The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of . The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe is involved in processing sensory input into derived meanings for the appropriate retention of visual memory, language comprehension, and emotion association.
Structure
The temporal lobe consists of structures that are vital for declarative or long-term memory. Declarative (denotative) or
Explicit memory memory is conscious memory divided into
semantic memory (facts) and
episodic memory (events).
The medial temporal lobe structures are critical for long-term memory, and include the hippocampal formation, perirhinal cortex, parahippocampal, and entorhinal neocortical regions.
Research has shown that lesions in the hippocampus of monkeys results in limited impairment of function, whereas extensive lesions that include the hippocampus and the medial temporal cortex result in severe impairment.
A form of epilepsy that involves the medial lobe is usually known as mesial temporal lobe epilepsy.
Function
Visual memories
The temporal lobe communicates with the
hippocampus and plays a key role in the formation of explicit
long-term memory modulated by the
amygdala.
Processing sensory input
- Visual
- The areas associated with vision in the temporal lobe interpret the meaning of visual stimuli and establish object recognition.
Language recognition
In humans, temporal lobe regions are critical for accessing the
semantics meaning of spoken words, printed words, and visual objects.
Wernicke's area, which spans the region between temporal and parietal lobes of the dominant cerebral hemisphere (the left, in the majority of cases), plays a key role (in tandem with Broca's area in the
frontal lobe) in language comprehension,
whether spoken language or signed language. FMRI imaging shows these portions of the brain are activated by signed or spoken languages.
These areas of the brain are active in children's language acquisition
whether accessed via hearing a spoken language, watching a signed language, or via
Tactile signing.
The functions of the left temporal lobe are not limited to low-level perception but extend to comprehension, naming, and verbal memory.
New memories
The medial temporal lobes (near the
sagittal plane) are thought to be involved in encoding declarative
Long-term memory.
The medial temporal lobes include the
hippocampus, which are essential for memory storage, therefore damage to this area can result in impairment in new memory formation leading to permanent or temporary anterograde amnesia.
Clinical significance
Unilateral temporal lesion
-
Contralateral homonymous upper quadrantanopia (sector anopsia)
-
Complex hallucinations (smell, sound, vision, memory)
Dominant hemisphere
Non-dominant hemisphere
-
Impaired non-verbal memory
-
Impaired musical skills
Bitemporal lesions (additional features)
-
Deafness
-
Apathy (affective indifference)
-
Impaired learning and memory
-
Amnesia, Korsakoff syndrome, Klüver–Bucy syndrome
Damage
Individuals who suffer from medial temporal lobe damage have a difficult time recalling visual stimuli. This neurotransmission deficit is not due to lacking perception of visual stimuli, but rather to the inability to interpret what is perceived.
The most common symptom of inferior temporal lobe damage is
visual agnosia, which involves impairment in the identification of familiar objects. Another less common type of inferior temporal lobe damage is
prosopagnosia which is an impairment in the recognition of faces and distinction of unique individual facial features.
Damage specifically to the anterior portion of the left temporal lobe can cause savant syndrome.
Disorders
Pick's disease, also known as
frontotemporal amnesia, is caused by atrophy of the frontotemporal lobe.
Emotional symptoms include mood changes, which the patient may be unaware of, including poor
attention span and aggressive behavior towards themselves or others. Language symptoms include loss of speech, inability to read or write, loss of vocabulary and overall degeneration of motor ability.
Temporal lobe epilepsy is a chronic neurological condition characterized by recurrent seizures; symptoms include a variety of sensory (visual, auditory, olfactory, and gustation) hallucinations, as well as an inability to process semantic and episodic memories.
Schizophrenia is a severe psychotic disorder characterized by severe disorientation. Its most explicit symptom is the perception of external voices in the form of auditory hallucinations. The cause of such hallucinations has been attributed to deficits in the left temporal lobe, specifically within the primary auditory cortex.
See also
External links
