The brain is divided vertically from front to back. While appearing like mirror images, there is some functional division between the lobes. These divisions are not absolute. In some people, the functions are reversed from side to side, while in others, the two halves appear to share all responsibility. Certain distributions of these lateralized functions are more common than others.
Brains display a consistent architecture. A predictable pattern of grooves and ridges demarcate each hemisphere into four lobes. The frontal lobe is at the front of the brain, while the occipital lobe is at the back. Between them lie the parietal and temporal lobes, with the parietal lobe situated above and back from the temporal. Much of our knowledge of differentiated lobe function stems from the observed pattern of deficits that occur with damage.
Frontal lobes
Personality and emotional control reside within the frontal lobes. Injury can produce personality changes that depend upon the affected lobe. According to the Center for Neuro Skills, left-sided damage can result in pseudodepression, featuring apathy, indifference, a lack of initiative, but no actual depression. Broca's area in the left frontal lobe is involved with the production of speech, with damage here causing Broca's aphasia. Speech becomes agrammatical and sputtering. A person may be unable to remember the names of things. Words may be substituted for one another. Repetition may not be possible.
Right frontal lobe injury can result in pseudopsychopathy, characterized by immature, tactless and unrestrained behavior. According to Dr. P. Shammi of the University of Toronto, right frontal lobe damage can also diminish a person's appreciation for, and response to, humor. A person may fail to smile or laugh when doing so would be appropriate.
In general, damage to the rear portion of the frontal lobes can cause weakness or paralysis. Each lobe affects the opposite side of the body, so right lobe damage causes left-sided weakness, and vice versa.
Parietal lobe
Left parietal damage produces confusion between right and left, language disorders, the inability to write and to do math. Familiar objects may be unrecognizable. This constellation of symptoms is called Gerstmann's syndrome.
Right parietal lobe damage can cause contralateral neglect. The person ignores his left side. He may not wash or properly dress that half of his body. He may be unable to make, draw or assemble things. Finally, he may deny the existence of his impairment.
Lesions along the left parietal-temporal divide cause difficulty with verbal memory, while those on the right side produce personality changes.
The Temporal Lobe
The temporal lobes process visual and auditory information and are involved in memory formation. Left side damage can impair verbal memory. Wernicke's aphasia is the consequence of damage to Wernicke's area in the left lobe. The National Institute on Deafness and Other Communication Disorders (NIDCD) describes this aphasia as being fluent, meaning that speech flows freely, but nonsensically. The speaker may be unaware of this. Also, she may not understand others.
Right lobe lesions cause uninhibited speech and an inability to recognize shapes and non-verbal sounds. A familiar tune becomes strange. Facial recognition may be lost, making old friends unrecognizable.
Occipital lobe
The occipital lobes process visual input. Damage typically causes the left or right side of the visual field to be blacked out in both eyes. The portion of the visual field blacked out depends on the location of the damage.
References
- Center for Neuro Skills; Brain Injury: Brain Map; Frontal Lobe
- "Brain; A Journal of Neurology"; Humor Appreciation: A Role for the Right Frontal Lobe; P. Shami and D .T. Stuss; April 1999
- Merck Online Medical Library, Home Edition; Brain, Spinal Cord and Nerve Disorders; Brain Dysfunction; Dysfunction by Location
- National Institute on Deafness and Other Communication Disorders; Health Info; Voice, Speech and Langage; Aphasia
