The map of the human motor cortex has lacked a representation for the intrinsic musculature of the larynx ever since the electrical stimulation studies of Penfield. In addition, there has been no attempt to localize this area using neuroimaging techniques. Because of the central importance of laryngeal function to vocalization, we sought to localize an area controlling the intrinsic muscles of the larynx by using functional magnetic resonance imaging and to place this area in a somatotopic context. We had subjects perform a series of oral tasks designed to isolate elementary components of phonation and articulation, including vocalization of a vowel, lip movement, and tongue movement. In addition, and for the first time in a neuroimaging study, we had subjects perform "glottal stops," in other words forced closure of the glottis in the absence of vocalizing. The results demonstrated a larynx-specific area in the motor cortex that is activated comparably by vocal and nonvocal laryngeal tasks. Converging evidence suggests that this area is the principal vocal center of the human motor cortex. Finally, the location of this larynx area is strikingly different from that reported in the monkey. We discuss the implications of this observation for the evolution of vocal communication in humans.
The TLI is reliable and capable of detecting subtle disorders. Some mild aberrations occurring in the speech of healthy individuals appear to be attenuated forms of the florid disorders characteristic of schizophrenia.
Previous research has demonstrated that patients with schizophrenia have an impaired ability to monitor erroneous responses to stimuli internally. Event-related potential (ERP) studies of error-eliciting tasks indicate that, in healthy adults, the commission of an erroneous response is associated with a fronto-centrally distributed negative voltage component termed the error negativity (Ne) or error-related negativity (ERN). In patients with schizophrenia, the Ne/ERN elicited by errors of commission (EoC) is reduced in amplitude compared with that elicited in healthy participants. Functional MRI (fMRI) studies and source localization analyses of ERP data in healthy participants suggest that EoC are associated with activity in the rostral anterior cingulate cortex (ACC). Using event-related fMRI, we examined the brain activity associated with EoC in a group of 10 patients with schizophrenia and 16 matched healthy participants. Patients were stable, partially remitted, medicated out-patients recruited from the community. Participants performed a Go/NoGo task variant that was shown previously to elicit a reduced Ne/ERN during EoC in patients with schizophrenia relative to healthy participants, as well as robust rostral ACC activation during EoC in healthy participants. Patients with schizophrenia were characterized by relative underactivity in the rostral ACC compared with healthy participants. There was also evidence for more widespread underactivity in the limbic system. In contrast to these regions of relative hypoactivity, patients with schizophrenia demonstrated hyperactivity relative to healthy participants in bilateral parietal cortex during both EoC and correctly rejected NoGo trials. Our results are consistent with previous ERP research demonstrating functional abnormalities during error processing in schizophrenia. In light of the role of the rostral ACC and other limbic structures in mediating affective and motivational behaviour, our results suggest there may be a disturbed affective or motivational response to the commission of errors in schizophrenia.
For the past several years it has been thought that cues, such as eye direction, can trigger reflexive shifts in attention because of their biological relevance and their specialized neural architecture. However, very recently, Ristic, Friesen, and Kingstone (2002) reported that other stimuli, such as arrows, trigger reflexive shifts in attention in a manner that is behaviourally identical to those triggered by eyes. Nevertheless these authors speculated that reflexive orienting to gaze direction may be subserved by a neural system-the superior temporal sulcus (STS)-that is specialized for processing eyes. The present study presents fMRI data that provide direct and compelling empirical support to this proposal. Subjects were presented with fixation stimuli that, based on instruction, could be perceived as eyes or as another type of directional cue. Both produced equivalent shifts in reflexive attention, replicating Ristic et al. However, the neural systems subserving the two forms of orienting were not equivalent-with the STS being engaged exceptionally when the fixation stimulus was perceived as eyes.
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