The 'Kindling Effect' on Bipolar Disorder is a fairly new discovery. The kindling effect, in fact, was discovered in research for epilepsy, and not Bipolar Disorder. It is widely known that Bipolar Disorder is caused by a chemical imbalance in the brain; specifically, a problem with the neurotransmitters. Although epilepsy is a completely different illness, anticonvulsants, or anti-seizure medications, have been found to be effective in treatment of some of the symptoms of people with Bipolar Disorder.
The term 'kindling' is actually borrowed from neurology, where it is used to describe some forms of epilepsy that appear to worsen over time. In research models, what is observed is that each episode of the illness makes later episodes both more likely and more severe. This applies not only to epilepsy, but also applies to manic episodes of Bipolar Disorder.
Applying the kindling effect to Bipolar Disorder, it appears that, even with medication, the episodes of some patients with Bipolar Disorder become both more frequent and worsen as the patient gets older. One opinion is that the patient develops a tolerance to the medication; however, another recent theory is that the kindling effect may have a bearing upon this phenomenon. Yet another opinion of late is that the pattern is triggered by the use of antidepressants, at least in those patients using both antidepressants and mood stabilization medications at the same time; yet this theory is still surrounded by controversy.
The kindling phenomenon in epilepsy was discovered by accident at first in 1967 by Graham Goddard, who was actually studying the learning process in rats by using very low electrical stimulation of their brains—too low to cause convulsions. However, he found that after a few weeks, the rats still experienced convulsions when the electrical stimulation was applied. In other words, the brains of the rats had become sensitized to the electrical stimulation and, even though it should have been too low to cause them to have convulsions, they still did.
The term 'kindling' was chosen because this process was compared to the log in a fire—while the log itself is very hard to set fire to by itself in the first place, surrounding it by smaller, easy-to-light pieces of wood—kindling—the log itself would soon catch fire.
The kindling effect was first applied to Bipolar Disorder by Dr. Robert Post of the National Institute of Mental Health (NIMH). The idea is that if bipolar episodes are initially set off by stressors (episode triggers), over time, episodes could begin to happen even without these stressors; thus, the kindling effect. In other words, the brain of the person with Bipolar Disorder becomes 'kindled,' or sensitized, just like the rats in Graham Goddard’s epilepsy research, and the episodes will not only increase in frequency without triggers, but they will worsen over time.
Using the kindling effect analogy of a kindling log, for the person with Bipolar Disorder, this will be like the log that becomes so easy-to-light that eventually it will light without help—in other words, the episodes of the bipolar person will become like the fire that is already burning is harder to put out. Although the kindling effect on Bipolar Disorder is a new phenomenon, it bears further scrutiny.