Weighing in at about 3 pounds, with approximately 100 billion nerve cells, the human brain is arguably the most complex structure in the known universe. Neurons in the brain are capable of establishing tens of thousands of connections with other neurons. Within these connections lie the experiences of memory and emotion. These connections also enable you to understand the world that surrounds you, and to guide your responses to it.
Identification
The largest part of the brain is the cerebrum, which is divided into left and right hemispheres. Each hemisphere is further divided into lobes. The temporal lobes are located on the sides of your brain, with their middles roughly even with the tops of your ears. They are involved with the formation, storage and retrieval of memory; the generation of emotions; and the comprehension of visual and auditory information.
Function
Much of the knowledge of brain function comes from studying the deficits experienced by those who have incurred brain damage. Damage to the temporal lobes can produce disturbances of auditory and visual perception and disturbances of language comprehension and speech. Damage can be linked to the development of schizophrenia, depression, autism, various forms of amnesia, seizures and personality changes such as humorlessness, changes in sexual behavior and extreme religious perspectives. Some functions can be attributed specifically to one lobe or the other.
Right Temporal Lobe
The memory of non-verbal sounds such as music and the recognition of shapes tend to occur in the right lobe. People with right lobe damage may develop auditory agnosia, a condition in which sounds can be heard but not recognized. For instance, someone with auditory agnosia may not be able to tell whether a sound is a symphony or an approaching freight train. If a part of the temporal lobe known as the fusiform gyrus is damaged, facial recognition may be impaired. An old friend may be indistinguishable from a complete stranger. Right temporal lesions may also result in aprosodia, which is the inability to interpret the emotional content of speech. People with aprosodia may be unable to tell whether someone is happy with them, or angry.
Left Temporal Lobe
Left lobe damage can result in problems with comprehension and use of language. In most people, the upper rear of the left lobe is the location of Wernicke's area. Damage here produces difficulty with the comprehension of spoken and written language, a condition known as Wernicke's aphasia. The person may be able to speak fluently, with a normal rhythm, but the sentences come out as garbled nonsense referred to as a "word salad." Damage to Wernicke's area may also result in alexia, agraphia and anomia; the person cannot read, cannot write and cannot remember the names of objects.
The superior temporal gyrus is a ridge that runs across the outer surface of the temporal lobe. A smaller-than-normal gyrus in the left temporal lobe is strongly correlated with schizophrenia. Furthermore, if the diminished size is specific to the forward portion of the gyrus, auditory hallucinations are often the consequence. Diminished size further back in the gyrus is associated with altered thought processes. Auditory hallucinations and altered thought processes are two defining characteristics of schizophrenia.
Senses and Emotions
The two temporal lobes can each be divided into two distinct regions. The outer surface of each lobe processes sensory input so you can identify something that you are hearing or seeing. Deeper structures within the lobe participate in the formation of emotion in response to what is heard or seen. These deeper structures connect to the limbic system, part of the sympathetic nervous system, which is involved in generating the "fight or flight" response--the adrenaline rush you get when something makes you angry or frightened. Certain types of epileptic seizures can be generated in these deeper structures. These seizures are categorized as being "complex partial" in nature, resulting in impaired consciousness. They are characterized by olfactory and visual hallucinations, and automatic behaviors such as lip-smacking or purposeless movement of the limbs.
References
- Merck Manuals Online Medical Library: Brain
- Merck Manuals Online Medical Library: Seizure Disorders
- New Scientist: Instant Expert: The Human Brain
- Center for Neuro Skills: Temporal Lobes
- "The Brain and Behavior: An Introduction to Behavioral Neuroanatomy, 2nd ed."; David Lee Clark, Nashaat Boutros and Mario Mendez; 2005
