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Rodolfo Llinás
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2006) 18 (1): 97–109.
Published: 01 January 2006
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Most words in natural language are polysemous, that is, they can be used in more than one way. For example, paper can be used to refer to a substance made out of wood pulp or to a daily publication printed on that substance. Although virtually every sentence contains polysemy, there is little agreement as to how polysemy is represented in the mental lexicon. Do different uses of polysemous words involve access to a single representation or do our minds store distinct representations for each different sense? Here we investigated priming between senses with a combination of behavioral and magnetoencephalographic measures in order to test whether different senses of the same word involve identity or mere formal and semantic similarity. Our results show that polysemy effects are clearly distinct from similarity effects bilaterally. In the left hemisphere, sense-relatedness elicited shorter latencies of the M350 source, which has been hypothesized to index lexical activation. Concurrent activity in the right hemisphere, on the other hand, peaked later for sense-related than for unrelated target stimuli, suggesting competition between related senses. The obtained pattern of results supports models in which the representation of polysemy involves both representational identity and difference: Related senses connect to same abstract lexical representation, but are distinctly listed within that representation.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1999) 11 (6): 650–656.
Published: 01 November 1999
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A woman (LR), unconscious for 20 years, spontaneously produces infrequent, isolated words unrelated to any environmental context. Fluorodeoxy-glucose-positron emission tomography (FDG-PET) imaging coregistered with magnetic resonance imaging (MRI) revealed a mean brain metabolism equivalent to deep anesthesia. Nevertheless, PET imaging demonstrated islands of modestly higher metabolism that included Broca's and Wernicke's areas. Functional brain imaging with magnetoencephalographic (MEG) imaging, a technique providing a temporal resolution of better than 1 msec, identified preserved dynamic patterns of spontaneous and evoked brain activity in response to sensory stimulation. Specifically, we examined spontaneous gamma-band activity (near 40 Hz) and its reset or modification during early auditory processing, a measure that correlates with human perception of sensory stimuli (Joliot, Ribary, & Llinás, 1994). Evidence of abnormal and incomplete gamma-band responses appeared in the left hemisphere only in response to auditory or somatosensory stimulation. MEG single-dipole reconstructions localized to the auditory cortex in the left hemisphere and overlapped with metabolically active regions identified by FDG-PET. The observation demonstrates that isolated neuronal groups may express well-defined fragments of activity in a severely damaged, unconscious brain. The motor fixed-action pattern character of her expressed words supports the notion of brain modularity in word generation.