What causes motor laterality/ side dominance?

I would like to understand what leads up to motor laterality, or side dominance of motor skills. I made this assumption that it depends on neuroplasticity and the side in which one first learns the motor skill; whereas the more you practice, the more you strengthen that side. I appreciate your time and patience. Thank you; can't wait to discuss.

Frontal Lobe Syndrome

Neuroanatomically, the frontal lobe is the largest lobe of the brain lying in front of the central sulcus. It is divided into 3 major areas defined by their anatomy and function. They are the primary motor cortex, the supplemental and premotor cortex, and the prefrontal cortex. Damage to the primary motor, supplemental motor, and premotor areas lead to weakness and impaired execution of motor tasks of the contralateral side. The inferolateral areas of the dominant hemisphere are the expressive language area (Broca area, Brodmann areas 44 and 45), to which damage will result in a non-fluent expressive type of aphasia. Frontal lobe syndrome, in general, refers to a clinical syndrome resulting from damage, and impaired function of the prefrontal cortex, which is a large association area of the frontal lobe. The areas involved may include the anterior cingulate, the lateral prefrontal cortex, the orbitofrontal cortex, and the frontal poles.

Frontal lobe syndrome is a broad term used to describe the damage of higher functioning processes of the brain such as motivation, planning, social behavior, and language/speech production. Although the etiology may range from trauma to neurodegenerative disease, regardless of the cause frontal lobe syndrome poses a difficult and complicated condition for physicians. Classically considered unique among humans, the frontal lobes are involved in a variety of higher functioning processing, such as regulating emotions, social interactions, and personality. The frontal lobes are critical for more difficult decisions and interactions that are essential for human behavior. However, with the spread of neurosurgery and procedures such as lobotomy and leucotomy for the treatment of psychiatric disorders, a variety of cases have illustrated the significant behavioral and personality changes due to frontal lobe damage. Harlow first described this collection of symptoms as "frontal lobe syndrome" after his research on the famous Phineas Gage who suffered a dramatic change in behavior as a result of trauma. Thus, an abnormality in the frontal lobe could dramatically change not only processing but personality and goal-oriented directed behavior.

Prior research has sought to identify the major areas where lesions may occur to cause the behavioral changes in frontal lobe disorders.

Ventromedial Orbitofrontal Cortex

Commonly known to cause “frontal lobe personality”, lesions in the orbitofrontal areas classically cause dramatic changes in behavior leading to impulsivity and a lack of judgment. Lesions are usually found in Broadmann’s Areas 10, 11, 12, and 47 is associated with a loss of inhibition, emotional lability, and inability to function appropriately in social interactions. The most popular case involving a lesion in this area is the case of Phineas Gage who had major behavioral changes after his trauma. However, in a study by Tranel and Damasio et al., a variety of other etiologies such as stroke and neoplasms may cause “frontal lobe personality.”

Anterior Cingulate and Dorsolateral Syndromes

Lesions in the areas around Brodmann areas 9 and 46 may cause deficits within working memory, rule-learning, planning, attention, and motivation. Recent studies have reinforced that DLPFC is critical for working memory function and in particular for monitoring and manipulating the content of working memory. DLPFC may also affect attention as several cases have documented patients complaining of attentional deficits after brain trauma. There are also psychiatric implications due to injury to DPFMC. Previous studies have researched how lesions in the DLPFC may cause "pseudo-depressive" syndrome associated with DLPFC associated with a loss of initiative, decreased motivation, reduced verbal output, and behavioral slowness (abulia). Other processing issues include rule learning, task switching, planning/ problem solving, and novelty detection and exogenous attention. The anterior cingulate cortex is important for the motivation behind attention, but may also be involved in a variety of psychiatric disorders such as depression, post-traumatic stress disorder (PTSD), and obsessive-compulsive disorder (OCD).

