- Oct 2023
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postlab.psych.wisc.edu postlab.psych.wisc.edu
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C
bottom-horizontal fMRI images of someone wo experienced anoxic lesions to their posterior corpus callosum, resulting in permanent coma following head trauma.
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F
Sagittal fMRI image of an individual who displayed content-specific changes in experience (feeling of intention to move) following electrical stimulation of the temporoparietal cortex.
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D
Mid-sagittal fMRI image of an individual who displayed content-specific changes in experience (intrusive thoughts) following electrical stimulation of the ACC.
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E
Bottom-horizontal fMRI image of an individual who displayed content-specific changes in experience (inability to perceive faces) following electrical stimulation of the fusiform gyrus.
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Together, stimulation studies support the idea that some pos-terior cortical regions may contribute directly to specific contentsof experience, but the evidence for prefrontal regions is scarceand indirect.
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Many studies have demonstrated that electrical stimulation of the posterior cortex induces discrete changes in the content-specific NCC more reliably than electrical stimulation of the anterior cortex. Hence, most evidence suggests that posterior regions of the brain contribute more to the content-specific NCC than do anterior regions of the brain.
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For the most part, electrical and TMS stimulation of the frontal cortex does not elicit content-specific changes in experience. Stimulation of the ACC and MCC (posterior areas), however, does elicit some content-specific changes in experience, suggesting that posterior area stimulation is more likely to excite content-specific NCC than frontal area stimulation.
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Several studies have shown that electrical stimulation and EEG activation of posterior cortical areas is effective at restoring consciousness in subjects where it is impaired, demonstrating that the excitability of the full NCC can be modulated through arousal systems.
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Electrical stimulation during neurosurgery is an important source ofevidence for a direct contribution of different brain areas to con-sciousness (Penfield, 1959; Desmurget et al., 2013), as indicatedby its superior value in predicting postoperative deficits com-pared with fMRI or diffusion tensor imaging (Borchers et al.,2011).
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diffusion tensor imaging
A technique that detects how water travels along the white matter tracts in the brain.
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Figure 2.
anatomical images depicting clinical evidence for the full (A, B, C) and content-specific (D, E, F) NCC.
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Although frontal injuries can slightlyincrease the threshold for perceiving some brief (16 ms) andmasked visual stimuli, patients still experience them (Del Cul etal., 2009), suggesting that these frontal regions may modulate theNCC (i.e., act as background conditions) rather than contribut-ing directly to consciousness (Kozuch, 2014).
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By contrast, there is little evidence for loss of specific con-scious contents after frontal damage (Penfield and Jasper, 1954).
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prosody
Patterns of rhythm and sound used in poetry.
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With regards to content-specific NCC, there is abundant neu-rological evidence that lesions in the posterior cortex can cause aloss of specific contents of experience (Farah, 2004).
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B
mid-sagittal fMRI image of someone who experienced anoxic lesions to their posterior corpus callosum, resulting in permanent VS following head trauma.
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traumatic lesions to the posterior corpus callosum appear to permanently cause states of VS (coma, or impeded consciousness), whereas traumatic lesions to the frontal lobe do not seem to do this.
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VS
Behavioral state similar to coma.
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A,
Bilateral view of the left and right frontal lobes of someone who experienced extensive prefrontal lobe damage without a noticeable change in consciousness, with certain anatomical regions labeled (top). Lateral view of the left and right hemispheres of that same individual, with certain anatomical regions labeled (bottom).
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There are many examples of people who have experienced bilateral lesions to the frontal lobe and still retained most, if not all aspects of consciousness. These instances lend credence to the idea that the anterior cortex may not account for the full NCC. Even when such damage causes deficits in cognition, perception, or executive function, consciousness does not appear to be significantly altered and effected individuals still seem capable of living normal lives.
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