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Broca's Region$

Yosef Grodzinsky and Katrin Amunts

Print publication date: 2006

Print ISBN-13: 9780195177640

Published to Oxford Scholarship Online: May 2009

DOI: 10.1093/acprof:oso/9780195177640.001.0001

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Broca’s Area and Lexical-Semantic Processing

Broca’s Area and Lexical-Semantic Processing

(p.187) 12 Broca’s Area and Lexical-Semantic Processing
Broca's Region

Stefano F. Cappa

Daniela Perani

Oxford University Press

Abstract and Keywords

This chapter focuses on the relationship between Broca's area and lexical-semantic processing. The first section reviews the aphasiological evidence for lexical and/or semantic impairment in the syndrome of Broca's aphasia. The second section considers the relationship between damage to Broca's area and neighboring structures and specific aspects of linguistic impairment in the syndrome, including disorders of lexical/semantic processing. Finally, the chapter reviews the contribution of functional imaging to the issue of the role of Broca's area in lexical/semantic processing.

Keywords:   Broca's region, Broca's aphasia, lexical disorders, semantic impairment, lexical processing

Every neurologist gets acquainted early in her training with the syndrome of Broca’s aphasia. It is a fairly common consequence of an acute lesion, usually a left-sided infarction in the territory of the anterior branches of the middle cerebral artery, and the clinical presentation is relatively straightforward. The patients’ speech is impaired, which is what would be expected in a condition bearing the rather pessimistic name of aphasia. The articulation is affected, resulting in speech production, which is often hard to understand; what the listener often grasps are a few isolated words, which do not appear to be integrated in proper sentences. On the other hand, the patient appears to understand what is said, at least in the limited context of a neurological examination: simple commands, such as close your eyes, raise your arms, etc. During our neurology training, which took place in sophisticated aphasiological environments, we soon became aware that the idea of “articulated language” sitting in a small chunk of brain tissue, namely the foot of the left third frontal convolution, was fairly simplistic. As a possible consequence of this, we were hooked up to the relationship between language and the brain for the rest of our life. It was not a bad time to get into this area. In the late seventies, the availability of computerized axial tomography (CAT scan) was revamping the rather stale field of clinicoanatomical correlations in neurology. Aphasia, the traditional battlefield of localizer and antilocalizer, was of course immediately invested by the new developments.

In the present chapter our arbitrary choice, due to reasons of space, is to focus the review on the relationship between Broca’s area and lexical-semantic processing starting from that period. In the first section, we will briefly review the aphasiological evidence for lexical and/or semantic impairment in the syndrome of Broca’s aphasia. In the second, we will consider the relationship between damage to Broca’s area and neighboring structures and specific aspects of linguistic impairment in the syndrome, including (p.188) disorders of lexical/semantic processing. Finally, we will review the contribution of functional imaging to the issue of the role of Broca’s area in lexical/semantic processing.


The classic description of the syndrome of Broca’s aphasia is centered on a cluster of symptoms of speech and language impairment. Goodglass and Kaplan (1972) provide a concise description: “its essential characteristics are awkward articulation, restricted vocabulary, restriction of grammar to the simplest, more over-learned forms, and relative preservation of auditory comprehension.” A lexical disorder was thus considered to be an integral part of the syndrome of Broca’s aphasia. Actually, Goodglass and Kaplan observe that, in the case of good recovery, Broca’s aphasia loses its distinctive features, leaving a residual picture of word-finding difficulties, which makes it “barely distinguishable” from anomic aphasia. A more precise description of naming difficulties in Broca’s aphasia can be found in an earlier, classic paper about “semantic word categories in aphasia” (Goodglass et al., 1966). Here, Broca’s aphasics are shown to be defective in naming all categories of stimuli (objects, action words, colors, numbers and letters), with an overall performance level which is not different from fluent aphasics. As for error types, Kohn and Goodglass (1985) found that the production of semantic and phonological errors in picture naming was comparable for all diagnostic categories. In other words, Broca’s aphasics were as likely to produce semantic and phonemic paraphasias as Wernicke’s. However, Goodglass and coworkers clearly formulated the concept that a similar level of performance can be associated to different mechanisms of impairment. The finding that Broca’s aphasics, but not Wernicke’s, are facilitated by phonemic cueing, and show the TOT phenomenon was taken to indicate that the naming disorder in BA reflects a “difficulty in the programming of phonological information for articulation.”

