Neurocognition of Language/Acquired Disorders of Speech and Language

Introduction
Acquired speech and language disorders, i.e., aphasias, comprise varying degrees and combinations of deficits of speech production or comprehension, or even the complete loss of the ability to communicate. Besides speech, sign language (cf. Chapter 9) can also be affected by acquired language disorders. Acquired language disorders can affect phonology, syntax, lexical memory, or semantics and can also affect the ability to read and write. Most commonly, symptoms derive from neurological damage to the left hemisphere of the brain. Often (approx. 80%), this is caused by a stroke (cf. Subchapter Causes), resulting in an cerebral undersupply of blood (Schneider, Wehmeyer & Grötzbach, 2012). Complete recovery from acute states only rarely occurs without treatment, but logopedic therapy and various training methods have been proven effective in recent studies, even in chronic states or progressive forms, which had not been treated acutely (e.g., Barthel, Meinzer, Djundja & Rockstroh, 2008). While aphasic symptoms have been reported since antiquity, e.g.,the earliest reported case of aphasia in the ancient Egyptian Edwin Smith Papyrus (Minagar, Ragheb & Kelley, 2003), the discoveries of the functional speech areas and subsequent theorizing on the functional organization of the human brain in the late 19th century, mainly due to the pioneering work of Broca and Wernicke, led to the categorization and understanding of various speech disorders. Even more notable, these paved the way to modern neuroanatomy, which derived from developments of the localizationist-view (cf. Localizationist-view box) and as the American psychologist and historian Stanley Finger (2000) describes as the “[...] key turning point in the history of the brain sciences”. The initial two categories of aphasias were named after their founders, Paul Broca and Carl Wernicke. Therefore, the first section will illustrate the early historical advances in aphasiology and their taxonomy. Subsequently, the different types of aphasic syndromes and other acquired speech and language disorders will be described in detail, along with common causes, diagnostic procedures and therapeutic measures.

Broca’s discoveries
In 1861, Pierre Paul Broca (1824 - 1880), a French physician, surgeon, anatomist and anthropologist, visited an anthropology symposium about the localization of speech. There a colleague, Ernest Auburtin (son-in-law of Jean-Baptiste Bouillaud, a most famous and major supporter of the localizationist view) held a lecture. Afterwards, he talked to Broca and described an interesting case concerning a patient named Leborgne. Broca was greatly interested in this case and asked Auburtin to examine Leborgne himself. Leborgne, called „Tantan“,had recovered from a left sided head injury and even though he was able to speak, yet could say nothing but the word“tan“. Although this was the only syllable he could express, it appeared as if he was still able to understand spoken words relatively well, judging from his reactions and intonation, and seemed to be irritated by the fact that he could not make himself understood. As Leborgne died, Broca made an autopsy and found a lesion of the left hemisphere in the frontolateral area (Figure 1). Broca concluded that the “centre of language” had to be localized in this specific cerebral area. This was consistent with other theories, as some of the proclaimers of the localizationist views had already suspected the area to be in the frontal lobe, albeit somewhere behind the eyes (Gibson, 1962). Modern examinations of the preserved brain of patient Leborgne showed that Broca, who decided not to make a dissection, located his “speech centre” area on the basis of the superficial lesion scars a bit too far in the frontolateral area. Modern brain mapping localizes Broca’s area more in the medial insula area, on the junction of the Rolandic and Sylvian fissure (Dronkers, Plaisant, Iba-Zizen & Cabanis, 2007). Also remarkably is the fact that relatively late, based on many subsequent autopsies, Broca confirmed his suspicion concerning the left sided localization of the speech centre not until 1864.

Broca named the clinical pattern from the loss of speech due to a lesion in the area he identified in his patients as „aphemie“. This name was criticized by his colleagues as „aphemie“ has a deprecatory meaning of „disgraced“ in ancient Greek, and finally the definition „aphasia“ was agreed upon. Interestingly, a similar case was presented before, during a medical congress 1836 in Montpellier. Marc Dax, a less well-known French physician, presented a theory of a connection between stroke patients with right side paralysis and the loss of speech. At that time, little notice was taken of this report. Dax’ son accused Broca after his publications of using the reports from his father in order to claim the discovery as his own. Broca denied any knowledge of Dax' reports and from the historical point of view, this accusation could never be finally settled. Because of the better clinical description of the resulting disorder, the asymmetric relation to the handedness, the clear distinction from purely motoric (cf. subchapter apraxia and dysarthria) language loss, and especially the more accurate hemispheric localization, however, the name of Broca remained associated with both the neuroanatomical area and the aphasic syndrome (Springer & Deutsch, 1993; Obler & Gjerlow, 1999).

