Depression can be the cause of several things. Depression and its relationship to brain cell death is relatively new. The research on depression and brain cell death is an exciting area because it will invoke new treatments and therapy. The human brain increases significantly during the first year of life (Glaser, 2000). During the embryonic stage and early postnatal life is when neurons in the brain are formed and migrate to an assigned position. However, there is an exception. This is the olfactory region and hippocampal (involved with learning memory) neurons where neurons continue to be formed in adult life (Glaser).
During the first two years of life, the brain experiences rapid growth, and there is an overproduction of axons and dendrites. (See How the Brain Works for more details). During this stage, synapses compete for binding sites on the receiving neuron. This process is genetically determined, and many synaptic connections will not survive and will eventually die (Glaser, 2000).
As infants age, brain development occurs in response to experiences in the environment. For instance, a study by Turner and Greenough (1985) showed that weaned rats reared for 30 days in a group complex environment were found to have 20-25 percent more synapses per neuron in the upper visual cortex than rats reared socially or individually in standard cages. It is also believed that growth from experiences does not only occur during the first few years of life; but, complex interconnections between different areas of the brain are known to evolve according to their own timetable such that environmental inputs contribute to brain development of new synapses throughout life (Glaser, 2000).
Today, research shows that neurogenesis continues throughout adulthood. For instance, thousands of new granule cells are produced daily in the dentate gyrus of adult rats, which suggests that new neuron development plays a role in function of the hippocampus (Mirescu, Peters, & Gould, 2004). In addition, it lives in the dentate gyrus of the hippocampus of mice (Kempermann, Kuhn, & Gage, 1998), in monkeys and humans (Jacobs, van Praag, & Gage, 2000), and in the neocortrex of adult primates (Gould, Reeves, Graziano, & Charles, 1999).
There are important stimuli in the environment that help the brain to develop. However, early negative stimuli may hinder the brain’s structural development. For instance, early traumatic experiences inhibit growth and create complications for development (Glaser, 2000) such as by altering the way the brain structures itself (Mirescu, Peters, & Gould, 2004), and “neglect and failure of environmental stimulation during critical periods of the brain’s development may influence deficits in cognitive abilities” (p. 4).
Painful stimuli in one’s environment influences brain function. For instance, an important part of the brain that is affected by negative stimuli is the hippocampus, but this is not fully understood. McEwen (2001) has studied the effects of painful stimuli on the brain by means of lab rats. McEwen shows that “lesions of the dorsal hippocampus in rats increased the vocalization threshold of painful stimuli” (p. 266). In addition, “electrophysiological recordings from the hippocampus of subject rats revealed that CA1 pyramidal neurons have prolonged decreases in pyramidal cell activity in response to painful stimuli” (p. 266).
Painful stimuli can initiate stress, which also influences brain function. Research shows that alteration of the hippocampus’s function takes place after various types of acute and chronic stress because neurogenesis is inhibited by stress (McEwen, 2001). Mirescu and colleagues (2004) show that maternal deprivation produces persistent abnormalities in behavior and neuroendoctrine functions associated with the hippocampus by reporting a decrease in cell proliferation and immature neuron production in the dentate gyrus of adult rats that are maternally separated as pups. Neonatal handling, on the other hand, has been shown to influence brain development in various positive aspects including enhance learning performance, brain growth and development, emotional regulation, and stress responses (Tang, 2001). Early life maternal neonatal handling was found to lead to retardation of cognitive aging measured in the hippocampus (Meaney, Aiken, Bhatnager, Vanberkel, & Sapolsky, 1988) and persists in development throughout adulthood (Tang).
The loss of hippocampal volume is associated with deficits that accompany major depression (Steffens, Byrum, McQuoid, Greenberg, & Payne, et al., 2000; Sapolsky, 2001). For instance, in one study, rats that were injected repeatedly with glucocorticoids developed hippocampus neuronal loss (Joels, Alfarex, Heine, & Qin, 2006). This research and others may raise the possibility that humans experiencing recurrent depressive episodes and elevated levels of glucocorticoids may also sustain neurotoxin damage to hippocampal neurons (Sheline, Wang, Gado, Csernansky, & Vannier, 1996).
Furthermore, smaller hippocampus volume has been observed in women with borderline personality disorder (Driessen, Martin, Herrmann, Stahl, & Zwaan, 2000).
Smaller hippocampal volume has been observed in women who were victims of childhood sexual abuse. Sexually abused women as children had five percent smaller left-sided hippocampal volume, and the size of the left hippocampus volume was associated with severity of depressive symptoms, but not with explicit memory function. And, this research was consistent with previous research of combat veterans with posttraumatic stress disorder and smaller hippocampal volume (Stein, Koverola, Hanna, & Torchia, 1997).
