Wernicke's area
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Wernicke's area (Template:IPAc-en; Template:IPA), also called Wernicke's speech area, is one of the two parts of the brain that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to Broca's area, which is primarily involved in the production of language. It is traditionally thought to reside in Brodmann area 22, located in the superior temporal gyrus in the dominant cerebral hemisphere, which is the left hemisphere in about 95% of right-handed individuals and 70% of left-handed individuals.<ref>Template:Cite journal</ref>
Damage caused to Wernicke's area results in receptive, fluent aphasia. This means that the person with aphasia will be able to fluently connect words, but the phrases will lack meaning. This is unlike non-fluent aphasia, in which the person will use meaningful words, but in a non-fluent, telegraphic manner.<ref name="urlAphasia: Signs & Symptoms">Template:Cite web</ref>
Emerging research on the developmental trajectory of Wernicke's area highlights its evolving role in language acquisition and processing during childhood. This includes studies on the maturation of neural pathways associated with this region, which contribute to the progressive complexity of language comprehension and production abilities in developing individuals.<ref>Template:Cite journal</ref>
Structure
Wernicke's area, more precisely defined, spans the posterior part of the superior temporal gyrus (STG) and extends to involve adjacent areas like the angular gyrus and parts of the parietal lobe reflecting a more intricate neuroanatomical network than previously understood. This area shows considerable variability in its exact location and extent among individuals, challenging the traditional view of a uniformly located language center.<ref name="Binder 2170–2175">Template:Cite journal</ref>
However, there is an absence of consistent definitions as to the location.<ref name="Bogen">Template:Cite journal</ref><ref name="Nakai_2017">Template:Cite journal</ref> Some identify it with the unimodal auditory association in the superior temporal gyrus anterior to the primary auditory cortex (the anterior part of BA 22).<ref>Template:Cite journal</ref> This is the site most consistently implicated in auditory word recognition by functional brain imaging experiments.<ref name="DeWitt Rauschecker 2012">Template:Cite journal</ref><ref name="DeWitt Rauschecker 2013">Template:Cite journal</ref> Others include also adjacent parts of the heteromodal cortex in BA 39 and BA40 in the parietal lobe.<ref>Template:Cite journal</ref> Despite the overwhelming notion of a specifically defined "Wernicke's Area", the most careful current research suggests that it is not a unified concept.
While previously thought to connect Wernicke's area and Broca's area, new research demonstrates that the arcuate fasciculus instead connects to posterior receptive areas with premotor/motor areas, and not to Broca's area.<ref>Template:Cite journal</ref> Consistent with the word recognition site identified in brain imaging, the uncinate fasciculus connects anterior superior temporal regions with Broca's area.<ref>Template:Cite journal</ref>
Function
Right homologous area
Research using Transcranial magnetic stimulation suggests that the area corresponding to the Wernicke's area in the non-dominant cerebral hemisphere has a role in processing and resolution of subordinate meanings of ambiguous words—such as "river" when given the ambiguous word "bank". In contrast, the Wernicke's area in the dominant hemisphere processes dominant word meanings ("teller" given "bank").<ref>Template:Cite journal</ref>
Modern views
Emerging research, including advanced neuroimaging studies, underscores a more distributed network of brain regions involved in language processing, challenging the traditional dichotomy of Wernicke's and Broca's areas. This includes findings on how Wernicke's area collaborates with other brain regions in processing both verbal and non-verbal auditory information, reshaping our understanding of its functional significance.<ref name="Binder 2170–2175"/>
Support for a broad range of speech processing areas was furthered by a recent study carried out at the University of Rochester in which American Sign Language native speakers were subject to MRI while interpreting sentences that identified a relationship using either syntax (relationship is determined by the word order) or inflection (relationship is determined by physical motion of "moving hands through space or signing on one side of the body"). Distinct areas of the brain were activated with the frontal cortex (associated with ability to put information into sequences) being more active in the syntax condition and the temporal lobes (associated with dividing information into its constituent parts) being more active in the inflection condition. However, these areas are not mutually exclusive and show a large amount of overlap. These findings imply that while speech processing is a very complex process, the brain may be using fairly basic, preexisting computational methods.<ref name="Newman2010">Template:Cite journal</ref>
Recent neuroimaging studies suggest that Wernicke's area plays a pivotal role in the nuanced aspects of language processing, including the interpretation of ambiguous words and the integration of linguistic context. Its functions extend beyond mere speech comprehension, encompassing complex cognitive tasks like semantic processing, discerning metaphorical language, and even contributing to the understanding of non-verbal elements in communication.<ref>Template:Cite journal</ref>
Comparative neurology studies have shed light on the evolutionary aspects of Wernicke's area. Similar regions have been identified in non-human primates, suggesting an evolutionary trajectory for language and communication skills. This comparative approach helps in understanding the fundamental neurobiological underpinnings of language and its evolutionary significance.<ref>Template:Cite journal</ref>
Clinical significance
Aphasia
Wernicke's area is named after Carl Wernicke, a German neurologist and psychiatrist who, in 1874, hypothesized a link between the left posterior section of the superior temporal gyrus and the reflexive mimicking of words and their syllables that associated the sensory and motor images of spoken words.<ref>Template:Cite book</ref> He did this on the basis of the location of brain injuries that caused aphasia. Receptive aphasia in which such abilities are preserved is also known as Wernicke's aphasia. In this condition there is a major impairment of language comprehension, while speech retains a natural-sounding rhythm and a relatively normal syntax. Language as a result is largely meaningless (a condition sometimes called fluent or jargon aphasia).
