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Temporal Lobe Lesions

Functions of the Temporal Lobe

The temporal lobe, located behind the ears and below the temples, is one of the 4 lobes of the brain. It consists of three gyri; the superior temporal gyrus, the medial temporal gyrus, and the inferior temporal gyrus. This part of the brain is responsible for several functions that have a tremendous impact on our every day lives. Some of the main functions include processing of semantic memory, episodic memory, and declarative memory. The temporal lobe is also essential in sound processing, speech comprehension, and visual perception.

Located throughout the temporal lobe are important structures that play a key role in these functions. The primary auditory cortex is located within the sylvian fissure and is responsible for auditory perception (the primary function of the temporal lobe). Wernicke's area, located posterior to the primary auditory cortex, is essential in language comprehension. On the inferior and posterior portion of the temporal lobe are the fusiform gyrus, which is responsible for facial recognition, and the parahippocampal gyrus, which is responsible for landscape recognition and memory encoding. The hippocampus, located in the medial temporal lobe, converts short term memory into long term memory. Lastly, the amygdala is located in the anterior medial portion of the temporal lobe, and is responsible for emotional regulation. Although these functions can be found in the temporal lobe, it is critical to understand that some of these structures may have roles in other parts of the brain and that their roles listed here can vary as well depending on what other structures they are working with.

A lateral view of the temporal lobe, pointing out the three main gyri of the temporal lobe

Cortical view of the human brain. The portion in color represents the temporal lobe.

Brain Lesion Causes

A brain lesion is an abnormality within the brain tissue. These are seen by using brain imaging techniques, including magnetic resonance imaging (MRI), or computerized tomography (CT). Brain lesions can range from mild to life threatening depending on the size, location, and impact of the lesion. They can also be caused externally or internally. Causes of lesions include aneurysms, inflammation, abnormal formation of brain vessels, epilepsy, stroke, traumatic brain injury, and unknown causes. It is important to understand that lesions and concussions are not synonymous. Although they may occur simultaneously, concussions are usually diagnosed by symptoms, whereas lesions are diagnosed by imaging tests.

Neuropsychological Symptoms

In 1990 Kolb and Wishaw discovered the eight symptoms of a temporal lobe lesion. These eight symptoms include disturbances in auditory perception, impairments in selective attention of auditory and visual input, visual perception disorders, impairments in organizing verbal material, language comprehension disturbances, impaired long term memory, altered personality and behavior, and altered sexual behavior. Symptoms of temporal lobe lesions are dependent on where the lesion occurs, specifically in the right or left hemisphere. This is because the structures in each hemisphere may have different functions.

Visual and Auditory Perception

The fusiform gyrus and parahippocampal gyrus are responsible for facial and scene recognition. Damage to the fusiform gyrus (fusiform face area) can result in prosopagnosia, which is the inability to recognize familiar faces. It is also known as face blindness. Left side lesions can lead to impairments in recall of visual stimuli, while right side lesions can lead to impairments in recognition of visual content. There are different forms of visual agnosia that can occur from temporal lobe damage. Associative agnosia, which is an impairment in being able to recognize familiar objects and scenes and difficulties putting meaning with them, can occur when the ventral temporal cortex is damaged. A patient with associative agnosia is able to copy a line drawing, but they fail to recognize what they have drawn. Apperceptive agnosia, an impairment in perception that causes a failure in recognition of objects, can occur if the occipito-temporal vision area(s) of the brain is damaged.

Language

The left temporal lobe plays key roles in language comprehension and the learning and memorization of verbal material. This part of the brain is home to Wernicke's area, which is responsible for the processing of language. Wernicke's area is essential in understanding written and spoken language, as well as putting meaning with words. Damage to this area will cause Wernicke's Aphasia; a speech disorder that results in the difficulty of understanding both written and spoken language. Although speech may be spared, many patients often times use non-exsistent words when speaking, making them difficult to understand. This means that both understanding others and being understood can be confusing and difficult. Due to the inability to understand written language as well, those with Wernicke's Aphasia may show profound deficits in reading comprehension. Wernicke's Aphasia is generally though to have a main function in the left lobe and therefore may occur more commonly in left side lesions. Damage to the right temporal lobe can cause persistent talking.

Memory

The hippocampus is essential in the storage of memories, as well as converting information into long term memories, especially declarative long-term memory. Damage to the medial temporal lobe, where the hippocampus is located, can result in permanent or temporary anterograde amnesia; the inability to form new memories. Aside from damage to the hippocampus, lesions in the left temporal lobe can have the outcome of impaired verbal memory, while lesions in the right temporal lobe can result in impaired non-verbal memory in things such as music or drawings.

Other Syndromes and Disorders

Lesions can also occur bilaterally, meaning that both lobes are affected. Külver-Bucy Syndrome is quite rare but can occur after a bilateral temporal lobe lesion. Oral fixations, memory loss, hyper-sexuality, visual agnosia and distractibility, and placidity are all symptoms of this syndrome. Bilateral anterior temporal lobe damage is the primary cause of this syndrome. Another possible outcome of temporal lobe damage is seizures, or temporal lobe epilepsy. This can have a severe impact on a person's every day life with things including personality, rage, paranoia, perseverative speech, and altered sexual behavior. Seizures can also cause further damage in the brain.

