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Receptive aphasia, also known as Wernicke’s aphasia, sensory aphasia or fluent aphasia, is a type of aphasia characterised by a difficulty in understanding auditory language and in producing coherent speech.

Aphasia is a language disorder that can be found in speech, reading or writing due to dysfunction of specific brain regions. Causes of aphasia include organic brain diseases, head injuries, tumours and, most commonly, strokes (thought to cause 85% of all cases of aphasia).

Receptive aphasia is thought to be caused by damage to areas of the temporal lobe, commonly in the left hemisphere of the brain. Receptive aphasia is usually treated with speech and language therapy, with language abilities most likely to be recovered within the first few months following the onset of the disorder.

History
The Edwin Smith surgical papyrus dating from 3500 BC discusses a patient with language difficulties following a temporal lobe injury. However, it was not until the 19th century that Bastian (1869) and Schmidt (1871) wrote about patients suffering from difficulties with comprehension. These observations were followed by a monograph written in 1874 by Carl Wernicke describing patients who confused words, who were unable to retrieve words, who had difficulties understanding and expressing language and who were unaware of their impairments. Wernicke described this aphasia as being sensory in nature and located these difficulties to lesions of the posterior superior temporal gyrus, or Wernicke's area.

Signs and symptoms
Receptive aphasia is associated with difficulties categorising sounds into phonemes and isolating the phonemes that create words and sentences. Individuals with receptive aphasia do not experience difficulties in producing speech, however they can understand neither their own speech nor that of others. Typical symptoms of receptive aphasia include:


 * Speech that is correct in terms of sentence structure and articulation but with no sense to its content.
 * Problems with auditory and written comprehension, especially sentence comprehension.
 * Very fast speech.
 * Unawareness of difficulties, especially when beginning to suffer from aphasia.
 * Word salad, where random words and phrases are combined, causing the content of speech to become unintelligible. This is thought to be due to the confusion of phonetic characters, for example, 'I am going to Christmas with danger who is the telephone'.
 * Paraphrasic speech (adhering to the general rules of language but with errors in terms of phonemes and words). In extreme cases speech only contains nonsense words. For example, 'momputer' could be used instead of 'computer', and in extreme cases 'garfer' could be used instead of 'car'.
 * Using neologisms (e.g. 'loliphant' for 'elephant'), semantic paraphrasias (e.g. 'binoculars' for 'spectacles') and using general words (e.g. 'people' for 'women').
 * Imprecision in speech and difficulties retrieving words (e.g. the use of ‘thing’ and ‘it’)
 * Paragrammatism (the use of imprecise grammar).
 * Circumlocution (the use of ambiguous or long-winded speech e.g. describing a dog as ‘an animal with four legs and a tail that barks’ rather than using the word ‘dog’ itself).
 * Complete agraphia (inability to write), although the extent to which reading and writing is affected depends on the location of brain lesions. If able to write, writing is similar to speech in terms of its structure and errors.
 * The social conventions of conversation are conserved. For example, an individual with receptive aphasia may listen to their partner in the conversation and wait their turn before speaking, despite having great difficulty in comprehending the speech of the person they are talking to.

These communication impairments cause substantial difficulties in everyday life and interaction for receptive aphasics.

Symptom cross-over
The main presenting problems of receptive aphasia are not always as clear-cut as they first appear, which can cause difficulties. For example, aphasia itself is not the only disorder associated with aphasia-like symptoms. Similar symptoms can also be found in individuals with poor vision or hearing, impaired perception and impaired movement, thus causing difficulties in speech comprehension and production. Aphasia-like symptoms can also be found in conditions such as autism, dementia and schizophrenia, thus potentially causing misdiagnosis of aphasia.

A second difficulty is placing aphasic individuals in specific categories of aphasia. This is highlighted as around 40% of aphasic patients do not fit into specific diagnostic categories for aphasia such as receptive aphasia.

Localisation
In 1965 Geschwind, like Wernicke before him, proposed that receptive aphasia was caused by a lesion in Wernicke's area, located in the posterior area of the superior temporal gyrus. However, advances in research have shown the organisation of language to be more complex than first thought and that the key difficulties of receptive aphasia are not necessarily caused by damage to Wernicke's area.

