Papers
Functional MRI of oropharyngeal air-pulse stimulation.
Soros P, Lalone E, Smith R, Stevens T, Theurer J, Menon R, Martin R. Neuroscience 2008, 153: 1300-1308.
Although the posterior oral cavity and oropharynx play a major role in swallowing, their central representation is poorly understood. 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 six healthy adults. Bilateral air-pulse stimulation was associated with the activation of a bilateral network including the primary somatosensory cortex and the thalamus, classic motor areas (primary motor cortex, supplementary motor area, cingulate motor areas), and polymodal areas (including the insula and frontal cortex). 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.
Functional MRI of working memory and selective attention in vibrotactile frequency discrimination.
Sörös P, Marmurek J, Tam F, Baker N, Staines WR, Graham SJ. BMC Neuroscience 2007; 8:48.
BACKGROUND: Focal lesions of the frontal, parietal and temporal lobe may interfere with tactile working memory and attention. To characterise the neural correlates of intact vibrotactile working memory and attention, functional MRI was conducted 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-randomized (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. CONCLUSION: 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.
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No indication of brain reorganization after unilateral ischemic lesions of the auditory cortex.
Sörös P, Dziewas R, Manemann E, Teismann IK, Lütkenhöner B. Neurology 2006;67(1):1059-1061.
We used magnetoencephalography to study contralesional auditory reorganization in three men with chronic unilateral ischemic lesions of the auditory cortex. Although 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 seems to lack contralateral reorganization, presumably because patients are typically not aware of hearing deficits and thus do not perform training.
The neurochemical basis of human cortical auditory processing: Combining proton magnetic resonance spectroscopy and magnetoencephalography.
Sörös P, Michael N, Tollkötter M, Pfleiderer B. BMC Biology 2006;4:25.
BACKGROUND: 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.
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Clustered functional MRI of overt speech production.
Sörös P, Sokoloff LG, Bose A, McIntosh AR, Graham SJ, Stuss DT. Clustered functional MRI of overt speech production. Neuroimage 2006;32:376-387
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.
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Auditory temporal processing in healthy aging: a
BMC Neuroscience 2009;10:34
Background: Impaired speech perception is one of the major sequelae of aging. In addition to peripheral hearing loss, central deficits of auditory processing are supposed to contribute to the deterioration of speech perception in older individuals. To test the hypothesis that auditory temporal processing is compromised in aging, auditory evoked magnetic fields were recorded during stimulation with sequences of 4 rapidly recurring speech sounds in 28 healthy individuals aged 20 – 78 years.
Results: The decrement of the N1m amplitude during rapid auditory stimulation was not significantly different between older and younger adults. The amplitudes of the middle-latency P1m wave and of the long-latency N1m, however, were significantly larger in older than in younger participants.
Conclusion: The results of the present study do not provide evidence for the hypothesis that auditory temporal processing, as measured by the decrement (short-term habituation) of the major auditory evoked component, the N1m wave, is impaired in aging. The differences between these magnetoencephalographic findings and previously published behavioral data might be explained by differences in the experimental setting between the present study and previous behavioral studies, in terms of speech rate, attention, and masking noise. Significantly larger amplitudes of the P1m and N1m waves suggest that the cortical processing of individual sounds differs between younger and older individuals. This result adds to the growing evidence that brain functions, such as sensory processing, motor control and cognitive processing, can change during healthy aging, presumably due to experience-dependent neuroplastic mechanisms.
Age-related changes in the cerebral control of movements: An activation likelihood estimation meta-analysis
Poster at the Human Brain Mapping conference, San Francisco June 2009
Healthy aging is often accompanied by a decline in motor function, in particular a decrease in the speed of movements and a loss of coordination. Functional brain imaging makes it possible to compare movement-related brain activity between younger and older individuals. In many of these studies, brain function of older participants has been characterized by under- and over-activation in parts of the neural circuitry when compared with younger adults. These functional changes may result from neuroplasticity in the aging brain, compensat- ing for loss of sensorimotor function and contribut- ing to maintaining of behavioral performance. Our results indicate that healthy aging is associated with changes in the cerebral control of movements. These changes are characterized by areas of over- activation (in particular, the supplementary motor area) and under-activation (including the sensori- motor cortex, cingulate motor area, insula, and cere- bellar hemispheres) in the aging brain as compared to younger adults. Increased activation in brain areas that subserve movement initiation and control is compatible with the hypothesis that healthy aging is accompanied by a shift from automatic to a more controlled pro- cessing of movement (Heuninckx et al. 2005). The underlying patho-anatomical mechanisms for this cerebral reorganization of movement control are un- clear and might involve gray matter atrophy, disrup- tion of white matter fiber tracts, and alterations in regional neurotransmission. More studies are war- ranted to illicit structural and functional changes in the healthy aging brain.
