Language

In human beings, it is the left hemisphere that usually contains the specialized language areas. While this holds true for 97% of right-handed people, about 19% of left-handed people have their language areas in the right hemisphere and as many as 68% of them have some language abilities in both the left and the right hemisphere. The two hemispheres are thought to contribute to the processing and understanding of language: the left hemisphere processes the of (or, the rhythm, stress, and intonation of connected speech, while the right hemisphere processes the emotions conveyed by prosody. Studies of children have shown that if a child has damage to the left hemisphere, the child may develop language in the right hemisphere instead. The younger the child, the better the recovery. So, although the "natural" tendency is for language to develop on the left, human brains are capable of adapting to difficult circumstances, if the damage occurs early enough.

The first language area within the left hemisphere to be discovered is , named after who discovered the area while studying patients with a language disorder. Broca's area doesn't just handle getting language out in a motor sense, though. It seems to be more generally involved in the ability to process grammar itself, at least the more complex aspects of grammar. For example, it handles distinguishing a sentence in passive form from a simpler subject-verb-object sentence — the difference between "The boy was hit by the girl" and "The girl hit the boy."

The second language area to be discovered is called , after , a German neurologist who discovered the area while studying patients who had similar symptoms to Broca's area patients but damage to a different part of their brain is the term for the disorder occurring upon damage to a patient's Wernicke's area.

Wernicke's aphasia does not only affect speech comprehension. People with Wernicke's aphasia also have difficulty recalling the names of objects, often responding with words that sound similar, or the names of related things, as if they are having a hard time recalling word associations

Making sense of Brain

Making sense of the brain's mind-boggling complexity isn't easy. What we do know is that it's the organ that makes us human, giving people the capacity for art, language, moral judgments, rational thought. It's also responsible for each individual's personality, memories, movements and how we sense the world.

All this comes from a jellylike mass of fat and protein weighing about 3 pounds (1.4 kilograms). It is, nevertheless, one of the body's biggest organs, consisting of some 100 billion nerve cells that not only put together thoughts and highly coordinated physical actions but regulate our unconscious body processes, such as digestion and breathing.

The brain's nerve cells are known as neurons, which make up the organ's so-called "gray matter." The neurons transmit and gather electrochemical signals that are communicated via a network of millions of nerve fibers called dendrites and axons. These are the brain's "white matter."

The cerebrum is the largest part of the brain, accounting for 85 percent of the organ's weight. The distinctive, deeply wrinkled outer surface is the cerebral cortex, which consists of gray matter. Beneath this lies the white matter. It's the cerebrum that makes the human brain—and therefore humans—so formidable. Whereas animals such as elephants, dolphins, and whales have larger brains, humans have the most developed cerebrum. It's packed to capacity inside our skulls, enveloping the rest of the brain, with the deep folds cleverly maximizing the cortex area.

The cerebrum has two halves, or hemispheres. It is further divided into four regions, or lobes, in each hemisphere. The frontal lobes, located behind the forehead, are involved with speech, thought, learning, emotion, and movement. Behind them are the parietal lobes, which process sensory information such as touch, temperature, and pain. At the rear of the brain are the occipital lobes, dealing with vision. Lastly, there are the temporal lobes, near the temples, which are involved with hearing and memory.

Movement and Balance

The second largest part of the brain is the cerebellum, which sits beneath the back of the cerebrum. It is responsible for coordinating muscle movement and controlling our balance. Consisting of both grey and white matter, the cerebellum transmits information to the spinal cord and other parts of the brain.

The diencephalon is located in the core of the brain. A complex of structures roughly the size of an apricot, the two major sections are the thalamus and hypothalamus. The thalamus acts as a relay station for incoming nerve impulses from around the body that are then forwarded to the appropriate brain region for processing. The hypothalamus controls hormone secretions from the nearby pituitary gland. These hormones govern growth and instinctual behavior such as eating, drinking, sex, anger, and reproduction. The hypothalamus, for instance, controls when a new mother starts to lactate.

The brain stem, at the organ's base, controls reflexes and crucial, basic life functions such as heart rate, breathing, and blood pressure. It also regulates when you feel sleepy or awake.

The brain is extremely sensitive and delicate, and so requires maximum protection. This is provided by the surrounding skull and three tough membranes called meninges. The spaces between these membranes are filled with fluid that cushions the brain and keeps it from being damaged by contact with the inside of the skull.

Types Of Brain Waves

In normal healthy people most waves in the EEG can be classified as alpha,beta,theta and delta waves, which are shown in graph.

Alpha waves are rhythmical waves that occur at frequencies between 8 and 13 cycles per second and are found in the EEG of almost all normal adult people when they are awake and in a quiet, resting state of cerebration.These waves occur most intensely in the occipital region but can also be recorded from the parietal and frontal regions of the scalp.Their voltage usually is about fifty microvolts.During deep sleep, the alpha waves disappear.
Beta waves occur at frequencies greater than 14 cycles per second and as high as 80 cycles per second.They are recorded mainly from the parietal and frontal regions during specific activation of these part of the brain.
Theta waves have frequencies between 4 and 7 cycles per second.They occur normally in the parietal and temporal regions in children, but they also occur during emotional stress in some adults,particularly during disappointment and frustration.Theta waves also occur in many brain disorders, often in degenerative brain states.
Delta waves include all the waves of the EEG with frequencies less than 3.5 cycles per second, and they often have voltage two to four times greater than most other types of brain waves.They occur in very deep sleep, in infancy, and in serious organic brain disease.Therefore delta waves can occur strictly in the cortex independent of activities in lower regions of the brain.

