● Our amazing human hand
They have one of the most enormous jobs in our body, so when one doesn’t work, it is complicated to make a new one,
They are always there: waiting, responsive, available to do our bidding whenever we want. They caress and tap and grasp at our command. They are designed to be stronger than they look and can convey some of the deepest of human emotions. A gesture of one can change the meaning of our very words or cause the most severe of offence. Only primates have them. Most of us have two. When they don’t work properly or are injured, it profoundly changes our world.
Of all the incredible organs in the human body, our hands have one of the most enormous jobs. We need their many abilities in nearly everything we do — to work, eat, show emotions, create and fix things, communicate, clean ourselves.
Our understanding of these loyal appendages is fairly patchy. Did you know that your fingers have no muscles? Or that — so complex are our many hand movements — the largest part of our brain’s motor cortex, the area that controls all muscle movement, is responsible for directing only the hands? How about this one: happy and stress-reducing hormones surge when we feel a friendly hand on our body?
Opposable thumbs, not unique to humans, evolved for primates’ common ancestors to better grasp branches and support their entire body weight while swinging. Over time, claws disappeared, replaced by flat fingernails and wider fingertip pads. Most primates can exercise both strength and precision in their fingertips. Humans, for example, can both grip a hammer tightly and delicately steer a pen to write.
Muscles in the palm and the forearm, not the fingers themselves, work together to give fingers their strength and nimbleness. Like puppets on a string, fingers are moved by the short, bulky muscles in the palm and the long, stretchy muscles in the forearm, connected by flexible tendons.
Try this: Bend the small, ring and middle fingers one at a time. Notice the finger next to them moving a little too? The tendons that move these fingers are controlled by the same muscle in the forearm. The adjacent fingers move with the finger you’re trying to flex because they share the same muscular source of control.
The complexity of the human hand becomes even more clear when we try to replicate it robotically.
Prosthetic arms and hands can’t feel pressure, says Alison Wilding, a musculoskeletal physiotherapist hand therapist at In Touch Hand Therapy, Christchurch.
“Human hands treat an egg differently to a tennis ball. Artificial limbs don’t have the sensory perceptions to know the difference in order to send the right messages back to the brain.”
There is a lot of interest in this area at the moment, she explains, especially involving the use of muscle contractions in the forearm and upper arm to control the prosthetic hand. Trouble is, she says, “they break very easily. Prosthetics aren’t yet strong enough to stand up to repeated use that is always going to be useful to the user.”
But robotic hands are providing great promise to amputees thanks to today’s 3D printing capabilities and materials such as silicone and PVC.
David Lovegrove and the design team at 4ormfunction in Christchurch designed a world-leading bionic hand and are now creating a much smaller version for children.
The Taska hand is strong enough to crush a tennis ball but delicate enough to grasp an egg without breaking the shell.
Designers spent thousands of hours improving the hand, which has a tiny motor, gearbox and clutch for each finger and two for its thumb. It’s worth $35,000.
Dunedin sculptor Gavin Wilson, who lost a hand six years ago after he put his arm in a shredding machine he thought was turned off, has one. Wilson has had a number of prosthetics but told the Herald on
Sunday in September the robotic sensors in the Taska hand let him to do “nearly everything”.
One of the questions that has been raised in prosthetics is: do we need our replacement hand to look like the other one?
In fact, two different robotic hands, each designed with different abilities, might be more useful for a double amputee. For example, one could be designed for gross motor skills such as gripping and turning, while the other would be used for fine motor movements, eg writing and picking up small objects.
“Society says yes, that we should have symmetrical limbs,” says Wilding.
“But two different limbs would probably work better than two of the same design. Prosthetics gives us the opportunity to get more creative in our thinking about hands and limbs.
“Artificial intelligence and prosthetics are coming rapidly at us. How we choose to use this technology is going to be interesting to watch.”
Biomechanical abilities and diversity of positions allow us to do everything from play piano and knead dough, to perform dentistry and sculpt masterpieces.
But the real thing has a connection to the nervous system that is difficult to replicate.
Hands host some of the densest areas of nerve endings in our bodies; skin on the fingertips have evolved to be highly specialised in the perceptions of pressure, temperature, pain, and touch. This increased sensitivity means hands are closely associated with not just our physical world, but our emotional one as well.
When we touch or are touched in a supportive and friendly manner, the brain releases oxytocin, a feel-good hormone that brings about feelings of trust, bonding and affection. The stress hormone cortisol is also reduced by positive touching and acts as a psychological buffer in stressful situations, which is probably why we hug a stressed loved one or touch a colleague’s shoulder to wish them well before a presentation. Research from the University of California demonstrated how people can convey emotions through touch alone. Dr Dacher Keltner’s experiment separated participants by a barrier so they could not see or talk to each other. Touch recipients received a touch to the forearm, then were asked which of 12 emotions, such as anger or compassion, the toucher intended to convey. Participants guessed correctly more than half the time, with increased accuracy for the more positive emotions. Our expressive hands can help tell a story as we gesticulate, turn towards a listener to express humility, and demonstrate confidence in ourselves by steepling and pointing. In his work with mock juries, Joe Navarro, in a Psychology Today article found that lawyers and witnesses who hid their hands while speaking were perceived to be less open and less honest by the jurors.
