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Lobes of the brain

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Brain Lobes.jpg

The lobes of the brain are regions of characterized activity within the brain. There are four generally recognized. The frontal lobe deals with cognitive and reasoning functions, as well as motor skills. The parietal lobe interprets the senses, such as touch and taste. The occipital lobe analyzes visual input from the eyes, and the temporal lobe processes sound and language. Altogether, these incredible regions of the body's most sophisticated organ work in harmony to distinguish humans as unique beings created in the image of God.

Contents

Frontal

The frontal lobe lies just beneath the forehead, or frontal bone. It is separated from the temporal lobe by the lateral sulcus, and the central sulcus separates it from the parietal lobe. Primarily, the frontal lobe is engaged in the chief thinking functions of the brain, such as critical and analytical reasoning, and judgment (the ability to identify future consequences of current actions). Cognition, memory, language skills, and a person's emotional traits are also stored in the frontal lobe. Within the frontal lobe are the premotor cortex and motor cortex. The premotor cortex acts as storage for some voluntary activities and for motor patterns. The motor cortex controls voluntary motor activity. [1]

The frontal lobe.

Other functions of the frontal lobe include:

  • Personality
  • Arousal and motivation skills
  • Awareness of self
  • Responses to environment and self
  • Consciousness of environment
  • Emotional stability and reaction
  • Memory of motor activity or habits
  • Use of language
  • Meanings and associations of words. [2]
This topographical drawing of the primary motor cortex on the central sulcus details the areas that represent various parts of the body.

It appears that one of the ways the frontal lobe completes these various functions is by acting as a temporary storage site, "allowing one idea to be kept in mind while other ideas are considered." [3] One section of the frontal lobe, known as the dorsolateral frontal cortex, controls working memory (recently gained information). Another part, the left posteroinferior frontal cortex or Broca's area, coordinates the expression of language. [4] Broca's area is part of the premotor area, which determines the kind and number of action potentials necessary for fine motor movement. Broca's area in particular, prepares and organizes the minute sequencing of these action potentials[5]. Broca's area also controls facial neurons, speech production, and language comprehension and processing. Researchers believe that this area aids the brain's interpretation of various modes of stimulus, and may even direct the production of language by directly controlling the organs involved in speech. [6]

The frontal lobe is divided into left and right parts. The left frontal lobe governs effective prescription, diagnosis, and calculation skills. It perceives the functional relationships of objects and controls logical analysis. The right frontal lobe however, contains the imagination, and the ability to notice abstract relationships or patterns. It is this portion of the brain for instance, that identifies the caricature of a person's face, rather than the general shape of the head or the structures of the face (eyes, nose, etc.). [7]

If the frontal lobe is injured, many of these functions can be impaired. For example, it can become difficult to manage the proper sequence of steps to complete a complex task like brewing coffee. People with severe head injuries who have damaged their frontal lobe can also suffer from paralysis, language impairment, a lack concentration, perseveration (repeating comments or actions without realizing it), mood swings, or even changes in social interaction or personality. [2]

Parietal

The parietal lobe.

The parietal lobe is posterior to the frontal lobe and superior to the occipital lobe; it is protected by the parietal bone of the skull. Like the frontal lobe, the parietal lobe is separated from the temporal lobe by the lateral sulcus. This lobe processes basic sensations like temperature, pressure, touch, pain, and proprioception (joint movement). Storage of data, and the development of tactile sensation (which helps in the recognition of familiar objects via touch without visual aid), are also functions of the parietal lobe. This lobe enables the brain to discriminate the intensity of a stimulus, such as cold versus freezing or lukewarm versus scalding hot. The parietal lobe also processes spatial relationships, having the ability to distinguish the precise point of a tactile sensation (two-point discrimination). [1]

The parietal lobe can be divided into two separate regions with different functions. The first area combines sensory information, mostly from visual input, into cognition, or a single perception. The other region builds a three-dimensional plane so the brain can interpret the physical world. [8] The forward part of the parietal lobe houses the sensory areas; these register sensory data like taste, touch, and bodily movement. Remaining overall functions of the parietal lobe include arithmetic, reading [3], the manipulation of objects, and "goal-directed voluntary movements." [2] Sections of the midparietal lobe are responsible for skills like writing, finger recognition, calculation, and right-left orientation. Abilities such as drawing come from the nondominant portion of the parietal lobe, which perceives one's environment and space. [4]

The parietal lobe constructs a 3D plane so the brain can determine the body's position.

