The current study addresses the controversial issue of how different grammatical categories are neurally processed. Several lesion-deficit studies suggest that distinct neural substrates underlie the representation of nouns and verbs, with verb deficits associated with damage to left inferior frontal gyrus (LIFG) and noun deficits with damage to left temporal cortex. However, this view is not universally shared by neuropsychological and neuroimaging studies. We have suggested that these inconsistencies may reflect interactions between the morphological structure of nouns and verbs and the processing implications of this, rather than differences in their neural representations (Tyler et al. 2004). We tested this hypothesis using eventrelated functional magnetic resonance imaging, to scan subjects performing a valence judgment on unambiguous nouns and verbs, presented as stems (‘snail, hear’) and inflected forms (‘snails, hears’). We predicted that activations for noun and verb stems would not differ, whereas inflected verbs would generate more activation in left frontotemporal areas than inflected nouns. Our findings supported this hypothesis, with greater activation of this network for inflected verbs compared with inflected nouns. These results support the claim that form class is not a first-order organizing principle underlying the representation of words but rather interacts with the processes that operate over lexical representations.

The way in which meaning is represented and processed in the brain is a key issue in cognitive neuroscience, which can be usefully addressed by functional imaging techniques. In contrast to previous imaging studies of semantic knowledge, which have primarily used blocked designs, in this study we use an eventrelated fMRI (erfMRI) design, which has the advantage of enabling events to be presented pseudorandomly, thus reducing strategic processes and enabling more direct comparison with psychological behavioral studies. We used a semantic categorization task in which events were words representing either artifact or natural kinds concepts. Significant areas of activation for semantic processing included inferior frontal lobe bilaterally (BA 47) and left temporal regions, both inferior (BA 36 and 20) and middle (BA 21). These are areas that have been identified in previous neuroimaging studies of semantic knowledge. However, there were no significant differences between artifact and natural kinds concepts. These results are consistent with our previous imaging studies using blocked designs and suggest that conceptual knowledge is represented in a unitary, distributed neural system undifferentiated by domain of knowledge. These findings demonstrate that event-related designs can generate activations that are similar to those seen in blocked designs investigating semantics and, moreover, offer a greater capacity for interpretation free from the confounds of block effects. © 2002 Elsevier Science (USA)

It has been widely argued that the left inferior frontal gyrus (LIFG) is involved in the control of retrieval of information from long-term memory. Recent claims that the LIFG is involved in selecting among semantic alternatives have been challenged on the grounds that the manipulation of selection demands may have been confounded with controlled retrieval. The current study used an event-related functional magnetic resonance paradigm to re-examine the possibility that LIFG activation is involved in selection processes. In order to minimize potential confounding effects of controlled retrieval, we used an automatic retrieval task (picture naming) and held retrieval demands constant, while varying selection demands by way of competitor priming from earlier semantically related trials. We found significant activation in LIFG as a function of increased selection demands; activation centred on two peaks, one in anterior LIFG and a second more superior and posterior region. These data support the view that LIFG plays a role in selection among semantic information, even in the absence of controlled retrieval processes.

A prevailing neurobiological theory of semantic memory proposes that part of our knowledge about concrete, highly imageable concepts is stored in the form of sensory–motor representations. While this theory predicts differential activation of the semantic system by concrete and abstract words, previous functional imaging studies employing this contrast have provided relatively little supporting evidence. We acquired event-related functional magnetic resonance imaging (fMRI) data while participants performed a semantic similarity judgment task on a large number of concrete and abstract noun triads. Task difficulty was manipulated by varying the degree to which the words in the triad were similar in meaning. Concrete nouns, relative to abstract nouns, produced greater activation in a bilateral network of multimodal and heteromodal association areas, including ventral and medial temporal, posterior–inferior parietal, dorsal prefrontal, and posterior cingulate cortex. In contrast, abstract nouns produced greater activation almost

We tested aphasic patients ’ comprehension of actions to examine processing deficits in the linguistic and non-linguistic domains and their lesion correlates. 29 left-hemisphere injured patients and 18 age-matched control subjects matched pictured actions (with the objects missing) or their linguistic equivalents (printed sentences with the object missing) to one of two visually-presented pictures of objects. Aphasic patients performed poorly not only in the linguistic domain but also in the non-linguistic domain. A subset of the patients, largely consisting of severe and non-fluent aphasics, showed a greater deficit in the linguistic domain compared with the non-linguistic domain and across the patient group, deficits in the linguistic and non-linguistic domains were not tightly correlated. Poor performance in pantomime interpretation was associated with lesions in the inferior frontal, premotor and motor cortex, a portion of somatosensory cortex, and the caudate, while poor reading comprehension of actions was associated with lesions around the anterior superior temporal lobe, the anterior insula and the anterior portion of the inferior parietal lobe. Lesion size did not correlate with deficits. The lesion results for pantomime interpretation deficits demonstrate that lesions in the frontal component of the human analog of the “mirror neuron system ” are associated with deficits in non-linguistic action understanding. For reading comprehension deficits, the

