Anomic Aphasia

Anomia refers to the inability to name things: that is, an impairment in retrieving words for things such as concrete entities (named by nouns), actions (named by verbs), or spatial relationships (named by prepositions). Anomia is a frequent part of the symptom complex that characterizes patients with aphasia (Goodglass & Wingfield, 1997; Tranel & Anderson, 1999), which refers to disturbances of the comprehension and formulation of verbal messages caused by acquired damage to language-related brain structures (typically in the left hemisphere). In some patients, however, anomia occurs as an isolated manifestation of acquired brain dysfunction, and in this situation the designation of anomic aphasia applies.

The ability to name—that is, to retrieve a particular word to designate an entity or event—is different from the ability to retrieve conceptual knowledge regarding that entity or event (Caramazza & Shelton, 1998; Gainotti, Silveri, Daniele, & Giustolisi, 1995; Pulvermüller, 1999; Tranel, 2001; Tranel, Damasio, & Damasio, 1997). Knowing what something is (its meaning, sometimes termed semantics) is referred to as recognition, and this is distinct from knowing what something is called (referred to as naming). In anomic aphasia, patients have lost the ability to retrieve names of things, but they have not lost the ability to recognize what things are. Hence, even when they cannot name things, anomic aphasics can usually produce accurate descriptions of those things or indicate by gestures that they have normal knowledge of things. For example, when shown a picture of a camel, the patient may say, "That is an animal that has humps on its back, lives in the desert, and can go for a long time without water." Or when shown a picture of Bill

Clinton, the patient may say, "That guy was a president, had an affair, had a southern accent." A related phenomenon occurs fairly frequently in the realm of normal experience, particularly under conditions of fatigue, distraction, or in connection with normal aging—that is, normal individuals may experience the inability to retrieve a particular name (especially proper names) even though they know perfectly well what it is that they are attempting to name (Burke, MacKay, Worthley, & Wade, 1991). This is sometimes referred to as a "tip-of-the-tongue" state (Schwartz, 1999).

Anomia can occur in connection with any sensory modal-ity—for example, when attempting to name a picture of something, a sound, a smell, or something that is felt by the hand. Also, anomia can occur in the course of verbal discourse, as when one is speaking and suddenly cannot retrieve the name for a particular concept that is part of the intended utterance. The majority of scientific inquiries into the phenomenon of anomia, however, have focused on the visual modality and have used paradigms in which subjects are presented pictures (or actual objects) and asked to name them (Goodglass & Wingfield, 1997). This format, known as visual confrontation naming, is also the standard paradigm for assessing naming in patients with brain injuries. As a consequence, most of our current knowledge regarding the brain underpinnings of word retrieval (H. Damasio, Tranel, Grabowski, Adolphs, & Damasio, in press), and most theoretical accounts of this process (Dell, Schwartz, Martin, Saffran, & Gagnon, 1997; Levelt, Roelofs, & Meyer, 1999), are heavily tied to the visual modality.

The classic aphasia syndromes, including Broca's ("non-fluent") and Wernicke's ("fluent") aphasia, which include anomia as part of the symptom complex but which also involve other defects in speech and language, are associated with brain damage in the vicinity of the sylvian fissure in the left hemisphere (the left hemisphere being dominant for language in the vast majority [about 98%] of right-handed individuals and in the majority [about 70%] of left-handed individuals). Isolated defects in naming, though, which define anomic aphasia, are associated primarily with damage to structures in the left hemisphere outside the classic language regions. Specifically, anomic aphasia is most often caused by damage to the left anterior temporal lobe, to the inferior and lateral aspect of the left temporal lobe, or to the left occipitotemporal junction. Scientific investigations of patients with anomic aphasia, using modern neuroanatomical and neuropsychological techniques, have revealed a number of intriguing associations between specific brain structures and specific types of naming abilities (Caramazza & Hillis, 1991; Damasio & Tranel, 1993; H. Damasio, Grabowski, Tranel, Hichwa, & Damasio, 1996; H. Damasio et al., in press; Hart & Gordon, 1992; Hillis & Caramazza, 1995; Tranel, Adolphs, Damasio, & Damasio, 2001). Studies in normal subjects, using functional neuro-imaging procedures (positron emission tomography, functional magnetic resonance imaging), have corroborated sev eral of these findings (Chao & Martin, 2000; H. Damasio et al., 1996, in press; Grabowski et al., 2001; Grafton, Fadiga, Arbib, & Rizzolatti, 1997; Martin, Haxby, Lalonde, Wiggs, & Ungerleider, 1995; Martin, Wiggs, Ungerleider, & Haxby, 1996; Warburton et al., 1996).

