously to measure general decline (macro)
• Interrelatedness of cognitive functions (executive control, attention, perception,
working memory, etc.)
• Fluid vs. Crystallized (Cattell, 1941; 1971)
• Crystallized cognition is well-practiced, experience-based, overlearned
• E.g., vocabulary, deduction based on past experience
• Fluid cognition is applied in novel contexts, experience-independent
• E.g., unfamiliar reasoning, problem solving, working memory
Cognitive decline
• Most individuals follow the trend of cognitive decline – a gradual and
systematic decrease in cognitive abilities
• Mild Cognitive Impairment is an official diagnosis
• Affects fluid cognition before crystallized cognition
• General consensus is that cognitive decline accelerates at
Cognitive decline
• Most individuals follow the trend of cognitive decline – a gradual and
systematic decrease in cognitive abilities
• Mild Cognitive Impairment is an official diagnosis
• Affects fluid cognition before crystallized cognition
• General consensus is that cognitive decline accelerates at 60-65
• Subject to tremendous individual differences – some do not show decline until
70
• Some empirical evidence suggests signs of decline of fluid cognitive skills can
appear as early as ~30
Salthouse (2009) – cross-sectional
Cognitive decline
• Most individuals follow the trend of cognitive decline – a gradual and
systematic decrease in cognitive abilities
• Mild Cognitive Impairment is an official diagnosis
• Affects fluid cognition before crystallized cognition
• General consensus is that cognitive decline accelerates at 60-65
• Subject to tremendous individual differences – some do not show decline until
70
• Some empirical evidence suggests signs of decline of fluid cognitive skills can
appear as early as ~30
• If this is the case, then it appears the magnitude of decline accelerates after 60-65
• If cognitive decline occurs gradually from 30-onwards, why is it not as
evident?
Cognitive decline
• If cognitive decline occurs gradually from 30-onwards, why is it not as
evident? (Salthouse, 2004)
• Cognitive ability is just one aspect of functioning – motivation, experience,
persistence are part of the equation and can overcome ability deficits
• Humans don’t often have to perform at maximum capacity (parallel with
physical decline)
• People can adapt to age-related changes
very fancy and precise graph
Neuroscience of aging
• Most of cognitive decline can be attributed to neurons shrinking in size
and an overall decrease in synaptic density – “brain shrinkage”
• Due to morphological changes to the neurons themselves, unwanted protein
buildups
• In addition, sometimes cells die
• Neural decline is most severe in prefrontal cortex – executive function
• Other lobes show more moderate decline
Cognitive decline – processing speed
• Processing speed (in any process) declines over time and seems to underlie
many other aspects of cognitive aging
• Any cognitive test (language processing, working memory, problem solving) will rely
on processing speed
• Or: does the decline of all the other processes lead to reduced speed?
• Decline in processing speed is gradual and linear (Salthouse, 2019)
• Neural explanantions:
• As synaptic density decreases and neurons shrink, information has to take
longer, more circuitous routes → decrease in speed (Salthouse, 1985)
• Propogation of electrical signal along neurons slows over time (Miller,
1994)
Cognitive decline – visual perception
• Physical changes in the pupil, lens, retina lead to degradation of the
visual sensory system
• Loss of illuminance even before the signal reaches the brain → noisier
signal → increased difficulty with identifying low-level features
• Difficulty with feature detection leads to slower object recognition,
slower serial search (Madden et al., 2005)
• Processing of spatial relations remains fairly intact
• Evidence of a gradual de-differentiation of ventral and dorsal
processing with aging (Chen et al., 2002)
• Perhaps an example of compensation
Cognitive decline – attention
• Difficulties in multitasking and attention-
switching performance – decline in both
divided and selective attention
• Bottleneck of attention shrinks; switching time
between attentional tasks increases
• Potentially due to declining executive control –
degradation in prefrontal cortex
• Attention differences are more obvious at
low and high levels of arousal (remember
the bell curve)
• The ability to link a cue to spatial attention
in simple tasks seems to be unaffected by
age (still susceptible to visual and general
slowdowns)
Cognitive decline – long term memory
• Declarative memory – episodic memory shows gradual lifelong
decline; semantic memory shows late life decline (Ronnlund et al.,
2005)
• Decline in episodic memory seems to be more executive function-related
(Spaan, 2015)
• Procedural memory stays more or less intact throughout the lifespan
(Lezak et al., 2012)
Cognitive decline – long term memory
• Declines occur in encoding, storage, and retrieval
‒ Making new memories (rate of acquisition)
‒ Ability to access newly-learned memories
± Retention of existing memories (recognition > recall)
• Increased reliance on cues
Cognitive decline – working memory
• Evidence that working memory maintenance (visual, verbal, spatial)
undergoes age-related decline
• Age-related neural activation differences irrespective of task
performance (Reuter-Lorenz & Sylvester, 2005)
• Observations of older adults having less neural activity in some regions than
younger adults
• Observations of older adults having more neural activity in some regions than
younger adults
• Perhaps compensation?
