Ask a Neuroscientist: The Limits of Handedness

Hi, I’m not sure if this is the right place to ask this but I play video games competitively and I was wondering about two things. Firstly, I am naturally left handed but I rely on my right first finger to tap a button as quickly as possible. Am I at a disadvantage to people using there natural hand since it is their dominant hand or can I train my non dominant hand to be as quick as my left hand? Also, when I am playing I realise I am using the thumb of my non dominant hand to make extremely precise movements. I have been playing for 4 years but am I still at a disadvantage to people who are using the thumb from their dominant hand to make precise movements. Is the thumb from the dominant hand more precise in tiny movements or after 4 years has my left thumb been trained to be as precise as my dominant hand? Does hand dominance only affect the movement of the hand itself or are the fingers and thumbs effected by the hand dominance? Also, in general If I hadn’t been training my non dominant hand to make precise movements, would the thumb of the dominant hand be naturally better?

Thanks a lot! I was just wondering because I often play xbox competitively in tournaments and dexterity matters!!
— Ben Sanders

Dear Ben,

You’ve asked some questions that really resonate with me. I’ll bet they also resonate with at least 10% of the rest of the population. I’ve done some investigation, and it turns out neuroscience has a lot to say on the subject of handedness. Let’s see if it can answer your inquiries!

Dominant Hand Versus Preferred Hand

First off, handedness comes in a variety of flavors, not just “lefty” and “righty.” Our own Astra Bryant recently wrote a relevant post about this for the Neuroblog. There you can read her description of how handedness falls along a spectrum rather than a binary. It’s quite common for a person to prefer one hand for many tasks and the other hand for a selection of different tasks. Take, for example, LeBron James, the basketball icon who, apparently, prefers his left hand for writing and his right hand for shooting. 

For simplicity, my use of “dominant” in this post refers to your most dexterous hand. By contrast, I’ll use “preferred” for the hand you choose to perform a specific task. Ben, it sounds like in your case, your preferred hand for the video game controller is your dominant (left) hand; however, you have been forced to use your non-dominant (right) hand because of the controller layout. In other words, the positions of the buttons require you to make quick and precise movements with the digits on your right hand.

Digit Dexterity and Hand Dominance

Because quickness and precision can profoundly affect your game, you are concerned whether hand dominance applies to the fingers and thumb. If the answer is no, then left-handed and right-handed video gamers would presumably be on a level playing field. This is an interesting problem, especially considering that some tasks seem easier than others for the non-dominant hand to pick up. Is gaming one of them? In my experience, learning to fret a stringed instrument or manipulate a pipette with my non-dominant hand has been less difficult than learning to write with it. So does that mean that there are levels of difficulty for the non-dominant hand that depend on how complex a task is? Or are tasks that only use the fingers, such as tapping a button, exempt from handedness?

The common criteria for determining handedness (again, see Astra’s post linked above) don’t really require fine coordination or quick movements of the fingers. At most, the fingers must hold a manipulated object, as in the case of threading a needle or striking a match. But the absence of finger dexterity in these criteria does not suggest that the fingers lack handedness. In fact, as it turns out, finger tapping itself is often used to determine hand dominance.

There are a few variations on the finger tapping test for determining hand dominance. But the basic motion is probably similar to the motion you make when you rapidly tap the button on your video game controller. If you were to take this test, you would be told to tap a lever with your index finger as quickly as possible for 10 seconds. You would then do the same with the index finger of your other hand, then repeat with the first hand for a total of ten trials for each hand. Importantly, you would be cautioned against tapping using a “well-controlled tremor” so that full taps with defined endpoints of travel are produced.

Over and over again, this test has shown that the dominant hand taps significantly faster than the non-dominant hand. But where does this difference come from? Does the non-dominant hand tire out more quickly? Is the dominant hand better at switching directions? When you’re tapping the button on your videogame controller, which of these different factors most contributes to the variance between your hands? Fortunately for us, this has already been figured out:

Finger Tapping Breakdown

One aspect of the tapping motion is the time between taps, or the “intertap interval.” Tapping tests from many individuals of different handedness show that the average of the last three intertap intervals for each trial is consistently longer than the average for the entire trial, no matter which hand is being tested. This suggests that each hand equally slows down over time.

Left-handedness and Video Gamers

Being completely naïve to the world of video games, I began my search for your answer by polling my right-handed housemates, who are in the heat of a perpetual Madden tournament.

Housemate 1 conjectured that over four years of playing, you have probably developed better dexterity in your non-dominant hand in this context. Therefore, it’s not just as precise as your dominant hand is, but more precise. But could your dominant hand be even better? Is the upper limit of dexterity always higher in the dominant hand? The only way to test this would be to get a custom controller and train your dominant hand to see how long it takes to become as good as your non-dominant hand. Could you surpass yourself within that time?

Housemate 2 added that LeBron James, a lefty, shoots with his right hand.

So if late-trial fatigue is similar between the dominant and non-dominant hands, which aspect of the tapping motion is clearly different? If we break down tapping into individual directions (top-to-bottom, bottom-to-top, full cycle down/up, full cycle up/down, and transition from down to up) and observe the speed of each, we would see that the total time to complete a full cycle is shorter for the preferred hand, as would be expected. We would also find that the biggest factor contributing to this difference is the time taken to reverse directions from down to up. In other words, the difference between hands for single directions is quite small, but the difference for transition times is quite large. Ben, if your right index finger were a triathlete, its weakness would be transitioning from swimming to biking and from biking to running.

