08 July, 2011
Abnormal Brain Activity in the Left Temporal Lobe
The temporal lobes are brain areas that sit behind the eye sockets and under the temple on each side. Seen from the side, the brain looks like a boxing glove with the thumb pointing in the direction of your gaze. Each temporal lobe is where the thumb would be. The temporal lobes process sound, language and visual shape and store memories of words. Abnormal activity in the left temporal lobe can result from damage to the left temporal lobe itself or an area that feeds information into it. Left temporal lobe dysfunction occurs in conjunction with a variety of conditions and illnesses. Common ones are dyslexia, attention-deficit disorder, dementia, epilepsy and schizophrenia.
Dyslexia is a learning disability that impairs your ability to read. It affects 4 to 10 percent of all people. Brain imaging studies have shown that the disability is rooted in difficulties integrating letters with their speech sounds. Neuropsychologists at University of Maastricht looked at brain scans of dyslexic and normal adult readers presented with letters, speech sounds or a matching or non-matching combination of the two. They found that, compared to normal readers, the dyslexic adults have less activity in the left superior temporal gyrus, a part of the temporal lobe, in response to a sound or matching letter-sound combination. The study also showed that where normal people have more activity when sound and letter match, dyslexic have the same in matching and non-matching cases.
Attention Deficit Disorder
Attention-Deficit Disorder (ADD) is a neurological disorder that impairs your ability stay focused. There are at least six types of ADD. In temporal lobe ADD, there is abnormal activity in the left frontal and temporal lobes. It remains unknown what triggers the altered neuron firing. In children, lead exposure may be a contributing factor, reports psychological scientist Joel Nigg of the Oregon Health & Science University. He suspects that the metal sticks to cortical brain areas and in that way hinders or delays normal brain development.
Alzheimer’s disease is the most common form of dementia. It is characterized by a gradual degradation of memory and intellectual abilities. In affected patients, the hippocampus, the brain's major memory site, literally shrinks. While memory loss is the most significant symptom of Alzheimer's, researchers believe the temporal lobe is to blame. Brain imaging expert Perrick Bourgeat from the Australian e-Health Research Centre and his team found that protein deposits in the temporal inferior cortex, the first part of the temporal lobe, block communication with the memory center. The brain abides by the principle "use it or lose it." So, with no activity entering, the neurons wither and die, suggests the team.
Epilepsy is a neurological condition characterized by recurrent seizures. The temporal lobes are the most common site for localized seizures. From there, the localized seizure can spread to whole brain, causing a global seizure. In people with a healthy brain, the enzyme glutamine synthetase regulates neuron firings. In people with epilepsy, short supply of this enzyme leads to uncontrollably excited neurons, reports neuroscientist Douglas Coulter from Children's Hospital in Philadelphia. He conducted a study on neuronal circuitry in brain slices from mice and found that the epilepsy trigger is swelling of brain cells called "astrocytes." When these neurons dilate, they fail to generate enough of the important enzyme, Coulter says.
Researchers have known for some time that schizophrenics have reductions in the gray matter of the left temporal lobe, and that the severity of the thought disorder is inversely related to brain size. They have now found that there is also a progressive reduction in brain size that is unrelated to Alzheimer's and other forms of dementia. The finding came from a brain imaging study led by psychiatrist Daniel Mathalon from Yale School of Medicine. "This [result] is consistent with the emerging, yet, unproven, idea that having psychotic symptoms might actually be associated with some kind of toxicity to the brain," said Mathalon.
- Science Daily: Unraveling The Roots Of Dyslexia
- Science Daily: Lead May Be the Culprit in ADHD
- Science Daily: Uncovering Early Stages of Alzheimer's Disease
- Science Daily: Studying Altered Brain Cells Sheds Light on Epilepsy
- Science Daily: Men With Chronic Schizophrenia Lose Brain Volume Faster
- "New England Journal of Medicine"; Abnormalities of the Left Temporal Lobe; M. Shenton et al.; 1992
- Frontiers: Left Temporal Lobe Structural and Functional Abnormality
- Neuropsychiatry Online: Temporal Lobe Epilepsy, Temporal Lobectomy, and Major Depression
- Frontiers: Electrical Stimulation of the Human Brain
- Science Daily: USC Study Finds Faulty Wiring In Psychopaths
- BananaStock/BananaStock/Getty Images