Two important regions of the parietal lobe are the primary somatic sensory area and the somatic sensory association area. The primary somatic sensory area is located on the postcentral gyrus (posterior to the central sulcus), and its function is to localize the signals coming from the body; within this area, there are individual sections that respond to sensation from different parts of the body, allowing the brain to identify the part stimulated. The somatic sensory association area distinguishes the nature of a stimulus, referring to a sensory memory and placing the sensation in the correct context; for example, this is how the brain determines whether a punch on the shoulder is a sign of comraderie or a threat[9].

Damage to the parietal lobe can result in difficulty interpreting personal awareness of body space and limb position, as well as problems reading and recognizing objects and people. Traumatic brain injury usually eliminates or severely decreases the ability to multi-task, do mathematics, and differentiate between left and right. [10] Head injuries that harm the parietal lobe can also impair the ability to focus on one object at a time, write words (agraphia),and name objects (anomia). Poor hand-eye coordination, weak visual perception, and apraxia ("lack of awareness of certain body parts and/or surrounding space...that leads to difficulties in self-care") are also possible detriments resulting from damage to the parietal lobe.[2]

Occipital

The occipital lobe.

The smallest lobe in the brain, the occipital lobe is located at the back of the brain, posterior to the parietal and temporal lobes, and is protected by the skull's occipital bone. The occipital lobe is positioned on a process of the dura mater, known as the tentorium cerebelli, which divides the cerebrum from the cerebellum. Several lateral gyri, separated by the lateral occipital sulcus, are located around the periphery of the occipital lobe. The main function of this lobe is to process visual impulses via the visual pathway. [1] The occipital lobe interprets visual images from the eyes and connects this information with images found in the memory. [3]

Reproduction of a Gray's Anatomy lithograph drawing that illustrates the optic pathway from the eyes to the occipital lobe.

The occipital lobe houses the visual cortex and the visual association area. The visual cortex interprets the action potentials from the optic nerves (which are connected to the eyes); this region processes the visual basics like size, color, and shape. From the visual cortex, the action potentials are sent to the visual association area, which is the portion of the occipital lobe that links images to past experiences, enabling a person to recognize someone's face, a location, etc.[11]. The Peristriate region processes visuospatial information, as well as distinguishing color and movement. [8]

Because the occipital lobe is at the back of the brain, it is relatively well-protected, which is vital as it is the center of the body's visual perception system. If the occipital lobe is injured however, visual illusions or hallucinations can occur; visual illusions are when objects appear smaller or larger than in reality, appear discolored, or lack color entirely; visual hallucinations are when a person "sees" images that do not exist in their immediate surroundings. Even if only one side of the occipital lobe is damaged, a person can lose their sight entirely. Other potential visual defects include changes in the visual field and scotomas (blind island-like gaps in the visual field). [8] If lesions appear on the primary visual cortex, a person can develop Anton's syndrome, a form of blindness in which a person is mostly oblivious of their disabilities even though they are unable to visually identify an object. [4] Other limitations incurred by damage to the occipital lobe can include: visual aphasia (word blindness), difficulty noticing movement or identifying drawn objects, a loss of academic abilities (writing, reading, etc.), and color agnosia (difficulty in color recognition). [2]

Temporal

The temporal lobe.

The temporal lobe is located on both sides of the brain, just beneath the lateral Sylvian fissure. This lobe registers the olfactory sense (smell), and is very involved in the processing of auditory input (sound). Speech, memory, and emotion are also partly controlled by this lobe. [1] In general, the temporal lobe distinguishes various sounds and smells, as well as sort newly acquired data; it is also thought to play a role in short-term memory. The left and the right lobes differ in some of their primary functions. The left lobe for example, houses verbal memory (names, words, etc.), but the right lobe is involved with visual memory (faces, pictures, places, etc.). [12] The region of the temporal lobe that interprets auditory information from the ears is on the upper side of the lobe; the underside of the temporal lobe forms and retrieves memories. Other areas of the lobe are thought to link the senses of touch, taste, sight, and sound with associated memories. [3]