What’s more, a modified tapping test was designed to get volunteers to limit the excursion of digit movement to a minimum, moving the finger only far enough to operate the lever. The non-dominant hand performed far worse at this task than the dominant, which confirmed that the biggest difference between hands is the ability to precisely modulate the tapping force.

In short, the dominant hand does indeed tap more quickly than the non-dominant. And this difference is exacerbated if you tap just enough to operate a lever, because the preferred hand is more precise at modulating force, not necessarily quicker at trembling. Over multiple consecutive taps, the deficiency in your non-dominant hand translates to noticeably slower tapping.

So, yes, one can be, decidedly, “left thumb dominant.”

But perhaps it’s comforting for you to know that the tapping difference between hands was lower for left-handers than for right-handers. Why is that? Let’s delve deeper into the brain to see if we can find out.

The sensory homunculus.   Illustration from Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/

The sensory homunculus.  

Illustration from Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/

Cortical Plasticity in Musicians

Neural connections from the fingers and hands map to regions within the motor cortex and somatosensory cortex, the parts of the brain responsible for controlling movement and perceiving touch.

Measuring these parts of the brain and comparing their sizes across hemispheres can predict handedness. The left hemisphere controls the right hand and the right hemisphere controls the left, so a larger hand area in the left motor cortex correlates with right-handedness in humans and other primates. And these differences can be observed right down to the individual finger maps.

Now that we know that digit dexterity does correlate with hand dominance, we can address the second part of your question: even after years of training your non-dominant hand, are you still at a disadvantage to right-handed video gamers? In other words, for certain tasks, can you train your non-preferred hand/digits to be as good as your preferred?

The region of your brain that receives sensory input from the fingers has an impressive capacity for re-wiring in response to changes in your behavior, environment, and physicality. We refer to this capability as neuroplasticity, or the ability of the neurons in your brain to form new connections. See this recent Neuroblog post, or this one, or this one, for more information on and a fascinating example of neuroplasticity.

remarkable demonstration of plasticity occurred in two adults who underwent corrective surgery for syndactyly (webbed fingers). Within one to five weeks after surgical separation of the digits, the topographic maps in the hand areas of each somatosensory cortex reorganized to represent separate digits where before there was no separation between the digits. One patient reported feeling the fingers as “individual entities for the first time in his life.” So even in adults, the finger representation area in the somatosensory cortex is extraordinarily plastic.

The example of corrective surgery is rather extreme, but you can simply train your non-preferred hand to be better at a chosen task. Exactly how much better can your non-dominant hand get, and can it ever be as proficient as your preferred hand? Musicians, especially keyboard and string players, can offer clues to help us answer this question. In one intriguing study, researchers compared the sizes of the left and right primary motor cortex of right-handed keyboard players and right-handed non-musicians. As I alluded to above, normally, right-handers show a left-larger-than-right motor cortex (the left hemisphere controls the right hand), which offers a “structural correlate” of handedness, and thus, dexterity. Incredibly, the size difference between the two hemispheres, or “left-right asymmetry,” was not as pronounced in keyboard players as in non-musicians, providing evidence that long-term use of the non-dominant hand can lead to gross anatomical changes in the non-dominant motor cortex.  

What is even more revealing is that it appears that the earlier the keyboard players began their musical training, the more symmetrical their motor hand representation areas were. But there was no correlation between the duration of training in years and the symmetry of their motor cortices. And, it’s important to note, they all still exhibited leftward asymmetry, both in motor cortical sizes and in distal hand/finger motor skills as assessed by the finger-tapping test described above.

Similar results were found in a study of nine right-handed string players. For both the keyboard players and the string players, the amount of neural reorganization appeared to decline steadily between those who started playing at 3 years of age to those who started playing at 12, leading to the conclusion that the brain is most plastic during the early years of life. The parts of the brain that send and receive input from the fingers can indeed grow and reorganize in response to long-term stimulation, but if we take anything away from our musical training, it’s that the earlier these behaviors begin, the better. Brain plasticity decreases with age, and the most significant changes appear to occur early in life.

Young musicians may also answer why there appears to be a smaller difference in tapping ability for left-handers: lefties are born into a right-handed world, where they are systemically trained to use their non-dominant hand for certain tasks. This early training could lead to long-lasting changes in the hand areas of the right cortex.

Conclusions: Innate But Plastic

All hope is not lost for those of us who missed out on our calling to be musical toddlers. Even in adulthood, improved dexterity and cortical reorganization can occur after only 3o minutes of shaping exercises, like those used for rehabilitation after stroke or paralysis. So even if all the gaming in the world could never make your non-dominant cortex as large as your dominant (in the hand area), you can still rewire your brain to be better, if not good enough.

In conclusion, neuroscience tells us a lot about handedness. Here are the most important points:

  • Finger dexterity exhibits handedness.
  • Handedness is biologically determined, and, we can predict which hand is dominant by observing differences in your brain.
  • The cortex is plastic, and you can train your non-dominant hand to be more proficient, which results in cortical reorganization.
  • Your brain loses plasticity as you age, so the earlier you start training your non-dominant hand, the better your brain is able to rewire.
  • Even if you start training at a very young age, there seems to be an upper limit to how much your non-dominant cortex can reorganize.

So, Ben, without being able to directly compare the performance of your trained non-dominant hand to that of your comparably trained dominant hand, I hypothesize that you’re at a slight disadvantage to naturally right-handed gamers. But how noticeable the disadvantage is, if at all, is determined by how early in life you started training and by how much you would have preferred your dominant hand for this specific task in the first place.