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The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
The temporal lobe is involved in processing sensory input into derived meanings for the appropriate retention of visual memory, language comprehension, and emotion association.<ref name=smith07>Template:Cite book</ref>Template:Rp Temporal refers to the head's temples.
StructureEdit
The temporal lobe consists of structures that are vital for declarative or long-term memory. Declarative (denotative) or explicit memory is conscious memory divided into semantic memory (facts) and episodic memory (events).<ref name=smith07 />Template:Rp
The medial temporal lobe structures are critical for long-term memory, and include the hippocampal formation, perirhinal cortex, parahippocampal, and entorhinal neocortical regions.<ref name=smith07 />Template:Rp<ref name="van Staalduinen">Template:Cite journal</ref> The hippocampus is critical for memory formation, and the surrounding medial temporal cortex is currently theorized to be critical for memory storage.<ref name=smith07 />Template:Rp The prefrontal and visual cortices are also involved in explicit memory.<ref name=smith07 />Template:Rp
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.<ref>Template:Cite journal</ref>
A form of epilepsy that involves the medial lobe is usually known as mesial temporal lobe epilepsy.<ref name="Leach">Template:Cite journal</ref>
FunctionEdit
Visual memoriesEdit
The temporal lobe communicates with the hippocampus and plays a key role in the formation of explicit long-term memory modulated by the amygdala.<ref name=smith07 />Template:Rp
Processing sensory inputEdit
- Auditory
- Adjacent areas in the superior, posterior, and lateral parts of the temporal lobes are involved in high-level auditory processing. The temporal lobe is involved in primary auditory perception, such as hearing, and holds the primary auditory cortex.<ref name=schacter10>Template:Cite bookTemplate:Page needed</ref> The primary auditory cortex receives sensory information from the ears and secondary areas process the information into meaningful units such as speech and words.<ref name="schacter10" /> The superior temporal gyrus includes an area (within the lateral fissure) where auditory signals from the cochlea first reach the cerebral cortex and are processed by the primary auditory cortex in the left temporal lobe.Template:Citation needed
- Visual
- The areas associated with vision in the temporal lobe interpret the meaning of visual stimuliTemplate:Clarify and establish object recognition.<ref>Template:Cite journal</ref> The ventral part of the temporal cortices appears to be involved in high-level visual processing of complex stimuli such as faces (fusiform gyrus)<ref>Template:Cite journal</ref> and scenes (parahippocampal gyrus).<ref>Template:Cite journal</ref> Anterior parts of this ventral stream for visual processing are involved in object perception and recognition.<ref name="schacter10" />
Language recognitionEdit
In humans, temporal lobe regions are critical for accessing the semantic meaning of spoken words, printed words, and visual objects.<ref>Template:Cite journal</ref> 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,<ref>Template:Cite journal</ref> whether spoken language or signed language. FMRI imaging shows these portions of the brain are activated by signed or spoken languages.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref> These areas of the brain are active in children's language acquisition<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> whether accessed via hearing a spoken language, watching a signed language, or via hand-over-hand tactile versions of a signed language.<ref name="pmid22472091">Template:Cite journal</ref>
The functions of the left temporal lobe are not limited to low-level perception but extend to comprehension, naming, and verbal memory.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
New memoriesEdit
Template:See also The medial temporal lobes (near the sagittal plane) are thought to be involved in encoding declarative long term memory.<ref name=smith07 />Template:Rp The medial temporal lobes include the hippocampi, 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.<ref name=smith07 />Template:Rp
Clinical significanceEdit
Unilateral temporal lesionEdit
- Contralateral homonymous upper quadrantanopia (sector anopsia)
- Complex hallucinations (smell, sound, vision, memory)
Dominant hemisphereEdit
- Receptive aphasia
- Dyslexia
- Impaired verbal memory
- Word agnosia, word deafness
Non-dominant hemisphereEdit
- Impaired non-verbal memory
- Impaired musical skills
Bitemporal lesions (additional features)Edit
- Deafness
- Apathy (affective indifference)
- Impaired learning and memory
- Amnesia, Korsakoff syndrome, Klüver–Bucy syndrome
DamageEdit
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.<ref>Template:Cite journal</ref> 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.<ref name="pmid19938677">Template:Cite journal</ref>
Damage specifically to the anterior portion of the left temporal lobe can cause savant syndrome.<ref>Template:Cite journal</ref>
DisordersEdit
Pick's disease, also known as frontotemporal amnesia, is caused by atrophy of the frontotemporal lobe.<ref>Template:Cite book</ref> 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.<ref>Template:Cite journal</ref>
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.<ref name="pmid24245928">Template:Cite journal</ref>
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.<ref name="ReferenceA">Template:Cite journal</ref><ref name="pmid19753095">Template:Cite journal</ref> Decreased gray matter, among other cellular deficits, contribute to spontaneous neural activity that affects the primary auditory cortex as if it were experiencing acoustic auditory input. The misrepresentation of speech in the auditory cortex results in the perception of external voices in the form of auditory hallucinations in schizophrenic patients.<ref name="pmid26275927">Template:Cite journal</ref> Structural and functional MRI techniques have accounted for this neural activity by testing affected and non-affected individuals with external auditory stimuli.<ref name="ReferenceA"/>