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Oct 5, 2007, 05:11 PM
The Brain & Its Functions – The Basics



By Dr Michael Egbejumi-David


Like every other organ in the body, the brain is made up of cells. They number about 40 billion nerve cells known as neurones. Everyone is born with a similar amount and, unlike other cells, neurons are not able to replace themselves. In fact, as we get older there is a gradual decrease in their number.

There has been past suggestions that the right brain is responsible for creativity & emotion and the left brain is responsible for logic & reasoning. However, these are broad generalizations with very little support basis. Both hemispheres process the same data. The difference is that the left brain processes in a linear, or sequential manner. The right brain processes data simultaneously, so does not connect plausible explanations immediately to each step in the process, but instead trusts the left brain to later link the reasoning behind beliefs or decisions.

The best evidence of one sided domination of the brain over the other side in only in language. Both of the major areas involved in language skills are in the left hemisphere. If some parts of the brain (mainly to do with perceptual info) are injured or destroyed, their functions can sometimes be recovered by neighboring brain regions - even opposite hemispheres. This depends more on the age and extent of damage than anything else.

However, in general, there are higher levels of norepinephrine or noradrenaline (a stress hormone responsible for attention and responding action) on the right; and higher levels of dopamine (the main hormone associated to the pleasure system of the brain; ie food, sex, drinking, drug use, gambling, etc) on the left. There is more white-matter on right and more grey-matter on the left (generally, white matter are the parts of the brain and spinal cord responsible for information transmission (axons); whereas, grey matter is mainly responsible for information processing (neuron bodies).


Looking at both hemispheres….
Cerebrum - is the largest area of the brain and is concerned with all higher mental functions, such as thinking and memory. (Plural: cerebral. Hence clever people are sometimes said to be very cerebral). The right cerebral hemisphere controls the left side of the body and the left cerebral hemisphere controls the right side of the body.

Cerebellum - This is the back part of the brain and is concerned with balance and muscle co-ordination. These activities are carried out automatically (ie, subconsciously) by this area of the brain and are not under the person's control.

Brain stem - The brain stem controls the basic functions essential to maintaining life, including blood pressure, breathing, digestion, heart beat and also eye movements, swallowing and arousal (ie, being awake and alert). It is the bottom part of the brain and connects the cerebral hemispheres to the spinal cord.



Each cerebral hemisphere is divided into four areas, known as lobes: the frontal, parietal, temporal and occipital lobes. Each lobe controls a different range of activities



Frontal Lobe
Functions:
- Cognition and memory. Planning, organising, problem solving, selective attention
- The ability to concentrate and elaboration of thought. The "Gatekeeper"; (judgment, inhibition). Personality and emotional traits
- Storage of motor (movement) patterns and voluntary activities
- Language: motor speech

* Cerebral Cortex (Outermost layer of the Cerebral Hemisphere) Both hemispheres are able to analyze sensory data, perform memory functions, learn new information, form thoughts and make decisions.

Left Hemisphere: Sequential Analysis: systematic, logical interpretation of information. Interpretation and production of symbolic information, language, mathematics, abstraction and reasoning. Memory stored in a language format
Right Hemisphere: Processing multi-sensory input simultaneously to provide "holistic" picture of one's environment. Holistic functions such as dancing and gymnastics are coordinated. Memory is stored in auditory, visual and spatial modalities

Symptoms:
- Inattentiveness, inability to concentrate, behaviour disorders, difficulty in learning new information
- Lack of inhibition (inappropriate social and/or sexual behaviour
- Emotionally "flat"
- Aphasia (partial or total loss of the ability to communicate, esp. in speech or writing)




Parietal Lobe
Functions:
- Processing of sensory input
- Body orientation
- Sensation controls (touch, pressure. Judgment of texture, weight, size, shape)

Symptoms:
- Inability to discriminate between sensory stimuli
- Inability to locate and recognise parts of the body

Left Lobe: Disrupt ability to understand spoken and/or written language.
Right Lobe: Visuo-spatial deficits – difficulty finding way around new or even familiar places.




Temporal Lobe
Functions:
- Auditory reception
- Short term memory

Left Lobe: Memory for words & names
Right Lobe: Memory for picture and faces
Distinguishing smells & sounds

Symptoms:
- Hearing deficits
- Agitation, irritability, childish behaviour
- Short-term memory deficits




Occipital Lobe
Functions:
- Visual reception
- Recognition of shapes & colours
- Visual deficits

Symptoms:
- Loss of vision (opposite field). "Flash of light", "stars"




* Limbic System/Lobes
On the medial surface of the temporal lobe are a few structures critical for normal human functioning. They are the olfactory cortex, hypothalamus (homeostasis – thermostat), the amygdale (fear), and the hippocampus (memory). They are often grouped together as "the limbic system".
Functions:
- Basic emotions, Emotional response & Emotional memory
- Motivation/Mood
- Olfactory pathways
- Sex, rage, fear
- Hormonal secretion


Symptoms:
- Loss of sense of smell
- Agitation, loss of control of emotion. Loss of recent memory



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