Brain waves measured
The researchers tested pain responses in 70 people. All those involved
in the study were healthy and young, with a mean age of 24 years. The
majority were male.
They recorded results from two different experiments. The first had 22
participants, the second 48.
In the first, participants were given repeated pain stimuli and touch stimuli
to the back of the right hand on two occasions, two weeks apart. The pain
stimulus was produced by a
Tm:YAG laser. The participants scored both stimuli from zero to 10.
In the second experiment, participants received high- and low-intensity
pain stimuli from an
Nd:YAG laser. Each person received 80 high and 80 low-intensity stimuli. They
were asked to rate them from zero for no pain to 100 for maximum tolerable pain.
In both experiments, participants wore an electrode cap during the stimuli
electroencephalogram (EEG) data from which the researchers analyzed the gamma responses.
Toward an objective measurement of pain
Dr. Vernon Williams, a sports neurologist, pain management specialist, and founding director
of the Center for Sports Neurology and Pain Medicine at Cedars-Sinai Kerlan-Jobe
Institute in Los Angeles, not involved in this study, explained to
Medical News Today:
“Pain is defined as an unpleasant sensory and emotional experience
associated with, or resembling that associated with actual or potential
tissue damage. It is not a ‘sensation,’ it is an ‘experience’.
As such, it is always personal and individual, and subjective. So, it
is not surprising that the gamma oscillations vary significantly from
person to person.”
Not only did the pattern of gamma oscillations differ between different
individuals, but the researchers found that, for each individual doing
the repeat experiment, the pattern remained constant.
Dr. Valentini explained: “Our work clearly demonstrates that there
is a remarkable stability: Participants with high/no gamma activity and
high/no pain ratings in the former recording had high/no gamma activity
and high/no pain ratings two weeks later.”
According to Dr. Williams, this could be useful for pain management: “It
is interesting that the findings are reproducible within an individual,
and that may have future implications regarding objective measures of
pain and objective measures to assess pain interventions/treatments —
particularly in the short term.”
However, Dr. Valentini added a note of caution: “Our study highlights
that the importance of gamma oscillations for pain processing may be highly
overstated. [It] acts as a timely reminder that even when a strong group-level
correlation is replicated by several studies we may still be fooled in
drawing causal interpretations.”
Do the findings have clinical relevance?
“In a nutshell, we suggest that gamma oscillations are not required
for pain, but when present, they are a stable and replicable feature of
the individual,” said Dr. Valentini
Their findings could lead to more personalized pain management, as Dr.
Valentini went on to explain: “Our work resonates with the idea
of personalized medicine whereby clinicians may focus on the specific
individual’s biological patterns as to achieve faster and better
diagnosis or treatment.”
“Thus, whilst our findings have no immediate clinical implication,
they pave the way to a more precise assessment of neural responses mediating
the experience of pain,” he told us.
Dr. Williams agreed that there were grounds for optimism. “In the
studies, ‘reproducible’ meant that individuals had similar
findings when tested two weeks apart,“ he told us.
“That may not be true if tested 2 months apart or 2 years apart,
[or] if there are changes in biological, psychological, or social conditions
between tests. If changes occur under different conditions, that might
mean that the person’s ‘fingerprint’ can change over
time (or if circumstances change), as well,” added Dr. Williams.
“That provides reason for optimism, because that would mean their
experience (the pain they feel) can be reduced, improved, or eliminated
with the right combination of interventions. Chronic pain does not have
to be ‘for ever’,” he noted.
Dr. Valentini plans further research: “Together with my collaborators,
we feel that gamma and other brain oscillations are a crucial field of
investigation for pain neuroscience. […] Perhaps, some of us will
be able to replicate these analyses in chronic pain patients or patients
with acute pain, thus addressing more directly the clinical relevance
of our investigation.”