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. The temporal lobes are involved in the retention
of visual memories, processing sensory input, comprehending language, storing new memories,
emotion, and deriving meaning.
Structure Medial temporal lobe
The medial temporal lobe consists of structures that are vital for declarative or long-term
memory. Declarative or explicit memory is conscious memory divided into semantic memory
and episodic memory. Medial temporal lobe structures that are critical for long-term
memory include the amygdala, brainstem, and hippocampus, along with the surrounding hippocampal
region consisting of the perirhinal, parahippocampal, and entorhinal neocortical regions. The hippocampus
is critical for memory formation, and the surrounding medial temporal cortex is currently
theorized to be critical for memory storage. The prefrontal and visual cortices are also
involved in explicit memory. 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.
Function Visual memories
The temporal lobe contains the hippocampus and plays a key role in the formation of explicit
long-term memory modulated by the amygdala. Processing sensory input
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. The primary auditory cortex receives sensory information from the
ears and secondary areas process the information into meaningful units such as speech and words.
The superior temporal gyrus includes an area where auditory signals from the cochlea first
reach the cerebral cortex and are processed by the primary auditory cortex in the left
temporal lobe. Visual
The areas associated with vision in the temporal lobe interpret the meaning of visual stimuli
and establish object recognition. The ventral part of the temporal cortices appear to be
involved in high-level visual processing of complex stimuli such as faces and scenes.
Anterior parts of this ventral stream for visual processing are involved in object perception
and recognition.
Language recognition The left temporal lobe holds the primary auditory
cortex, which is important for the processing of semantics in both speech and vision in
humans. Wernicke's area, which spans the region between temporal and parietal lobes, plays
a key role in speech comprehension. The functions of the left temporal lobe are not limited
to low-level perception but extend to comprehension, naming, verbal memory.
New memories
The medial temporal lobes are thought to be involved in encoding declarative long term
memory. 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.
Clinical significance Features of Temporal lobe lesions are as follows:
Unilateral temporal lesion Contralateral homonymous upper quadrantanopia
Complex hallucinations Dominant hemisphere
Receptive aphasia Wernicke's aphasia
Anomic aphasia
Dyslexia Impaired verbal memory
Word agnosia, word deafness Non dominant hemisphere
Impaired non-verbal memory Impaired musical skills
Prosopagnosia Bitemporal lesions
Deafness Apathy
Impaired learning and memory Amnesia, Korsakoff syndrome, Kluver Bucy syndrome
Damage Individuals who suffer from medial temporal
lobe damage have a difficult time recalling visual stimuli. This is due to the inability
to connect the visual stimuli perceived to the visual processing and interpretation centers.
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 and/or others. Language
symptoms include loss of speech, inability to read and/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 hallucinations,
as well as an inability to process semantic and episodic memories.
References
External links The medial temporal lobe memory system
H. M.’s Medial Temporal Lobe Lesion: Findings from Magnetic Resonance Imaging