Aphasia or Agnosia?




(1)
Department of Neurosurgery, St Elisabeth-Tweesteden Hospital, Tilburg, The Netherlands

 



Wernicke proposed that knowledge of the outside world was conceptualized and that the necessary information that makes up these concepts is stored in many different and interconnected areas of the brain. He clearly made a distinction between knowledge of a word itself (i.e. the sound or pronunciation of it) and knowledge of its meaning or ‘concept’. Since the era of the diagram makers (see also Chap. 4), there has been a discussion of how concepts are anatomically represented in the brain. Several of the earlier researchers truly considered a ‘centre’ for conceptual knowledge, similar to the anatomical centres for motor or speech functions. Some, for example Mills, even believed that this concept centre was identical to the naming centre [1]. Most others, like Wernicke or Lichtheim, considered the concept centre more of a theoretical construct with a largely heuristic purpose, at least not something with a strict anatomical definition. To them, the true meaning of words and sentences emerged as the result of the complex interplay (association) between many different areas.

With this in mind, it can be better understood that when a patient has difficulties with naming, it does not automatically imply that there is a language disorder, or that the lesion is necessarily located in language areas. There can also be a dysfunction in several other systems that precludes correct naming, in particular in areas that sustain conceptual information. In fact, the localization of an anomic disturbance has been a point of controversy for a long time [2]. As put forward by Geschwind (1967), there were two opposing views in the literature: ‘one which insisted that anomia resulted from a lesion of the left temporoparietal regions while the other claimed that it was the result of a diffuse disorder of the brain’ [3]. Here is how Benson and Ardila formulated this (1996):



Word-finding deficits (anomia) are noted and complained about by patients with structural damage to any cerebral area in either hemisphere. Virtually every aphasic patient suffers some degree of naming disturbance; however, the characteristics of the word-finding problem can vary considerably in the different aphasia syndromes. (…) It is important to bear in mind that anomia is a term with a double meaning in aphasiology. In one usage, the term is synonymous with naming disorder; in this broad sense all aphasic patients are anomic. When used in the broad sense of a word-finding disorder (eg, decreased performance on a confrontation naming task), anomia is not of localizing value. In attempts to be more specific, some aphasiologists limit use of the term to those patients whose word-finding difficulty leads to circumlocutions and/or verbal paraphasias as observed in some patients with fluent aphasia. In this more tightly defined sense, anomia becomes synonymous with anomic aphasia, nominal aphasia, or amnestic aphasia. It is important to keep in mind that naming difficulties, often called anomia, are present in all aphasics but that the term anomia is also used to refer to a particular aphasia syndrome (anomic aphasia).

Naming difficulties can result from a deficit at different stages of the naming process: perception (decoding), storage, selection, retrieval, or actual production of the word (encoding). Furthermore, acquired naming difficulties can be restricted to specific semantic categories and even to a particular modality of representation. Naming disorders can result from the patient’s inability to perceive or to identify the target object and as such can be considered a perceptual or agnostic deficits [4].

As we have seen in the previous chapter, Wernicke was well aware of the intimate relationship between aphasia and agnosia, and these disorders were already the subject of research and discussion in his time.1 One of Wernicke’s assistants, Heinrich Lissauer (1861–1891), published an early case of visual agnosia in 1890 [6]. Lissauer is also considered the first to have provided a detailed account of this type of agnosia as well as an important classification that is still used today [7].2 Wernicke was involved during clinical observation and treatment of the patient and had already given a talk about this case at a meeting in Breslau [8, 9]. Another important paper that was published at that time (1889) was on a closely related disorder. It was written by Carl Freund (1862–1932), and it described a patient with a modality-specific naming disorder that he referred to as optic aphasia (the term optic anomia is probably more appropriate) [10]. Both papers not only share a similar topic (impaired naming) but also a common historical basis: at the time of publication, both Lissauer and Freund were working in Breslau under the direction of Wernicke [10]. They are discussed here at some length not only for historical reasons but also to illustrate how difficult, if not impossible, it is to disentangle language and non-language disturbances both from a practical and a more theoretical point of view.


