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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2004) 16 (4): 702–713.
Published: 01 May 2004
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It is easier to produce and comprehend a series of sentences when they have similar syntactic structures. This “syntactic priming” effect was investigated during silent sentence reading using (i) blood oxygenation level-dependent (BOLD) response as a physiological measure in an f MRI study and (ii) reading time as a behavioral measure in a complementary selfpaced reading paradigm. We found that reading time and left anterior temporal activation were decreased when subjects read sentences with similar relative to dissimilar syntactic forms. Thus, syntactic adaptation during sentence comprehension is demonstrated in a neural area that has previously been linked to both lexical semantic and sentence processing.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2002) 14 (4): 550–560.
Published: 15 May 2002
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The meaning of a sentence differs from the sum of the meanings of its constituents. Left anterior temporal cortex responds to sentences more strongly than to unconnected words. We hypothesized that the anterior temporal response to sentences is due to this difference in meaning (compositional semantics). Using positron emission tomography (PET), we studied four experimental conditions (2 × 2 factorial design): In one condition, subjects read normal sentences. In a second condition, they read grammatically correct sentences containing numerous semantic violations (semantically random sentences). In a third condition, we scrambled the word order within the normal sentences, and, in a fourth condition, the word order was scrambled within the semantically random sentences. The left anterior temporal pole responded strongly to sentences compared to scrambled versions of sentences. A similar although weaker response occurred in the left anterior superior temporal sulcus and the left posterior middle temporal gyrus. A subset of voxels within the left anterior temporal pole responded more to semantically random sentences and their scrambled versions than to normal sentences and the corresponding scrambled versions (main effect of semantic randomness). Finally, the grammatical and the semantic factor interacted in a subset of voxels within the anterior temporal pole: Activity was higher when subjects read normal sentences compared to their scrambled versions but not for semantically random sentences compared to their corresponding scrambled versions. The effects of grammar and meaning and, most importantly, the interaction between grammatical and semantic factors are compatible with the hypothesis that the left anterior temporal pole contributes to the composition of sentence meaning.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2001) 13 (6): 754–765.
Published: 15 August 2001
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Several previous functional imaging experiments have demonstrated that auditory presentation of speech, relative to tones or scrambled speech, activate the superior temporal sulci (STS) bilaterally. In this study, we attempted to segregate the neural responses to phonological, lexical, and semantic input by contrasting activation elicited by heard words, meaningless syllables, and environmental sounds. Inevitable differences between the duration and amplitude of each stimulus type were controlled with auditory noise bursts matched to each activation stimulus. Half the subjects were instructed to say “okay” in response to presentation of all stimuli. The other half repeated back the words and syllables, named the source of the sounds, and said “okay” to the control stimuli (noise bursts). We looked for stimulus effects that were consistent across task. The results revealed that central regions in the STS were equally responsive to speech (words and syllables) and familiar sounds, whereas the posterior and anterior regions of the left superior temporal gyrus were more active for speech. The effect of semantic input was small but revealed more activation in the inferior temporal cortex for words and familiar sounds than syllables and noise. In addition, words (relative to syllables, sounds, and noise) enhanced activation in the temporo-parietal areas that have previously been linked to modality independent semantic processing. Thus, in cognitive terms, we dissociate phono-logical (speech) and semantic responses and propose that word specificity arises from functional integration among shared phonological and semantic areas.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2001) 13 (4): 419–429.
Published: 15 May 2001
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Functional neuroimaging was used to investigate how lesions to the Broca's area impair neuronal responses in remote undamaged cortical regions. Four patients with speech output problems, but relatively preserved comprehension, were scanned while viewing words relative to consonant letter strings. In normal subjects, this results in left lateralized activation in the posterior inferior frontal, middle temporal, and posterior inferior temporal cortices. Each patient activated normally in the middle temporal region but abnormally in the damaged posterior inferior frontal cortex and the undamaged posterior inferior temporal cortex. In the damaged frontal region, activity was insensitive to the presence of words but in the undamaged posterior inferior temporal region, activity decreased in the presence of words rather than increasing as it did in the normal individuals. The reversal of responses in the left posterior inferior temporal region illustrate the context-sensitive nature of the abnormality and that failure to activate the left posterior temporal region could not simply be accounted for by insufficient demands on the underlying function. We propose that, in normal individuals, visual word presentation changes the effective connectivity among reading areas and, in patients, posterior temporal responses are abnormal when they depend upon inputs from the damaged inferior frontal cortex. Our results serve to introduce the concept of dynamic diaschisis; the anatomically remote and context-sensitive effects of focal brain lesions. Dynamic diaschisis reveals abnormalities of functional integration that may have profound implications for neuropsychological inference, functional anatomy and, vicariously, cognitive rehabilitation.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1999) 11 (4): 371–382.
