The Trail of Evidence From Treatment To Causes of Depression
When a person is depressed, the primary characteristic is a subjective awareness of mood change: the person has an ongoing feeling of sadness or emptiness. This feeling is often accompanied by eating disturbances, feelings of hopelessness, inability to concentrate, indecisiveness, sleep disturbances, lost interest in enjoyable activities, psychomotor retardation, fatigue, sluggishness or lethargy, and is often co-morbid with other disorders, especially anxiety.
This constellation of feelings and observable behaviors give rise the term depression. In cases where the depression is not severe or recurrent, psychotherapy ...view middle of the document...
Put differently, if the nervous system is constantly changing, and we recognize that some of the changes are more temporary while others reflect more lasting modifications, the patients for whom psychotherapy alone is effective perhaps reflect more transient underlying nervous system changes.
In terms of a biosocial stress-diathesis model (diathesis refers to biological predisposition and stress to environmental contribution), these psychotherapy-receptive patients may have a low diathesis, and whatever environmental stressors have occurred to induce depression, have not done so to the extent that they have altered the biological system in a pervasive and lasting way. Therefore, the scope of this paper will not further address this group of depression sufferers, concentrating instead on those who experience persistent, severe and/or recurrent depression, whose manifestations and course suggest stable changes to the nervous system in a variety of ways, that whatever the original cause (biological predisposition or change as a result of experience), will necessarily require more invasive intervention.
It is, of course, cause that concerns me greatly: underlying the mental and physical manifestations, can we discover neurobiological correlates, causes?.And here, I define "cause" as "mechanism." What biological factors, or set of factors, give rise to depression? The discussion that follows will highlight observations that have suggested the involvement of neurotransmitters, hormones and maladaptive electrical activity patterns in the brain.
The neurotransmitters seratonin and norepinepherine have increasingly become a focus of interest in the study of depression. The brain is an electro-chemical system. Information is carried within the neuron electrically (via action potentials and passive current) and between neurons chemically. Specifically, each neuron has its own set of neurotransmitters that are released from its axon terminal into the synapse, a small space between neurons. When these free-floating neurotransmitters attach to the dendrite of a nearby postsynaptic neuron, this in turn causes permeability changes in that neuron, and ultimately set off electrical changes, firing down the axon to repeat the process again as they induce neurotransmitters to be released into the synapse.
Theoretically, the chemical (neurtransmitter) end of the system can malfunction in two ways: if the postsynaptic neuron is insensitive and doesn't allow enough of the neurotransmitters to attach, or if the presynaptic neuron doesn't release enough neurotransmitter into the synapse. (1) fMRI studies and cereberospinal fluid studies have suggested that the problem has to do with underrepresentation of seratonin and norepinepherine in the synapse rather than insensitivity in the postsynaptic neuron. (2)
As further evidence, the therapeutic effect of tricyclics, selective seratonin reuptake inhibitors (SSRI's) and a new drug, reboxetine (a...