The deficits associated with receptive aphasia have been connected with damage to the language-dominant temporal lobe (the left temporal lobe for the majority of right-handed aphasics) and to areas within it which include:
 * The first and posterior part of the second convolutions of the superior temporal gyrus adjacent to Heschl’s gyrus in the auditory association cortex.
 * The planum temporale in the left hemisphere - this is thought to be associated with memory for speech sounds and with linking the meaning of words to auditory representations.
 * The underlying white matter of the medial temporal lobe - damage here is thought to destroy local language regions and to cut off core language regions from areas of the temporal, parietal and occipital lobes.

Despite the research, the study of the neural basis of language is laden with complexity as it is likely that most of the brain has some role to play in language processes. This means that care is needed when determining the anatomical bases of receptive aphasia.

Stroke
Approximately 13% of all patients who develop aphasia following stroke have receptive aphasia. Stroke in the territory of the middle cerebral artery is the leading cause of receptive aphasia. The probability of middle cerebral artery strokes causing this disorder increases with age. Ischaemic strokes are the cause of 78% of receptive aphasia cases following stroke. In particular, ischaemic strokes due to cardiac emboli often affect the inferior division of the middle cerebral artery. This division irrigates the left brain hemisphere regions responsible for the functions impaired in receptive aphasia. Receptive aphasia following emboli occurs in 55% of cases due to ischaemic stroke, while 39% of these cases are due to cardiac emboli.

Haemorrhagic strokes may also lead to receptive aphasia. Haemorrhagic strokes may be due to hypertension, or due to the rupture of an aneurysm or arteriovenous malformation.

Trauma
Traumatic brain injuries in the form of focal contusions and closed head injuries also cause receptive aphasia. Contusions in the perisylvian region are a typical factor, since predominantly superficial lesions are sufficient for receptive aphasia to occur. Receptive aphasia is also present when focal contusions cause large lesions extending into the lateral temporal lobe or the white matter underneath it. Closed head injuries can consist of large subdural or epidural haematomas. In the presence of temporal contusion, such haematomas lead to a very severe receptive aphasia by causing occipito-temporal ischaemic strokes. Receptive aphasia is the second most frequent type of aphasia occurring after closed head injuries.

Tumours
Tumours are another cause of receptive aphasia, although a large tumour produces less impairment than an ischaemic stroke of the same size. This is due to the gradual disruption of function caused by tumours, which allows other parts of the brain to compensate for the loss of function. This usually leads to a slowly progressive receptive aphasia. However, the rate of growth and malignancy of the tumour also play a role in the speed of onset.

Other causes
Other causes of receptive aphasia include transient ischaemic attacks, migraine, and left temporal epileptic seizures. Such causes usually lead to transient aphasia, which may recur if the disease returns. Receptive aphasia may also appear as part of the migrainous aura, a phenomenon most likely due to the depression of neural activity induced by migraine. Language deterioration in Alzheimer's disease may also cause receptive aphasia before it progresses to global aphasia. Herpes simplex encephalitis is a rare condition which affects the medial temporal lobes and can thus cause receptive aphasia.

Causes of receptive aphasia in children
Traumatic brain injuries are the leading cause of receptive aphasia in children. Tumours are not likely to cause a specific type of aphasia such as receptive aphasia. In children, the lesions caused by herpes simplex encephalitis to the temporal lobe are much more severe compared to those caused by other damage, which may thus lead to receptive aphasia. The Landau–Kleffner syndrome, an age-related epileptic encephalopathy, may cause intermittent short episodes of receptive aphasia in children, with almost complete recovery between these episodes.

Assessment
The purpose of neurological and neuropsychological assessment of people with receptive aphasia is not only to diagnose the condition, but also to monitor change in symptoms over time and to devise a plan for therapy. As a consequence, examinations are not devised specifically for receptive aphasia. Rather, they are meant to assess a variety of language and other cognitive impairments present in aphasia and related disorders, in order to allow for differential diagnosis.

