Background: Although the posterior oral cavity and oropharynx play a major role in swallowing, their central representation is poorly understood.

Methods: High-field functional magnetic resonance imaging of the brain was used to study the central processing of brief air-pulses, delivered to the peritonsillar region of the lateral oropharynx, in 6 healthy adults.

Results: Bilateral air-pulse stimulation was associated with the activation of a bilateral network including the primary somatosensory cortex and the thalamus, classical motor areas (primary motor cortex, supplementary motor area, cingulate motor areas), and polymodal areas (including the insula and frontal cortex).

Conclusions: These results suggest that oropharyngeal stimulation can activate a bilaterally distributed cortical network that overlaps cortical regions previously implicated in oral and pharyngeal sensorimotor functions such as tongue movement, mastication, and swallowing. The present study also demonstrates the utility of air-pulse stimulation in investigating oropharyngeal sensorimotor processing in functional brain imaging experiments.

A more detailed description of this study can be found here.

The following oral presentation, given at the Dysphagia Research Society 2008 in Charleston, SC, USA, presents a study on somatosensory processing of brief air-pulse stimuli. A more detailed description of this study can be found here.

Sörös P, Lalone E, Smith R, Stevens T, Theurer J, Menon R, Martin R. Functional MRI of oropharyngeal air-pulse stimulation. Download

A second talk presented the results of a quantitative, voxel-wise meta-analysis of swallowing-related brain activity in humans, based on fMRI, PET, and MEG studies.

Sörös P, Inamoto Y, Martin R. Functional brain imaging of swallowing: An activation likelihood meta-analysis. Download

Aim: We tested the hypothesis that reduced nutritional status or the degree of tissue catabolism are associated with the presence of hepatic encephalopathy in 223 patients with histologically confirmed non-alcoholic cirrhosis.
Results: Nutritional status and tissue catabolism were not significantly different between patients with and without hepatic encephalopathy.
Conclusions: Our data do not support the hypothesis that malnutrition or tissue catabolism are independent risk factors for the presence of hepatic encephalopathy in patients with non-alcoholic cirrhosis.

Background. To characterise the neural correlates of intact vibrotactile working memory and attention, we conducted functional MRI in 12 healthy young adults. Participants performed a forced-choice vibrotactile frequency discrimination task, comparing a cue stimulus of fixed frequency to their right thumb with a probe stimulus of identical or higher frequency. To investigate working memory, the time interval between the 2 stimuli was pseudo-randomised (either 2 or 8 s). To investigate selective attention, a distractor stimulus was occasionally presented contralaterally, simultaneous to the probe.

Results. Delayed vibrotactile frequency discrimination, following a probe presented 8 s after the cue in contrast to a probe presented 2 s after the cue, was associated with activation in the bilateral anterior insula and the right inferior parietal cortex. Frequency discrimination under distraction was correlated with activation in the right anterior insula, in the bilateral posterior parietal cortex, and in the right middle temporal gyrus.

Conclusions. These results support the notion that working memory and attention are organised in partly overlapping neural circuits. In contrast to previous reports in the visual or auditory domain, this study emphasises the involvement of the anterior insula in vibrotactile working memory and selective attention. ]]> http://neuroactivity.org/2007/07/18/fmri-of-vibrotactile-processing/feed/ http://neuroactivity.org/2007/03/18/functional-imaging-of-speech-production/ http://neuroactivity.org/2007/03/18/functional-imaging-of-speech-production/#comments Sun, 18 Mar 2007 11:49:55 +0000 http://neuroactivity.org/2007/03/18/functional-imaging-of-speech-production/

This is a presentation I gave at the Ontario Aphasia Interest Group Teleconference in December 2006. It summarizes the findings of my fMRI study on speech production in healthy younger adults (Neuroimage 2006;32(1):376-387). The presentation is available as Flash web presentation or as a pdf (6 MB).