A new area of research within the dorsolateral frontal cortices revolves around "intuition." The frontal lobes can communicate with the limbic system and association cortex. In turn, this emotional influence associated with abstract decisions to create more efficient or “intuitive” decisions in a short span of time.

Principles of Hormone Function

Often two or more hormones work synergistically. In a classic 1957 experiment, Skoog and Miller provided evidence that auxins and cytokinins work together in the differentiation of plant organs. Using tobacco tissue culture, they showed that when a tissue culture medium contains low concentrations of auxin and optimal cytokinin levels, then formation of shoots is favored. In contrast, when the culture medium is supplied with optimal concentrations of auxin combined with low concentrations of cytokinins, root formation is favored.

Hormones sometimes work antagonistically. Apical dominance is a process in which lateral buds of stems remain dormant as long as the stem apex remains intact. It has been shown that auxin produced in the stem apex is responsible for maintaining lateral bud dormancy by causing cells in the lateral buds to produce another hormone, ethylene, which is a growth inhibitor. During early spring, rapidly growing root tips will generate a high concentration of cytokinin that counteracts the effect of ethylene on the lateral buds of the stem. The lateral buds released from dormancy by cytokinins can then begin growth on their own.

What is Ambidexterity?

Mixed Dominance or Ambidexterity?

Is my child ambidextrous? Isn’t that what mixed dominance is? These are two questions that therapists get asked frequently when evaluating a child for the first time for mixed dominance and other concerns. The answer is no, they are not the same thing.

A child with mixed dominance demonstrates clear, stronger patterns based on the side of the body they are utilizing to complete the task. For example, a child who is left hand dominant will develop a stronger fine motor pattern then a child who is not left side dominant but compensating for fatigue and is moderately adept at utilizing the left hand as a coping skill.

A child who is truly ambidextrous will be equally as skilled at utilizing both sides of the body and it will look and feel natural to the child. Statistically, only 1% of the population is truly ambidextrous—it’s really very rare, and it is more likely that your child is experiencing mixed dominance patterns.

True ambidexterity requires both hands to be used with equal precision and there is no true preference in either the right or left hand for either both fine or gross motor tasks.

What Causes Mixed Dominance?

This is a tricky area. Therapists recognize mixed dominance as a miscommunication or poor integration of the left and right sides of the brain and that’s how it’s explained to parents. However, there is a lot of information out there on this topic that may or may not be relevant to your child and her struggles— keep this in mind when Googling information.

It is more likely, that your child’s brain is utilizing the left and right sides for very specific motor skills such as writing, eating and throwing a ball. This can lead to motor confusion—this is where the poor integration and lack of communication between the left and right sides of the brain comes into play. When the child is not utilizing one side of the brain more dominantly for motor patterns, confusion and poor motor learning occur leading to delays and deficits in motor skills.
It is unclear why the brain develops this way, but it does happen, and it is okay. In fact, it is easily addressed by an occupational therapist.

Mixed Dominance and Motor Development

I already touched on this a little, but a child with mixed dominance may switch sides for task completion when experiencing fatigue. Due to this, their motor development and precision is typically delayed. The most common area that this is noted in is in fine motor development for handwriting. This is because the child is equally, but poorly skilled with both hands, and will switch hands to compensate for fatigue.

Motor delays may also be noticed later on when it comes to the reciprocal movements needed to throw/catch or kick a ball and when skipping. A child with mixed dominance may attempt to catch and throw with the same hand, hold a bat with a backwards grip, or stand on the opposite side of the plate when hitting.

They may also experience a moderate level of confusion, and frustration as they are unsure of how to make the two sides of their body work together leading to overall poor hand/foot-eye coordination skills.

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I'm literally all over the place with my mixed handedness. I never think about it, but now that I am, it's mind-boggling. I wonder what makes us this way? Anyone else have an issue when you write with one hand, yet use a computer mouse with the other and have to electronically sign your name, underline, circle, draw an arrow, etc. using a mouse? It's an absolute nightmare. I've even tried moving the mouse to my dominant writing hand and reversing the clicker, but I literally can't even use the mouse with that hand at all. So weird.