The clinical observation that the production of patients with Broca’s aphasia might be characterized by a difficulty with verbs, both at the single word and at the sentence level, has opened an active field of psycholinguistic investigation. The representation of lexical items includes syntactic and semantic information. In the case of verbs, crucial aspects are subcategorization frame, argument structure and thematic roles (see Shapiro and Nagel, 1995). Since agrammatism is one of the crucial aspects of Broca’s aphasia, it has been hypothesized that defective verb retrieval may reflect an impairment in dealing with lexical items associated with complex argument structure (Thompson et al., 1997; see also Collina et al., 2001). The situation however appears to be more complex. Shapiro and Levine (1990) found that, during sentence comprehension, agrammatic Broca’s aphasics activate complex argument structures at the same level as normal subjects, suggesting a preservation of this information in real-time verb processing. Further, there is evidence from production indicating the role of morphological impairment. The verbs, which are produced by agrammatic subjects, are often lacking in inflection (Miceli et al., 1989). Grodzinsky (1984) observed that in the case of languages in which the production of inflectional morphology is required for lexical or lexical/phonological well formedness (such as Italian and Hebrew), the most frequent errors are morphological substitutions, usually towards a default form (typically the infinitive).

It is noteworthy that most of the case reports of patients with selective, or relatively selective, disorders in the processing of nouns and verbs have capitalized on the results of tasks at the single word level (typically, picture naming and word-picture matching; Miceli et al., 1988). In general, these case studies were not aimed at the definition of the anatomical correlates of the observed dissociation. However, an analysis of the reported lesion sites, assessed with computerized brain tomography, indicated that, while patients with selective disorders of noun processing had lesions centered on the left temporal lobe, verb impairment was associated to damage involving, or limited, to the left prefrontal cortex. The first careful anatomical study of a patient with selective action naming impairment was reported by Damasio and Tranel in 1993. The MRI lesion involved the left premotor frontal cortex. In a recent study, Tranel et al. (2001) have shown that damage to a region involving the left frontal operculum, the inferior sector of the pre-central and post-central gyri and the anterior part of the insula is associated with severe action-naming impairment. However, patients with lesions involving this area were often impaired also in object naming, and damage to other posterior areas (mesial occipital cortex, white matter underlying the posterior temporoparietal region) was also associated with action naming impairment. A striking disorder of action (p.189) naming and comprehension has also been reported in motor neuron disease patients with pathologically verified involvement of Ba 44 and 45 (Bak et al., 2001). More recently, several case reports have indicated the presence of a severe, selective disorder of action naming in patients with nonfluent progressive aphasia, the variant of fronto-temporal dementia associated with prevalent atrophy in the Broca’s region (Gorno-Tempini et al., 2004; Hillis et al., 2004).

Other case reports further indicate that action naming impairment can be associated with lesions sparing Broca’s area. Lesions centered in the left parietal lobe were observed in several patients with a disproportionate deficit in verb processing (see, for example, Silveri and Di Betta, 1997).

These findings indicate that patients with a selective difficulty in action naming and, maybe, also of other aspects of language processing involving the grammatical category of verbs are as a rule affected by lesions which involve the frontal and parietal part of the left perisylvian language areas. The temporal lobe, and in particular its anterior part, are usually spared in these patients. It is noteworthy that, within the category of nouns, an interesting pattern of anatomical correlation has been derived from the investigation of patients with category-specific semantic disorders. Patients with defective naming of animals and persons usually have lesions affecting the temporal lobe, in particular its anterior part, while tool naming impairments are associated with perisylvian damage in the temporo-parietal and frontal areas (Damasio et al., 1996; Saffran and Schwartz, 1994).

Taken together, these findings support the hypothesis of a crucial role of areas in the left hemispheric convexity, including Broca’s area, in the retrieval of lexical items related to action. These include verbs, but also nouns referring to tools. This issue will be discussed in more detail in the section on functional imaging studies.