Abstract
A combination of magnetoencephalography and proton magnetic resonance spectroscopy was used to correlate the electrophysiology of rapid auditory processing and the neurochemistry of the auditory cortex in 15 healthy adults. To assess rapid auditory processing in the left auditory cortex, the amplitude and decrement of the N1m peak, the major component of the late auditory evoked response, were measured during rapidly successive presentation of acoustic stimuli. We tested the hypothesis that: (i) the amplitude of the N1m response and (ii) its decrement during rapid stimulation are associated with the cortical neurochemistry as determined by proton magnetic resonance spectroscopy.

Results. Our results demonstrated a significant association between the concentrations of N-acetylaspartate, a marker of neuronal integrity, and the amplitudes of individual N1m responses. In addition, the concentrations of choline-containing compounds, representing the functional integrity of membranes, were significantly associated with N1m amplitudes. No significant association was found between the concentrations of the glutamate/glutamine pool and the amplitudes of the first N1m. No significant associations were seen between the decrement of the N1m (the relative amplitude of the second N1m peak) and the concentrations of N-acetylaspartate, choline-containing compounds, or the glutamate/glutamine pool. However, there was a trend for higher glutamate/glutamine concentrations in individuals with higher relative N1m amplitude.

Conclusion. These results suggest that neuronal and membrane functions are important for rapid auditory processing. This investigation provides a first link between the electrophysiology, as recorded by magnetoencephalography, and the neurochemistry, as assessed by proton magnetic resonance spectroscopy, of the auditory cortex.

Sörös P, Dziewas R, Manemann E, Teismann IK, Lütkenhöner B. No indication of brain reorganization after unilateral ischemic lesions of the auditory cortex. Neurology 2006;67:1059-1061 PubMed Reprint

Abstract
We used magnetoencephalography to study contralesional auditory reorganization in three men with chronic unilateral ischemic lesions of the auditory cortex. While no response was found over the lesioned hemisphere, processing in the unaffected hemisphere was indistinguishable vs. healthy controls. In contrast to sensorimotor and language systems, the auditory system appears to lack contralateral reorganization, presumably because patients are typically not aware of hearing deficits and thus do not perform training.

This poster depicts the neural network involved in speech production as found in 9 young adults, based on my paper in Neuroimage.

Sörös P, Guttman Sokoloff L, Bose A, McIntosh AR, Graham SJ, Stuss DT. Clustered fMRI of speech production. Neuroimage 2006;31(Supplement 1):S113. Download

Age-related reorganization of the functional neuroanatomy of speech production.

This poster describes the differences in brain activation associated with speech production between young and old individuals.

Sörös P, Guttman Sokoloff L, Bose A, McIntosh AR, Graham SJ, Stuss DT. Age-related reorganization of the functional neuroanatomy of speech production. Neuroimage 2006;31(Supplement 1):S2944. Download

MR-compatible registration of speech-related movements using a bend sensor.

This poster introduces a new method to monitor speech-related jaw movements using a fiber optic sensor.

Sörös P, Tam F, Graham SJ. MR-compatible registration of speech-related movements using a bend sensor. Neuroimage 2006;31(Supplement 1):S138. Download

Sörös P, Sokoloff LG, Bose A, McIntosh AR, Graham SJ, Stuss DT. Clustered functional MRI of overt speech production. Neuroimage. 2006;32(1):376-387. PubMed Reprint

Abstract
To investigate the neural network of overt speech production, event-related fMRI was performed in 9 young healthy adult volunteers. A clustered image acquisition technique was chosen to minimize speech-related movement artifacts. Functional images were acquired during the production of oral movements and of speech of increasing complexity (isolated vowel as well as monosyllabic and trisyllabic utterances). This imaging technique and behavioral task enabled depiction of the articulo-phonologic network of speech production from the supplementary motor area at the cranial end to the red nucleus at the caudal end. Speaking a single vowel and performing simple oral movements involved very similar activation of the cortical and subcortical motor systems. More complex, polysyllabic utterances were associated with additional activation in the bilateral cerebellum, reflecting increased demand on speech motor control, and additional activation in the bilateral temporal cortex, reflecting the stronger involvement of phonologic processing.