• Suggests plasticity
Cognitive decline – working memory
• Working memory operations undergo more significant decline
• Neuroimaging evidence points to role of prefrontal cortex (executive
function) in this decline
• Less evidence for compensation
• This function/these regions have less plasticity
Cognitive decline – executive function
• Importance of executive function in other processes (selective
attention, working memory, inhibition, monitoring, etc.)
• Evidence that the prefrontal cortex undergoes more significant
degradation than other brain regions
• Prefrontal cortex is where executive function is housed
• Perhaps executive function declining underlies much of the general
cognitive decline observed (Braver & West, 2008)
Alzheimer’s Disease
• Individuals with Alzheimer’s undergo accelerated neuronal degradation (the
levels of synaptic density present in those with AD is roughly equivalent to
that of a neurotypical adult at 130 years old)
• Buildup of amyloid-Beta protein at synapses eventually leads to synapse
destruction
• This protein is produced naturally, but in non-Alzheimer’s brains, there are microglia
mechanisms that typically sweep up these proteins to clear out the synapse
• In Alzheimer’s brains, these proteins accumulate into plaques and the synapse reaches
a tipping point much faster
• Significant differences in amyloid-Beta and tau tangles between control
group and MCI group and Alzheimer’s group (Small et al., 2006)
Fighting cognitive decline
• Brain reserve – defined in terms of the number of synapses an
individual has during progression of pathology
• If someone has a lot of synapses, losing some synapses to degeneration will
have less of an impact than someone who starts out with fewer synapses
• Cognitive reserve – defined in terms of functional capabilities of the
mind (Stein, 2012)
• If someone has strong compensatory mechanisms, they may be able to maintain
functional equivalence in spite of shrinking synapse count
Fighting cognitive decline
• Nun Study (1986-) – longitudinal study documenting behavioral
measures, life experiences, and posthumous brain scans of a large
sample of nuns
• Onset of pathology in the brain doesn’t always lead to the behavioral
deficiencies of the disease – a range of factors combine to make up the
expression of the disease
• Cognitive reserve!
Fighting cognitive decline
• Healthy diet
• Exercise
• Higher education and occupational complexity
• Continued mental exercise
• How to prevent Alzheimer’s – Lisa Genova
Bilingual Advantage?
• The theory of bilingual advantage states that learning multiple
languages is an effective defense against cognitive decline (see work
by Bialystok)
Bilingual Advantage?
• The theory of bilingual advantage states that learning multiple
languages is an effective defense against cognitive decline (see work
by Bialystok)
• The claim is that learning multiple languages requires increased executive
function (i.e., greater connectivity, increased task-switching performance) and
increasing executive function
• More recent evidence suggests that the bilingual advantage is
overstated, inconsistent, and clouded by other factors (e.g.,
socioeconomic status – Morton & Harper (2007))
• Publication bias?
Harada et al. (2013)
Mostly yes
The Myth of Cognitive Decline?????
The Myth of Cognitive Decline?????
1. What is the authors’ main point and how does this theory differ from
the typical account of aging we discussed in class?
2. What evidence do they provide to support this main point? Be
detailed, describe what the evidence is!
3. What counterarguments might you make? / What further questions
might you have for the authors?