Extinction or the Art of Learning to Unlearn
Sometimes old behavioral patterns or routines that have been practiced wrong need a course correction: that's when learning by extinction steps in. Ironically, this active process of "unlearning and relearning" turns out to be one of the most important forms of learning overall, making it the subject of intense ongoing research.
Scientific support: Ingrid Ehrlich
- Extinction learning is an active form of relearning. Existing memory content is not deleted, however, as the term might suggest.
- Relearning is much more demanding than learning something new, because old traces of memory remain and must be repressed.
- Small triggers can bring old memories back to life. Such triggers include visual stimuli encountered during the learning as well as emotional states. Experts call this phenomenon "renewal".
- In cognitive behavioral therapy patients can learn to suppress a pathological behavior through relearning. Virtual training has a particularly potent effect.
- Extinction learning involves several brain centers and can potentially be enhanced through medication.
Unter „Emotionen“ verstehen Neurowissenschaftler psychische Prozesse, die durch äußere Reize ausgelöst werden und eine Handlungsbereitschaft zur Folge haben. Emotionen entstehen im limbischen System, einem stammesgeschichtlich alten Teil des Gehirns. Der Psychologe Paul Ekman hat sechs kulturübergreifende Basisemotionen definiert, die sich in charakteristischen Gesichtsausdrücken widerspiegeln: Freude, Ärger, Angst, Überraschung, Trauer und Ekel.
It only happened once, on a pleasant summer night under the flickering glow of a streetlight. The woman heard steps behind her – fast, determined steps. Then came the terrifying sensation of a man's hand on her shoulder. To this day, she has been able to shake off the fear of that moment. Merely at the sound of footsteps, she now retreats until the passers-by have moved ahead. There have been no further incidents, but once was enough. At the slightest hint of a similar situation, she panics – a behavior which seems engrained in her brain.
Many people – particularly women – have had similar experiences, according to Onur Güntürkün, a biopsychologist at the Ruhr University in Bochum, Germany. "The particulars differ, but this makes it a good example to demonstrate how fear can be overcome by 'unlearning'." He's referring to extinction learning, a term researchers have given to the process by which an old behavioral pattern can be replaced by a new one.
“First the brain has to learn to suppress its habitual reaction to a stimulus," Güntürkün says. "This requires focusing attention on potential environmental triggers and becoming aware of them – so that a man who's just out walking his dog is perceived as just that, and not as a threat." But this alone isn't enough, he says. "Her brain has to learn that she can keep walking normally; she doesn't need to wait for him to pass by."
This process is less common for children, who continually face unfamiliar stimuli; there the challenge is to learn an appropriate response. This initial learning is what scientists call "classical conditioning," and it's based on the brain's growing collection of memories. Adults are also constantly acquiring new knowledge, but this often requires replacing outdated information, or changing behavior that is the result of faulty practice. This makes extinction one of the most important means by which adults learn – whether the task is to stop leaving dirty socks strewn across the floor or to stop becoming angry when criticized by the boss.
In addition to its central role in normal, healthy learning, extinction is a core tool in modern therapies. It's considered the only route to a cure for addictions, in which the brain has to unlearn its craving for a drug. It's also helpful in anxiety and post-traumatic stress disorders. But while extinction has been known for over a century, scientists still know relatively little about how it works. A great amount of data has been collected, but some of it is contradictory. This was one motivation behind the German Research Association's creation of Research Area 1581, which has drawn together a number of German scientists in an intensive effort to figure out the biological and clinical basis of this learning process.
Memory is stubborn
It's harder to let go of the old than to learn the new. Güntürkün observed this in grade schools where children were being taught a hearing-based method of writing. "To produce the same German word, 'Vater', one child wrote 'Vata', another 'Fater' and a third 'Fadter'. None of them were corrected – the goal was just to show them that writing is fun." After one or two years of school, however, they are expected to have relearned the word and adjusted it to the correct form. And at that point they have trouble calling up the proper spelling."
"The problem is that they don't forget the original mistake," Güntürkün says. The old information hasn't been erased; it's still there in the mind. Extinction learning, which literally means “elimination learning,” is an active form of learning of a modified behavior as opposed to simply “wiping out” the old one. “Instead of just learning the new, we must also learn how to unlearn the old. This is much harder,” Güntürkün says. As a result the biopsychologist considers the didactic approach of teaching writing by hearing seriously flawed. He adds that language experts have recognized similar problems in adults: foreigners often make habitual mistakes in grammar and pronunciation over a period of years. They stubbornly resist change, even through extinction learning, at which point linguists call them "fossilized".
