New Worlds: Adversity does not sharpen senses

The findings may help explain how post-traumatic stress syndrome and other anxiety disorders develop in some people.

By
May 21, 2011 23:16
3 minute read.
Stress [illustrative photo]

Stress worried smoking cigarette 311 (R). (photo credit: TIM WIMBORNE / Reuters)

We are told that adversity heightens our senses, imprinting sights and sounds on our memories.

However, new research at the Weizmann Institute of Science that appeared recently in Nature Neuroscience suggests that the opposite may be the case: Perceptions experienced in an aversive context are not as sharp as those learned in other circumstances.

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The findings, which hint that this tendency is rooted in our evolution, may help explain how post-traumatic stress syndrome and other anxiety disorders develop in some people. To investigate learning in unfavorable situations, Dr. Rony Paz of the Rehovot institute’s neurobiology department, together with student Jennifer Resnik, had volunteers learn that some tones lead to an offensive outcome (such as a very bad odor), while other tones are followed by pleasant a outcome, or else by nothing. The volunteers were later tested for their perceptual thresholds – that is, how well they were able to distinguish either the “bad” or “good” tones from other similar tones.

As expected from previous studies, in the neutral or positive conditions, practice made them better at discriminating between tones. But surprisingly, when they found themselves exposed to a negative, possibly disturbing stimulus, their performance worsened. The differences in learning were really very basic differences in perception. After learning that a stimulus is associated with highly unpleasant experience, the subjects could not distinguish it from other similar stimuli, even though they could do so beforehand, or in normal conditions.

Thus, no matter how well they normally learned new things, subjects receiving the “aversive reinforcement” experienced the two tones as the same.

Paz explained that “this likely made sense in our evolutionary past: If you’ve previously heard the sound of a lion attacking, your survival might depend on a similar noise sounding the same to you – and pushing the same emotional buttons. Your instincts, then, will tell you to run.”

The Weizmann researcher believes that this tendency might be stronger in people suffering from posttraumatic stress syndrome (PTSD), which is more common among victims of terror or soldiers in war. As an example, he points to the Twin Towers terror attacks in New York. Many of those who witnessed the strikes on the towers developed PTSD, which, for many of them, can be triggered by tall buildings. Intellectually, they may know the building before them bears little similarity to the destroyed towers, but on a more instinctive level, they might perceive all tall buildings to be the same, and thus associate them with terrifying destruction.

The scientists are now investigating this idea in continuing research, in which they hope, among other things, to identify the areas in the brain that are involved in setting the different levels of perception. Paz concludes: “We think this is a trick of the brain that evolved to help us cope with threats, but is now dysfunctional in many cases. Besides revealing this very basic aspect of our perception, we hope to shed light on the development of such anxiety disorders as posttraumatic stress syndrome.”

SWISS-ISRAELI BRAIN RESEARCH COOPERATION A major neuroscience collaboration to better understand how the brain functions and how to fix it when diseased – as in Alzheimer’s and Parkinson’s diseases and autism – has been signed by the Edmond and Lilly Safra Center for Brain Sciences (ELSC) at the Hebrew University of Jerusalem and Switzerland’s Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland. The ceremony in Switzerland was signed recently in the presence of President Shimon Peres, with HU president Prof. Menahem Ben-Sasson and the academic head of ELSC Prof. Eilon Vaadia also present.

A combined investment of $10 million to be raised by the two institutions for the first five years of operations, which are to include joint laboratories and research projects and fellowships for graduate students. The fund constitutes the opening round in a strategic program encouraged by Peres to establish Israel as a leading player in international brain research, as it has become in his other “love,” nanotechnology.


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