Crossing arms reduces pain: mini-lecture (UCL)

Uploaded by UCLTV on 20.04.2011

[ Music ]
>> I'm Giandomenico Lannetti from the Department of Neuroscience,
Physiology and Pharmacology of University College London,
and my research deals with pain and how the brain reacts
to external stimuli which are perceived as pain,
for example when we touch a hot object.
It is well known if you apply painful stimuli to the hand
of a healthy subject, like using this laser heat,
you get some pain and the stronger the stimulus,
the more intense the pain perceived.
What we found out is that if you deliver exactly the same
stimuli, always from the dorsum of the hands,
but when the hands are crossed over the midline,
like in this case, the sensation of pain produced
by the stimuli is reduced.
So there is small but significant analgesia:
we perceive less pain.
To study pain, we need this laser device
because that is a way of giving a pure pain sensation
without any touch because the laser hits the skin
and activates some pain-specific nerve fibres.
That tells the brain that that heating has happened
and that results in a sensation of pain.
We need to measure this pain in some way:
for example by asking,
using some scales to rate the intensity of pain perceived,
and then we also want to measure the brain activity
to understand how the brain reacts to this painful stimuli.
And that we can do, for example, by placing electrodes on the head
of the subject and recording the so-called
electroencephalogram, which is basically, as we can see here,
a plot of the electrical activity
of the neurons composing the brain.
So basically, what we found out - and we can try
to do that live now - when we deliver pure pain
without any touch to the hand of our subject,
we can see the brain reaction.
For example, we give a stimulus now and if we look
at the activity here, we can see
that when the stimulus is delivered,
which is this blue line, there is a small response
in the ongoing activity of the brain.
And then if we deliver the same stimulus,
but when the hands are crossed over the midline,
like in this case, we can again deliver a stimulus
and record the activity in the electroencephalogram
and we can see again here, there is a stimulus
and there is the small deflection,
which is basically the brain reaction
to the external painful stimulus.
So if we do that on many subjects
and we repeat the stimuli many, many times, what we observed,
we observed that when the stimuli delivers on the hands
in a crossed position, the subject perceives less pain
and the electrical response from the brain,
that part which is more correlated to the awareness
of the stimulus, is actually reduced.
So we get this analgesia in response to stimuli delivered
when the hards are in an uncommon position.
So why is that?
Well, we believe that the reason is
because the brain gets confused when we cross the hands.
And if you think about that, when we interact
with the world, for example when we pick up an object
with our right hand, the brain areas dealing
with the right hand responsible for the sensations coming
from the right hand are activated together
with the brain areas responsible for the right side
of the world. But when we cross our hands
and we have a stimulus, for example, on my right hand
when that is on the left side of the space,
we activate brain areas responsible for the right hand
and for the left side of the world,
which are less commonly activated at the same time.
And that results in a less effective processing
of the sensory stimulus and in a reduced perception, even
in a reduced pain perception.
We believe that this result is important
because it might potentially lead to novel treatments
for patients with chronic pain by creating this conflict
between the brain areas responsible for the body
and for the external space.