Why is the sense of touch important to humans
The Science of Touching and Feeling | David Linden | TEDxUNC
my god there are a lot of you here so
thank you for having me thank you for
letting me close out your conference
sound because I'm the last speaker I
think I should talk for a moment about
what I think that being human is I've
been listening to all these wonderful
presentations and I think if there's a
summary it's that to be human is to be
emotional to feel things and for all of
us the sense of touch is intrinsically
emotional and we don't need scientific
investigations to know that we can just
look at our common expressions that we
use every day I'm touched by your
concern I didn't mean to hurt your
feelings I can't stand that slippery
politician you can guess which one I
mean could be any of them really when we
encounter someone who's emotionally
clumsy we call her tactless literally
she lacks touch so how does this
connection between emotion and the sense
of touch form and it begins to form very
early in life
and we know that if you're born blind
without sight that you can develop a
great mind and a great body and have a
great life and likewise if you're born
deaf you can develop a great mind and a
great body and have a great life but if
you're born with the biological
components for a sense of touch but you
do not receive touch during your infancy
and when you're a toddler than a
disaster unfolds and we know this mostly
from what happened in orphanages in
Romania during the Ceausescu regime in
the 1970s and what followed in the 1980s
and these were situations where there
were grossly understaffed orphanages
there was no one to hug or hold or
caress
or be loving in a tactile way towards
these children and they develop horrible
compulsive self soothing rocking motions
later they had attachment disorders
cognitive delays and it wasn't just
neuropsychiatric problems their growth
was stunted and they had problems with
the development of their
gastrointestinal systems and their
immune systems and we know that this is
because of touch deprivation because in
some cases volunteers came in and gave
just 30 minutes a day of loving touch a
little hugging a little limb
manipulation and that was enough to
completely reverse all of these
deleterious effects but only if it
occurred in the first two years of life
it happen if the intervention came after
age two all those problems would persist
for the rest of life now the critical
role of touch in childhood development
wasn't always understood as a matter of
fact in the 1920s John B Watson the
founder of the psychological movement
called behaviorism advised parents never
touch your children never hug them if
you must when they have done an
extraordinarily good job at a difficult
task Pat them on the head give them a
handshake at the end of the day now of
course today most parents don't raise
their children this way but it's a very
different situation outside of the home
where we have promulgated no touch
policies for supervisory adults like
teachers and coaches that while
well-meaning have had a disastrous
effect when a kindergartner reaches to
get a reassuring hug from the teacher
and the teacher isn't allowed to have to
stand their stock still that is not a
social good an opportunity to create
bonds of trust and cooperation and
empathy is lost and you might say well
okay understand babies are really
sensitive kids are sensitive but what's
your once you're an adult does all this
touchy-feely stuff really matter and the
answer is yes it does touch is social
glue it's what binds sexual partners
into lasting couples it's what
ion's parents and their children and
siblings it binds together people in the
community in the workplace in two
effective teams we know that doctors who
appropriately touch their patients
during an exam are rated as more caring
and more importantly their patients have
better better medical outcomes and lower
stress hormone levels in terms of actual
teams we know that in the National
Basketball Association there was a
wonderful study was done by dr. kelmer's
group at UC Berkeley and what he did is
he got video tapes of all the NBA games
of all the teams in the first half of
the season and then he had people look
at them and score all of the celebratory
touch all the Pat's on the rear end on
the chest bumps on the high fives and
everything that people do to celebrate a
basket and he came up with an index of
celebratory touch for each team and he
asked does that index for the first half
of the basketball season predict
anything about what's going to happen in
the second half of the season and the
answer is the teams that engage in more
celebratory touch both win more games in
the second half of the season and more
importantly they play in a more
cooperative fashion for example the star
would be more likely to pass off the
ball to another player who had a better
shot so what I'm drawing what am I
trying to tell you here it's not that
touch is good or even that touch is
important rather it's that the specifics
of our touch experience from skin to
nerves to brain are weird and strange
and counterintuitive and these strange
and counterintuitive facets of touch
profoundly affect our human experience
and our human society and let's explore
that point number one we think of touch
as being a unified sensation we
experience it as a unified sensation but
actually it's created by many different
specialized sensors working in parallel
so what do I mean if we looked in your
skin we would see many different kinds
of nerve endings each one a micro
machine specialized to transfer a
certain kind of information we'd find
one nerve ending for heat and another
for cold one for pain
and one for each one for sexual
sensation vibration pressure texture
fine tactile form there are nerve
endings specialized for all these things
and the density of these nerve endings
in different parts of your skin gives
rise to the way you experience touch on
different parts of your body for example
if you want to read Braille dots which
require appreciating fine tactile form
you're likely to use your fingertip
because your fingertip is very
well-endowed it has a high density of