Left: writing, eating, sewing, brushing teeth and hair, smoking, using toilet paper (lol). Also Left eye Dominant.

Right: drinking, scissors, playing all sports, throwing and catching, using a computer mouse, arm wrestling, darts, bowling, holding a gun, holding a phone, shaking hands, flipping someone the bird (lmao). Also Right ear and Right foot dominant.

All I can think of right now. Sorry for being so brief. Lol. anon998036 April 4, 2017

I use my left hand for writing and my right hand for almost everything else - playing musical instruments, golf, tennis, throwing. Right hand and ear for the telephone. I'm undecided for shooting and darts since my dominant eye confuses aiming. Left foot for kicking. Right foot strictly for standing on!

I write right handed but do everything left footed. anon993479 November 18, 2015

I am cross dominant and somewhat ambidextrous. I do fine motor skill activities mostly with my left, and gross motor skill activities mostly with my right. From the earlier posts this seems to be fairly common, though I've never heard anyone discuss it in these terms. This is why I write on paper with my left, yet use my right to write on a chalkboard. anon993464 November 17, 2015

I do most things right-handed including writing. But I brush my teeth and comb my hair left-handed. I am terrible at sports, especially if aiming is required. I excel at math and music. anon991037 May 22, 2015

I'm definitely a clumsy person and am bad at math. Most of these people in the comments I can relate to. I would love to have more studies about this topic, it could help us understand more about us and maybe help some people. My brother is also cross dominance but is my opposite cross dominance and he has slight autism , maybe if we get more info we could determine why this phenomenon happens and see more traits that are associated with it. anon991033 May 22, 2015

Same case here, so that's what I'm called. A cross-dominant person. Eat and write on the right but play sports on the left. But never been clumsy the whole time. And hey, quite good in match. anon990477 April 23, 2015

Dunno if this is rare or not. I actually don't know anyone with this type of "condition" besides myself. I'm still doing a list of things that I do with my hands, for instance:

Right hand: Throwing balls, basketball, handball, arm wrestling, preferred foot for football, using a compass, writing with chalk, computer mouse, holding a sabre.

Left hand: Preferred eye, writing with a pen/pencil on a paper, scissors, playing darts, toothbrush, brush, ping-pong/badminton rackets, snooker cue, holding a rifle. anon990102 April 6, 2015

I used both my hands to write or play sports. People say that is weird but I don't care. anon984599 January 9, 2015

I didn't knew this was actually a physical motor skill phenomenon, I use mostly the right hand for writing, holding equipment like hammers and spanners, but I use the left hand mostly for throwing like in baseball for example.

I also seem to have a stronger left foot than the right one when shooting in football as well.

As for problems, I seem to be a bit clumsy every now and then but I don't seem to have bad perception, balance or aim (in fact quite the other way around), and Maths was always one of my favorite subjects. anon964942 August 8, 2014

I did not know this was a common phenomenon. I use my right hand for writing, holding a screwdriver, ironing, hitting, etc. I use my left hand for basketball, throwing a baseball, arrow and other. In some activities I am totally mixed. I hold the fork with my right hand, but if I eat with a fork and a knife, I have to hold the fork in my left hand. I play soccer with my right leg. I was never good at maths and have memory problems. I could otherwise be considered an intelligent person. anon960129 July 8, 2014

I'm cross dominant too. I write, eat, brush my teeth my left, and play sport and use scissors with my right. The annoying thing is when people keep asking me to try play a sport like Badminton with my left hand, which I can't do. anon958289 June 26, 2014

I thought I was one of only a few, relatively, who are like this. I write, play golf, darts, pool, snooker left handed (just to name a few) but I kick a ball with my right foot. Although, I've never noticed it to affect the way I do things, just that it's there. anon953383 yesterday