Diagnosis

A key component of diagnosis is an in depth history of symptoms that the patient is experiencing, as well history of symptoms from a loved one, friend, co-worker or someone that spends enough time with the patient to notice differences. This can be very helpful because the patient may not be aware of symptoms that others notice. Because the symptoms of a temporal lobe lesions can be quite complicated, several specialists may work together to determine what symptoms are caused by the lesion. The best and most efficient way to find the location of the lesion is through a neuroimaging test, such as an MRI or CT. Aside from neuroimaging tests, neuropsychology tests may be used to test areas like memory, vision, and perception.

Neuropsychological Tests

Neuropsychological tests are used to better understand what areas are damaged after a lesion and what cognitive components have been affected. Tests that measure whether or not someone has temporal lobe damage will generally include verbal memory, visual memory, auditory perception, and visual perception tasks. There are many different tests used for brain injury patients and it it is up to the neuropsychologist to determine which test(s) will be most suitable.

An example of a patient copy of the Rey-Osterrieth Complex Figure Test.

Rey-Osterrieth Complex Figure Test (ROCF)

The Rey-Osterrieth Complex Figure Test(ROCF) is used to measure visuospatial, constructional, and visual memory. This test consists of three conditions; copy, immediate recall, and delayed recall. The patient is given a stimulus card with a geometrical figure on it and are asked to copy the figure while being able to look at the stimulus. Immediately after copying the figure, the stimulus is removed and they are asked to draw the figure from memory. After a certain amount of time has passed (usually at least 15 minutes), they are once again asked to draw the figure from memory. The time in between the second and third condition may be used to complete different cognitive tests. The score of the ROCF is based on location, accuracy, and organization. This test usually takes around 30 minutes to complete.

Rey Auditory Verbal Learning Test (RAVLT)

The Rey Auditory Verbal Learning Test (RAVLT) evaluates short term memory, verbal memory, rate of learning, and retention of memory. The patient is told a list of 15 random words and asked to perform immediate recall after being given the words. The immediate recall will occur for 5 trials. After the 5 trials, a list of 15 unrelated words is told to the patient and the patient must then repeat the original list of 15 words from the first 5 trials. Lastly, after 30 minutes, the patient will once again repeat the original list of 15 words. The words are unconnected and given several times, making the nature of the test both stressful and complex for someone with injury. Therefore, it is not uncommon to witness frustration in many patients. An important aspect of this test is that it measures the rate of learning, which numerous memory tests lack.

Wechsler Memory Scale

The Wechsler Memory Scale (WMS-IV) is a test that measures different memory functions for people ages 16 to 90. There are seven subtests in the WMS-IV; spatial addition, symbol span, design memory, general cognitive screener, logical memory (I &II), verbal paired associated (I & II), and visual reproduction (I & II). The five types of memory that are assessed and reported are auditory memory, visual working memory, immediate memory, and delayed memory. If a patient has been diagnosed with various psychiatric and/or development disorders, there is also an optional cognitive exam that asses global cognitive deficits.

Neurorehabilitation

The length and difficulties of  the rehabilitation process for a brain lesion is dependent on the severity of the lesion. Patients may see several different specialists, including speech therapists, neurologists, neuropsychologists, etc., depending on the outcome(s) of the lesion. The main goal of neurorehabilitation is finding alternative ways for the patient to return to their every day lives by healthily coping with the remaining struggles or disabilities. Patients often have difficulties with relationships, personality changes, problems returning to work, and depression/anxiety after brain damage. These are all aspects that the rehabilitation process aims to help.

Including family and close friends in the rehabilitation process is critical because they will be affected as well. If a patient experiences personality and behavior changes, those who are close with the patient will be impacted and may experience rage or frustration if they are not full aware of the symptoms or the rehabilitation process. By including them in rehabilitation they can increase their understanding of what is happening and the progress of healing will be smoother.

It is also crucial to understand that every individual is different and the symptoms of a similar lesion can vary vastly from person to person. For example, children and younger adults have brains that enable them to use other parts of the brain to compensate for the damaged areas, allowing them to regain more function. This mechanism is known as plasticity. This ability decreases as we age. Therefore, the symptoms will probably be more severe for those of older age.

There are three types of rehabilitation settings; impatient rehabilitation, outpatient rehabilitation, and community rehabilitation. Impatient care is for those who are not quite ready to return home from the hospital after their brain injury. This is the most intensive type of rehabilitation. Outpatient rehabilitation is for those who are able to return home and use outside sources, rehabilitation clinic or local hospital, for further rehabilitation. Lastly, there is community rehabilitation, which may involve the patient being transferred to an assisted living unit to develop or increase their every day living skills. This can also involve a therapist coming to a patient's home.