Tag Archives: coordination

Nine Brains Are Better Than One: An Octopus’ Nervous System

Picture this: Earth has made its first contact with an extraterrestrial species, and, as to be expected, their anatomy and nervous system are entirely different from our own. Rather than having a single brain where all sensory information and motor controls are processed, they have nine brains. Rather than having a rigid skeleton, they have compact arrays of muscle tissue that stiffen and soften when they move, and their many limbs have an infinite number of degrees of freedom. Oh, and they can only breath underwater, too.

What was just described isn’t an alien at all, but actually the complex anatomy belonging to a common octopus, otherwise known as Octopus Vulgaris, and there is a lot we can learn from it. So how does an octopus fully control all eight of its flexible limbs? The answer lies in its partially de-centralized nervous system. When most people think of a nervous system, they think of a single brain sending out messages to move our arms and legs, then gathering information back to process everything we touch, see or hear. For an octopus, though, this process is much more complicated.

Independent Thinkers

Each arm of an octopus is able to control itself semi-independently from the central brain. An octopus has about 500 million neurons in its body, two-thirds of which are distributed amongst its limbs. This means that there are about 40 million neurons in each tentacle. That’s more than two times the number of neurons the average frog has in its entire body! An experiment conducted by German Sumbre et al. showed that even when a disconnected arm was electrically stimulated, it would still move in the same basic patterns of a tentacle being controlled naturally by an octopus. The arm even adapted its movement patterns the same way a still-connected tentacle did when the arm’s environment and initial posture were changed.

There are two columns of images. The left shows an octopus outstretching its arm over the course of 920 seconds. An arrow tracks the movement of a bend in the arm that travels along the arm until it is fully stretched out. The right column shows a single, detached octopus arm outstretching over a similar time frame. The single tentacle follows a similar movement pattern as the original octopus' arm. Another arrow also follows a similar bend that travels along the single arm as it stretches out.
An experiment shows that an electrically stimulated octopus arm (right), when detached from its central nervous system , will still move in the same basic patterns as an arm naturally controlled by an octopus (left). Image modified from G. Sumbre, Science Magazine.

Master Delegaters

So how does this partially de-centralized nervous system work? The octopus does, in fact, have a central brain located between its eyes containing about 180 million neurons. This is the part of the nervous system that determines what the octopus wants or needs, such as if it needs to search for food. These are sent as messages through groupings of neurons. Commands like “search for food” are then received by each of the tentacles, who all have their own smaller, independent brains. With these commands in mind, each tentacle gathers its own sensory and position data, processes it, and then issues its own commands on how to move by stiffening or relaxing different parts of the arm, all without consulting the central brain upstairs. As the tentacle moves, it keeps collecting and processing sensory information, and any relevant information, such as the location of food, gets sent back to the central brain to make larger decisions.

Beyond the Octopus

There is still a lot left unknown about how exactly an octopus’ nervous system functions. However, new and upcoming fields such as soft robotics and artificial intelligence are starting to look towards the opportunity for innovation that octopuses present. Learn more about how the anatomy of an octopus is being applied to science and technology here and here!

Further Reading

Sources

Sumbre, G. “Control of Octopus Arm Extension by a Peripheral Motor Program.” Science, vol. 293, no. 5536, Sept. 2001, pp. 1845–48. DOI.org (Crossref), doi:10.1126/science.1060976.

Zullo, L., Eichenstein, H., Maiole, F. et al. Motor control pathways in the nervous system of Octopus vulgaris arm. J Comp Physiol A 205, 271–279 (2019). https://doi.org/10.1007/s00359-019-01332-6

Levy, Guy, et al. “Arm Coordination in Octopus Crawling Involves Unique Motor Control Strategies.” Current Biology, vol. 25, no. 9, May 2015, pp. 1195–200. DOI.org (Crossref), doi:10.1016/j.cub.2015.02.064.

Attention Deficit Handwriting Details: The Effects of ADHD on Handwriting

Imagine you’re in college and struggling to focus during a boring lecture with a monotone professor. Now imagine that same struggle, but every little thing around you is a distraction making it difficult to focus on everyday tasks, not just the boring ones. Individuals with Attention Deficit Hyperactive Disorder (ADHD) battle this inability to focus constantly. Yet for individuals with ADHD, about 1 in 20 children (basically a lot of children), the struggle does not stop there: these individuals who struggle to focus often exhibit fine motor coordination impairments as well.

It just so happens, writing requires fine-motor coordination. Even with computers and evolving technology, writing is a necessary skill used by most individuals throughout their lifetime. It is well-known that when taking notes, you are more likely to retain information when writing notes as opposed to typing them. We have to write when we take exams (hopefully more so once the pandemic is over because I am tired of computer glitches during online exams). We write to communicate different ideas to each other, or even to communicate ideas to future self that we wish to remember.

