Kevin Shapiro

Cortical signatures of noun and verb production

Categories like “noun” and “verb” represent the basic units of grammar in all human languages, and the retrieval of categorical information associated with words is an essential step in the production of grammatical speech. Studies of brain-damaged patients suggest that knowledge of nouns and verbs can be spared or impaired selectively; however, the neuroanatomical correlates of this dissociation are not well understood. We used event-related functional MRI to identify cortical regions that were active when English-speaking subjects produced nouns or verbs in the context of short phrases. Two regions, in the left prefrontal cortex and left superior parietal lobule, were selectively activated for verb trials compared with noun trials; one region in the left inferior temporal lobe was more active during noun production than verb production. We propose that these regions are involved in representing core conceptual properties of nouns and verbs.

Grammatical Distinctions in the Left Frontal Cortex

Selective deficits in producing verbs relative to nouns in speech are well documented in neuropsychology and have been associated with left hemisphere frontal cortical lesions resulting from stroke and other neurological disorders. The basis for these impairments is unresolved: Do they arise because of differences in the way grammatical categories of words are organized in the brain, or because of differences in the neural representation of actions and objects? We used repetitive transcranial magnetic stimulation (rTMS) to suppress the excitability of a portion of left prefrontal cortex and to assess its role in producing nouns and verbs. In one experiment subjects generated real words; in a second, they produced pseudowords as nouns or verbs. In both experiments, response latencies increased for verbs but were unaffected for nouns following rTMS. These results demonstrate that grammatical categories have a neuroanatomical basis and that the left prefrontal cortex is selectively engaged in processing verbs as grammatical objects.

The representation of grammatical categories in the brain

Language relies on the rule-based combination of words with different grammatical properties, such as nouns and verbs. Yet most research on the problem of word retrieval has focused on the production of concrete nouns, leaving open a crucial question: how is knowledge about different grammatical categories represented in the brain, and what components of the language production system make use of it? Drawing on evidence from neuropsychology, electrophysiology and neuroimaging, we argue that information about a words grammatical category might be represented independently of its meaning at the levels of word form and morphological computation.

Grammatical class in lexical production and morhpological processing: Evidence from a case of fluent aphasia

We present the case of a fluent aphasic patient who is impaired at producing nouns relative to verbs in picture naming, sentence completion, and sentence generation tasks, but is better at both producing and comprehending concrete nouns than abstract nouns. Moreover, he displays a selective difficulty in producing the plural forms of some nouns and pseudowords presented as nouns, but was able to produce the phonologically identical third-person singular forms of corresponding verb homonyms and of the same pseudowords presented as verbs. This pattern of performance casts doubt on the hypothesis that grammatical class effects are always epiphenomena of more general semantic impairments that affect the naming of actions or of concrete objects, and suggests that these effects may arise instead from damage to syntactic processes pertaining specifically to the grammatical properties of words. We also discuss the implications of such damage for models of morphological processing.

Grammatical processing of nouns and verbs in left frontal cortex

We report the case of a brain-damaged subject R.C. who is more impaired at producing grammatical forms of words and pseudo-words used as verbs (he judges, he wugs) than of the same words used as nouns (the judges, the wugs). This pattern of performance constitutes the first clear demonstration that grammatical knowledge about verbs can be selectively impaired following brain damage. A comparison of R.C.s behavioral and neurological profile with that of a patient who shows similar difficulties with nouns suggests that nouns and verbs are processed by separate neural systems with components in the left frontal lobe.

All Talk and No Action: A Transcranial Magnetic Stimulation Study of Motor Cortex Activation during Action Word Production

A number of researchers have proposed that the premotor and motor areas are critical for the representation of words that refer to actions, but not objects. Recent evidence against this hypothesis indicates that the left premotor cortex is more sensitive to grammatical differences than to conceptual differences between words. However, it may still be the case that other anterior motor regions are engaged in processing a words sensorimotor features. In the present study, we used singleand paired-pulse transcranial magnetic stimulation to test the hypothesis that left primary motor cortex is activated during the retrieval of words (nouns and verbs) associated with specific actions. We found that activation in the motor cortex increased for action words compared with non-action words, but was not sensitive to the grammatical category of the word being produced. These results complement previous findings and support the notion that producing a word activates some brain regions relevant to the sensorimotor properties associated with that word regardless of its grammatical category.

Dissociating neural correlates for nouns and verbs

Dissociations in the ability to produce words of different grammatical categories are well established in neuropsychology but have not been corroborated fully with evidence from brain imaging. Here we report on a PET study designed to reveal the anatomical correlates of grammatical processes involving nouns and verbs. German-speaking subjects were asked to produce either plural and singular nouns, or first-person plural and singular verbs. Verbs, relative to nouns, activated a left frontal cortical network, while the opposite contrast (nouns-verbs) showed greater activation in temporal regions bilaterally. Similar patterns emerged when subjects performed the task with pseudowords used as nouns or as verbs. These results converge with findings from lesion studies and suggest that grammatical category is an important dimension of organization for knowledge of language in the brain.

Processing nouns and verbs in the left frontal cortex: A transcranial magnetic stimulation study

Neuropsychological and neurophysiological studies suggest that the production of verbs in speech depends on cortical regions in the left frontal lobe. However, the precise topography of these regions, and their functional roles in verb production, remains matters of debate. In an earlier study with repetitive transcranial magnetic stimulation (rTMS), we showed that stimulation to the left anterior midfrontal gyrus disrupted verb production, but not noun production, in a task that required subjects to perform simple morphological alternations. This result raises a number of questions: for example, is the effect of stimulation focal and specific to that brain region? Is the behavioral effect limited to rule-based, regular transformations, or can it be generalized over the grammatical category? In the present study, we used rTMS to suppress the excitability of distinct parts of the left prefrontal cortex to assess their role in producing regular and irregular verbs compared to nouns. We compared rTMS to sham stimulation and to stimulation of homologous areas in the right hemisphere. Response latencies increased for verbs, but were unaffected for nouns, following stimulation to the left anterior midfrontal gyrus. No significant interference specific for verbs resulted after stimulation to two other areas in the left frontal lobe, the posterior midfrontal gyrus and Brocas area. These results therefore reinforce the idea that the left anterior midfrontal cortex is critical for processing verbs. Moreover, none of the regions stimulated was preferentially engaged in the production of regular or irregular inflection, raising questions about the role of the frontal lobes in processing inflectional morphology.

Early and effective treatment of KCNQ2 encephalopathy

To describe the antiepileptic drug (AED) treatment of patients with early infantile epileptic encephalopathy due to KCNQ2 mutations during the neonatal phase and the first year of life.

Looming a loom: evidence for independent access to grammatical and phonological properties in verb retrieval

In principle, a specific deficit in processing verbs relative to nouns might arise as a result of damage to any of several mechanisms involved in speech planning and lexical production. Here we describe a fluent aphasic patient HG who is much worse at retrieving verbs relative to nouns in picture naming and sentence generation, but who retains the ability to produce verbal morphology and even to generate novel verbs productively from nominal roots when she is unable to retrieve appropriate action words (e.g. ‘looming’ for weaving ). Moreover, the results of single word and sentence comprehension tasks suggest that her ability to access lexical forms of verbs is sensitive to their thematic properties. When contrasted with patients who have specific deficits in processing morphosyntactic properties of verbs [J. Neurolinguist. 15 (2002) 265], HG’s pattern of performance can be seen as evidence that grammatical properties are functionally distinct from other aspects of lexical representation. We discuss the implications of this dissociation, and of HG’s performance specifically, in light of various models of lexical access. q 2002 Elsevier Science Ltd. All rights reserved.