The Scientist - USA (2020-01 & 2020-02)

01/02.2020 | THE SCIENTIST 55

W

hen people ask me about the

“mind-body connection,” I

typically suggest walking on

an icy sidewalk. Skip the yoga, mindful-

ness, or meditation, and head to the cor-

ner on a cold, windy, snowy da y. Every

winter, much of North America becomes

exceedingly slippery with ice. Emergency

rooms across the continent see a sharp

uptick in fractured limbs and hips as

people confidently trudge outside in such

conditions, unveiling a profound dis-

connection between what people believe

and what they can actually do with their

bodies. One might think that a person

could call on experience from years past

to adjust their movement or provide a

little insight or caution. But the truth is

that the body forgets what it takes to stay

upright in these perilous conditions. Why

is there so much forgetting and relearning

on an annual basis? We remember how

to ride a bike. Why can’t we remember

how to walk on ice?

I attempt to answer this and other

questions concerning the connection

(or lack thereof ) between motion in the

mind and motion by the body in my new

book, Physical Intelligence: The Science

of How the Body and the Mind Guide

Each Other Through Life.

Falling on ice reveals a delicate tradeoff

that the brain must reconcile as it pilots

the body. On the one hand, it needs to

build refined motor programs to execute

skills such as walking, running, and

throwing. On the other hand, those pro-

grams can’t be too specific. There is a

constant need to tweak motor plans to

account for dynamic conditions. When I

throw a backpack on, my legs don’t walk

in the same way as they do without the

pack: my stance widens, my stride short-

ens. Often, the tweaking needs to happen in

moments. As I pick the pack up, I need

to lean in or I could tip myself over. Just

as importantly, as soon as I put it down,

I need to forget I ever held it in the

first place.

In my lab at the University of Cali-

fornia, Santa Barbara, we investigate the

mechanisms the brain employs to make

these super-fast adaptations. We have

participants pick up tippy objects the

size of a desk stapler that are weighted to

roll to the left or right. After only a few

trials with one object, subjects typically

succeed without any mistakes. Then, we

switch the object. The tipping is back,

but in the opposite direction. The sub-

jects learn yet again.

We know from neurophysiologic

recordings and brain imaging that the

skills necessary to pick up objects are

controlled by motor areas of the cortex,

the brain stem, and the spinal cord. From

fMRI scans we know the cerebellum is

a key area for acquiring and forgetting

these rapid adaptations of finger forces.

Pattern analysis of the brain scans sug-

gests that when a participant must learn

how to successfully lift a new object, the

brain can completely erase the pattern

previously used to lift the one that rolled

in the opposite direction. The brain falls

back to a generic pattern for lift forces

that it applies whenever it has to

refamiliarize itself with the dynamic prop-

erties of the object. Fast adaptation like

this occurs whenever a person’s body is in

motion, whether it is an adjustment of the

fingers to pick up an object or of the legs

to walk down a slippery sidewalk.

We are usually unaware of the count-

less small tweaks we make to our move-

ment patterns as we adapt to changing

conditions. It is one of the many aspects

of physical intelligence that we take for

granted. A lack of insight into the for-

getting in particular is one explanation

for why people fall on ice. As winter sets

in, the tweaks necessary to stay upright

on the ice are long since forgotten. We

simply don’t retain this kind of dynamic

knowledge. The only way to adapt to a

slippery surface is to experience it anew

through direct contact. A marathon of

virtual reality exposure wouldn’t help a

bit. Only by shuffling, sliding, and feel-

ing the grip of our shoes can we adapt

and learn what is physically possible in

those specific conditions. As this cross-

talk between mind and body helps us

attain equilibrium, beliefs and motions

are brought into harmony. And the ice

walker trods steadily on.g

Scott Grafton is a neuroscientist at the

University of California, Santa Barbara.

Read an excerpt of Physical Intelligence at

the-scientist.com.

Pantheon, January 2020

Navigating a wintry landscape forces the mind and body to come

to a constructive equilibrium and reveals the fascinating dialogue

between the two elements of a human being.

BY SCOTT GRAFTON

Slip Sliding Away

READING FRAMES