Emotion was played out in the 2014 RoboCop remake. Detroit-based police officer Alex Murphy suffers burns to most of his body after a car explosion.
In the original, the character has only his face and brain salvaged and is transformed into a cyborg. In the remake, Murphy has one hand salvaged, while the other is robotic.
The Detroit Metro Times revealed a deleted scene that shows on the DVD version.
“Can you save his right hand?” says Michael Keaton’s character, Raymond Sellars. “My father always said you can tell a lot about a man by his handshake.”
And at the recent Consumer Electronics Show in Las Vegas — the world’s biggest technology fair — a pet robot, complete with fuzzy teddy bear arms, was a hit.
Designed as a loyal companion for lonely elderly people, the Lovot is packed with sensors to respond to human touch and coos when its owner strokes it. When it wants to be cuddled, it waves its arms in the air, and will trail around adoringly behind its owner on wheels. It will even fall asleep in their arms if offered a cuddle.
Meanwhile researchers at
Cleveland’s Laboratory for Bionic Integration have recreated the feeling of kinesthesia — the intuitive sense of knowing where your limbs are, as well as the positions they’re making.
Finely tuned vibrations were sent into the skin of the upper arms and shoulders of six arm amputees.
The approach improved their ability to feel and control their prosthetic arms when performing actions such as gripping and pinching.
Aucklander Nick Ward, age 50, whose ability to express his emotions with his hands is nearly gone due to the progression of motor neuron disease, still finds handholding with his partner emotionally satisfying.
“When she holds my hand it feels really nice. But not having the ability to respond by squeezing her hand is hard for me. She has learned to put her hand on the top of my hand, cupping it from above while my hand rests on the arm of my wheelchair.
“We can sometimes do the traditional palm-to-palm handhold and this feels more rewarding because I can participate, using the fingers that still work to squeeze so it’s more reciprocal and mutual. This is more emotionally charged for me.”
Ward no longer has the use of one of his hands. The other still enjoys the partial movement of three of his fingers and, on good days, a compliant thumb. Muscle atrophy, he says, has occurred over the past 18 months mostly in his palm and top of his hand, rather than his fingers.
Despite the partial use of one hand, he says his hand movements are “clumsy, not refined. Hands work best if fingers and thumb are healthy. They rely on each like an orchestra. With each finger losing strength and movement, the hand becomes even more redundant.”
The Cerebral Cortex of Man, a study by American-Canadian neurosurgeon Dr Wilder Penfield, illustrates how very much attention is paid, neurologically, to our hands. Developed in 1950 to represent the brain areas dedicated to processing different anatomical parts of the body, it tells a story of how a vast array of pulses and possibilities is involved in driving our hands’ actions.
Think, for a moment, about the electrical triggers of your motor cortex right now. If you were reading this story on your phone, four fingers would be shaped in a soft but firm curve around the back of your phone, while the thumb stroked the screen with just the right amount of learned pressure to scroll according to your reading speed.
If you were reading on a computer, one hand would be touching a mouse and sparking the muscles in your palm and forearms to point the index finger to scroll or click. The other hand might be resting on your thigh or scratching your chin.
However, you are reading in hard copy — maybe while reclined on a beach towel in the sand or on a soft chair under a tree — and your hands will be busier than your mind; holding the pages steadily, unconsciously securing something as thin and delicate as a piece of paper.
Your fingers somehow know the exact dimensions of the paper so that it can grasp it without tearing the page. Then, your hand will turn the page by flicking a wrist — also part of the ecosystem at work here — to command the paper to rest without complaint on the page opposite. Magic.
So why did evolution deny fingers autonomy from the rest of the hand, leaving them without muscles? Wilding says that this may have to do with the size of the hand muscles.
“The fingers need to bend and when a muscle contracts, it bulks up,” she explains. “There isn’t room for muscle contraction in the fingers without losing fine motor movement. Fingers have the ability for delicate motor control because they are slender and fine, not bulky.”
Muscle-less fingers also need to be able to adapt to different shapes and textures, says Wilding.
“Hands must be mobile and mould around so many different things: a doorknob, a baby’s finger, a steering wheel.
“Unlike the foot whose main role is to bear weight, hands are nonweight-bearing, so you can have the movement, manipulation, and the sensations, as well as being strong.”
These wide-ranging abilities require the hands to make an enormous combination of movements. Given the complexity of this task, it’s no wonder that a disproportionate amount of the brain’s motor cortex is devoted to operating the hands.
Next time you’re holding someone’s hand, be grateful for the symphony of bones, neurological pulses, muscles and hormonal surges that serve you, mostly without even thinking.
When she holds my hand it feels really nice. But not having the ability to respond by squeezing her hand is hard.
Nick Ward