How Does Bilateral Auditory Stimulation Rewire the Brain’s Fear Response?

Boukezzi S, et al. Bilateral Alternating Auditory Stimulations Facilitate Fear Extinction and Retrieval. Frontiers in Psychology, 2017. Read the paper.

Participants: 18 healthy volunteers.

• First, participants were conditioned to fear a triangle by repeatedly pairing its presentation with a mild electric shock, creating a conditioned fear response.
• As a result, the brain learned to associate the triangle with danger. Simply seeing the triangle triggered an anticipatory physiological fear response.
• During the extinction phase, the triangle was presented without the electric shock. The brain’s task was to learn that the stimulus no longer predicted danger and to update the previously acquired fear memory.
• During this phase, one group listened to alternating bilateral auditory tones presented at 1 Hz (60 BPM), while the control condition was completed without bilateral stimulation. Researchers measured both subjective fear expectations and physiological responses.

1. Bilateral stimulation accelerated fear extinction.

Participants who received bilateral auditory stimulation showed a faster reduction in their expectation of receiving an electric shock compared with the condition without stimulation.

2. The effect persisted the following day.

During the extinction recall test, participants who had received BLS exhibited significantly lower skin conductance responses (SCR), an objective physiological marker closely associated with amygdala-mediated fear processing. This suggests that their brains retained the new “safe” association more effectively, even when participants were not consciously aware of the difference.

“Our results demonstrate the importance of BLS to reduce negative emotions, and provide a successful model to further explore the neural mechanisms underlying the sole BLS effect in the EMDR.”

3. Bilateral stimulation appears to influence brain circuits involved in emotional memory.

The findings suggest that BLS helps modify activity within fear-related neural systems, particularly those involving the amygdala, allowing previously learned threat associations to be updated when the stimulus is no longer dangerous.

“Since the SCRs are known to be modulated by the brain structure underlying the fear response, that is, the amygdala (Knight et al., 2005), the BLS effect during fear extinction retrieval may reflect an action of BLS on these structures.”

Even simple alternating auditory stimulation reduced both subjective fear expectancy and physiological markers of fear. These findings provide experimental evidence that bilateral stimulation actively facilitates fear extinction by helping the brain consolidate new, safe learning.

A later study by the same group put the same paradigm inside a scanner to see which networks are involved — bilateral stimulation under fMRI. For the mechanism this points at, see how and why bilateral stimulation works; for the practice itself, what bilateral stimulation is.