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Kindling and stress—how experience affects the brain

Brain neuron

Is it possible that chronic stress, through a process called kindling, can create hard-wired, hypersensitive neural networks capable of dictating and automating symptoms from a wide range of instinctual behavior patterns? In his video course, Biology and Human Behavior: The Neurological Origins of Individuality, 2nd edition, Robert M. Sapolsky examines how communication between neurons is strengthened as a result of experience. When the dendritic spines of neurons are stimulated rapidly, the synapses between the communicating neurons become "hyper-responsive or potentiated" due to chemical changes within the neural environment. Subsequently, less stimulation is necessary to again prod the neuron to fire—the moment when an electrical signal bursts through the neuron's axon, prompting release of chemical messengers called neurotransmitters into the synapse between neurons, often increasing the likelihood that other neurons will fire in a sort of chain reaction. In other words, Sapolsky says, the neuron's "action potential" is increased. What's called "long-term potentiation" is thus the basis for learning and memory, possibly including injurious forms of learning such as post-traumatic stress disorder (PTSD).

Brain stem structures and the reticular formation:

In Listening to Prozac: A Psychiatrist Explores Antidepressant Drugs and the Remaking of the Self (1993), Peter D. Kramer writes, "Kindling rewires the brain. … the brain reshapes itself anatomically in response to small noxious stimuli. … Kindling appears to be a kind of learning, but a learning that can occur independent of cognition. … Illness, once expressed, can become responsive to ever smaller stimuli and, in time, independent of stimuli altogether. The expression of the disorder becomes more complex over time."

In "Psychosomatic disease and the 'visceral' brain: Recent developments bearing on the Papez theory of emotion" (1949), Paul D. Maclean theorized about the kindling process. "It is possible that if a certain electrical pattern of information were to reverberate for a prolonged period or at repeated intervals in the neuronal circuit, the nerve cells (perhaps, say, as the result of enzymatic catalysis in the dentritic processes at specific axone-dendritic junctions) would be permanently 'sensitized' to respond to this particular pattern at some future time. Such a mechanism would provide for one variety of enduring memory in a way that is remotely analogous to a wire recorder. These hypothetical considerations suggest how oft-repeated childhood emotional patterns could persist to exert themselves in adult life."

As MacLean suggests in using the term visceral, certain reactions are not embedded in language and intellect, they are more like "gut feelings" that can remain in primordial memory systems and that can be strengthened through kindling. Winifred Gallagher explains kindling in an article in The Atlantic Monthly, "How We Become What We Are" (September 1994). Gallagher writes:

The illustration below (image links to source) is borrowed from the Society for Neuroscience website. This image appears in an article on post-traumatic stress disorder (PTSD). In addition to depicting the amygdala, the illustration depicts the location of the prefrontal cortex. The prefrontal cortex is often referred to simply as the frontal lobe or frontal cortex. This area of the neocortex lies in front of cortical motor areas. We will discuss the frontal cortex and cortical motor areas later in this narrative. For now, suffice to say that the frontal cortex (or prefrontal cortex) is involved in executive functions and the expression of personality. The Wikipedia entry for prefrontal cortex explains that this area of the brain orchestrates "thoughts and actions in accordance with internal goals." The point to be made here, regarding the subcortical amygdalae, is that during normal functioning, the enlarged prefrontal cortex in humans can modulate emotional impulses generated in the amygdalae.

Over time, repeated stressful experiences can literally, not just figuratively, alter the nervous systems of the temperamentally vulnerable. Animal research has shown that when a rat is given a small shock, it shows no marked reaction; when exposed to such stressors for five consecutive days, it shows signs of the stress response; when exposed for seven or eight days, the rat has a seizure, and thereafter this 'kindled' animal will seize with little or no provocation. Experiments of this kind are of course not done with people, but Philip Gold and other neuroscientists now think that in human beings, too, by triggering a cascade of chemical reactions, serious chronic stress, particularly in early life, causes changes in the way genes within a brain cell function, permanently altering the neuron's biology. Because they require a particular type of input to turn on or off, only some of a neuron's thousands of genes, each of which is involved in some aspect of cellular structure or communication, are activated at any given moment. When a temperamentally vulnerable person is constantly bombarded with upsetting stimuli, Gold says, the genes that get turned on are those involved in the cellular components of the stress response."

It is contended here that neurotransmission in the amygdalae and their target structures is sometimes kindled to generate dopamine-driven behaviors aimed at solving problems including restoring order, control, and most importantly–confidence. Under normal circumstances, this could be construed as a survival instinct. Under extreme stress, however, especially when an outlet for pent-up energy is not available, these behaviors may turn into obsessions or compulsions. We will discuss such neurotransmission in greater detail in Part 3 of For now, It is pointed out that in Monkeyluv and Other Essays on Our Lives as Animals (2005), Robert M. Sapolsky describes how monkeys release dopamine in anticipation of a food reward. They get most excited when a light first comes on signaling that they may now perform a learned task and upon completion, will receive food. Their excitement does not peak when the food finally appears; it peaks well before that point. Sapolsky writes, "It's about the anticipation of reward. It's about mastery and expectation and confidence."

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