Introducing
Your new presentation assistant.
Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.
Trending searches
?
1. Why do humans developed a contralateral movement control?
2. Why and when do human expressed hand dominance (handedness)?
3. Why do changes in mobility alter the contralateral control?
1. Avoidance behavior hypothesis (Cajal RY 1899)
2. Image-forming eye hypothesis (Sarnat HB, Netsky M, 1976)
3. Binocularity hypothesis (Serge et al., 2005)
4. Bilaterality hypothesis (Polyak 1957)
5. Mobility hypothesis (Whitehead and Banihani 2017):
Wellness equation (functionality of the system after injury)
n = Fixed number greater than one indicating degree of non-linearity
f = Destruction fraction between 0 and 1
W= Represents the functionality of the system after injury or "wellness".
Probability of survival equation
Given a W of 0.8 the probability of survival will be P= 67%
When left and right hemisphere are included in the equation ( computing 1,000 trials)
Over a random sampling of these scenarios, contralateral control provides a survival advantage of 5% higher than ipsilateral control.
Why?
To accommodate increasingly complex and coordinated behaviors (i.e., bimanual activities) during the course of evolution required the development of a more extensive neural circuits to carry out the underlying computations.
Option 1: Expanding brain size (too be costly in terms of energy and distance).
Option 2: Specialization of neural circuits within one hemisphere in order to develop more efficient local circuits. Yes!
Motor lateralization identifies two different computational processes associated with voluntary motor control:
1) Left Hemisphere: Predictive control that specifies trajectories and accounts for initiation movement dynamics including energetics
2) Right Hemisphere: Impedance control that specifies velocity and final position accuracy as well as robustness against unpredictable perturbations. It is feedback-dependent to correct ongoing movements.
Developed as a response of the Progressive Lateralization Theory of Lenneberg (1967) suggesting that there is a critical period for language acquisition and as such, hemispheric specialization of function for language occurs during that same period of development. Since hemispheric specialization for language is highly related to specialization for handedness (Knecht, et al. 2000).
The Invariat Lateralization Theory suggest that head turning can be seen as a precursor of locomotion toward one side. There is a relationship between the direction of the most frequent head turning in the infant and subsequent hand preference. At the intrauterine age of 32 weeks (Turkewitz, 1977) showed that there is asymmetric tonic neck response.
Kinsbourne (1970) proposed that a motor bias that in most individuals is targeted rightward clearly exists as early as at birth or even before and is a major determinant of the side of the subsequently preferred hand. Contrary to the assumption that handedness emerges from diffuse movement patterns in infancy.
1. Insults to the Central Nervousness System (CNS): Stroke, cerebral palsy, hemispherectomy, etc.
2. Limb Immobilization: Surgical interventions, trauma to the soft and skeletal system, forced limb immobilization, pain, spinal cord injury, etc.
3. Congenital and acquired limb deficiency: Traumatic limb loss, surgical interventions, congenital reduction deficiencies, amniotic band syndrome, malformations, etc.
1. Does contralateral control remains?
2. What is the role of the non-affected hand?
3. How do children adapt to a prosthesis?
Theoretical Support:
An experimental group of children with unilateral upper-limb reduction deficiency on the left side. A sex- and age matched control group performed a gross manual dexterity task with the preferred (right) and non-preferred (left) sides while measuring motor cortical activity in both hemispheres.
The experimental group performed the motor task wearing a prosthesis on the non-preferred side (affected left side) and similarly, the control group performed the same task wearing a prosthetic simulator on the non-preferred side (also left side).
All children (experimental and control groups) showed right-hand preference.
TD Right Hand Task
TD Left Hand Task
ULD Right Hand Task
ULD Left Hand Task
The major findings of the present investigation are in agreement with our hypotheses indicating
Several investigations have reported increases in motor skills, motor learning, and motor performance in the affected, untrained upper limb after training the non-affected limb
The ipsilateral dominance found in the present investigation may provide an opportunity to effectively train the non-affected side to improve the functional performance of the affected side using prosthetic simulators.