3.1 Lissauer


Lissauer starts his seminal paper by referring to related works of Wilbrand (1887) [11] and Freund (1889) [12], but states that ‘in particular a case such as the one described below cannot be surpassed by any clinical cases reported to date in terms of the severity of its symptoms and their clear-cut manifestation’ [9]. He gives an extensive description of the medical history and the physical status of the patient. The latter is in fact a very comprehensive neurological examination. Today, the largest part of such an examination would be performed by neuropsychologists and ophthalmologists rather than neurologists. Over a span of 12 pages, Lissauer lists observations and test results in 13 categories that cover several different cognitive domains. These categories are summed up here to illustrate the thoroughness of Lissauer’s report: ‘refraction; visual fields; visual acuity; colour perception; visual estimating; stereoscopic vision; visual memory; memory for past visual experience; drawing; reading and writing; form perception; topographical orientation; reaction times to visual stimuli’. The examination revealed a complete right-sided hemianopia, but no other focal neurological deficits. Speech was fluent with intact comprehension and an unimpaired vocabulary. We should keep in mind that the tests that were applied by these historical authors were not standardized and that population norms were lacking. Still, their level of observation and methods of physical examination were often impressive, even by our current standards.

The patient was an 80-year-old former shopkeeper who reported that he had hit his head against a wooden fence during a severe storm. He retired to bed for 2–3 days because he did not feel well and complained that he was not able to see as well as before. Here is a part of the description given by Lissauer:



In the morning, when he wanted to have a wash, the patient searched his room for the wash-stand, which was in its usual place. He also searched for his boots which were, as usual, under the bed, but he looked for these behind the stove and in the kitchen. He frequently mistook articles of clothing, for instance mistaking his jacket for his trousers. He thought that a number of pictures in his room were boxes and tried to search in them for things he had lost. When eating he mixed up pieces of cutlery. He used his spoon wrongly, by dipping the handle into the soup. Once he tried to put his hand into the food and once into a cup of coffee.

Since his accident the patient no longer read. He gave his letters to his daughter saying that his vision was not clear enough. He continuously complained about the deterioration of his eyesight. He insisted that this visual problem had started suddenly on 3rd August following his accident and fall, though in view of his weak memory one cannot rely too much on this statement [9].

When objects were visually presented to the patient he was unable to recognize many of them, although there were marked fluctuations in his performance. When stimuli were perceived auditorily or via touch, his responses were normal. The patient seemed for the most part unaware of his inappropriate responses, although, as Lissauer writes, ‘His answers were never given with the complete assurance with which a normal subject would make a statement about the name or characteristic of a familiar object’ [9]. Clearly there was a naming disorder, but without dysphasic characteristics. Lissauer therefore considered the visual anomia in his patient a disorder of recognition and not of language: a visual agnosia.



The way in which our patient tended to express himself could have produced the suspicion that there were some transcortical speech disturbances. In fact this was not the case. Our patient never mixed up words in a paraphasic fashion. For example, when he spoke of spectacles he meant just that: an instrument made of glass which he had put on to read or write a hundred times. However, when he said that a fork was a pair of glasses it was not that he used the wrong word for the correct concept but that the concept itself was wrong. For anyone who worked with the patient there was not the least doubt about this [9].

Lissauer divided the process of recognition into two stages, based upon his connectionist view of cortical areas with subcortical connections. In the first stage, causing apperceptive agnosia, recognition of an object may fail because of impaired visuospatial perception (strictly speaking this is not a real disorder of recognition, but of perception only). The lesion is located in the visual cortex. Lissauer gives credit to Munk for the term ‘visual agnosia’ [13]. In the second stage, recognition is not possible despite intact perceptual skills. This is caused by a disconnection whereby the visual cortex itself remains largely intact, but white matter connections are lesioned in such a manner that information is unable to reach distant areas that are needed for higher-order recognition [8, 14]. The resulting disorder is called associative agnosia. It is to be noted that Lissauer clearly states that he does not expect to find patients with a pure form of one of these agnosias. He considers a pure associative agnosia ‘a contradiction in terms’. His patient had impairments in apperception, but his associative agnosia dominated.



It would seem to be obvious that apperception as a special mental process should be thought of as separate from the understanding of its meaning with its manifold associations. I came to this conclusion for two reasons. First, according to the theory of localization with which I agree completely, those processes which occur in only one modality and are therefore localized should be separated from those which involve a variety of associations and so are the product of the whole cortex. A process of the first kind involves only apperception and it must be followed by a process of the second kind before the act of recognition can be completed. Secondly my observations force me to make this distinction. There is no doubt that our patient perceived many things without comprehending them; that is, he purely apperceived some objects but did not recognize them. Therefore the first stage occurred without the second stage. Thus indeed under certain pathological conditions the first stage may occur in isolation [9].

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Oct 25, 2017 | Posted by in NEUROLOGY | Comments Off on Aphasia or Agnosia?
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