The evidence from this research indicates that the retrieval of proper nouns—that is, names denoting unique entities such as persons and places—is associated with the temporal polar region in the anterior left temporal lobe. Immediately behind the temporal pole, in the inferior and lateral aspect of the temporal lobe, is a region that has been associated with the retrieval of names for animals. And further back, in the vicinity of the temporal-occipital junction, is a region that has been associated with the retrieval of names for tools. These associations may appear arbitrary or even bizarre, but there are principled accounts of why the human brain may be organized in such a fashion (H. Damasio et al., 1996, in press; Forde & Humphreys, 1999; Gai-notti et al., 1995; Gordon, 1997; Humphreys & Forde, 2001; Saffran & Sholl, 1999; Tranel, Logan, Frank, & Damasio, 1997). For example, factors such as whether an entity is unique (e.g., Tom Hanks) or nonunique (e.g., a screwdriver), whether it is living (e.g., a pig) or nonliving (e.g., a hammer), whether it is manipulable (e.g., a wrench) or nonma-nipulable (e.g., a giraffe), or whether it makes a distinctive sound (e.g., a rooster) or not (e.g., a thimble), are important in determining which neural structures will be used in the mapping and retrieval of knowledge for entities, including their names (H. Damasio et al., in press; Tranel, Logan, et al., 1997). Interestingly, the modality in which a stimulus is perceived may not make much difference: For example, retrieving the name rooster when confronted with a picture of a rooster, or when confronted with the characteristic sound of a rooster, appears to depend on the same left temporal lobe region (Tranel, Damasio, Eichhorn, Grabowski, Ponto, & Hichwa, 2003).

There are also intriguing distinctions between words that come from different grammatical categories, for example, nouns versus verbs. The brain regions that are important for retrieving nouns are partially separate from those that are important for retrieving verbs. As noted earlier, the retrieval of nouns is related to structures in the left temporal lobe. The retrieval of verbs, by contrast, is related to structures in the left frontal lobe, in the frontal opercu-lum (in front of the Rolandic sulcus). And some studies have suggested that noun-verb homophones—for example, words like hammer or duck, which are used frequently as either nouns or verbs—are retrieved by the brain system that fits the context in which the word is being used: If hammer is being used as a noun, the temporal lobe system will be used, but if hammer is being used as a verb, the frontal lobe system will be used (Tranel, 2001). Again, such dissociations may appear rather curious on the surface, but there are compelling explanations of why the brain has organized knowledge in different regions to subserve words from different grammatical categories (Caramazza &

Hillis, 1991; Damasio & Tranel, 1993; Kemmerer, Tranel, & Barrash, 2001; Tranel et al., 2001).

Pure forms of anomic aphasia—that is, severe naming impairments unaccompanied by other speech or linguistic deficits—are relatively rare, occurring far less frequently than most of the so-called classic aphasia syndromes. Nonetheless, patients with anomic aphasia have provided a unique opportunity to learn how the brain operates the processes associated with word retrieval, and how different brain structures are specialized for different types of words and different categories of entities. Thus, while anomic aphasia is important as a clinical disorder, its particular interest lies in the realm of scientific study of how the human brain operates language processes. This, in turn, can help inform rehabilitation efforts aimed at patients with acquired disturbances of naming.

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Daniel Tranel

University of Iowa College of Medicine

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