Brain Waves

Electrical recordings from the surface of the brain or even from the outer surface of the head demonstrate that there is continuous electrical activity in the brain.Both the intensity and the patterns of this electrical activity are determined by the level of excitation of different parts of the brain resulting from sleep, wakefulness, or brain diseases such as epilepsy or even psychoses.The undulations in the recorded electrical potentials, shown in the picture , are called brain waves,and the entire record is called an EEG.
The intensities of brain waves recorded from the surface of the scalp range from 0 to 200 microvolts, and their frequencies range from once every few seconds to 50 or more per second.The character of the waves is dependent on the degree of activity in respective parts of the cerebral cortex and the waves change markedly between the status of wakefulness and sleep and coma.
Much of the time the brain waves are irregular,and no specific pattern can be discerned in the EEG.At other times distinct patterns do appear some of which are characteristic of specific abnormalities of the brain such as epilepsy which is discussed later.

Physiologic Effects of Sleep

Sleep causes two major types of physiologic effect: First effects on the nervous system itself and second effects on other functional systems of the body.The nervous system effects seem to be by far the more important because any person who has a transected spinal cord in the neck shows no harmful effects in the body beneath the level of transection that can be attributed directly to a sleep wakefulness cycle.
Lack of sleep certainly does however affect the functions of the central nervous system.Prolonged wakefulness is often associated with progressive mal-function of the thought process and sometimes even causes abnormal behavioral activities.
We are all familiar with the increased sluggishness of thought that occurs toward the end of a prolonged wakeful period but in addition a person can become irritate or even psychotic after forced wakefulness.Therefore we can assume that sleep in multiple ways restores both normal levels of brain activity and normal"balance" among the differnt functions of the central nervous system.This might be likened to the "rezeroing" of electronic analog computers of this type gradually lose their "baseline" of operation; it is reasonable to assume that the same effect occurs in the central nervous system because overuse of some brain areas during wakefulness could easily throw these areas out of balance with the remainder of the nervous system.
The specific physiologic functions of sleep remain a mystery, and they are the subject of much research.

REM Sleep

In a normal night of sleep, bouts of REM sleep lasting 5 to 30 minutes usually appear on the average every 90 minutes.When the person is extremely sleepy, each bout of REM sleep is short and it mayeven be absent.Conversely, as the person becomes more rested through the night, the durations of the REM bouts increase.
There are several important characteristics of REM sleep:
1.It is usually associated with active dreaming and active bodily muscle movements.
2.The person is even more difficult to arouse by sensory stimuli than during deep slow-wave sleep,and yet people usually awaken spontaneously in the morning during an episode of REM sleep.
3.Muscle tone throughout the body is exceedingly depressed, including strong inhibition of the spinal muscle control areas.
4.Heart rate and respiratory rate usually become irregular which is characteristic of the dream state.
5.Despite the extreme inhibition of the peripheral muscles,irregular muscle movements do occur.These are in addition to the rapid movements of the eye.
6.The brain is highly active in REM sleep, and overall brain metabolism may be increased as much as 20 per cent.The electroencephalogram shows a pattern of brain waves similar to those that occur during wakefulness.This type of sleep is called paradoxical sleep because it is a paradox that a person can still be asleep despite marked activity in the brain.
In summary REM sleep is a type of sleep in which the brain is quite active.

Slow-Wave Sleep

Most of us can understand the characteristics of deep slow-wave by remembering the last time we were kept awake for more than 24 hours and then the deep sleep that occured during the first hour after going to sleep.This sleep is exceedingly restful and is associated with decrease in both peripheral vascular tone and many other vegetative function of the body.For instance there are 10 to 30 percent decreases in blood pressure respiratory rate and basal metabolic rate.
Although slow-wave sleep is frequently called"dreams and sometimes even nightmares do occur during slow-wave sleep.The difference between the dreams that occur in slow-wave sleep and those that occur in REM sleep is that those of REM sleep are associated with more bodily muscle activity and the dreams of slow wave sleep usually are not remembered.That is, during slow-wave sleep consolidation of the dreams in memory does not occur.

Sleep

Sleep is defined as unconsciousness from which the person can be aroused by sensory or other stimuli.It is to be distinguished from coma, which is unconsciousness from which the person cannot be aroused. There are multiple stages of sleep, from very light sleep to very deep sleep;sleep researchers also divide into two entirely different types of sleep that have different types of sleep that have different qualities, as follows.
Two types of Sleep:
During each night, a person goes through stages of two types of sleep that alternate with each other.They are called (1) slow-wave sleep,because in this type of sleep the brain waves are very strong very low frequency,as we discus later,and (2) rapid eye movement sleep (REM sleep), because in this type opf sleep the eyes undergo rapid movements despite the fact that the person is
still asleep.
Most sleep during each night is of the slow wave variety; this is the deep restful sleep that the person experiences during the first hour of sleep after having been awake for many hours.REM sleep, on the other hand, occurs in episodes that normally recurs about every 90 minutes.This type of sleep is not so restful and it is usually associated with vivid dreaming.

Brain Activity

All of us are aware of the many different states of brain activity,including sleep, wakefulness, extreme excitement,and even different levels of mood such as exhilaration, depression, and fear.All these states result from different activating or inhibiting forces generated usually within the brain itself. The human brain is the center of the human and is a highly complex organ. Enclosed in the , it has the same general structure as the brains of other , but is over three times as large as the brain of a typical mammal with an equivalent body size. Most of the expansion comes from the, a convoluted layer of neural tissue that covers the surface of the brain. Especially expanded are the frontal lobes, which are associated with such as self-control, planning, reasoning, and abstract thought. The portion of the brain devoted to vision is also greatly enlarged in human beings. In this site we present brief surveys of specific states of brain activity, beginning with sleep.