As indicated in the introduction, we will neglect many years of active research and hot debate about the language function of Broca’s area, leaving out of the story important contributors such as Marie, Moutier, and Niessl von Mayendorf. A landmark of “modern” investigation of the role of Broca’s area in language is the study of surgical lesions of “F3” by Hecaen and Consoli (1973). The sample of 19 patients was very heterogeneous from the point of view of the etiology (mostly tumor ablations) and of time post surgery (from 12 days to 17 years!). However, lesion localization appears to have been exceptionally careful, and a relatively detailed neurolinguistic examination was available for all patients. All the patients showed some aspect of language impairment, with the exception of the two angioma cases (the latter finding suggests that some reorganization of the language areas can be expected to take place in the case of congenital lesions). It is noteworthy that disorders of lexical retrieval in spontaneous production were observed in some of the patients. Impaired picture naming was found in five patients, in which it was associated with defective auditory comprehension. None of the patients with right-sided lesions had a similar pattern of impairment.

Only a few years later, several investigators started to apply the new technology of CT brain scanning to the investigation of the lesion correlates of aphasia syndromes. These were defined according to traditional classification schemes, based on the patient’s performance on a cluster of language task. For example, in the Milan study (Mazzocchi and Vignolo, 1979), Broca’s aphasia was defined on the basis of the results of a standardized examination. The Boston series was based on the results of the BDAE (Naeser and Hayward, 1978). The main result of these early investigations was that the syndrome of Broca’s aphasia is associated with lesions, which extend beyond Broca’s area proper, extending to other regions of the left hemisphere (motor cortex, insula, subcortical white matter, basal ganglia). No attempt was made at this time to fractionate the components of Broca’s aphasia, with a remarkable exception. Jay P. Mohr and his colleagues (1978) published a remarkable paper, which was based on a personal series of 22 cases of Broca’s aphasia, in which lesion information was available on the basis of “autopsy, CT scan, radionuclide brain scan or angiography” and included a review of cases published “from 1820 onward.” The main result of this study, which expanded earlier reports by the same author, was that lesion limited to Broca’s area proper were only associated with “mild, transient anomia.” The authors’ conclusion is that the multiple aspects of language function that are affected in the full-fledged syndrome reflect the synergistic function of the entire opercular and insular region. Within this area, there is no strict localization of function, but a sort of “team action,” with ample possibility for vicariation due to neural plasticity. The authors underline that this rejection of a specific role for (p.190) Broca’s area does not imply a complete denial of language localization. The deficit in Broca’s aphasia is not the same as in Wernicke’s aphasia, and it “involves grammar in particular.”

In the following years, the Boston VA group, in particular, attempted an anatomical fractionation of the components of the syndrome. Tonkonogy and Goodglass (1981) provided important evidence, based on two pathologically verified cases, for the fractionation of articulatory impairment, due to damage to the rolandic operculum, and lexical impairment, associated with lesion of Broca’s area proper. Naeser et al. (1989) correlated severe nonfluency to damage to specific white matter tracts. A crucial role of insular damage in the production of apraxia of speech was indicated by the lesion study of Dronkers (1996).


Given the association of Broca’s areas with multiple aspects of language processing indicated by clinical studies, the engagement of the same regions in normal subjects in tasks going beyond “speech production” should not have came as much surprise. An early language activation study with positron emission tomography clearly established, for example, that a purely input task, such as phoneme discrimination, resulted in activation of Broca’s area (Zatorre et al., 1992). Many different tasks have been applied to the investigation of the brain correlates of lexical selection and retrieval. A very widely used task has been single word production according to a cue. The first published PET study of language activation (Petersen et al., 1988) showed that, in comparison to repetition, generating a “use” for a presented word resulted in an activation of several areas in left dorsolateral prefrontal cortex, as well as in anterior cingulate. The latter activation was attributed to the non-language-specific requirement for response selection, while the prefrontal activity was suggested to reflect, “some computation related to semantic processing or association between words” (Petersen and Fiez, 1993).1 It is noteworthy that the foci of activation included areas 45 and 47, but not area 44. This finding opened a lively discussion about the convergence of imaging and lesion data. The reaction from the aphasiological community was that semantic dysfunction is not typically observed in Broca’s aphasia. On the other hand, prefrontal lesions are associated with defective performance in “fluency” tasks, in which the patient is asked to generate as many items as possible belonging to a given category. Frith et al. (1991a) reported that generation of words (following semantic—names of jobs—or orthographic—beginning with a—cues) resulted in activation in area 46, i.e., in the same region activated by random movements generation (Frith et al., 1991b). This was interpreted as reflecting a nonlinguistic (“intrinsic generation”) rather than a semantic role of the prefrontal activity. No activation in Broca’s area and surrounding region was observed during lexical decision, which extensively activated superior temporal areas (including BA 22) bilaterally. The conclusion was compatible with traditional views of language representation in the brain: the superior temporal regions were suggested to be “the store of word representations” (Wortschatz). We have summarized this debate, which now may seem outdated (even if it was only 12 years ago!), in some detail, because it includes all the crucial issues presently under investigation. First, is there a specific role of Broca’s area in lexical-semantic processing, or are we observing in activation data a reflection of nonspecific aspects, such as selection among competitors, retrieval effort, working memory, etc.? Second, the classical question: what are we talking about, in terms of anatomy of Broca’s area? Let us now consider analytically other imaging studies, subdivided according to the task involved.