I am cross dominant too, but I am not clumsy nor do I have problems with math. As a matter of fact (I am a bit crazy, I guess), I took calculus as an elective rather than marketing that I found to be extremely boring. I eat, write, play tennis and bowl right handed. I kick a ball, bat, throw, and clean left handed. anon950565 May 11, 2014

I am cross dominant. I write with my right hand and play soccer with my left foot. I am clumsy and I hate math! anon943401 April 1, 2014

Are people cross dominant if they write with their right hand but they throw a football or shoot a basketball with their left? Does this make them left handed also? If someone asks me if I am right-handed or left-handed, can I say both? anon352954 yesterday

Always knew I was, just didn't know what to call it. I throw a ball right-handed, I write right-handed. But anything to do with using two hands, such as swinging a baseball, golf, pool (billiards), and I do it naturally left handed. That's just what feels right to me and always has. I recently took an online left brain / right brain test and I came up equal. anon345834 August 22, 2013

I always knew I was cross dominant, but only now found out that it is relatively common I didn't even know there was a name for it.

I am super-clumsy, cannot play golf or mini golf (so what!) and cannot find things right in front of me. In spite of my motor skills being somewhat awkward, I do make a good living as an draughtsman. All in all a bit odd, but it seems to work.

Glad there are others out there (hi), never knew! anon337792 June 7, 2013

I'm cross dominant and I actually find it very useful, although I am pretty clumsy, and I find it hard to find something that someone tells me is directly in front of me. anon316177 14 hours ago

I'm cross dominant and I find it helpful with certain activities. anon291439 September 14, 2012

I am cross dominant and I find it very useful. One time I was working on some needlepoint (right handed) and I also had some unusable yarn that had to be cut up to use a stuffing for a pillow (cut left handed). I would do needlepoint for a while and then cut for a while. My mother had the same projects but had to take a break because she is 100 percent right handed and got tired. I also have found that I am an excellent typist because of this ability. anon261792 April 17, 2012

This is all very good and interesting, but I want to know if there is a reason behind the many famous people of the arts and science, such as Beethoven, Einstein and Leonardo di Vinci all having cross-dominance. Perhaps it helps in connecting the two sides of the brain?

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I am sorry to tell you guys this, but I am left handed. Okay so I can learn to be ambidextrous. Sorry, no, that is not a choice. Maybe I could manage if I lost my arm but absolutely no, I am not learning to use my right hand.

When I was a child, I began writing my name completely backwards. It took me longer to learn how to even see things correctly and transfer them to my hand and duplicate it the way society wanted it. I got that far but that's it. Left handedness is not a choice, so stop trying to force people to learn how to use their right hand. That is just stupid. anon931779 February 10, 2014

I write and eat left handed but do everything else right handed. My sister who is left handed taught me to write, so we assume that's why I write and eat left handed. anon231232 November 23, 2011

I have a girl. She is only 11 months old and she uses her left hand. I want to know why it happened. Is there any problem? anon181081 May 28, 2011

I'm probably more cross dominant. I write with my right. Everything else is bilateral. It actually has helped me very well as a physician and in racquetball, tennis, and martial arts. However, this phenomenon is not without an occasional quirk or disadvantage. anon78613 April 19, 2010

The article is fairly superficial, but probably OK for the average person. Being ambidextrous should not be a goal unless your dominant hand is not functioning due to injury/stroke.

The latest research shows that persons who are ambidextrous are more likely to have learning disabilities in reading and writing, and may also be more prone to psychiatric diagnoses. anon69283 March 7, 2010


Background and Purpose— The present study hypothesized that side of stroke and level of recovery influence motor system organization after stroke.

Methods— Functional MRI was performed on 14 control subjects and 21 patients with chronic stroke during index finger tapping (control subjects, right patients, recovered side).