Clinical testing
In the acute phase of the disorder, the first assessment done is a bedside examination, usually part of a mental status examination administered by a neurologist. This examination includes tests of conversational speech, repetition, comprehension, naming or word finding, as well as, more briefly, reading and writing. The clinical test begins with an observation of the patient's conversational speech, which in receptive aphasia would be fluent and marked by paraphasias. Then, repetition is evaluated by asking the patient to repeat digits or single-syllable words, building up to complex sentences. A patient with receptive aphasia would have impaired repetition due to the inability to comprehend language. To test comprehension, the neurologist asks the patient to follow verbal commands increasing in complexity. Patients with receptive aphasia would have much difficulty comprehending these commands. A naming task consists of showing the patient various objects and actions and asking them to name them. Patients with receptive aphasia would be impaired on this task due to their anomia. While this clinical test is a very general overview of language functions, an experienced clinician would be able to draw preliminary inferences whether receptive aphasia is present.

Neuropsychological assessment
The neuropsychological assessment of aphasia is done in the non-acute phase of the disorder, and consists of psychometric tests administered by a neuropsychologist or a speech pathologist. There are two methods which can be used for the neuropsychological assessment of aphasia: aphasia screening tests and aphasia test batteries.

Aphasia screening tests
The aphasia screening tests are psychometric tests which may identify whether an aphasic disorder is present, but they are not generally used to diagnose receptive aphasia, as they are not as comprehensive as aphasia test batteries. A common screening test is the Token Test, which consists of twenty “tokens” in the shape of circles and squares, small and large, in five different colours. These tokens are laid out in front of the patient, who is asked to touch or manipulate a token of a specific shape, size, and colour, with instructions progressively increasing in complexity. The Token Test is useful for showing impaired comprehension in the case of receptive aphasia, and also tests for immediate memory span and syntax use.

Aphasia test batteries
In contrast to the screening tests, aphasia test batteries contain many different subtests which can generate a much more accurate description of the extent and quality of an aphasic impairment. These tests help distinguish between the different types of aphasic disorders, and can hence help a clinician diagnose receptive aphasia. Since they are much more comprehensive than screening tests, they usually require several hours to complete, and may be administered over the course of several days. Test batteries assess auditory and visual comprehension, word recognition, reading, writing, speaking and fluency, repetition, and naming. Some common test batteries in use include: the Boston Diagnostic Aphasia Examination and its abbreviated version, the Western Aphasia Battery; the Aphasia Diagnostic Profiles; and the Psycholinguistic Assessment of Language Processing in Aphasia.

Recovery
Decades of research on aphasia shows that recovery is possible, even in the extremely severe cases. Recovery from receptive aphasia is contingent on general factors like age, handedness, education level, premorbid status and social support system. Recovery also depends on more specific factors like cause of injury, lesion size and location, initial severity and initial comprehension. Likewise, the degree to which certain brain structures are involved as well as time since onset play a significant role in determining the extent of recovery. Compared to other forms of aphasia, receptive aphasia generally has a moderate prognosis.

Spontaneous recovery rates are highest in the initial three months and tend to decline after a year of onset. Often, the aphasia changes to a less severe form, like anomia. In the case of aphasia caused by stroke, the prognosis depends on the severity of stroke and the initial severity of aphasia.

Age is an important factor in predicting the outcome of receptive aphasia. Since age is negatively correlated with recovery rates in receptive aphasia patients, younger patients have greater chances of recovery, especially in traumatic brain injury cases. On the other hand, there is no evidence of different patterns of recovery with respect to sex. Language is one of the few functions in the human brain that have an asymmetrical distribution. While only 10% of right-handed individuals do not have left hemisphere dominance of language, nearly 30% of left-handed individuals have either right hemisphere dominance or recruit both hemispheres almost equally. Because aphasia generally results from left hemisphere injury, left-handed individuals tend to have a better prognosis for recovery. Higher premorbid intelligence as well as a higher education level contribute to a good prognosis.

A study on recovery pattern of receptive aphasia concluded that individuals with better initial scores and less use of paraphasias are more likely to recover, but overall, there seems to be a 'bi-modal pattern of recovery'. Thus, in some individuals with receptive aphasia, initial high scores predicted better outcomes and low scores suggested a poor prognosis. On the other hand, some individuals with receptive aphasia continued to use phonemic paraphasias (e.g. "ped" for "bed") for many years. After this, their use of phonemic paraphasias gradually began to decline, only to be replaced by other language deficits like semantic paraphasias (e.g. "fingers" for "toes") and anomia.