Word Generation

Phonological vs. Semantic Cues

There is considerable evidence that retrieving a word following a phonological or semantic cue results in a differential pattern of activity within Broca’s area. Mummery et al. (1996) found a selective activation of BA 44/6 during phonological fluency. Using fMRI, we found an engagement of area 44 only in the case of phonological cues, while both engaged Ba 45 (Paulesu et al., 1997).

Semantic Category Effects

Martin et al. (1995) were the first to show that the semantic content of the word to be retrieved mattered. In particular, generating action words (action associated (p.191) with an achromatic object picture) activated Broca’s area (BA 44) more extensively than generating the color of the object. A similarly located activation was found by Warburton et al. (1996) in the comparison between generating multiple actions appropriate to a heard concrete noun, and generating nouns belonging to a heard superordinate noun. The contrast between generating natural kinds versus objects, and vice versa, did not result in prefrontal differences in the PET study by Mummery et al. (1996). Recently, we have performed a functional magnetic resonance study of semantic fluency for animal and tool names (Vitali et al., 2005). A similar network of left prefrontal and premotor, parietal, and occipital regions was active for both conditions, but the direct comparisons revealed areas selectively engaged by the retrieval of tool names. An effective connectivity analysis indicated the existence of two partially segregated systems of functional integration. During the tool condition, there was an enhancement of the effective connectivity between left hemispheric regions including the inferior prefrontal, and premotor cortex, the inferoparietal lobule and the lateral fusi form gyrus/inferotemporal cortex; during the animal condition, there was an enhanced pattern of connectivity in the left visual associative regions. Noteworthy, the left inferofrontal gyrus (Brodmann’s area 45) was more connected with the lateral part of the fusiform gyrus during tool production and with its medial part during animal production. Taken together, these studies indicate a relationship between retrieval of names of action and tools, and Broca’s area activation.

Picture Naming

The brain activations observed when subjects retrieve the name of a visually presented stimulus reflects complex cognitive performance involving visual perceptual processes, semantic identification, lexical retrieval, and speech production. A careful consideration of the experimental conditions is thus necessary in order to interpret the possible contribution of Broca’s area. A particularly relevant investigation in this respect is the PET study of (Murtha et al., 1999), which clearly indicated the presence of activation in BA 44, 45, and 46 during semantic judgment and picture naming.

A number of studies suggest that, as in the case of word generation, semantic category, and/or grammatical class play an important role in recruiting prefrontal regions during picture naming. Martin et al. (1996) found an extensive activation of BA 44/6 when comparing tool naming with animal naming. It is noteworthy that a close area of activation (BA 45/46) had been reported a few months before by our group in a picture-matching task, contrasting animals with man-made tools (Perani et al., 1995). Martin et al. (1995) found that the comparison between color naming and action naming indicated selective activations related to action naming in the left frontoparietal cortex, the middle temporal gyrus, and the cerebellum. Another investigation of the cerebral correlates of action naming has been recently reported by Damasio et al. (2001). Naming actions, compared to a perceptual baseline (verbal judgment of the orientation of unknown faces), resulted in left frontal, temporal, and parietal activations. A comparison of naming actions performed with an implement, with naming tools and implements resulted in bilateral activations in area MT in the temporal lobe, a region associated with motion processing. We have recently compared the cerebral activations associated with naming pictures of manipulation and nonmanipulation actions, with those associated with naming tools and objects which cannot be manipulated (Saccuman et al., submitted). The items related to manipulation, independent from their noun-verb status, selectively activated Broca’s area, suggesting that semantic reference, independent of grammatical class, plays a crucial role in the recruitment of this area.

