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Resilience and Survival in Extreme Environments 163

improvements in auditory and visual reaction time. Hawkins et al. also

observed a significant interaction between exercise and task diffi culty, such

that a more difficult dual-stimulus reaction time task was relatively more sen-

sitive to the exercise effect than either of the single-modality tasks. However,

this study did not quantify fitness level and made no attempt to manipulate
the intensity of exercise.
Other studies provide additional evidence that physical fitness can serve

to attenuate age- and stress-related decline in cognitive abilities (Brown, 1991;
Bunce, Barrowclough & Morris, 1996; Roth & Holmes, 1985). Improved cog-
nition may be related to capillary density and general cardiovascular func-
tion, which supports the supply of oxygenated blood to the brain (Cotman &

Berchtold, 2002), positive effects on the efficiency of neural biochemical and

metabolic processes (Gibson & Peterson, 1982; Van Praag, Kempermann &
Gage, 1999; Van Praag, Shubert, Zhao & Gage, 2005), maintenance of sen-
sory systems (Era, Parssinen, Pykala, Jokela & Souminen, 1994), and perhaps
most critically, maintenance of brain tissue densities (Colcombe et al., 2003).
Regular physical training stimulates growth factors (e.g., IGF1, GDNF) that
are important to neuro-protection and neurogenesis. It may be through this
neuro-protective effect that exercise and physical training protects the brain

from damage due to neurotoxin exposure, including intraventricular injec-
tion of 6-hydroxydopamine and free radical damage from MPP+ (used in
animal models of Parkinson’s Disease) (Cohen, Tillerson, Smith, Schallert &
Zigmond, 2003; Faherty, Raviie-Shepherd, Herasimtschuk & Smeyne, 2005;
Smith & Zigmond, 2003).
Other benefits of exercise are mediated through cytokine responses,

such as increases in IL-6, which inhibit proinfl ammatory cytokines

(Petersen & Pedersen, 2005). Through other largely unknown mechanisms,
exercise is known to improve mood and sense of well-being (Dishman et al.,
2006). Habitual exercisers who stop exercising may suff er mood disturbance
(Mondin et al., 1996; Morgan, Costill, Flynn, Raglin & O’Connor, 1988) and
in some cases may even develop symptoms of chronic multisymptom ill-
nesses (Glass et al., 2004). One of the most important lessons derived from
the medical treatment of chronic multisymptom illness is that physical and
mental activity can help to prevent the development of chronic stress-related

symptoms and difficulties that might otherwise develop after exposure to
traumatic stress (McLean, Clauw, Abelson & Liberzon, 2005). In fact, this
factor alone may distinguish those who are least susceptible (most resilient)
to chronic symptoms of stress-related trauma (McLean & Clauw, 2004).
Recently, the U.S. Army funded a series of studies to explore cognitive

and dietary interventions to overcome effects of lifetime stress on progressive

oxidative damage that occurs with aging. The results demonstrated positive

effects on learning and memory in dogs that were fed a diet rich in a variety of
antioxidants (Milgram et al., 2005). Conceivably, exercise may also stimulate

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