Published: 01 July 1999
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This paper demonstrates how functional imaging studies of neuropsychological patients can provide a way of determining which areas in a cognitive network are jointly necessary and sufficient. The approach is illustrated with an investigation of the neural system underlying semantic similarity judgments. Functional neuroimaging demonstrates that normal subjects activate left temporal, parietal, and inferior frontal cortices during this task relative to physical size judgments. Neuropsychology demonstrates that damage to the temporal and parietal regions results in semantic deficits, indicating that these areas are necessary for task performance. In contrast, damage to the inferior frontal cortex does not impair task performance, indicating that the inferior frontal cortex might not be necessary. However, there are two other possible accounts of intact performance following frontal lobe damage: (1) there is functional reorganization involving the right frontal cortex and (2) there is peri-infarct activity around the damaged left-hemisphere tissue. Functional imaging of the patient is required to discount these possibilities. We investigated a patient (SW), who was able to associate words and pictures on the basis of semantic relationships despite extensive damage to the left frontal, inferior parietal, and superior temporal cortices. Although SW showed peri-infarct activation in left extrasylvian temporal cortices, no activity was observed in either left or right inferior frontal cortices. These ªndings demonstrate that activity in extrasylvian temporo-parietal and medial superior frontal regions is sufªcient to perform semantic similarity judgments. In contrast, the left inferior frontal activations detected in each control subject appear not to be necessary for task performance. In conclusion, necessary and sufªcient brain systems can be delineated by functional imaging of brain-damaged patients who are not functionally impaired.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1998) 10 (6): 766–777.
Published: 01 November 1998
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Studies of patients with brain damage suggest that specific brain regions may be differentially involved in representing/processing certain categories of conceptual knowledge. With regard to the dissociation that has received the most attention—between the domains of living things and artifacts—a debate continues as to whether these category-specific effects reflect neural implementation of categories directly or some more basic properties of brain organization. The present positron emission tomography (PET) study addressed this issue by probing explicitly for differential activation associated with written names of objects from the domains of living things or artifacts during similarity judgments about different attributes of these objects. Subjects viewed triads of written object names and selected one of two response words as more similar to a target word according to a specified perceptual attribute (typical color of the objects) or an associative attribute (typical location of the objects). The control task required a similarity judgment about the number of syllables in the target and response words. All tasks were performed under two different stimulus conditions: names of living things and names of artifacts. Judgments for both domains and both attribute types activated an extensive, distributed, left-hemisphere semantic system, but showed some differential activation-particularly as a function of attribute type. The left temporooccipito-parietal junction showed enhanced activity for judgments about object location, whereas the left anteromedial temporal cortex and caudate nucleus were differentially activated by color judgments. Smaller differences were seen for living and nonliving domains, the positive findings being largely consistent with previous studies using objects; in particular, words denoting artifacts produced enhanced activation in the left posterior middle temporal gyrus. These results suggest that, within a distributed conceptual system activated by words, the more prominent neural distinction relates to type of attribute.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1998) 10 (3): 303–315.
Published: 01 May 1998
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Deep dyslexia is a striking reading disorder that results from left-hemisphere brain damage and is characterized by semantic errors in reading single words aloud (e.g., reading spirit as whisky ). Two types of explanation for this syndrome have been advanced. One is that deep dyslexia results from a residual left-hemisphere reading system that has lost the ability to pronounce a printed word without reference to meaning. The second is that deep dyslexia reflects right-hemisphere word processing. Although previous attempts to adjudicate between these hypotheses have been inconclusive, the controversy can now be addressed by mapping functional anatomy. In this study, we demonstrate that reading by two deep dyslexic patients (CJ and JG) involves normal or enhanced activity in spared left-hemisphere regions associated with naming (Broca's area and the left posterior inferior temporal cortex) and with the meanings of words (the left posterior temporo-parietal cortex and the left anterior temporal cortex). In the right-hemisphere homologues of these regions, there was inconsistent activation within the normal group and between the deep dyslexic patients. One (CJ) showed enhanced activity (relative to the normals) in the right anterior inferior temporal cortex, the other (JG) in the right Broca's area, and both in the right frontal operculum. Although these differential right-hemisphere activations may have influenced the reading behavior of the patients, their activation patterns primarily reflect semantic and phonological systems in spared regions of the left hemisphere. These results preclude an explanation of deep dyslexia in terms of purely right-hemisphere word processing.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1997) 9 (6): 727–733.
Published: 01 November 1997
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A number of previous functional neuroimaging studies have linked activation of the left inferior frontal gyms with semantic processing, yet damage to the frontal lobes does not critically impair semantic knowledge. This study distinguishes between semantic knowledge and the strategic processes required to make verbal decisions. Using positron emission tomography (PET), we identify the neural correlates of semantic knowledge by contrasting semantic decision on visually presented words to phonological decision on the same words. Both tasks involve identical stimuli and a verbal decision on central lingual codes (semantics and phonology), but the explicit task demands directed attention either to meaning or to the segmentation of phonology. Relative to the phonological task, the semantic task was associated with activations in left extrasylvian temporal cortex with the highest activity in the left temporal pole and a posterior region of the left middle temporal cortex (BA 39) close to the angular gyrus. The reverse contrast showed increased activity in both supramarginal gyri, the left precentral sulcus, and the cuneus with a trend toward enhanced activation in the inferior frontal cortex. These results fit well with neuropsychological evidence, associating semantic knowledge with the extrasylvian left temporal cortex and the segmentation of phonology with the perisylvian cortex.