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The temporal lobe is one of the four main regions of the cerebral cortex that is located beneath the sylvain fissure (also known as the lateral sulcus) on both cerebral hemispheres of the mammalian brain. Approximately 17% of the volume of the cerebral cortex shapes the surface of the temporal lobes.


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The temporal lobes are easily recognisable structures with a thumb like appearance when laterally viewed. The lateral sulcus (Sylvain Fissure) which is the deep cortical fissure indicates the separation of the temporal lobe from the frontal lobe and parietal lobe. However, the posterior section of the temporal lobe shares borders with the occipital lobe behind and parietal lobe above. The temporal lobe has two significant sulci running horizontally and parallel to the Sylvain Fissure. They separate the temporal lobe into three gyri; the superior temporal gyrus, the middle temporal gyrus and the inferior temporal gyrus.

The temporal lobe is home to structures involved in the auditory, olfactory, vestibular and visual senses, along with the perception of spoken and written language. The temporal lobe also homes the hippocampus which is located in the medial temporal lobe. The hippocampus is a component important for establishing information from short-term memory to long-term memory.

Anatomy
The Temporal lobes are located inferior to the parietal and frontal lobes and located anterior to the occipital lobes. The temporal lobes are separated from the frontal lobes and anterior areas of the parietal lobes by the sylvian fissure or lateral sulcus. The angular gyrus divides the temporal lobe from the posterior area of the parietal lobe.

The temporal lobe has a lateral, a medial, a superior, and an inferior surface. The Lateral surface is made up of three parallel (superior, middle and inferior) gyri separated by two sulci (superior and inferior). The sulci act as the borders and separate the three temporal lobe sections. The inferior gyrus curves onto the inferior surface of the temporal lobe and posteriorly onto the occipital lobe. The remaining gyri that make up the inferior surface are called the occipitotemporal gyrus (also known as the fusiform gyrus) and the parahippocampal gyrus. The parahippocampal gyrus then curves to form a hook called the Uncus.

The medial surface of the temporal lobe reaches from the sylvian fissure to the parieto-occipital fissure. Within the sylvian fissure are short convultions that run mediolaterally (towards the middle of the brain) and make up the transverse temporal gyri and the Heschl’s gyrus. These along with the planum polare and the planum temporale make up the superior surface of the temporal lobe.

The temporal lobe can be divided into three lobe sections: the superior temporal lobe, the middle temporal lobe and the inferior temporal lobe. The superior temporal lobe holds the primary auditory cortex which is the area of the brain that is responsible for processing sound. The middle temporal lobe encompasses most of the lateral temporal cortex, the region that processes language, auditory and some memory information. The inferior temporal lobe corresponds to the inferior temporal gyrus.

The temporal lobe is home to the medial temporal lobe which contains structures of the Limbic system including the and parahippocampal gyrus. The limbic system is a collection of cortical structures that are positioned in the and. The amygdala is a component of the Limbic system that can be found in the temporal lobe. The lies just beneath the Uncus and processes emotions

The hippocampus is a scrolled structure located in the medial temporal lobe it contains the Dentate gyrus (dense layer of cells at the tip of the hippocampus) which is associated with the formation of new memories. Some components of the Olfactory Cortex (where smells are processed) are also located in the medial temporal lobe.

A well-known German psychologist Carl Wernicke, discovered that a lesion on the left temporal hemisphere left his patient unable to interpret and understand language. This area was later named the Wernicke's area after the doctor. However, there is some speculation as to the exact location of this area.

Function
The several anatomical structures located within the temporal lobe suggests that this lobe organises numerous functions. These functions include memory and learning, emotion and behaviour, language, auditory senses, visual senses and olfactory perception.

Memory and Learning
The ability to remember and learn information has been accredited to the hippocampus, and the hippocampal formation, the parahippocampal gyrus and the dentate gyrus all located within the temporal lobe. The hippocampus is involved in the attainment of new information and the ability to form new memories about experienced events rather than the retrieval of former memories and information.

The medial temporal lobe consists of a system of anatomically related components that are essential for memory function. A relationship between the medial temporal lobe and memory function can be identified in clinical material more than a century old. , However, the idea only became firmly established when Brenda Milner systematically recorded the profound effects of the medial temporal lobe resections on memory in a patient who has come to be known as H.M. Patient H.M underwent a bilateral surgical removal of the medial temporal lobe which resulted in profound long lasting anterograde amnesia.

The medial temporal lobe homes the hippocampus regions and the parahippocampal gyrus, which consists of the perirhinal, parahippocampal and entorhinal cortex. These structures, presumably by the feature of their extensive and reciprocal connections with neocortex, are vital for establishing long-term memory for fact and events known as (Declarative memory). The medial lobe memory system is essential to bind together the storage site in necortex that represent a whole memory. As time passes after learning, memories stored in neocortex gradually become independent of the medial temporal lobe structures, assuring that the medial temporal lobe system is continuously available for the acquisition of new stimuli.