Small stimuli reactivate old memory pathways
One interesting feature of extinction learning is that it is often temporary: a small trigger can evoke old patterns in the mind. To return to Güntürkün's example from earlier, even if therapy has helped a woman overcome her panic of footsteps in the night, a flickering street light like the one she saw the night of the attack can bring terrifying memories of that night back to life. Experts call this recall effect "Renewal" (Wenn Verlernen misslingt). In stressful situations (Mit Stress besser verlernen?), we also typically revert to old behavioral patterns, rather than engage the new behavior learned through the extinction process.
In fact, Güntürkün believes, the brain may only truly lose experiences that are seldom "retrieved" (remembered). "Current thinking is that if complete erasure of a memory trace occurs at all, it can only happen in a small timeframe, from 10-30 minutes after something has been recalled, in a phase during which memories are unstable." Within this window memories might still be overwritten and perhaps permanently deleted. But this probably can't happen with events that are often and actively recalled, making them more stable. “The city of Rome, for example, is woven into so many of our synapses that it would be impossible to erase from our minds.”
Virtual reality: a path to relearning?
The mind's inability to erase frequently-followed memory paths is bad news for those suffering from mental illness, who are trying to unburden themselves of memories and behavioral patterns they have often relived hundreds of times. Cognitive behavioral therapy aims to teach bulimic patients to keep their food down and alcoholics from automatically reaching for the bottle (Alkoholsucht verlernen). Extinction learning should also be helpful against drug addiction, but a recipe for real success has yet to be found.
Putting the method to work for patients with post-traumatic stress disorder (PTSD), which arises after they experience something terrible, is a project being undertaken by Herta Flor, a clinical neuroscientist at the Central Institute of Mental Health in Mannheim. "These patients experience a hyperactivity of the brain center called the amygdala, but lack the normal inhibitory response of the hippocampus," Flor says. This probably prevents them from properly categorizing environmental information; instead, they are locked into repeated cycles of déjà vu in which they relive the traumatic experience time and time again.
Cognitive behavioral therapy teaches patients to suppress their fear by confronting situations that evoke it, to become aware of their behavioral patterns and finally, to consciously change them. This promotes greater brain neuroplasticity: amplifying certain contacts between nerve cells, weakening others, and forming entirely new ones. Cognitive behavioral therapy enables the rewiring of the contacts between nerve cells that contributes to a healthier state of mind. "For traumatized soldiers, virtual reality is a good example of a method that fits extinction learning particularly well," Flor says. "It creates an environment that comes particularly close to the threatening reality of a war zone for such patients." (Wie sich Traumata verlernen lassen).
Nerve cells restructure their connections by releasing specific molecules that act as chemical messengers; these, in turn, have to dock onto particular molecules on the surfaces of neighboring cells to deliver instructions. Their targets are usually receptor proteins. The messenger N-methyl-D-aspartate (NMDA) binds to corresponding NMDA receptors, a family of related molecules which play a crucial role in intercellular communication, as do cannabinoid receptors. In a study currently being carried out by Flor’s team, patients are administered a very small dose of cannabis before behavioral therapy sessions. The amount is too low to cause intoxication, but it is enough to activate cannabinoid receptors and, Flors hopes, accelerate extinction learning during therapy. Experiments in rats support the idea that the NMDA plays a role in the process: blocking the receptor – thus making it unable to receive chemical messages – virtually eliminated the animals' capacity for extinction learning.
The healthy side of extinction
The efficiency of extinction learning varies between individuals. “Patients with a smaller hippocampus have more difficulties,” Flor says. Illness also has diverse effects on the process. Half of addiction patients fall off the wagon again after receiving therapy. Relearning is a demanding process in its own right, and it is made much more difficult by the molecular and physical alterations in the brain that occur through drug use. "The relearning centers of such patients are basically hijacked," Flor says. But in the treatment of phobia, the method is highly successful: 80 to 90 percent of those who receive therapy experience a complete recovery. Onur Güntürkün says it has helped the woman whose panic attacks were triggered by footsteps and the flickering light of streetlamps. Thanks to extinction learning, her control over her fears has improved.
- Bouton M et al.: Contextual and Temporal Modulation of Extinction: Behavioural and Biological Mechanisms. Biological Psychiatry, 2006, 60, S. 352 – 360 (zum Abstract).
- Quirk G, Mueller D: Neural Mechanisms of Extinction Learning and Retrieval. Neuropsychopharmacology Review, 2008, 33, S. 56 – 72 (zum Abstract).
- DFG-Forschungsprojekt zum Extinktionslernen; URL: http://gepris.dfg.de/gepris/projekt/179167628 [Stand 23.09.2014] (zur Webseite).