Another study examining patients who completely recovered from receptive aphasia demonstrated the ability to perform a verb generation task despite extensive damage to Wernicke's area. These individuals also showed preserved activation in Broca’s area and lateral prefrontal cortex. In the patients, right hemisphere activation was witnessed in the homologue of Wernicke's area and the inferior premotor cortex. The healthy controls had similar activation patterns, but in the left hemisphere. Thus, this study demonstrated the functional reorganization of the brain in recovery from receptive aphasia.

Treatment
The research on treatment of aphasia is still in its early stages. Language recovery in aphasia was earlier believed to peak in the initial few months and plateau after about a year. Although it is true that treatment is most effective in the initial months, research suggests that some intensive therapies like constraint-induced language therapy are effective even years later.

Speech and Language Therapy (SLT)
One of the most widely used methods for treatment of aphasia, speech therapy is generally tailored to suit the treatment needs of the individuals, after assessing their strengths and weaknesses. The objective of SLT is to maximise an individual’s ability to communicate successfully, through verbal speech or non-verbal channels, such as gestures. Speech therapy interventions vary in their applications, from conventional to intensive and from volunteer-facilitated to computer-mediated. For example, in one study, less severe receptive aphasia caused by a stroke was treated with speech therapy and transcranial direct-current stimulation (tDCS). Using tDCS, Brodmann area 45 and the contralateral forehead above the orbit were stimulated for a total of 20 minutes. This method showed significant improvement, especially if the treatment was given in the initial 30 days after onset. The following table summarises the various forms of speech therapy that are effective in treating receptive aphasia:

Constraint-Induced Language Therapy (CILT)
CILT is a form of speech and language therapy which is currently one of the most popular treatment methods for aphasia. It relies on the following three principles:

1. Providing intensive therapy in short intervals instead of spanning it over a longer interval (for example 6 hours a day for 2 weeks instead of 3 hours a day for 4 weeks);

2. Forcing use of usually avoided communication channels by use of behavioral shaping and reinforcement;

3. Adopting therapy techniques relevant to communication and behaviour in daily life.

CILT therapy initially begins with consolidating the already present or preserved skills, and then gradually increasing the level of difficulty. Individuals with aphasia often avoid using communication methods that require effort. For example, a person with receptive aphasia would tend to use filler words like ‘you know’, because of the difficulty faced in word finding. The rationale of CILT is to restrict the use of such words, thereby constraining usage of more meaningful words instead of empty phrases. Over a period of time, this process may result in formation of new links between the neurons, ultimately leading to improvement in language function.

In CILT, language games such as the Matching Card Game are used to improve communication. This game involves a few participants sitting around a table with visual barriers in front of them. Each patient is given a set of cards with pictures on them. Using verbal speech only, the participants have to request a matching card from another participant by describing the picture denoted on the card. The other participant may or may not have the matching card, and will respond accordingly. An appropriate response will be possible only if the request is fully understood. Thus, by placing emphasis on correctly responding to a request, comprehension can be improved in individuals with receptive aphasia. The barriers restrict the use of any non-verbal communication channels like gesturing, pointing, or nodding. This makes it impossible for receptive aphasia patients to understand what is being said solely by using cues like facial expressions. Individualized reinforcements are provided for every successful attempt.

Promoting Aphasic Communicative Effectiveness (PACE)
PACE therapy mainly focuses on enhancing an individual’s ability to use language by honing existing communication skills. Unlike CILT, it does not involve re-learning of language or restriction of use of any modality of communication, verbal or non-verbal. Instead, it strives to make use of all possible resources to facilitate communication. In PACE therapy, the therapist and the individual converse equally, like partners. Instead of becoming a critique for the patient’s skills, the therapist confirms whether or not the information was conveyed in an understandable manner.

Pharmacological treatment
Several drugs like Piracetam and Donepezil have shown beneficial effects. However, no one drug has yet proved to do more good than harm.

Aphasia affects all realms of a patient’s life, and hence, treatment focuses not only on improving communication, but also on improving overall competence of the individual.