Results— On functional MRI, stroke patients with right arm involvement showed (1) significantly smaller activation in contralateral motor cortexes compared with control subjects (2) smaller ipsilateral (nonstroke) premotor and larger contralateral (stroke-side) sensorimotor activation compared with patients with left arm involvement, although electromyogram across groups was similar and (3) 2.7-fold–larger contralateral sensorimotor cortex activation, ventrally, in those with full recovery compared with those with partial recovery, despite similar tapping force, frequency, range of motion, and electromyogram between groups. Supplementary motor area activation was unrelated to level of recovery.

Conclusions— After stroke that causes mild to moderate initial impairment and mild residual hand weakness, cortical organization varies with side of injury and with final motor status. The findings may have implications for treatment after stroke.

Limited data are available relating level of final motor status after stroke to features of functional imaging brain activation maps. One goal of this study was to test the hypothesis that functional MRI (fMRI) motor activation maps vary in relation to final motor status.

Nondominant hand movements normally have different cortical organization than dominant hand movements, the former being more bilaterally organized in dextrals. 1,2 However, functional imaging studies have not examined whether motor system reorganization after stroke differs when nondominant compared with dominant hand is affected. When side of stroke influences poststroke physiotherapy, it is usually on the basis of associated cognitive symptoms, but theoretically, differences in motor reorganization related to stroke side might also be important. The present study addressed the hypothesis that nondominant hand movements are organized differently than dominant hand movements chronically after stroke.

Materials and Methods

Subject Selection and Evaluation

Twenty-five patients with stroke >10 weeks previously that was associated with arm sensorimotor deficits and 14 control subjects gave informed consent. There were no differences in age or sex. Patients and control subjects were all right handed (Edinburgh Inventory). fMRI head motion eliminated 4 patients. Language or attention deficits were uncommon (1 of 21) and were unrelated to fMRI performance. Review of acute stroke records showed mostly mild strokes only 6 patients had complete hand function loss. Affected muscles improved by fMRI.

See Editorial Comment, page e26

Each subject spent <5 minutes practicing tapping just before fMRI, during which surface electromyograph (EMG) measured 5 right and 5 left arm muscles.

Image Acquisition

fMRI was acquired as described previously, 3 with 5 cycles of rest alternating with tapping. Control subjects tapped their right index fingers patients tapped their stroke-affected side on top of a force transducer. Wrist splints restricted metacarpophalangeal flexion and extension to 25°. An in-room examiner verified tapping performances. Subjects tapped at 50% of the maximum rate (2-Hz limit).

Data Analysis

Data were analyzed as described previously. 3 Significantly (Z>3) activated voxels were counted in precentral gyrus, postcentral gyrus, supplementary motor area (SMA), premotor cortex, parietal operculum, frontal operculum, and remaining parietal lobe. Contralateral precentral gyrus signal change was measured (1% and 0.5% threshold). A >10% difference in pegboard performance (normal right-left asymmetry) between affected and unaffected hands separated right-hand–affected patients into full or partial recovery. Group maps were generated in stereotaxic space and then contrasted pairwise by use of the 2-sample test statistic to reduce impact of different group sizes. Group and group contrast maps were then probed for significant (Z>4) activation clusters Wilcoxon signed-rank test compared continuous measures. An all motor area–laterality index 2 was calculated.


Effect of Stroke

No EMG leads showed significant differences between control subjects and right-arm–affected patients. Voxel counting found larger activation in control subjects within contralateral premotor cortex (P<0.03). When contrasting group maps, we found that control subjects showed significantly larger contralateral precentral gyrus and SMA activation.

Effect of Stroke Side

Patients who were right arm affected had no significant clinical differences compared with those who were left arm affected: smaller wrist extensor EMG on resting side (0% versus 19%, P<0.01), which was minute compared with active side (610% versus 498%, P=NS) smaller voxel counts within nonstroke (ipsilateral) premotor cortex (P<0.05, the Table and Figure 1) higher motor-laterality index (more contralateral, P<0.05) and when group maps were contrasted, significantly larger contralateral sensorimotor and smaller ipsilateral premotor plus SMA activation (Figure 2).