Lexical Decision

In a PET experiment with lexical decision, Perani et al. (1999) compared respectively, nouns referring to tools and psychological states, and manipulation and psychological verbs. The results indicated the existence of incompletely overlapping neurological substrates for verb and noun processing. There was no double dissociation between frontal and temporal cortex, but only the presence of “verb-specific” areas (Broca’s, left middle temporal gyrus). Noun and verb processing equally activated the other areas, associated with the lexical task. No significant interactions between grammatical class and semantic content were observed, suggesting that the observed difference is verb specific. A similar study has been recently reported by Tyler et al. (2001), with negative results. No differences were found between closely matched nouns and verbs, both in a lexical decision and in a (p.192) semantic judgment task. The reason for this discrepancy is unclear, and deserves further investigation.

Passive Listening to Single Words

Mazoyer et al. (1993) reported activation in Broca’s area while subjects were listening to words in their mother language, in comparison to stories in a language they could not understand. This is evidence for a role of lexical processing independent from speech production.

“Semantic Encoding”

This heading includes a number of tasks, characterized by the presentation (visual or auditory) of word lists, on which the subjects are asked to perform semantic decisions. Monitoring a list of words for the names of dangerous animals resulted in a left prefrontal activation (Petersen et al., 1989). Similar tasks are often used as the “encoding” phase of an episodic memory test. In comparison to “shallow” encoding of visual words (to decide if there was a letter “a”), a living-nonliving decision resulted in extensive activation in BA 45, 46, 47, and 10 (Kapur et al., 1994). Demb et al. (1995) showed that this activation could not be explained by “task difficulty,” as it was observed in the comparison with both an easy and a difficult shallow encoding task. A contrast between form-based and semantic judgment resulted in a fractionation of activity within LIPC similar to that observed for word generation (Mummery et al., 1996; Paulesu et al., 1997), indicating a prevalent role of the posterior part of Broca’s area in phonological processing, and of BA 45/47 for semantic processing (Poldrack et al., 1999).

We can conclude from this that, while the fractionation of semantic and grammatical factor has not been conclusively shown, there is strong evidence for separate activations in Broca’s area associated with phonological and semantic aspects of lexical retrieval.

Selection Demands and Other Task Manipulations

Other important evidence for the involvement of Broca’s area in semantic processing comes for studies, which have attempted to manipulate task requirements, using one of the paradigms described above. Murtha et al. (1999) contrasted word generation, semantic classification and comparison in different conditions. In the first task, the subjects had to generate a verb when confronted with a noun. The baseline was word reading. In the high selection (HS) condition, the noun had many possible associates, without a dominant response. In low selection (LS), the associates were few, or there was a clearly dominant response. For classification of pictures, the baseline was an identity judgment. HS involved pictures had to be classified according to a single feature, LS required an analysis of the entire representation. Comparison involved visual words: the HS required a judgment on a single feature (for example, color), LS, a global analysis. The HS-LS comparison yielded a significant activation in left BA 44, suggesting that the prefrontal activation is driven by the selection requirements of the task, rather than by semantic processing per se. This conclusion was supported by a lesion study in which patients with lesions affecting BAs 44/45 were impaired in producing actions associated to objects only in the HS condition (Thompson-Schill et al., 1998).

Task repetition can be expected to reduce retrieval demands (i.e., make the task “easier”). Raichle et al. (1994) found a decrease in activation of a network of areas (anterior cingulate-left prefrontal-left temporal and right cerebellum) during repetition of the generation of verbs to the same list of nouns. A decrease was also observed with repetition of a semantic encoding task (Demb et al., 1995). Thompson-Schill et al. (1999) attempted to contrast in the same experiment the effects of repetition and selection demands. The reasoning is as follows: if a subject is asked to generate an action word associated with an object name, and the task is repeated, the repetition priming effect is expected to reduce both retrieval demands and selection demands. If the repetition however requires the generation of a different word (a color) to the same stimulus, the reduction of retrieval demand is associated with an increase in selection demands. The fMRI findings indicated a decrease of LIFG activity with repetition, but an increase in the “different” task. It is noteworthy that behavioral priming (reaction time decrease) was present for both the repetition “same” and “different” conditions.