Wernicke‘s Sensory Aphasia and his Intercortical Connection Hypothesis
Whilst Broca focused on the expressive form of aphasia, he and other examiners almost completely neglected the comprehension deficits of language, that many of the individuals exhibited. These deficits often accompanied the aphatic syndromes, because in many cases the neurological impairment not only affected Broca’s Area, but other regions in the brain, as well. In 1874, Carl Wernicke (1848-1905), a German neurologist, was the first who presented a region posterior to Broca’s area in the temporal lobe (more precisely in the posterior portion of the left superior temporal gyrus) that proved to be vital for the reception and comprehension of language. This area has since then become known as Wernicke’s area. Wernicke accepted Broca’s findings and assumed the two identified language areas to be complementary in their relevance for speech. Thus, while Broca’s area is responsible for the processing of motoric aspects of speech production, aspects of comprehension, i.e., the translation of phonemes, words, and sentences into a meaningful form, relied on an sensory area in the temporal lobe, which is linked to the motoric area. Wernicke could demonstrate that lesions of the temporal gyrus would result in a different type of pathology, that he described as „sensory aphasia“. In contrast to Broca’s aphasia, individuals who had lesions in that area typically were fluent in speech, but had severe comprehension deficits. Additionally, these aphasics showed unique semantic characteristics, like a tendency to paraphrase, i.e., to produce so-called circumlocutions. Also, Wernicke’s aphasics exhibit phonematic or semantic substitution of phonemes, syllables, or whole words (paraphasis) and even sometimes new words (neologisms), to the extent of completely unrecognizable gibberish in extreme cases. Prosody and intonation, in contrast, appeared to be relatively intact, resulting in so-called semantic or phonematic jargon, which yielded in the expression of „logorrhea“, i.e., excessive or incoherent talkativeness. Besides the naming was not chosen coincidentally to be reminiscent of the clinical term “diarrhea”. Furthermore, Wernicke showed that anomic aphasia, postulated by Bouillaud earlier, is based on lesions in this area as well. Anomic (or amnesic) aphasia is – in brief – characterized as the inability of utilizing or “recovering“ well-known words. Symptoms of this relatively mild form of aphasia often are observable in other forms of aphasias as well. In general it is regarded as anomic aphasia, if these word finding problems occur as the major „feature“ of the aphasia, while speech production and comprehension are left relatively spared. Wernicke not only correctly postulated an anatomical connection between Broca’s and Wernicke‘s areas, but also notably predicted another type of aphasia. Conduction aphasia, according to Wernicke’s reasoning, should occur as a result of an intercortical disconnection, when these neural fibres, now known as arcuate fasciculus, would be impaired. This was confirmed in later studies (Murdoch, 2009). In conduction aphasia, comprehension and speech production is thought to remain relatively intact. However, a failure of transferring information from Wernicke’s to Broca’s area results in paraphasic symptoms and marked difficulties in repeating words presented by the examiner.

Wernicke-Lichtheim model
Based on Wernicke's publications, various models originated, mainly following localizationist theories. In this regard, the model of Lichtheim is probably the most cited of these models and therefore described here exemplarily. Ludwig Lichtheim (1845-1928), who was closely working with Wernicke (in fact, he was one of his scholars in Breslau, which Norman Geschwind called the “School of Breslau”)(Opp, 1994), postulated a scheme (1885) based on the prior findings of Broca and Wernicke with five interconnected cortical and subcortical centres involved in language, i.e., centres for expressive speech, audioverbal representation, concept, auditory input, and motoric output (see Figure 2). Importantly, Lichtheim proposed the existence of a semantic field or conceptual centre, which is represented subcortically in the left Hemisphere. In this centre, ideas and elaborated concepts, like willful expressions would emerge. The assumption of a subcortical concept centre also facilitated the prediction of additional subcortical types of aphasia, as well as the categorization and localization of these new pathologies. In this theory, an impairment of the connection between the concept centre and Broca’s area would result in poor spontaneous speech, because formulated ideas could not be sent to the motoric centre, whereas as repetition, oral reading or comprehension, would remain unaffected. Thus, strictly linguistic performance of the classical comprehension and motoric production centres (and their connections) are spared. This combination of syndromes was termed transcortical-motoric aphasia. In contrast to Broca’s aphasia, repetition and oral reading is much less impaired in trascortical-motor aphasia, whereas spontaneous speech would be restrained in a similar way.The relatively good ability to repeat, is therefore regarded as an important characteristic to distinct these transcortical aphasias. The same applies to the transcortical sensory type of aphasia. While the symptoms resembles Wernicke’s aphasia, repetition is typically good. Although individuals with transcortical sensory aphasia can exhibit further phenomena like echolalia, described in transcortical aphasia subchapter below. Supplementary he included two additional centres for reading (“visuoverbal centre”) and writing connected to Wernicke’s area (not shown in the basic house-like model in Figure 2). This could also provide an explanation for rare phenomena like alexia and agraphia (i.e., the inability to read or write), which can occur independently of the aphasias, depending on the integrity of the “neuronal pathways“ to other language and speech related centres in Lichtheim’s structural scheme (Murdoch, 2009). Lichtheim’s scheme came to be known as the Wernicke-Lichtheim model and became highly regarded as it was used to explain and categorize various and rare types of aphasias and accompanying symptoms (e.g., pure word deafness, alexia and agraphia).