Key Clinical and fMRI Results

Figure 1. Individual patient activation maps. In a, bilateral brain activation was accompanied by unilateral EMG activity. Large arrows indicate contralateral (stroke-side) sensorimotor cortex activation small arrows, ipsilateral (not stroke-side) motor-premotor cortex.

Figure 2. Group activation maps superimposed on normal brain anatomy. Arrows indicate central sulcus.

Effect of Recovery Level

Right-arm–affected patients with full recovery showed no clinical differences compared with those experiencing partial recovery, apart from pegboard results: in group maps, 2.7-fold–larger contralateral sensorimotor activation, with negligible differences in SMA no differences in tapping force (1.03 versus 1.2 N, P=NS) or EMG and when group maps were contrasted, a significant contralateral sensorimotor cortex focus ventrally at Talairach (30, −20, 45). Correlation analysis (SPM99), limited by the small sample size (n=11), did not find a linear relationship between activation and pegboard performance.

Reanalysis with threshold Z=4 (voxel counting) or Z=3 (cluster detection) minimally affected results. Contralateral percent signal change results did not differ between groups at either threshold and were not influenced by arterial disease. Negative activation maps showed no significant foci.


Side of stroke and final motor status are related to motor system organization after stroke. Measurement of prescan EMG plus in-scan tapping force suggests that findings are related to changes in brain function rather than divergent movement performances.

Side of stroke influenced results, a finding relevant to occupational therapy. Greater ipsilateral premotor cortex recruitment is normally seen with left compared with right hand movement. 1 Such ipsilateral recruitment increases after stroke. 2,4–7 Ipsilateral recruitment varies according to stroke side (see Figures 1 and 2). Conclusions would be stronger if control left tapping data were available.

The best return of motor function after dominant-hemisphere stroke is related to preservation of function in affected hemisphere sensorimotor cortex, especially ventrally. 5 Results are consistent with transcranial magnetic stimulation studies, 8 which suggest that neurophysiological integrity of the affected hemisphere corticospinal tract is important to motor outcome. The basis for smaller activation with lesser recovery, despite movements similar to those of patients with full recovery, may relate to activity of subcortical areas not imaged. 9

A previous functional imaging study found that stroke topography influences motor system reorganization. 10 Present results indicate that stroke side and final motor status are also important. Restorative therapy trials, as with acute and preventative trials, might reduce variance and increase power if patients are enrolled or stratified on the basis of clinical and physiological assessments relevant to recovery processes.

Why Lateralization is Important

We want children to establish laterality and dominance to prevent learning challenges as they grow older. Gaps in learning could stem from poor bilateral coordination and mixed dominance, which can prevent your child from tracking, reading, listening to the teacher, comprehension and expressive and receptive language. Here’s what to watch for in your child’s development.

Bilateral Integration

While laterality is the dominance of one side of the body, humans are bilateral animals because we have two sides of the body therefore we need bilateral activities and movements for greater learning. Bilateral integration creates the opportunity for your child to use both sides of their body in a coordinated manner. This includes hands, eyes, arms, legs, feet and the brain. Your child must develop bilateral coordination in all parts of the body to perform fine motor skills, gross motor tasks, walking, logical thinking, studying, and the list goes on and on. This is why you see a two-year-old frequently eating with both hands, why they scribble with a crayon in either hand, why they push a wagon with both feet, and why they jump off the playground with both feet at the same time.

If your child has plenty of opportunity to experience sensory and motor experiences as a baby and toddler, the brain matures sequentially and their bilateral integration transitions smoothly. However, when it comes to certain functions and tasks, your child will establish dominance and the brain will start to specialize in one side of the brain.