Functional Brain Imaging of Swallowing: An Activation Likelihood Meta-Analysis
Published as: Sörös P, Inamoto Y, Martin RE. Functional brain imaging of swallowing: An activation likelihood estimation meta-analysis. Hum Brain Mapp 2009;30(8):2426-39.
The neuroanatomy and functional significance of swallowing- related networks in humans are not entirely clear. Activa- tion likelihood estimation (ALE), a novel quantitative meta- analysis technique, was employed to pool the results of func- tional brain imaging studies for the investigation of the cortical control of swallowing (Sörös et al. 2009). This meta-analysis emphasizes the distributed and partly overlapping cortical networks involved in the control of wa- ter and saliva swallowing. Water swallowing is associated with right inferior parietal activation, likely reflecting the sensory processing of intraoral water stimulation. Saliva swallowing more strongly involves premotor areas, which are crucial for the initiation and control of movements.
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Age-related changes in the functional neuroanatomy of overt speech production
Co-authored with Bose A, Sokoloff LG, Graham SJ, Stuss DT. Neurobiology of Aging 2009 (in press)
Alterations of existing neural networks during healthy aging, resulting in behavioral deficits and changes in brain activity, have been described for cognitive, motor, and sensory functions. To investigate age-related changes in the neural circuitry underlying overt non-lexical speech production, functional MRI was performed in 14 healthy younger (21-32 years) and 14 healthy older individuals (62-84 years). The experimental task involved the acoustically cued overt production of the vowel /a/ and the polysyllabic utterance /pataka/. In younger and older individuals, overt speech production was associated with the activation of a widespread articulo-phonological network, including the primary motor cortex, the supplementary motor area, the cingulate motor areas, and the posterior superior temporal cortex, similar in the /a/ and /pataka/ condition. An analysis of variance with the factors age and condition revealed a significant main effect of age. Irrespective of the experimental condition, significantly greater activation was found in the bilateral posterior superior temporal cortex, the posterior temporal plane, and the transverse temporal gyri in younger compared to older individuals. Significantly greater activation was found in the bilateral middle temporal gyri, medial frontal gyri, middle frontal gyri, and inferior frontal gyri in older vs. younger individuals. The analysis of variance did not reveal a significant main effect of condition and no significant interaction of age and condition. These results suggest a complex reorganization of neural networks dedicated to the production of speech during healthy aging.
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Functional Brain Imaging of Swallowing: An Activation Likelihood Meta-Analysis
published as: Sörös P, Inamoto Y, Martin RE. Functional brain imaging of swallowing: An activation likelihood estimation meta-analysis. Hum Brain Mapp 2009;30(8):2426-39.
A quantitative, voxel-wise meta-analysis was performed to investigate the cortical control of water and saliva swallowing. Studies that were included in the meta-analysis (1) examined water swal- lowing, saliva swallowing, or both, and (2) reported brain activation as coordinates in standard space. Using these criteria, a systematic literature search identified seven studies that examined water swal- lowing and five studies of saliva swallowing. An activation likelihood estimation (ALE) meta-analysis of these studies was performed with GingerALE. For water swallowing, clusters with high activation likelihood were found in the bilateral sensorimotor cortex, right inferior parietal lobule, and right ante- rior insula. For saliva swallowing, clusters with high activation likelihood were found in the left senso- rimotor cortex, right motor cortex, and bilateral cingulate gyrus. A between-condition meta-analysis revealed clusters with higher activation likelihood for water than for saliva swallowing in the right in- ferior parietal lobule, right postcentral gyrus, and right anterior insula. Clusters with higher activation likelihood for saliva than for water swallowing were found in the bilateral supplementary motor area, bilateral anterior cingulate gyrus, and bilateral precentral gyrus. This meta-analysis emphasizes the distributed and partly overlapping cortical networks involved in the control of water and saliva swal- lowing. Water swallowing is associated with right inferior parietal activation, likely reflecting the sensory processing of intraoral water stimulation. Saliva swallowing more strongly involves premotor areas, which are crucial for the initiation and control of movements. Hum Brain Mapp 30:2426–2439, 2009.
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