Writing is still a necessary part of our everyday life, yet when this writing is difficult to read, its effectiveness diminishes. Imagine finally being able to focus enough during that boring class to take notes but not being able to read them. Imagine taking a timed exam but wasting this limited time to ensure the handwritten answers are legible. When compared, the handwriting of most individuals with ADHD is worse than individuals without this disorder.

There are three subtypes of ADHD: individuals are primarily hyperactive, primarily inattentive, or combined type (both hyperactive and inattentive). Individuals with ADHD who are primarily hyperactive are more likely to write faster with shorter strokes and to write more efficiently. On the other hand, individuals with ADHD who are primarily inattentive write with inconsistent letter sizes and spacing between the letters, along with diminished legibility. These individuals will exhibit this inconsistency in their writing due to a greater variability in stroke sizes.

Image of the handwriting with inconsistent letter sizes and spacing. There are 6 letters circled out of 10 letters. The letters are circled because they are illegible and it is difficult to know what the letters are supposed to be. The four letters not circled are: t, v, x, y.
Image of the handwriting with inconsistent letter sizes and spacing, along with illegibility of letters circled.
Source: https://doi.org/10.1177/0883073807309244


Individuals with combined type ADHD experience an inner battle between hyperactivity and inattentiveness, resulting in faster, more efficient writing at the expense of accuracy and legibility of their handwriting. Interestingly, these individuals on Methylphenidate, a stimulant used to treat ADHD symptoms, tend to write in the complete opposite fashion: the quality of their handwriting improves while the speed diminishes. Since the illegibility of the combined type ADHD individual’s handwriting is affected by their inattentiveness, the improved handwriting quality is due to the increased focus provided by this stimulant.

It is believed that the handwriting of primarily inattentive and combined typed individuals are the results of a form of Dysmetria. Dysmetria is a lack of coordination between movements, which would result in the irregular handwriting due to an under or overshoot of the desired writing size. These individuals are unable to process the information that they receive fast enough to generate the desired response.

While primarily hyperactive individuals tend to write faster and more efficiently, their handwriting does not necessarily differ from individuals without ADHD. On the other hand, the difference in quality of handwriting in individuals with ADHD compared to individuals without is more prominent in those with primarily inattentive or combined typed ADHD. There are many individuals out there who struggle with ADHD and are at a disadvantage because of this. Accommodations for individuals with ADHD should go beyond accommodating inattentiveness and hyperactivity since difficulties are only the root of them problem that stem into more obstacles such as reduced writing quality.

Sources

Rebecca A. Langmaid, Nicole Papadopoulos, Beth P. Johnson, James G. Phillips, Nicole J. Rinehart. Handwriting in Children With ADHD. Journal of Attention Disorders. https://doi.org/10.1177/1087054711434154. Original Research.

Marie Brossard-Racine, Michael Shevell, Laurie Snider, Stacey Ageronioti Bélanger, Marilyse Julien, Annette Majnemer. Persistent Handwriting Difficulties in Children With ADHD After Treatment With Stimulant Medication. Journal of Attention Disorders. https://doi.org/10.1177/1087054712461936. Original Research

Javier Fenollar-Cortes, Ana Gallego-Martinez, Luis J. Fuentes. The Role of Inattention and Hyperactivity/Impulsivity in the Fine Motor Coordination in Children with ADHD. Research in Developmental Disabilities. https://doi.org/10.1016/j.ridd.2017.08.003. Original Research.

Heads Up and Eyes Steady – The Optimized Mechanism for Human Running

In the insightful words of Bruce Springsteen, we as human beings were Born to Run. Humans have never been a sedentary species. The tendency to constantly relocate for survival purposes required skill in obtaining food efficiently, which heavily influenced early human evolution. Humans with optimal body mechanics for running ultimately held an advantage in hunting and gathering for food, and over time, the human body adapted to these survival requirements and developed a self-optimizing mechanism for running. This implies that initiating the act of running activates certain responses in the body to perform most efficiently.

Two aspects of the human body that the mechanism for running must account for, more so than other living species that depend on running for survival, is the bipedalism of humans and the disproportional size and weight of the head compared to other living species that run. For optimal locomotion, the head must remain stable while the body is in motion and experiencing the impacts of running not only to minimize the strain on the neck, but to allow for a steady gaze and safe navigation of the environment and potentially dangerous terrain. In order to achieve this, the human body has developed aspects within the mechanism for running that specifically protect against body pitching and head instability.

Plot title: Brain-to-Body Mass Ratio
X-axis: Body Mass (kg)
Y-axis: Brain Mass (kg)
where the ratio for humans is the largest compared to various other animals.
Image from Charlotte Swanson, Science World

The default mechanics of an individual’s natural stride minimize the shock through the body so that it may function as metabolically efficient as possible. This is true for most processes found in the universe; systems are constantly seeking a lower state of energy, and human beings are no different. Thus, as found in the research conducted by Michael A. Busa, Jongil Lim, Richard E. A. van Emmerik, and Joseph Hamill, the human body reacts to the external stimulus of running with a tendency toward an optimal stride frequency, which allows the head to be most stable during the motion.