The temporal lobe contains the hippocampus, primary auditory complex, and Wernicke's area, smaller regions with distinct functions [1]:

  • Hippocampus--brain structure located on both sides of the brain under the medial portion of the temporal lobe; helps in the formation of recent memories, factual and autobiographical; may also act as the "gateway" of memories on their way to permanent storage in the brain. [13]
  • Primary auditory complex (area)--processes the basics of sound, that is, pitch and volume; identifies the general range of pitch or volume strength, but sends the auditory signals onto the auditory association area in order to recognize the sound (this is how sounds are put into historical context within the brain, enabling a person to wake to an alarm or recognize a song)[14].
  • Wernicke's area--found behind the primary auditory complex in the left temporal lobe; responsible for the comprehension, interpretation, and recognition of language, as well as semantic processing. [15]
The auditory cortex in the temporal lobe processes and interprets the action potentials sent by the ear as it responds to soundwaves.

Remaining functions of the temporal lobe include long-term memory, the categorization of objects, and a little visual perception [2].

Because the two temporal lobes perform slightly different functions, the impairments of a head injury to the lobes differ. Right temporal lobe damage can alter visual and tonal sequences recognition, as well as musical abilities; other effects can include the recollection of nonverbal material (drawings, music, etc.) and the inability to inhibit speech. Injury of the left temporal lobe decreases the capability to remember visual and verbal content, even that of comprehending speech. Further, a damaged left lobe can result in a difficulty recognizing words. In the Fundamentals of Human Neuropsychology (1990), authors and top researchers Bryan Kolb and Ian Q. Whishaw identified eight key symptoms of temporal lobe injury:

  • "Disturbance of auditory sensation and perception
  • Disturbance of selective attention of auditory and visual input
  • Disorders of visual perception
  • Impaired organization and categorization of verbal material
  • Disturbance of language comprehension
  • Impaired long-term memory
  • Altered personality and affective behavior
  • Altered sexual behavior." [16]

Other impairments associated with temporal lobe damage include aggressive behavior, seizure disorders, short-term memory loss, concentration difficulties, long-term memory interference, and trouble identifying or locating objects in an environment. [2]

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References

  1. 1.0 1.1 1.2 1.3 1.4 Diagram of the Brain and its Functions Buzzle.com. ©2000-2009, 2010.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Brain Map Brain Injury Resource Center. Copyright © 1998 Head Injury Hotline.
  3. 3.0 3.1 3.2 3.3 Brain Basics: Know Your Brain Office of Communications and Public Liaison. National Institute of Neurological Disorders and Stroke. National Institutes of Health. 1 May 2007.
  4. 4.0 4.1 4.2 Introduction: Frontal Lobes Alexander Auchus, MD. Function and Dysfunction of the Cerebral Lobes. The Merck Manuals Online Medical Library. September 2008.
  5. Wile, Jay L., Shannon, Marilyn M., The Human Body: Fearfully and Wonderfully Made! 2001. Published by Apologia Educational Ministries, Inc. Anderson, IN. Printed by CJK. Cincinnati, OH. Sixth Printing 2008. (p 227)
  6. What is Broca's Area? Shannon Kietzman. wisegeek.com. Copyright © 2003 - 2010.
  7. The Human Brain Katherine Benziger, Ph.D., Sue Holmes. benziger.org. KBA The Human Resource Technology Company. © 1996.
  8. 8.0 8.1 8.2 Parietal Lobes Centre for Neuro Skills. TBI Resource Guide. © 2009.
  9. Wile p225-226
  10. Parietal Lobe Brain Injury Brain Injury. brainandspinalcord.org. Sponsored by Newsome Law Firm.
  11. Wile p226-227
  12. About Brain Injury: A Guide to Brain Anatomy Attorney Gordon S. Johnson, Jr. waiting.com © 2002 - 2009.
  13. Glossary: Hippocampus Catherine E. Myers. Memory Loss and the Brain. Memory Disorders Project. Rutgers University. Copyright © 2006.
  14. Wile p227
  15. Wernicke's Area Regina Bailey. About.com: Biology. The New York Times Company. © 2010 About.com.
  16. Temporal Lobes Centre for Neuro Skills. TBI Resource Guide. © 2009.

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