Laterality describes an important change in your child’s brain where it becomes aware of the two sides of the body and its differences and similarities. The brain starts to recognize that perhaps one hand or one foot is better at certain skills than the other. Eventually, you will want your child to choose a dominant foot, eye, ear and hand for learning, preferably on the same side of the body to prevent confusion in the brain.

If your child shows signs of mixed dominance, for some, it could create learning challenges as they grow older. Because the brain is divided into two hemispheres (right and the left), you may notice your child living more in the right side of the brain while they are younger (creative) and eventually work toward the left side of their brain as they grow older, which is used for more higher learning tasks (logical thinking, reading, writing).

Mixed Dominance

If your child displays signs of mixed dominance , they typically use alternating hands, feet, eyes and ears for different tasks or they switch back and forth between different hands, feet and eyes for different activities. For example, your child may have a dominant left eye, but a dominant right hand (opposite dominance).

Many children have mixed dominance and show no signs of learning challenges, but for some, this can create confusion in the brain when it comes to their learning ability. The reasoning behind this concept is because the left and right hemispheres of the brain store different information. For example, visual information comes in through the left eye and is stored in the right hemisphere, where all auditory information comes in through the right ear and is stored in the left hemisphere of the brain. What you have to ask yourself is how does your child receive and interpret different information? Are they a visual learner or an auditory learner? If possible, establishing same-side dominance will help them store and receive information better in the classroom.

In Reflexes, Learning and Behavior , Sally Goddard says, “The effect of mixed laterality can be failure to send information to the most efficient center in the brain for that skill competition between two centers may occur which is rather like having two people in the front of a car, both wanting to drive and both trying to navigate.”

Cross Laterality

When your child is young and hand dominance is not yet set, you may notice they constantly cross over the midline to reach an object. They will use their right hand on the left side of the body and vice versa. This means they are exercising those neural pathways in the brain, setting up the body and brain for excelling in motor skills and higher learning. This is a great sign that they are developing their cross laterality milestones, which is also important for developing their bilateral coordination. It means the two sides of the brain are talking with each other, which is how your child will eventually learn their letters, recognize sounds, shapes, colors, numbers and follow instructions.

If your child struggles to cross the midline and does not develop their cross laterality milestones, you may notice a breakdown in their auditory and visual learning abilities in the classroom. For instance, they may struggle with simple tasks that require bi-lateralization, like holding their paper with their left hand while they write across the page with their right hand. Your child could also show signs of a retained Asymmetrical Tonic Neck Reflex (ATNR) , which stems from birth and prevents your child from crossing the midline .

Materials and Methods

(a) Birds, field site and flight tunnel

Experiments were conducted at the Cornell University Experimental Ponds Facility in Ithaca, New York, U. S. A. (42°30′N, 76°28′W). Twenty-four female tree swallows were captured from their nest boxes during incubation between 24 May and 31 May 2006. Birds were aged by plumage [24], and right and left tarsi and flattened wing lengths were measured (±0.1 mm). During experiments (see below), birds were released individually into an outdoor plywood flight tunnel (1.22 * 1.22 * 9.75 m long) from a lightproof box centred on top of the southwest end. The walls and ceiling of the tunnel were painted matte white and the floor covered with white limestone pebbles in an effort to minimize unintended perceptual asymmetries. The tunnel was illuminated by ten lights distributed equally along the two long walls (for further details of tunnel and study site see [25]. Within the tunnel, 3.22 m from the southwest end, the lower half (h61*w122 cm) was blocked using a light blue Styrofoam sheet (2.5 cm thick). The upper half was partially blocked using sheets 61 cm in height and of various widths (see Figure 1). Each bird flew through the tunnel four times and was caught at the end of the tunnel in a mist net, and was then released at point of capture.