Sentence Processing

There is ample evidence for the contribution of Broca’s area to morphological and syntactic level processing, thus confirming aphasiological evidence. A general conclusion we can draw from our own studies (p.193)

table 12–1. Talairach Coordinates of Broca’s Area Activation in Four Different Experiments


Lexical decision on verbs (Perani et al., 1999)

BA 46/9




BA 45/46




Listening to action-related sentences (Tettamanti et al., 2005)

BA 44





Detection of morphosyntactic anomalies (Moro et al., 2001)

BA 45




Learning of possible rules (Musso et al., 2003)

BA 45




of Broca’s area activation during “lexical-semantic” versus morphosyntactic tasks is that the activations which we consider to be related to the processing of action-related language do not seem to coincide with those observed in the case of tasks which emphasize morphological and syntactic processing (see Table 12–1). The evidence on which this finding is based is too limited in its anatomical precision to allow further speculation about the precise correlates of each aspect of language processing. The presently available improvements in the anatomical localization of functional activations, however, will probably allow a more precise answer in the near future.


The convergence of findings derived from both lesion and functional imaging studies provides firm indication that Broca’s area plays a necessary role in lexical retrieval (Friston and Price, 2003). The semantic dimension of action (in particular manipulative action), interacting with the grammatical distinction between noun and verb, appears to be a crucial determinant of Broca’s area involvement. Whether these two aspects are independent in the anatomical sense, i.e. reflected in an anatomical segregation, or interactive is a question that cannot be answered with confidence at the present time. There is however some evidence supporting the hypothesis that the activations associated with “action words” involve the same component (pars opercularis, BA 44) of Broca’s area that are activated by motor imagery (Binkofski et al., 1999). It has been proposed that this area represents the human homologue of monkey area F5, containing mirror neurons, i.e. an observation/execution matching system (Rizzolatti et al., 2001).

What are the implications of these findings for lexical theories? While the brain system underlying somatosensory and motor functions is well known, very little is known about the format assumed by the conceptual level representations accessed by language. Two main theories have been proposed. The first claims that the meaning of an action, when verbally presented, is accessed using abstract and amodal units (Fodor, 2001; Pylyshyn, 1984). An alternative hypothesis suggests that understanding words semantically related to actions depends upon the motor structures involved in the execution of the very same actions (Lakoff and Johnson, 1999; Pulvermueller, 2002). The findings reviewed in this chapter appear to support the latter theory. A possible criticism is that the activation shown by functional imaging may represent a form of mental imagery (visual or motor), which is associated with tasks such as naming, controlled associations, etc., but is not necessary to perform the task. The data from patient studies, however, appear to support the hypothesis of a functional role of dorsal prefrontal (as well as of parietal) areas in the processing of action-related language.

While Broca’s area appears to be part of this network, there is ample evidence that its role is not limited to it. The evidence for its participation in a variety of tasks involving word form has also been briefly discussed here. Its involvement in morphological and syntactic processing has been mentioned in this chapter only in relationship with the lexicon, and is dealt with extensively in other chapters. This multi-functional role leads to the issue of the anatomical fractionation of the Broca’s region (including neighboring structures, such as the rolandic operculum, the insula, the basal ganglia) according to the linguistic distinctions between phonology, lexical-semantics, and morpho-syntax. Lesion data and functional imaging results support the idea of subcomponents, but the precise assignment of specific roles to definite areas may be premature. A more advanced understanding of the cortical anatomy of functional activations and of anatomical and functional connectivity is required to allow a more precise definition of the networks involved in specific aspects of linguistic processing.

(p.194) Note


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(1.) The same authors later modified this interpretation. In a subsequent study with the same task (in which the focus of prefrontal activation was actually in area 46), they conclude for a role in using internalized knowledge to guide behavior, when the response is not based on strong association with the presented stimuli (Raichle et al., 1994)