Few would doubt the benefits of exercise on one's physical well-being. However, the
benefits of exercise on one's mental abilities are not nearly as extolled. More directly,
the perspective that our bodies have a significant influence on our minds is still
relatively new, though reviews by Rosenbaum (2005) and Madan and Singhal (2012a) suggest
that this is beginning to change. This idea is also in line with the embodied approach
to cognition (e.g., Clark, 1997; Lakoff and Johnson, 1999; Wilson, 2002; Anderson,
2003; Barsalou, 2008; Fischer and Zwaan, 2008). Briefly, embodied cognition suggests
that physical properties of the human body, particularly the perceptual and motor
systems, play an important role in cognition—the body influences the mind just as
the mind influences the body. This approach is further supported by findings that
individual body properties such as handedness can influence how individuals understand
abstract concepts (Casasanto, 2009, 2011). One particularly interesting facet of the
idea that our body can affect cognition is the influence of actions, gestures, and
exercise on memory performance: the hypothesis is that our physical movements, and
even the amount that we exercise, can affect our ability to remember. In the current
paper we will provide an overview on the disparate research paradigms that support
this hypothesis, and their resulting implications.
Reading, imagining, seeing, and doing
While the majority of studies investigating human memory use words or images as stimuli,
Cohen (1981) asked participants to perform actions, to observe an experimenter perform
the actions, or simply hear/read the instructions for the actions without it being
performed. Participants were subsequently tested for their ability to recall the actions
(e.g., “break the tooth-pick”). In later literature, these conditions were termed
as self- or subject-performed tasks (SPT), experimenter-performed tasks (EPT), and
verbal tasks (VT), respectively. Cohen found that participants were significantly
more likely to remember SPTs or EPTs than VTs. Extending this finding, Denis et al.
(1991) observed better memory for SPTs than actions that were imagined, testing imagined
actions through both visual and motor imagery. Apart from the two studies described
here, the work by Cohen and Engelkamp were the beginnings of a new field of research:
memory of action events (for reviews, see Engelkamp and Zimmer, 1989; Engelkamp and
Cohen, 1991; Zimmer and Cohen, 2001. The primary finding of this field was “the enactment
effect”: enhanced memory for SPTs, lending an early source of support to the embodied
cognition perspective.
The leading theories proposed to explain the enactment effect were based on two main
ideas: (A) Performed actions involve much richer and elaborative representations than
mere verbal phrases, and (B) enacted actions engage the motor system whereas other
methods of encoding do not. From perspective A, the finding that the enactment enhances
memory by serving as an elaborative encoding strategy is also in-line with Craik and
Lockhart's (1972) levels-of-processing framework, where information that is processed
more deeply/elaboratively is remembered better than information that is only processed
relatively shallowly/superficially. However, the nuances by which the enactment effect
enhances memory [e.g., lack of a primacy efficacy, some resilience to aging-related
attenuations; discussed in Engelkamp and Cohen (1991)] supports the possibility that
engaging the motor system during encoding is dissimilar to how information is usually
encoded through sensory-based modalities (e.g., visual, auditory; see Engelkamp and
Zimmer, 1984; Zimmer et al., 2000).
While the enactment effect itself is noteworthy, it leads to a broader question: under
what circumstances can actions enhance or impair memory? Here, a partial answer can
be found in a relatively unrelated field: research into gestures.
Gesture to remember
Gestures are motor actions that often accompany speech, and are intertwined with spoken
content (McNeill, 1992; Krauss, 1998; Kelly et al., 2008). Recent findings suggest
that gestures may be produced as a type of simulated action that arises when motor
activation due to mental imagery processes exceeds a certain threshold (Hostetter
and Alibali, 2008; Kelly et al., 2011), in close support of embodied cognition. Additionally,
gesturing has been shown to improve problem-solving abilities by decreasing working
memory load by conveying the same information through a second, image-based, modality
(Morsella and Krauss, 2004; Beilock and Goldin-Meadow, 2010; Cook et al., 2012). Since
motor actions enhance memory (enactment effect), it seems reasonable to expect that
gesturing may also affect memory encoding and retrieval. Supporting this notion, a
number of studies have found that memory is enhanced in participants who observe a
speaker who is also gesturing compared to observing a speaker who is not gesturing,
or a gesturer who is not speaking (e.g., Thompson, 1995; Kelly et al., 1999). Thus,
learning can be enhanced due to gesturing, even when one does not gesture themselves,
but simply observes another gesturing. Considering that findings regarding the enactment
effect found comparable recall rates with SPTs and EPTs, observing a gesture should
be comparable to gesturing yourself.
Taking a more direct approach, Cook et al. (2010) presented participants with a series
of short vignettes, after which they were asked to give detailed descriptions. The
vignettes were then classified as either eliciting gestures during their description
or not. Participants were given surprise free recall tasks after a brief delay, and
after a 3-week delay. Recall rates were higher for vignettes associated with gesturing
when described at both immediate and delayed tests, offering support for the notion
that gestures can enhance learning and memory. In a subsequent experiment, enhanced
memory performance was found even when participants were explicitly instructed to
either gesture or not, rather than being allowed to spontaneously gesture. Stevanoni
and Salmon (2005) found similar results with children, and recent studies have further
investigated the influence of gestures on learning and memory (e.g., Straube et al.,
2008; Macedonia et al., 2011; So et al., 2012).
Considering that motor actions can enhance memory for specific information, both through
enactment and through gesturing, a further question is whether they can also enhance
overall memory ability. In other words, can physical exercise enhance an individual's
memory capacity?