Smaller hippocampal volume was also observed in women who experienced childhood trauma and diagnosed with major depression (Vythilingam, Heim, Newport, Miller, & Anderson, et al., 2001). Patients with dissociative identity disorder had hippocampal volume that was 19.2 percent smaller and the amygdalar volume was 31.6 percent smaller than healthy subjects (Vermetten, Schmahl, Lindner, Loewenstein, & Bremner, 2006). And, abnormalities in neurogenesis have been reported in mice that were genetically engineered to contain human genes that predispose the mice to Alzheimer’s disease. It was found that mice engineered to overproduce a mutant form of the human amyloid precursor protein, had fewer neurons in the hippocampus than what is considered to be normal (Gage, 2003).
Neural Development and Healing the Brain
Apparently, the brain will attempt to repair itself after there has been damage to the brain. For instance, after a person has a stroke, neurogenesis commences in the hippocampus in effort to produce new neurons that will heal damaged brain tissue. However, most newborn cells die, but some successfully migrate to the damaged area and can become adult neurons (Gage, 2003).
New neurons arise spontaneously in the hippocampus of humans. Adding neurons to the regions of the brain is important to spur new connections and development of existing neurons. This action occurs in the brain from experiences within the environment (Gage, 2003).
It would appear that once there is a loss of neurons, it would be impossible to experience neurogenesis. But, research by Van Praag, Kempermann, and Gage (1999) show that neurogenesis in adults may not be as hard to generate as thought. They found that mice that exercised (ran) showed signs of increases in cell proliferation and neurogenesis in the adult mouse dentate gyrus. And, Gould, Beylin, Tanapat, Reeves, and Shors (1999) reported that rats that were exposed to learning environments generated double neurons in adult rat dentate gyrus in response to learning new tasks that required the use of the hippocampus. However, research by Shors, Townsend, Zhao, Kozorovitskiy, and Gould (2002) posit that neurogenesis may relate to some but not all types of hippocampal-dependent learning.
Mynors-Wallis, Gath, Day, and Baker (2000) researched the effects of problem solving treatment, antidepressant medication, and combined treatment for depression. They conclude that problem solving treatment is an effective treatment for depressive disorders. Although this one research does not give ample support that patient who learned problem solving had an increase in hippocampal neurogenesis, this may be an important aspect for future research.
To explain why education of these two skills is proposed as a successful means to treat depression, there are three areas of research that are of importance. First, as explained above, chronic stress affects the mind and body and may reduce the size of the hippocampus and inhibit neurogenesis. Second is the Cannon-Bard theory of emotion. This theory presents the idea that a stimulus initiates brain activity that results in an emotion and response (Weiten, 2005). Third, from the cognitive psychology perspective, the brain develops schemas - mental folders as Jean Pigeat called it. These three factors may help explain why depressives experience high levels of stress and habitual negative thinking.
I believe that depressives have the tendency or habit to bypass certain cognitive process and pathways when interpreting events or situations. Instead of reasoning out situations, some depressives tend to use the same cognitive processes as individual who respond to a stimuli that initiates a fear response such as the fight-or-flight response or theory of emotion proposed by Cannon and Bard. As information is stored, the individual develops schemas pertaining to those events. As a result, depressives continue to use those same schemas or mental folders and fight-or-flight cognitive processes to new events or past traumatic events. As a result, depressives experience more daily and prolonged stress and helpless thinking than nondepressives.
Further Benefits of Learning as Means for Overcoming Depression.
I believe that research results suggesting that early negative stimuli can alter the way the brain functions and structures - is highly probable. Yet, I also believe that people can learn, to an extent, to restructure the brain’s function. For instance, retraining the general way people think by means of education. I believe that education of a variety of skills are important. The benefits may include: (1) learn to understand that there are options (2) learn to critique one’s own negative thinking and perceptions of events (3) learn how to consider different perspectives and side to events, and (4) learn to stop predominantly emotional style (fight-or-flight) thinking or relying on intuition. And instead, an individual will learn how think independently, increase reasoning abilities, and develop new or improved methods for cognitive thinking, which may help the development of neurogenesis while reducing stress and its effects.
In addition, I believe that there are psychological benefits as well such as: (1) learn to rely more on oneself and become more independent (2) learn how to think happy because learning the skills can help an individual gain control over and change one’s life- which may reduce feelings of helpless (3) help one to change low self-esteem (4) and feel more empowered because a person can begin to experience meaning to life, purpose, content, and finally capable of reaching one’s potential- self-actualization instead of being stuck in psychological needs (e.g., Maslow’s hierarchy: love and self-esteem).