Looking even further into the human body’s mechanism for running, a study was conducted by Andrew K. Yegian and Yanish Tucker investigating the involvement of neuromechanics. The researchers hypothesized that there was a neuromechanical connection between the biceps brachii and the superior (or upper) trapezius that served to provide stability for the head during running.

Biceps brachii highlighted in color on skeletal diagram.
Image from Wikipedia “Biceps Brcachii”
Sections of the trapezius muscle, upper or superior in orange, middle in red, and lower in fuchsia
Image from Wikipedia “Trapezius”

Although the activation of these two muscles is seemingly uncorrelated, the connection points on the shoulder are very close to once another and the line of action of both muscles is almost parallel. Both muscles are known to resist rotational impulses, and thus body pitching initiated by the significant weight of the head, during the foot’s contact with the ground during running.

In the study, the researchers observed human subject running on a treadmill and tracked muscle activity with electromyographic (EMG) sensors. They found the timing of muscle activation to be strongly coincident, and the magnitudes of both activation levels in both muscles were generally larger when mass was added to the runner’s head to further test the neuromechanical linkage. Due to the approximately parallel lines of action, the coincident forces from the biceps brachii and the superior trapezius, which act in opposite directions, directly support the stability of the scapula, which ultimately controls the stability of the head and upper body above the torso during running.

At this time, it is unknown whether the neuromechanical linkage between the biceps and the upper trapezius muscles to stabilize the head during running is direct or indirect, so further research is required to determine the mechanism that causes the muscle coordination.

For more general information about the biomechanics of running, visit this article found in Psysiopedia.

Put One Foot in Front of the Other? It’s Not that Easy

From Christmas movies to pop songs to motivational posters, we are encouraged to keep putting “one foot in front of the other.” While the sentiment is inspiring, recent studies show that there is a lot more to the seemingly simple task of walking than this phrase would suggest. Understanding this is especially important for balance and mobility after an injury or as people age.

The steps that make up the human walking cycle. Order of steps: heel-strike right, toe-off left, midstance right, heel-strike left, toe-off right, midstance left, hell-strike right. The body spends the time between heel-strike and toe-off with double support and the midstances are single-leg support.

Image from Wikimedia Commons

The human gait has a set structure that switches the weight between each leg, with only 20% of the typical walking motion distributing the weight across both feet. Maintaining balance throughout this process requires coordination in the muscles controlling the hips, knees, ankles, and feet. Mechanically, these adjustments keep the body’s center of mass (also known as center of gravity) over the base formed by feet positioning.

Obstacles and challenges to balance require a body’s quick response to mitigate shifts in the acceleration and momentum at the center of mass. Lack of efficient control over these parameters results in a fall. Many conditions, as well as age, can affect a person’s ability to respond to mobility challenges.

One specific study looked at how people who had had a stroke and subsequent partial paralysis on one side (paresis) faced mobility challenges compared with healthy folks. This condition effects approximately 400,000-500,000 people in the United States annually. It presents a unique opportunity to compare an individual’s non-damaged stride with their deficient stride at the point in the gait at which only one leg is on the ground (SLS, or single-leg-stride). The timing of the gait, the body’s momentum in all three planes of the body, and the location of the center of mass were recorded in this study.

Anatomical planes of the body. The sagittal plane splits the body left and right. The coronal plane splits the body forward and back. The transverse plane splits the body top and bottom.
Image from Wikimedia Commons

Versus healthy people, stroke survivors had significant trouble regulating momentum in the coronal plane, making falls more likely. Although it makes sense that momentum regulation suffers when muscles are paretic, it is yet unclear why the coronal plane was most affected. Additionally, post-stroke individuals’ centers of gravity were higher, which is also linked to instability. For stroke survivors, the partially paralyzed SLS took longer and extended farther from the center of mass than the regular SLS. While this is not as immediately dangerous as increasing falling risk, it slows mobility, unevenly works muscles (which can lead to injury), and is less efficient.

Going forward, these findings can be used to improve mobility success in people with balance issues or after injuries. This could manifest in better technologies, such as walkers that better help settle a person’s center of mass and partial exoskeletons that would help a person mitigate acceleration and momentum changes, or more targeted and individualistic physical therapies to strengthen weakened muscles and practice patient-specific challenges, such as overcoming obstacles that threaten coronal-plane balance. Understanding more about balance adjustment when walking may make some common phrases trite, but its potential benefits have life-changing impacts for many.

Further Reading and Sources:

Stroke/Paresis Information

Stability of Stepping