Declarative memory refers to the ability to remember personal events, semantic information and other facts that we can be explicitly conscious of and therefore state or ‘declare’, both verbally or non-verbally (such as pressing a bottom during a computer task). Endel Tulving introduced a distinction between two types of declarative memory which he titled episodic and semantic. Episodic memory refers to memory for events personally experienced by an individual in a specific location and at a specific time. Semantic memory however, is referred to knowledge about the world that individuals share with other individuals in their cultural settings.

Emotion and Behaviour
The temporal lobe also plays a part in emotion and behaviour. Early research on rhesus monkeys showed that lesions to the temporal lobe resulted in significant social and emotional deficits. This observation was further studied by Heinrich Klüver and Paul Bucy who found that large lesions to the anterior temporal lobe resulted in noticeable changes, including loss of fear, overreaction to all objects, hypometionality, hypersexuality and hyperorality (a condition whereby inappropiate objects are placed in the mouth).

The hippocampal complex, by forming episodic representations of the emotional signiﬁcance and interpretation of events, can inﬂuence the amygdala response when emotional stimuli are encountered. The Amygdala is located deep within the medial temporal structure and has shown to play a significant role in mental states and regulating emotion. The left Amygdala has been associated with obsessive-compulsive disorders, anxiety and post traumatic stress. Studies have also shown that the amygdala plays a role in sexual orientation, social interaction, and aggression.

Language
One region related to the receptive aspect of language, concerning the perception of spoken language is located in the posterior superior temporal lobe; in Brodmann area (area 22) and Heschl's gyri (area 41 and 42). The posterior region of area 22 is known as Wernicke's area which is associated with the recognition and understanding of written and spoken language.

The anterior temporal lobe (ATL) has been found to play a role in language processing. Various research has shown that ATL is the binding site of the semantic/conceptual properties of words and objects (conceptual components by which a person understands words and sentences, and thus to supply an explanatory semantic representation). Other research has suggested that ATL is essential in lexical retrieval (a vital subprocess of productive language skills, which is essential in fluent speaking and writing).

Audition
The transverse gyri of Heschl within the temporal lobe homes the Primary auditory cortex where auditory signals are received from the cochlea (relayed via several subcortical nuclei). The primary auditory cortex is organised by layer and column and this anatomical design allows for the collection of auditory information from both ears, which in turn allows individuals to hear. Adjacent areas in the superior, posterior and lateral parts of the temporal lobes are involved in high-level auditory processing. In humans this includes speech, for which the left temporal lobe in particular seems to be specialised.

Vision
The inferior and middle temporal lobe complexities are engaged in visual functions including colour perception, stereopsis, and spatial orientation. The communication of the inferior temporal cortex with limbic and visual regions is important for the information processing of shape and face recognition. The underside (ventral) part of the temporal cortices appear to be involved in high-level visual processing of complex stimuli such as faces (fusiform gyrus) and scenes (parahippocampal gyrus). Anterior parts of this ventral stream for visual processing are involved in object perception and recognition (recognising an object from a variety of viewpoints). A region bordering both the temporal and occipital lobes known as the ventromedial occipitotemporal is vital for the perception of colour.

Olfactory Perception
The olfactory system which enables humans to interpret smells (known as olfaction) is contained within limbic system. It has been considered that the temporal lobe is a vital location for the integration of senses and the development of self-awareness due to the limbic systems vast communications with the medial aspect of the temporal lobe.

Temporal Lobe Lesions
The temporal lobe has many different functions such as the processing of auditory and visual information, memory, and emotional responses to stimuli. Based on these functions, important symptoms for temporal lobe damage have been identified. These are: the impairment of auditory, musical and visual processing, an impaired long-term memory and a change in an individual’s personality and sexual behaviour. . The main causes of temporal lobe damage are brain injury, tumours, strokes and epilepsy.

Disorders of Auditory and Music Perception
Impairments of auditory processing have been identified as a symptom of temporal lobe damage. Graham, Greenwood and Lecky, (1980) found that bilateral lesions to the primary auditory cortex resulted in cortical deafness where the individual could neither hear speech or any environmental sounds Lesions to each primary auditory cortex individually result in different auditory dysfunction. Fujii et al (1990) found that patients with a lesion to the right primary auditory cortex have an inability to recognise non-verbal environmental sounds such as animal cries and transportation noises. On the other hand, patients with lesions to the left primary auditory cortex have an inability to understand speech, also known as pure word deafness. These patients are unable to understand speech as they have an inability to discriminate between different speech sounds, although they still maintain the ability to read, write and speak. Pure word deafness occurs as a lesion in the left auditory cortex prevents auditory information reaching Wernicke's area, which has been found to be involved in the comprehension of speech.

