The Kindling Theory and Effect in Bipolar Disorder

If someone with bipolar disorder goes untreated for a period of years, could he or she begin to experience rapid cycling bipolar disorder or become resistant to treatments for the condition?

If normal life stressors initially set off bipolar episodes in someone, in time could episodes of the illness appear in that person without any such triggers?

Some research says the answer to these questions is yes, and some clinicians have speculated that the reason may be a process that has been termed "kindling."

However, the most recent research into the theory of kindling and bipolar disorder indicates the evidence for this theory is weaker than originally thought. Still, the concept of "kindling" in mental illness may fit into other ideas about the mechanisms underlying bipolar disorder.

What Is Kindling?

Most people think of kindling when building a fire: You use smaller, more flammable pieces of wood to help catch on fire the larger pieces, which don't ignite as quickly or readily. But kindling also is used as a term in medicine—specifically, in epilepsy and in bipolar disorder.

The phenomenon of kindling in epilepsy was first discovered by accident by researcher Graham Goddard in 1967. Goddard was studying the learning process in rats, and part of his studies included electrical stimulation of the rats' brains at a very low intensity, too low to cause any type of convulsing.

However, after a couple of weeks of this treatment, the rats did experience convulsions when the electrical stimulation was applied. Their brains had become sensitized to electricity, and even months later, one of these rats would convulse when stimulated. Goddard and others later demonstrated that it was possible to induce kindling chemically as well.

The name "kindling" was chosen because the process was likened to a log fire. The log itself, while it might be a suitable fuel for a fire, is very hard to set ablaze in the first place. But surround it with smaller, easy to light pieces of wood—kindling—and set those alight first, and soon the log itself will catch fire.

Kindling in Bipolar Disorder

Dr. Robert M. Post of the U.S. National Institute of Mental Health (NIMH) is credited with first applying the kindling model to bipolar disorder. Demitri and Janice Papolos, in their book The Bipolar Child, describe this model as follows:

"... initial periods of cycling may begin with an environmental stressor, but if the cycles continue or occur unchecked, the brain becomes kindled or sensitized - pathways inside the central nervous system are reinforced so to speak - and future episodes of depression, hypomania, or mania will occur by themselves (independently of an outside stimulus), with greater and greater frequency."

The theory also holds that it's possible to stop the process through aggressive treatment.

Could Kindling Play a Role in More Severe Illnesses?

Some researchers have speculated that kindling contributes to both rapid cycling and treatment-resistant bipolar disorder, and this theory also could be consistent with cases where cycling began with definite mood triggers, stressful or exciting events, and later became spontaneous.

In addition, it has been shown that substances such as cocaine and alcohol have their own kindling effects, which could, in turn, contribute to bipolar kindling. In fact, it was the knowledge that cocaine causes seizures that led Dr. Post to connect kindling in epilepsy with mood disorders after he had studied the unexpected effects of cocaine on severely depressed patients.

The kindling theory has been borne out by some research observations. For example, the more mood episodes someone has, the more difficult it is to treat each subsequent episode, possibly because more brain cells are sensitized and involved. However, the best-designed studies in the field of bipolar disorder don't provide strong backing for the kindling theory.

Still, regardless of what future research finds about the kindling theory of bipolar disorder, it's clear that early diagnosis and prompt, appropriate treatment are key to improving outcomes for those with the condition.