Wernicke's area receives information from the auditory cortex, and functions to assign word meanings.<ref name=":0">Template:Cite web</ref> This is why damage to this area results in meaningless speech, often with paraphasic errors and newly created words or expressions. Paraphasia can involve substituting one word for another, known as semantic paraphasia, or substituting one sound or syllable for another, defined as phonemic paraphasia.<ref name=":1">Template:Cite journal</ref> This speech is often referred to as "word salad", as speech sounds fluent but does not have sensible meaning. Normal sentence structure and prosody are preserved, with normal intonation, inflection, rate, and rhythm.<ref name=":1" /> This differs from Broca's aphasia, which is characterized by nonfluency. Patients are typically not aware that their speech is impaired in this way, as they have altered comprehension of their speech. Written language, reading, and repetition are affected as well.<ref name=":0" /><ref name=":1" />
Damage to the posterior temporal lobe of the dominant hemisphere is the cause of Wernicke's aphasia.<ref name=":1" /> The etiology of this damage can vary greatly, with the most common cause being a cerebrovascular event such as an ischemic stroke. Ischemic stroke is the result of a thrombus occluding a blood vessel, restricting blood supply to a particular area of the brain. Other causes of focal damage potentially leading to Wernicke's aphasia include head trauma, infections affecting the central nervous system, neurodegenerative disease, and neoplasms.<ref name=":1" /> A cerebrovascular event is more likely the cause in an acute-onset presentation of aphasia, whereas a degenerative disease should be suspected in aphasia with gradual progression over time.<ref name=":0" /> Imaging is often useful in identifying a lesion, with most common initial imaging consisting of computed tomography (CT) scan or magnetic resonance imaging (MRI).<ref name=":2">Template:Cite web</ref> Electroencephalography (EEG) can also be useful in patients with transient aphasia, where findings may be due to seizures, although this is a less common cause.<ref name=":0" />
Diagnosis of aphasia, as well as characterization of type of aphasia, is done with language testing by the provider. Testing should evaluate fluency of speech, comprehension, repetition, ability to name objects, and writing skills.<ref name=":1" /> Fluency is assessed by observing the patient's spontaneous speech. Abnormalities in fluency would include shortened phrases, decreased number of words per minute, increased effort with speech, and agrammatism.<ref name=":0" /> Patients with Wernicke's aphasia should have fluent speech, so abnormalities in fluency may indicate a different type of aphasia. Comprehension is assessed by giving the patient commands to follow, beginning with simple commands and progressing to more complex commands. Repetition is evaluated by having the patient repeat phrases, progressing from simple to more complex phrases.<ref name=":0" /> Both comprehension and repetition would be abnormal in Wernicke's aphasia. Content should also be assessed, by listening to a patient's spontaneous or instructed speech. Content abnormalities include paraphasic errors and neologisms, both indicative of a diagnosis of Wernicke's aphasia.<ref name=":0" /> Neologisms are novel words that may resemble existing words. Patients with severe Wernicke's aphasia may also produce strings of such neologisms with a few connecting words, known as jargon. Errors in the selection of phonemes of patients with Wernicke's aphasia include addition, omission, or change in position. Another symptom of Wernicke's aphasia is use of semantic paraphasias or "empty speech" which is the use of generic terms like "stuff" or "things" to stand in for the specific words that the patient cannot think of. Some Wernicke's aphasia patients also talk around missing words, which is called "circumlocution". Patients with Wernicke's aphasia can tend to run on when they talk, due to circumlocution combined with deficient self-monitoring. This overabundance of words or press of speech can be described as logorrhea. If symptoms are present, a full neurologic exam should also be done, which will help differentiate aphasia from other neurologic diagnoses potentially causing altered mental status with abnormal speech and comprehension.<ref name=":0" />
As an example, a patient with Wernicke's aphasia was asked what brought him to the hospital. His response was,<ref>Template:Cite journal</ref>
Is this some of the work that we work as we did before? ... All right ... From when wine [why] I'm here. What's wrong with me because I ... was myself until the taenz took something about the time between me and my regular time in that time and they took the time in that time here and that's when the time took around here and saw me around in it's started with me no time and I bekan [began] work of nothing else that's the way the doctor find me that way...
In diagnosing Wernicke's aphasia, clinicians employ a range of assessments focusing on speech fluency, comprehension, and repetition abilities. Treatment strategies extend beyond traditional speech therapy, incorporating multimodal approaches like music therapy and assistive communication technologies. Understanding the variability in the clinical presentation of aphasia is critical for tailoring individualized therapeutic interventions.<ref name="Binder 2170–2175"/>
While neuroimaging and lesion evidence generally support the idea that malfunction of or damage to Wernicke's area is common in people with receptive aphasia, this is not always so. Some people may use the right hemisphere for language, and isolated damage of Wernicke's area cortex (sparing white matter and other areas) may not cause severe receptive aphasia.<ref name="Bogen" /><ref>Template:Cite book</ref> Even when patients with Wernicke's area lesions have comprehension deficits, these are usually not restricted to language processing alone. For example, one study found that patients with posterior lesions also had trouble understanding nonverbal sounds like animal and machine noises.<ref>Template:Cite journal</ref> In fact, for Wernicke's area, the impairments in nonverbal sounds were statistically stronger than for verbal sounds.