Tag Archives: motor cortex

The Brain: The Cerebral Cortex

brain-lobes-diagram

The cerebral cortex is the intricate fabric of interconnected neural cells that covers the cerebral hemisphere. It serves as the ultimate control and information processing centre. Humans have larger cortexes which enables us to be more adaptable, which gives us the ability to learn and think beyond basic survival instincts.

The cerebral cortex is made up of a sheet of cells that is 1/8 of an inch think and contains approximately 30 billion nerve cells. Glial cells or glue cells as they are commonly called, hold the nervous system together. They are NOT neurons but their own category of cells. Glial cells serve to support, nourish and protect neurons by communicating with them. Scientists are currently attempting to find connection between glial cells and information transmission and memory.

brain lobes

Folds of the brain increase the brain’s surface area allowing for maximised function and activity. As most people know, the brain’s cerebral cortex consists of four lobes: the parietal lobe, the occipital lobe, the temporal lobe and the frontal lobe. The frontal lobe is the front portion of the cerebral cortex, lying right behind the forehead. The frontal lobe is involved in speaking, muscle movement, high level cognition (planning, judgment, reasoning). Damage to the frontal lobe can result in changes in social skills, libido, attention and risk-taking. The parietal lobe is the part of the cerebral cortex at the top of head, behind the frontal lobe towards the back. It includes the sensory cortex. This means the parietal lobe processes sensory information such as pain, touch and pressure. Damage to the parietal lobe results in sensory problems such as impaired verbal memory and language skills. The occipital lobe lies at the base of te head and includes the visual areas; it receives visual information from the opposite visual field. This means that what is seen by our right is processed by the left side of our occipital lobe and vice versa. The temporal lobe lies above the ears and includes the auditory areas. These two areas receive auditory information from the opposite ear much like how the eye and occipital lobe work. 

– Functions of the Cerebral Cortex –

German physicians Fritsch and Hitzig electrically stimulated the cerebral cortexes of dogs. Through their experiments, Fritsch and Hitzig found that they could make different parts of the dogs’ bodies move. However, their ability to make the dogs move through stimulation was selective. Movement was only observable when a specific arch-shaped area of the back of the frontal lobe was stimulated. This area is know known as the motor cortex. Furthermore, the physicians discovered that the parts of the body that were moved, corresponded to stimulation on the opposite side of the brain.

Neurosurgeons Foerster and Denfield also investigated the functions of the cerebral cortex through stimulation. They found that precise control requires the greatest amount of cortical space. Furthering this idea, Jose Delgado found that specific parts of the cerebral cortex correspond with certain actions. Today it is evident, through the use of MRI scans, that precise actions require overlapping cortical sites.

brain lobes 2

The cerebral cortex specialises in receiving information from the skin senses and the movement of body parts. The greater the area devoted to specific body region, the more sensitive this area becomes. As a paradigm, our lips are far smaller than our back; however, relative to size, the cerebral cortex dedicates far greater area to our lips making them far more sensitive and kisses so enjoyable. It also explains why our backs are far less sensitive to pain than say our stomachs.

– Association Functions – 

The association areas consist of 3/4 of the cerebral cortex. Association areas are uncommitted to sensory of muscular activity. They associate with various sensory inputs with stored memories. The functions of the association areas cannot be triggered by stimulation or any other forms of probing. The existence of these areas are vital in disproving the popular belief that 90% of our brain is dormant. Our brain relies heavily on these unassociated areas for interpretation, integration and acting on processed sensory information.

Citations:

Cherry, Kendra. “The Anatomy of the Brain.” The Four Lobes (2012): n. pag. About.com Psychology. Web. 03 Sept. 2012. <http://psychology.about.com/od/biopsychology/ss/brainstructure_2.htm&gt;.

Myers, David G. Psychology . 6. Worth Publishers, 2001. Print.Myers, David G. Psychology . 6. Worth Publishers,2001. Print.

Maps and Infinite Homuncular Regression

Although maps provide an excellent structural representation of what is going on the brain, in themselves they have no intrinsic value (Deacon, 2012). Maps do not really tell us about how the brain is interpreting or processing the information, only how it stores and forwards the information. To be fair, even that is only based on visual interpretation not on concrete behaviour. Unfortunately, that brings up the issue of whether or not topological maps are of any value. The retinotopic map may just be a consequence of development and evolution, an attempt to minimise wiring of the brain. Deacon (2012) stresses that there is massive flaw with the current use of mapping; he summarizes it as the ‘infinite homuncular regression.’ Basically, we have come to a point where other maps are just reading maps. The actual perceptual neurology has not been determined. Deacon warns scientists of the dangerous of neuroimaging and maps when trying to prove the existence of neural activity and behaviour. All this boils down to really is the classic argument in psychology; correlation does not prove causation.

1421_sensory_homunculus

Fortunately, Graziano and his colleges (2009) suggest that perhaps a homunculus does exist that can bridge perception and behaviour: the motor cortex. To put it plainly, a motor homunculus represents the sensitivity and innervation dedicated to particular muscles in our body. This homunculus can be mapped onto our motor cortex, and stimulation of these regions leads to an immediate motor response. Hence, we can bridge the gap between map and action. In other words, the motor cortex may in fact put an end to the infinite homoncular regression. A recent study carried out by Bouchard et al. (2013) found that when participants vocalised constants and vowels, scans showed smooth trajectories in the motor cortex.