Working out your body to expand your mind
While the idea that physical exercise could increase memory recall ability is recent
focus of research, it has been shown several decades ago in older adults (Powell,
1974; Diesfeldt and Diesfeldt-Groenendijk, 1977), and has even been shown to lead
to enhanced memory abilities as much as one year later (Perrig-Chiello et al., 1998).
More recently, daily physical exercise has been shown to reduce the cognitive decline
associated with aging as well as reduce the risk of developing Alzheimer's disease
(Buchman et al., 2012).
Apart from research on older adults specifically, there is a considerable body of
research on the effects of exercise on cognitive performance. Unfortunately, a comprehensive
examination at the literature reveals inconsistent findings, with some studies finding
an enhancement of cognitive ability due to exercise while others report impairments.
A detailed review by Tomporowski (2003) resolves these inconsistencies by accounting
for the nature of the physical activity used: intensive exercise to dehydration leads
to impairments in cognitive performance, while less intensive, aerobic, exercise leads
to enhanced performance, including enhanced memory ability. In addition to behavioral
measures of enhanced memory, structural MRI images of the brain before and after week-to-month
long exercise protocols have also shown increased hippocampal volume due to the exercise
intervention (Pereira et al., 2007; Erickson et al., 2011), extending the results
of a number of prior findings in rodents (Uysal et al., 2005; Pereira et al., 2007;
Wu et al., 2007; Clark et al., 2011). While it appears clear that exercise has beneficial
effects on memory and hippocampal neurogenesis, it should also be noted that the benefits
of exercise on cognition are not confined to only memory or the hippocampus, but also
extend to a wider range of cognitive processes, particularly executive function and
the prefrontal cortex and anterior cingulate cortex (see Hillman et al., 2008, for
a review).
Considering the long-term effects of physical exercise on memory ability, as well
as the structural changes observed in hippocampal volume, it is worth considering
if the opposite is also true: would obesity be correlated with decreases in memory
performance? One established indicator of obesity is the body mass index (BMI). Lending
some support to this hypothesis, Trakas et al. (2001) found obese individuals to self-report
being more forgetful. While this is in-line with our prediction, this result alone
is insufficient to evaluate if obesity is affecting memory ability itself, or perhaps
just memory confidence, or other-related processes. However, drawing conclusions from
two studies that tested this hypothesis directly with batteries of cognitive tasks
(Elias et al., 2003; Gunstad et al., 2006), it appears that the answer is “yes”, at
least in some cases. In a preliminary analysis, Elias et al. (2003) found no difference
in cognitive performance measures for normal weighted and overweight individuals and
thus grouped the data for these participants together as “non-obese”. When comparing
memory performance for non-obese and obese participants, the obese participants performed
worse in some memory tasks, but the effect was only observed in males. Gunstad et
al. (2006) classified participants as normal, overweight, or obese and found significant
memory impairments in a variety of memory tasks that correlated with BMI (and also
not interacting with age). Other studies have used longitudinal analyses, however,
results are mixed with some studies finding a relationship (Brubacher et al., 2004)
and others finding no correlation (Cournot et al., 2006). Recent research further
suggests that hippocampal neurogenesis may also be influenced by diet, insulin levels,
and genetic factors (Brubacher et al., 2004; Lindqvist et al., 2006; Nichol et al.,
2009; Wallner-Liebmann et al., 2010; Clark et al., 2011; Grillo et al., 2011). While
these results are likely not enough to make you think twice about skipping on a run
to watch TV, they do suggest that our mind and body may be more closely connected
than previously thought—and extend the boundaries commonly applied to embodied cognition.
Moving forward
Taken together, these unrelated lines of research all lead to one conclusion: our
minds and our bodies are more connected than previously thought, and we should not
choose between honing either our mind or our body. Related research can support this
conclusion even further, where movement-related properties (e.g., “affordances”, see
Gibson, 1977, 1979) of objects and even words can influence how we process information
(e.g., Handy et al., 2003; see Madan and Singhal, 2012a, for a review). In particular,
recent findings suggest that the motoric properties of words representing objects,
i.e., word manipulability, and how these words are processed can also influence verbal
processing Rueschemeyer et al. 2010; also see Just et al., 2010) as well as enhance
memory recall (Madan and Singhal, 2012b).
In addition to supporting embodied cognition, the idea that actions enhance memory
is also well in-line with the motor chauvinist perspective (Wolpert et al., 2001),
where it is hypothesized the brain and, in turn, cognitive function may have evolved
to facilitate an organism's ability move within their environment (also see Glenberg,
1997; Gallese and Sinigaglia, 2010; Madan and Singhal, 2012a). If this viewpoint is
correct, one would predict that movements should enhance memory function. That is,
actions that are executed should be remembered better than those that are read about.
Ideas that are communicated in parallel with actions (e.g., gestures) should be remembered
better than those that are communicated in the absences of movement. And, general
memory ability should be enhanced by physical exercise. Current evidence suggests
that all these predictions are valid.
An important idea that has emerged in cognitive science is that the body influences
the mind. The embodied cognition approach suggests that motor output is integral to
cognition, and the converging evidence of multiple avenues of research further indicate
that the role of our body in memory processes may be much more prevalent than previously
believed. The extent of this cannot be overstated, and has implications for all memory
research. For instance the gesture literature suggests that if a participant were
to use gestures while engaged in paired-associate learning, there is the chance that
the results could be contaminated with variability due to the gesturing itself. Even
more broadly, the majority of studies of memory rely on motor actions to provide behavioral
measures of cognition, usually in the form of a button/key press. For example, a widely
applied paradigm in cognition, the go/no-go task, requires overt motor responses on
some trials and overt inhibition of motor processes on others. However, if the interaction
between cognition and motor action is not a one-way process, that is, the action also
influences the memory, perhaps amplifying or attenuating the effect size—there is
the potential for other inferences to be drawn about the outcome.