Actual statistics for birds choosing a path is presented in the format x/y, where x represents the 12 birds from experiment one, and y represents the 12 birds from experiment two. In trial three, the side of the optimal choice depended on a bird's choice in trial two. To control for any initial size preference not related to optimality, half of the birds (Experiment 1) were given symmetrical, narrow openings in trial four, while half (Experiment 2) were given symmetrical, wide openings. The comparison of trial two to trial three is a test of optimality, while the comparison of trial two to trial four is a test of side-bias.

(b) Experiment 1

Twelve swallows served as subjects in experiment one. These animals did not serve as subjects in experiment two. The purpose of this experiment was to determine whether birds would demonstrate a side-bias while escaping the tunnel or, would make an optimal choice when presented with obstacles within the tunnel: in this case, a larger opening that would be easier to navigate.

First, two light blue h 61 * w 41 cm Styrofoam sections were put into place above the lower sheet flush with the sides of the tunnel, creating a h 61 * w 41 cm centred opening in the upper-half of the obstacle (Figure 1, trial 1). This trial was used to acclimate the bird to the tunnel. In the second trial, a single sheet was positioned such that two equal sized openings (h 61*w 41 cm) exist on either side (Figure 1, trial 2). The bird was released and scored as having used either the right or left opening. In the third trial, this centre section was moved 7.5 cm towards the side the bird had flown through on the previous trial (Figure 1, trial 3). After this trial, the bird was scored as either having made an optimal decision (large opening (h61*w48.5 cm), opposite of side chosen in trial one) or a non-optimal decision (small opening (h61*w33.5 cm), same side as chosen in trial one) and caught. In the fourth and final trial, the off-center upper section used in trial three was removed. A wider section (h61*w56cm) was positioned in the opening, leaving two equal sized openings (h61*w33.5cm) on either side (Figure 1, trial 4). The bird was scored as having used either the same or the opposite opening as used in trial two.

(c) Experiment 2

Twelve swallows served as subjects in experiment two. The purpose of this experiment was similar to that of the first experiment, but also controlled for a potential confounding variable in the experimental design: that a bird's preference for small or large openings might mask the test of side-bias.

Experiment two was identical to experiment one with the following exception: in the fourth and last trial, rather than use the wide section, a narrow section (h61*w33.5cm), creating two openings the size of the larger opening (h61*w48.5 cm) in trial three was used.

(d) Statistical analyses

Using the program R v. 2.3.1 [26], we ran custom randomization tests to determine if (a) the swallows exhibited a population-level side-bias by testing if the right or left side was chosen on trial two more often than expected by chance (results from two experiments pooled), (b) the optimal side was chosen by individuals more often than expected if both openings had been of equivalent size (results from two experiments pooled trial 2 versus trial 3), and (c) individuals exhibited a side-bias by testing if the side chosen in trial two was chosen more often than predicted by chance in trial four (tested separately between experiments). The absolute difference in wing and tarsus length between each appendage relative to the average of both appendages was measured. Paired t-tests were used to compare the magnitude of asymmetry (i.e. absolute value) between tarsi and wing lengths. G-tests of goodness of fit were used to test for a consistent direction of asymmetry (or lack thereof) in the tarsi and wings of individual birds and to test whether such direction of asymmetry in both tarsus and wings was related to side chosen in trial 2 of experiments 1 and 2.

Research Research

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • lists trials that are related to Amyotrophic lateral sclerosis. Click on the link to go to to read descriptions of these studies.

Patient Registry

  • The Clinical Research in Amyotrophic Lateral Sclerosis and Related Disorders for Therapeutic Development (CREATE) Consortium is an integrated group of academic medical centers, patient support organizations, and clinical research resources dedicated to conducting clinical research involving sporadic and familial forms of amyotrophic lateral sclerosis, frontotemporal dementia (FTD), primary lateral sclerosis (PLS), hereditary spastic paraplegia (HSP), and progressive muscular atrophy (PMA). The CREATE Consortium has a contact registry for patients who wish to be contacted about clinical research opportunities and updates on the progress of the research projects.

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