Scientists
say study may lead to treatment for pathological fears and phobias.
Imagine
being able to decouple bad memories from the fear and anxiety they
produce with just a pill.
That's the promise of a new report from Dutch researchers published
in the Feb. 15 online issue of Nature Neuroscience. Merel Kindt and
colleagues at the University of Amsterdam used a beta blocker called
propranolol (also known as Inderal) to erase, at least in the short
term, the fear response induced by a painful memory in humans that
was induced in the laboratory.
Such findings could one day help individuals suffering from pathological
anxiety disorders from the debilitating physiological effects of their
fears. Yet many questions remain, experts note, such as how permanent
the effect is, and whether it can affect traumatic memories that may
be decades old.
"I think it's a very interesting and exciting study," said
Jane Taylor, a professor of psychiatry at Yale University, who studies
memory reconsolidation in rats. "It will be interesting to know
how long lasting this effect is, and whether it only works on recently
consolidated memories."
Mark Bouton, Ph.D., a professor of psychology at the University of
Vermont, echoed that sentiment. "This study is a solid step forward
in our understanding of how to reduce fear," he said. "The
big question is whether this treatment will reduce all forms of relapse,
including the return of fear that can occur with the passage of time."
Human memory often is compared to computer storage. Some memories
exist in a sort of neurological flash RAM, whereas others are stored
for the long term, on the brain's hard disk. The analogy works to
a point, but it isn't perfect, as it turns out to be quite difficult
to permanently erase files in the brain's memory banks.
"Fear memories can be surprisingly resilient," Bouton explained.
To try to break at least the physiological hold these fears have over
individuals, Kindt induced a kind of Pavlovian fear response in 60
undergraduate students at the University of Amsterdam.
The study lasted three days. On the first day, the subjects learned
to associate images of spiders with a mild electrical shock. Fear
was measured by assessing each individual's startle response—how
much their eyes blinked in response to the stimulus. That fear memory
was then consolidated—or written to the hard disk, if you will.
The next day, the memory was recalled, but only after the subjects
had been given either a placebo or propranolol. The idea, Bouton explained,
is that at this point, the memory becomes "open to modification"—just
as a computer file can be changed and then rewritten to the hard disk.
Propranolol had already been shown to impact memory reconsolidation
in rodents; the question was, would it have the same effect in people?
The answer came on day three, when the subjects were tested again.
The physiological response to the fear-inducing cue—pictures
of spiders—was eliminated in the propranolol group, but not
in the placebo group, Kindt found.
"In principle," said Bouton, "this is a step toward
finding a clinical treatment for people with pathological fears."
Indeed, the authors noted that their findings "are consistent
with those of a recent preliminary study of patients with post-traumatic
stress disorder in which post-retrieval propranolol seemed to reduce
subsequent physiological responding to traumatic memory."
Yet much remains unknown. For instance, the current research involved
only a very short period of time. Though the memory appeared erased
on day three, would that still be true a month later? And, it's unclear
how effective will propranolol be against longer-term memories, such
as traumatic childhood memories that persist into adulthood.
Besides, the experimental memories were not exactly erased in this
study, Taylor noted: The propranolol-treated subjects no longer flinched
in reaction to the stimulus, yet they knew that they should. That,
Taylor suggested, could limit propranolol's clinical utility.
"Being afraid of something doesn't just involve a physiological
response," Taylor said, "it's how you think about it and
how it affects your behavior."