Wernicke-Geschwind model
The Wernicke-Lichtheim model was elaborated further more recently by the influential Austrian-American Neurologist Norman Geschwind, resulting in what became known as the Wernicke-Geschwind model or neurological model of language (Geschwind, 1965). In his work, Geschwind put emphasis on the neuronal transfer of language signals from Wernicke’s to Broca’s area via a defined white matter projection, i.e., the arcuate fasciculus (Figure 3). Even though Geschwind assumed that the link from Wernicke’s to Broca’s areas was unidirectional in nature, we know today that information flow along this neural pathway is – like all projections in the brain – in fact bidirectional.Through the availability of modern non-invasive structural neuroimaging methods, it is today possible to visualize the individual anatomy of the arcuate fascicle in vivo and thus to investigate its specific contribution to language in the healthy brain. First anatomical evidence for the existence of these neuronal fibres was provided by more recent workers (Catani, Jones, and Ffytche, 2005). Even if Geschwind’s model is regarded as obsolete today, his extensive research and examination of neurological structures and linguistic operations through speaking and reading from the visual parietal cortex to the angular gyrus in Wernicke’s area, contributed greatly to aphasiology and its research, as well as in various other fields (Kolb & Whishaw, 2003).

Diagnostic implications
Today, several models exist to explain the various aphasic syndromes and their specific combinations of symptoms. Nevertheless, the major advance in neuroanatomy and taxonomy of language disorders was conceived by Broca and Wernicke and resulted in models, such as the Wernicke-Lichtheim Model and the Wernicke-Geschwind Model. The pioneering work of these early neurologists made it possible to categorize speech disorders and to define them more precisely. Due to their findings, the localization of lesions could be estimated based on the symptoms, which was previously only possible postmortem by autopsy. Furthermore, a prediction of the likely occurring symptoms, caused by impairment, was made possible. Also, the association between deficits and impaired brain areas was put onto more firm grounds, so that today, a more hypothesis-driven approach to clinical neurolinguistics is possible. Despite the availability of modern neuroimaging techniques, the standardized tests that emerged from the early aphasiological work still have great importance in diagnostic procedures. However, diagnostic tests often emphasize functional examination rather than anatomical localization, nowadays. Still, even at the present day, most models are not regarded as completely accurate, as discrete areas have not been shown in modern neuroanatomy. Various cortical and subcortical structures involving the complex patterns of generating language and comprehension, are still not fully understood and objective to further examinations.

Definition of Aphasia
Aphasia (Greek ἀφασία Aphasia, “speechlessness”) is an acquired multimodal central language disorder, after (largely) completed language development, as a result of damage to the functional language centres of the (usually) left speech dominant hemisphere. The impairment of the language system can be more or less pronounced at different representational levels of language, such as phonology, syntax, lexicon, or semantics, along with constraints of performance in language comprehension and production. The language impairment can also include non-verbal linguistic performances, such as reading, writing, or sign language. In particular the former two, however, are also treated as separate syndrome categories, i.e., alexia and agraphia. The aphasic categories are seldom clearly distinguished from each other, since in natural occurrence, the neurological damage that leads to aphasic syndromes is rarely restricted to a clearly circumscribed brain region.

Broca‘s aphasia
Broca‘s, motoric or expressive aphasia is an impairment localized in the frontolateral area, around the medial insular cortex, supply area of arteria precentralis. It is characterized by slow, effortful speech and marked by pauses, stagnative utterances and therefore classified as an “non-fluent” aphasic syndrome. In addition, noticeable agrammatism occurs, so called „telegram style“ – the omission of grammatical attributes, e.g. articles, prepositions and correct declensions. Also in extreme cases, individuals cannot speak more than a few words, which are then often repeated frequently, as if in an desperate attempt to express themselves. Although, usually the articulation and intonation of these words appear to be fairly normal. Comprehension is regarded as mildly impaired, whereas complex syntactical content can arise greater difficulties.

Wernicke‘s aphasia
Wernicke‘s, sensory or receptive aphasia, derives from lesions of the dorsal parts of the gyrus temporalis superior (the first temporal gyrus in the “upper-back” of the temporal lobe), supply area of arteria temporalis posterior. Typically comprehension is heavily disturbed, whereas speech production is fluent and prosody and articulation remain intact. It is additionally characterized by paraphasic speech, the tendency to substitute words or phonemes (paraphasy), and even creating new words (neologism). In severe cases, this can lead to an unrecognizable, but fluent gibberish (semantic or phonematic jargon), which yielded in the term “logorrhoea” (excessive talkativeness). Also these aphasics typically lack of awareness of the latter condition.