Other auditory dysfunctions have been identified with temporal lobe lesions such as auditory hallucinations. . Verbal hallucinations have been reported in individuals’ with left temporal lobe damage. Verbal hallucinations may include voices giving commands, advice or simply saying sentences or words. Whereas some people may be aware of their hallucinations, others are not and will often respond to their verbal hallucinations. Non-verbal hallucinations have also been reported as, Penfield and Perot (1963) found that stimulation of the superior temporal gyrus in the right temporal lobe created musical hallucinations.

Temporal lobe lesions also impair an individual’s perception of music. Shankweiler (1966) found that lesions in the right temporal lobe result in an inability to discriminate between melodies. Right temporal lobe lesions also result in impairments in pitch and timbre perception.

Disorders of Visual Perception
The temporal lobe has been found to be crucial for visual perception. Research has found that lesions in the temporal lobe produce impairments in the visual recognition of stimuli. Individuals with lesions in the inferior temporal cortex, in an area called Fusiform face area (FFA), have impaired facial recognition, also called Prosopagnosia. Individuals with Prosopagnosia cannot even recognise the faces of their own family members. Patients with lesions in the inferior temporal cortex can also have visual agnosia and impaired colour recognition, in addition to impaired facial recognition. However, these types of agnosia usually occur separately.

Other visual dysfunctions have been identified with temporal lobe lesions. Lesions to the optic radiation in the temporal lobe can produce a deficit in the individuals’ visual field called Quadrantanopia. Quadrantanopia affects a quarter of the visual field and lesions to the optic radiation with result in a superior homonymous quadrantanopia, which is the loss of the same quarter of vision in both visual fields. Bilateral temporal lobe lesions also produce deficits in the visual field, as Kluver and Bucy (1937) found that after the removal of both temporal lobes in rhesus monkeys, a visual agnosia occurs and the monkeys can no longer recognise objects. Temporal lobe seizures can also affect an individuals’ visual perception with objects appearing larger (Macropsia)or smaller (Micropsia) then their normal size.

Impaired long-term memory
Impairment in the creation of new long-term memories is also a symptom of temporal lobe damage. The medial temporal region, particularly the hippocampus, has been found to be an important structure in the retention of current memories. Research has shown that bilateral damage to the medial temporal lobes including the amygdala and hippocampus result in profound anterograde amnesia (an inability to create new memories after the lesion has occurred) within the individual. Other memory deficits have also been found in individuals with temporal lobe damage. The recall of visual information such as faces and non-verbal information such as drawings are impaired in individuals with right temporal lesions. Whereas left temporal lesions impair the recall of verbal information.

Changes in personality and sexual behaviour
Temporal lobe lesions have also been found to affect an individuals’ personality. Personality characteristics such as increased paranoia and aggression, emphasis on trivial details, obsession with religion and egocentricity are more prevalent within patients with temporal lobe lesions. Bilateral lesions of the amygdala result in an individual developing Kluver-Bucy syndrome. Kluver-Bucy syndrome involves specific behaviour changes in the individual such as an inability to recognise familiar objects, increased sexual behaviour, a desire to examine objects orally and memory deficits. Davis (1992) found that feelings of fear and anxiety are increased if the amygdala is stimulated suggesting that damage to the amygdala could also influence the emotions of the individual. Not only can temporal lobe lesions influence personality characteristics but it has also been found that sexual behaviour can be influenced by temporal lobe damage. Miller et al, (1986) found that patients with temporal lobe damage report an increase in their sexual behaviour.

Temporal Lobe Epilepsy
Temporal lobe epilepsy is a type of partial onset epilepsy that occurs as recurrent epileptic seizures. It arises in or predominantly involves the temporal lobe(s) and their components.

There are two types of Temporal Lobe epilepsy:

Mesial temporal lobe epilepsy which emanates in the amygdala, parahippocampal gyrus and the hippocampus.

Lateral temporal lobe epilepsy which arises in the neocortex on the lateral surface of the temporal lobe.

Symptoms
People who have temporal lobe epilepsy experience seizures. Seizures can create involuntary actions, a reduction or loss of consciousness and obscure sensations.

There are three types of seizure that begin in the temporal lobe(s)and its structures:

Simple partial seizure that involve no loss of consciousness and are therefore commonly referred to as an 'aura'. Patients often experience olfactory, auditory and visual hallucinations during simple partial seizures.

Complex partial seizure that inhibit consciousness and impair awareness and responsiveness.

Seizures that originate in the temporal lobe and then expand to the rest of the brain are termed Secondarily Generalized Tonic-Clonic Seizures. The person loses consciousness and then experiences muscle tension (tonic phase) after which muscles erratically relax and contract creating convulsions (clonic phase).