the nerve ending called a Merkel ending
which is the best ending for detecting
fine tactile form and for some reason
you can't use your hand you can read
Braille dots with your lips because they
also have lots of merkel endings or your
tongue which also has lots of merkel
endings and I can I can see your
expressions out there in the audience
some of you are thinking I got some
other parts of my body that are kind of
sensitive could I use those and the
answer is no you cannot use the cornea
of your eye to read Braille dots ah so
you know when you get a piece of grip in
your eye it hurts like crazy but it's
very hard to tell precisely where in
your eye it is and this is because while
your eye is sensitive it's not
discriminative but that is to say you
can't read tactile form with your cornea
because it lacks Merkle endings and of
course I knew what you really think
about your think about your genitals
right
can you read Braille with your genitals
no you can and it's the same reason you
don't have Merkel endings in your
genitals so you can't read Braille there
it won't work now I know that all of you
want to do citizen science and this is a
cool thing right you don't want to take
my word for it so you're going to be out
on Franklin Street later tonight you're
going to wait till no one's around at
the ATM and you're going to test it
yourself all I ask is that bring a
disinfecting wipes for when you're done
point number two there is no sensation
without emotion the two go hand-in-hand
so all these streams of information that
I told you about
are coming to your spinal cord and
they're coming to your brain and they
distribute into two different systems
one of them in a region called the
somatosensory cortex is all about the
facts it's the discriminative system it
tells you where my body am I being
touched and in what fashion and how
intensely then there's a completely
separate system in a brain region called
the posterior insula and that's your
emotional touch system that's what gives
different kinds of touches their
particular emotional tone so for example
if I were to sneak up on you and whack
you on the thumb with a hammer you would
go out [ __ ] oh that hurts that's
awful my thumb is throbbing um however
if you had damage to your posterior
insula you would have a condition called
pain Easton boliya and then if I whacked
you on the thumb with a hammer you would
say in a very flat emotionless voice yep
that hurts all right it's on my thumb
it's throbbing now the pain would have
no emotional resonance for you
whatsoever because you need the
posterior insula to field out now what
about the converse what if you had
damage throughout your somatosensory
cortex it's a pretty rare thing but it
can occasionally happen then if I whack
you on the thumb with a hammer you would
say oh that's terrible that hurts so
badly and I'd say oh I'm so sorry where
does it hurt and you'd say I have no
idea so the point here is that we're
used to thinking of certain sensations
of having an intrinsic emotional tone
but this is a trick our brain plays on
us right we have the sensation of it's
the thumb that hurts and the negative
emotional tone that goes with that pain
only because these two different brain
systems are active at the same time
point number three point number three is
that we are hard-wired to pay attention
to sensations including touch sensations
that originate in the outside world but
discount ones that originate from our
own motion and so what do I mean imagine
that you're walking down the street and
as you walk down the street you're
moving your limbs and your torso and
your clothes are moving against your
body
and you're not thinking about it at all
it doesn't enter your consciousness one
bit those sensations are strongly
suppressed whereas if you imagine you're
stopped on the street corner and now
those same sensations come on your body
oh you'd be very very attentive to them
they would have great salience uh why is
that it's because we're hardwired to
suppress the sensations that result from
our own motion and this makes
evolutionary sense right because the
outside world that's where the things
are that we might want to eat that we
might want to mate with that we might
want to run away from so we want to pay
more attention to the outside world
then to the consequences of our own
motions and and the crucial medical
issue that is tied up with this is why
it is that it's so very hard to tickle
yourself right so when you go to tickle
yourself electrical signals are flowing
from the motor cortex in your brain down
to the muscles of your arm and your hand
to produce that tickling motion but
those a copy of those signals is going
to a part of the brain called the
cerebellum and the cerebellum transforms
those into inhibitory signals and feeds
them in to the somatosensory cortex the
fact-based touch Center and suppresses
suppresses those sensations and that's
why you can't tickle yourself very
easily there was a few people I'm sure
in this audience there's probably a
dozen people who will say yeah I can
tickle myself but it's pretty rare we
know however that people who sustained
damage to the cerebellum and interrupt
this hardwired circuits can indeed
tickle themselves now I'd like to
conclude so we like to think that we're
driving the bus and by that I mean we
like to believe that we can take in
reliable information through our senses
about the ex outside world and if
necessary make entirely rational non
emotional decisions about that
[ __ ] it's not true our senses are
not designed to give us the most
accurate representation of the outside
world rather they mess with the data
they emphasize some things and they
diminish others and by the time you're
first
aware of it that sensory information has
always been already been blended with
your emotional state and it's been
blended with expectations and I'm both
talking about your own personal
expectations that you have accrued
through your individual life experience
as well as the genetic expectations that
you have accrued through your DNA
through hominin evolution and your brain
serves it all up to you as real thank
you very much your attention