Anomic aphasia
Anomic or amnesic aphasia is commonly regarded as the mildest form. Its pathogenesis derives most commonly from temporoparietal lesions. Anomic aphasia is perceptibly marked by having extreme difficulties remembering simple words. Comprehension is only mildly affected and speech production is mostly fluent. As for Wernicke’s aphasia, paraphasy can occur. Most often these amnesic symptoms exhibit in other aphasic syndromes to some degree as well.

Global aphasia
In global aphasia large cerebral areas in the (usually) left hemisphere are impaired within the supply area of the arteria cerebri media, which is one of the three big arterials, distributing blood supply in the brain. Such large impairments ensue a broad variety of cognitive constraints, such as heavy impairments to speech production and comprehension occur. It is typically accompanied by paraphasic symptoms and neologism to the extend, that only speech automatism remain possible, recurring utterances, as constant repetition of words or syllables.

Conduction aphasia
Conduction aphasia, also called associative aphasia commonly results from impairment of the fasciculus arcuatus (Latin, curved bundle), which connects Broca’s and Wernicke’s area. The natural occurrence of this kind of aphasia is relatively rare, since the fasciculus arcuatus is impaired almost precisely, while comprehension and motoric speech centres are rather spared. Its marked by poor ability to repeat auditory received speech or reading aloud, while auditory and lexical comprehension remain intact and speech is fluent, yet paraphasic and especially phonematically impaired. As an aphasic patient would try to repeat a word presented by the examiner repeatedly to correct his mistake, as he is aware of his erroneous, it could seem like he would try to successively approximate the word phonetically.

Transcortical aphasia
Transcortical aphasia can exhibit in an sensory, motor or mixed type of aphasia. Wernicke’s and Broca’s area are assumed as relatively preserved (as well as the connection between them), whereas neuronal pathways (in specific areas of the temporal lobe or respectively anterior superior frontal lobe) connecting them to subcortical structures, involving parts of the Thalamus and basal ganglia, are impaired. Whether Wernicke’s or Broca’s area is “isolated”, defines the type of aphasia: Transcortical sensory aphasia or transcortical motor aphasia (or mixed) and respectively resembles Broca’s expressive or Wernicke’s receptive aphasia. All transcortical aphasias have a characteristically good performance in repetition in common, which differentiate them from expressive or receptive aphasia. In transcortical sensory aphasia spontaneous speech and comprehension is similar to sensory aphasia and individuals have a tendency to perseveration (“Sticking” to words or no longer relevant content). Also they can exhibit echolalia, a constant repetition of words. In transcortical motor aphasia, spontaneous speech is disordered and non-fluent as in motoric aphasia, but the ability to repeat, even repeating longer phrases fluently, is relatively good, since comprehension and the arcuate fasciculus remain unimpaired.

Pure word deafness
Pure word deafness is also referred to as auditory verbal agnosia. It is thought to be involving impairments to the Heschl‘s gyrus in the temporal lobe of the speech dominant hemisphere, interrupting fibres from the auditory receptive areas connected to the Wernicke’s area. It is regarded as a selective auditory deficit of comprehending speech and is characterized by the inability of understanding spoken language, while reading or writing, spontaneous speech and comprehension of non-verbal auditory input (e.g. music) remain unimpaired. It is therefore classified as pure “input disorder”.

Typical classification table of aphasias (Wikipedia)

Causes
Approximately 80% have vascular origin, most commonly caused by a cerebrovascular accident (CVA, commonly referred to as stroke), resulting in cerebral ischemia (i.e., an undersupply of blood) in 80% or haemorrhagic infarct (i.e., bleedings, which also lead secondarily to ischemia) in 20% of all CVA’s. The second and third highest prevalence are traumatic brain injuries (10%) and cerebral tumors (7%) (Schneider et al., 2012). Hemispherical prevalence: Impairment (as the speech dominant hemisphere) is localized in 96% of right-handers and 70% of left-handers in the left cerebral hemisphere (15% left-handers exhibit bilateral speech organization). The remaining 4% of the right-handers and 15% of the left-handers exhibit a soley right hemispherical speech organization (McCarthy & Warrington,1990). Most important causes are:

•	Strokes (cerebral apoplexy)*

•	Intracerebral hemorrhage, aneurysm*

•	Traumatic Brain Injury*

•	Cerebral tumor*

•	Bacterial or viral encephalitis*

•	Brain atrophy*

•	Neurological Disorders: Alzheimer, forms of dementia*

•	Intoxication by alcohol, drugs and medicines*

*(Wikipedia-links needed)