Evidences Supporting the Claim that the Right Side of the Brain Controls the Left Side of the Body
It is often claimed that the right side of the brain controls the left side of the body, and vice versa. This association is rooted in neurological evidence from various studies and techniques. In this article, we will discuss the various scientific evidences that support this claim through neuroanatomy, neurocognitive experiments, and brain imaging techniques.
Introduction to Brain Hemispheres and Motor Control
When discussing the control of the body by the brain hemispheres, it is important to understand the concept of contralateral control. Essentially, the right hemisphere of the brain controls the left side of the body, and the left hemisphere controls the right side. This is known as contralateral control.
Evidence From Neuroanatomy
The first line of evidence comes from the study of brain anatomy itself. Neuroanatomists have discovered that the motor cortex, the part of the brain responsible for initiating signals to the muscles of the body, has a specific arrangement that supports this claim. A series of nerve fibers, known as decussation, cross over from one hemisphere to the other before descending to the spinal cord.
The Process of Decussation
During the embryonic development of the central nervous system, nerve fibers from the motor cortex on one side of the brain cross over to the opposite side in the brainstem. This process is known as decussation. The decussation occurs in the medulla oblongata part of the brainstem, and approximately 90% of the motor fibers cross from the right side to the left hemisphere and vice versa.
Evidence From Neurocognitive Experiments
Unfortunate cases where one hemisphere of the brain is damaged can provide direct evidence for the contralateral control of the body. Patients with brain damage on the right side may suffer from partial loss of control over the left side of their body, while damage to the left hemisphere can lead to similar deficits in the right side of the body.
One example of such evidence comes from electrophysiological stimulation studies. By placing electrodes in exposed brain tissue during surgery, researchers can stimulate the motor cortex and observe the resulting muscle contractions in the opposite side of the body. This technique has been used to map specific regions of the motor cortex that control different body parts.
Evidence From Brain Imaging Techniques
Modern neuroimaging techniques, such as Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI), provide another line of evidence for contralateral control. These techniques allow researchers to observe changes in brain activity when specific tasks are performed.
Functional MRI Studies
During an fMRI study, subjects are instructed to perform certain movements, and the corresponding regions of the motor cortex "light up" on a computer-generated image. For instance, if a subject is asked to move their left hand, the right motor cortex will show increased activity.
Diffusion Tensor Imaging (DTI)
A more advanced modern imaging technique, DTI, can reveal the pathways of nerve fibers within the brain. Scientists use this technique to trace the connections between the motor cortex and the body's muscles. By visualizing these pathways, researchers can confirm the decussation of nerve fibers and the corresponding contralateral control.
Conclusion
The evidence supporting the claim that the right side of the brain controls the left side of the body is multifaceted, encompassing neuroanatomy, neurocognitive experiments, and advanced brain imaging techniques. These studies consistently demonstrate the contralateral control of the body by the brain, providing a robust scientific foundation for our understanding of brain function.