Lexical semantic ambiguity is the phenomenon when a word has multiple meanings (e.g. ‘bank’). The aim of this event-related functional MRI study was to identify those brain areas, which are involved ...in contextually driven ambiguity resolution. Ambiguous words were selected which have a most frequent, dominant, and less frequent, subordinate meaning. These words were presented in two types of sentences: (1) a sentence congruent with the dominant interpretation and (2) a sentence congruent with the subordinate interpretation. Sentences without ambiguous words served as a control condition. The ambiguous words always occurred early in the sentences and were biased towards one particular meaning by the final word(s) of the sentence; the event at the end of the sentences was modeled. The results indicate that a bilaterally distributed network supports semantic ambiguity comprehension: left (BA 45/44) and right (BA 47) inferior frontal gyri and left (BA 20/37) and right inferior/middle temporal gyri (BA 20). The pattern of activation is most consistent with a scenario in which initially a frequency-based probabilistic choice is made between the alternative meanings, and the meaning is updated when this interpretation does not fit into the final disambiguating context. The neural pattern is consistent with the results of other neuroimaging experiments which manipulated various aspects of integrative and context processing task demands. The presence of a bilateral network is also in line with the lesion and divided visual field literature, but contrary to earlier claims, the two hemispheres appear to play similar roles during semantic ambiguity resolution.
The goal of the current study was to identify the neural substrate of idiom comprehension using fMRI. Idioms are familiar, fixed expressions whose meaning is not dependent on the literal ...interpretation of the component words. We presented literally plausible idioms in a sentence forcing a figurative or a literal interpretation and contrasted them with sentences containing idioms for which no literal interpretation was available and with unambiguously literal sentences. The major finding of the current study is that figurative comprehension in the case of both ambiguous and unambiguous idioms is supported by bilateral inferior frontal gyri and left middle temporal gyrus. The right middle temporal gyrus is also involved, but seems to exclusively process the ambiguous idioms. Therefore, our data suggest a bilateral neural network underlying figurative comprehension, as opposed to the exclusive participation of the right hemisphere. The data also provide evidence against proposed models of idiom comprehension in which literal processing is by-passed, since figurative processing demanded more resources than literal processing in the language network.
We investigated (i) the central representation of lower urinary tract (LUT) control and (ii–iii) the acute and short-term central neuromodulatory effect of peripheral pudendal nerve stimulation in ...incomplete spinal cord injured (SCI) patients using functional magnetic resonance imaging (fMRI). The urinary bladder of eight SCI patients has been passively filled and emptied using a catheter, to identify the neural substrate of bladder control (i), and with simultaneous peripheral pudendal nerve stimulation to investigate its acute central neuromodulatory effect (ii). To identify the potential effects of pudendal nerve stimulation treatment (iii), six patients underwent a 2-week training using pudendal nerve stimulation followed by another fMRI session of bladder filling. The pre- and post-training fMRI results have been compared and correlated with the patient's pre- and post-training urological status. Our results suggest that the central representation of bladder filling sensation is preserved in the subacute stage of incomplete SCI. However, compared to earlier data from healthy subjects, it shows decreased neural response in right prefrontal areas and increased in left prefrontal regions, indicating diminished inhibitory micturition control as well as, compensatory or decompensatory reorganization of bladder control. We also provide evidence for a neuromodulatory effect of acute pudendal nerve stimulation, which was most prominent in the right posterior insula, a brain region implicated in homeostatic interoception in human. Pudendal stimulation training also induced significant neuromodulation, predominantly signal increases, in the normal cortical network of bladder control. Correlations with the patient's urological status indicate that this neuromodulatory effect may reflect the clinical improvement following training.
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