& Here we address the contentious issue of how nouns and verbs are represented in the brain. The co-occurrence of noun and verb deficits with damage to different neural regions has led to the view that they are differentially represented in the brain. Recent neuroimaging evidence and inconsistent lesion– behavior associations challenge this view. We have suggested that nouns and verbs are not differentially represented in the brain, but that different patterns of neural activity are triggered by the different linguistic functions carried by nouns and verbs. We test these claims in a functional magnetic resonance imaging study using homophones—words which function grammatically as nouns or verbs but have the same form and meaning—ensuring that any neural differences reflect differences in grammatical function. Words were presented as single stems and in phrases in which each homophone was preceded by an article to create a noun phrase (NP) or a pronoun to create a verb phrase (VP), thus establishing the word’s functional linguistic role. Activity for single-word homophones was not modulated by their frequency of usage as a noun or verb. In contrast, homophones marked as verbs by appearing in VPs elicited greater activity in the left posterior middle temporal gyrus (LpMTG) compared to homophones marked as nouns by occurring in NPs. Neuropsychological patients with grammatical deficits had lesions which overlapped with the greater LpMTG activity found for VPs. These results suggest that nouns and verbs do not invariably activate different neural regions; rather, differential cortical activity depends on the extent to which their different grammatical functions are engaged. &

The question of whether information relevant to meaning (semantics) and structure (syntax) relies on a common language processor or on separate subsystems has proved difficult to address definitively because of the confounds involved in comparing the two types of information. At the sentence level syntactic and semantic judgments make different cognitive demands, while at the single word level, the most commonly used syntactic distinction (between nouns and verbs) is confounded with a fundamental semantic difference (between objects and actions). The present study employs a different syntactic contrast (between count nouns and mass nouns), which is crossed with a semantic difference (between naturally occurring and man-made substances) applying to words within a circumscribed semantic field (foodstuffs). We show, first, that grammaticality judgments of a patient with semantic dementia are indistinguishable from those of a group of age-matched controls, and are similar regardless of the status of his semantic knowledge about the item. In a second experiment we use the triadic task in a group of age-matched controls to show that similarity judgments are influenced not only by meaning (natural vs. manmade), but also implicitly by syntactic information (count vs. mass). Using the same task in a patient with semantic dementia we show that the semantic influences on the syntactic dimension are unlikely to account for this pattern in normals. These data are discussed in relation to modular vs. nonmodular models of language processing, and in particular to the semantic-syntactic distinction.

Representations of linguistic information and the neural substrates that underlie them are incredibly complex. This chapter illustrates how connectionist modeling has furthered our understanding of normal and impaired processing in three related domains – semantic memory, knowledge of grammatical class, and word reading – and how the

Effective instructional methods are now an important national issue. We reviewed the current research techniques used in cognitive neuroscience and what is currently known about the neurocognition of reading and mathematics. We found that while the neurocognition aspects of reading and mathematics share common processes associated with language, certain aspects of semantics and comprehension are unique to reading and certain aspects of mathematics entail visual-spatial processing not observed during reading. We conclude that although significant advances have been made in the understanding of the underlying neurocognitive process in the last decade more research is needed before the neurosciences can make a direct contribution to instructional practice.

Neuropsychological studies have demonstrated that the production of nouns and verbs can be dissociated in aphasia. These reports have been taken as evidence for separate representations of nouns and verbs in the human brain. We used whole-head magnetoencephalography to record cortical dynamics of action and object naming in 10 healthy adults and in 1 anomic patient with superior naming of verbs compared with nouns due to a left posterior parietal lesion. A single set of 100 line drawings was used for both action and object naming. In normal subjects, the activation sequences in action and object naming were essentially identical, advancing from the occipital to posterior temporoparietal and further to the left frontal cortex, without consistent involvement of the classical left inferior frontal (Broca) and temporal (Wernicke) language areas. In the anomic patient, pronounced differences between action and object naming emerged in the left hemisphere. The activation sequence was disrupted at the level of the damaged parietal cortex and did not reach the left frontal cortex even in the relatively easier action naming. The more severely impaired object naming was associated with exceptionally strong and early activation of the left inferior frontal cortex (Broca) and subsequent pronounced activation of the left middle temporal cortex, silent in action naming. Verb and noun retrieval thus utilized a spatiotemporally similar neuronal network in healthy individuals. A clear dissociation in cortical correlates of verb and noun retrieval only became evident in our anomic patient, in whom damage to the language network has resulted in disproportionately worse performance in object than action naming.