Page 118 - Biobehavioral Resilence to Stress

Adaptation to Stress 95

and muscle protein, shortening of telomeres and reduced telomerase activity,
memory impairment, and increased anxiety. Over longer periods of time,
overt disease becomes more likely. Certainly, individuals vary in their genetic
and psychological vulnerability to disease. It is not yet known precisely to
what extent chronic stress increases vulnerability to specific types of illness,

but the well-known multiple biochemical effects of stress make it reasonable

to consider the potentially broad effects of chronic stress on multiple body
systems and disease-related processes.

Stress and the Brain

The brain is the gatekeeper to the social and physical environment
(see Figure 5.3). When an event is perceived as threatening, associated behav-
ioral and physiological responses are determined by processes in specifi c
brain structures. Stress alters the chemistry of the brain and can also eff ect
changes in brain circuitry. Evidence of neuroanatomical and neurochemical
changes indicate that the brain itself is sensitive to both acute and chronic

stress. The functional effects of these changes may include anxiety, memory

impairment, altered judgment, and increased sensitivity to drugs and alco-

hol. The biochemical mechanisms for these effects are complex, involving

circulating hormones as well as endogenous mediators such as neurotrans-
mitters and neurotrophins. In general, these effects can be attributed to

stress-related changes that occur in structures of the brain limbic system
(hypothalamus, amygdala, and hippocampus) and in the prefrontal cortex.

Environmental stressors Major life events Trauma, abuse
(work, home, neighborhood)

Perceived stress

Individual differences Behavioral responses
(genes, development, (fight or flight)
experience) (personal behavior – diet,
smoking, drinking, exercise)

Physiological
responses
Allostasis Adaptation

Allostatic load
Figure 5.3 The brain as gatekeeper for stress perception and behavioral
and physiological stress responses. (From McEwen, B.S., New Engl. J. Med., 338,
171–179, 1998. With permission.)

12/17/2007 3:27:52 PM
CRC_71777_Ch005.indd 95
CRC_71777_Ch005.indd 95 12/17/2007 3:27:52 PM