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Effects of dual-task interference on swallowing in healthy aging adults.
Krishnamurthy, R, Philip, R, Balasubramanium, RK, Rangarathnam, B
PloS one. 2021;(6):e0253550
Abstract
A wide body of literature has demonstrated that the neural representation of healthy swallowing is mostly bilateral, with one hemisphere dominant over the other. While several studies have demonstrated the presence of laterality for swallowing related functions among young adults, the data on older adults are still growing. The purpose of this paper is to investigate potential changes in hemispheric dominance in healthy aging adults for swallowing related tasks using a behavioral dual-task paradigm. A modified dual-task paradigm was designed to investigate the potential reduction in hemispherical specialization for swallowing function. Eighty healthy right-handed participants in the study were divided into two groups [Group 1: young adults (18-40 years) and Group 2: older adults (65 and above)]. All the participants performed a timed water swallow test at baseline and with two interference conditions (silent word repetition, and facial recognition). The results of the study revealed the following 1) a statistically significant effect of age on swallow performance; 2) statistically significant effect of each of the interference tasks on two of the swallow measures (VPS and VPT) in younger adults; and 3) no significant effect of the interference tasks on the swallowing performance of older adults. These findings suggest that aging substantially affects swallowing in older individuals, and this potentially accompanies a reduction in the hemispheric specialization for swallowing related tasks.
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Right-lateralized fronto-parietal network and phasic alertness in healthy aging.
Haupt, M, Ruiz-Rizzo, AL, Sorg, C, Finke, K
Scientific reports. 2020;(1):4823
Abstract
Phasic alerting cues temporarily increase the brain's arousal state. In younger and older participants, visual processing speed in a whole report task, estimated based on the theory of visual attention, is higher in cue than no-cue conditions. The present study assessed whether older participants' ability to profit from warning cues is related to intrinsic functional connectivity (iFC) in the cingulo-opercular and/or right fronto-parietal network. We acquired resting-state functional magnetic resonance imaging data from 31 older participants. By combining an independent component analysis and dual regression, we investigated iFC in both networks. A voxel-wise multiple regression in older participants yielded that higher phasic alerting effects on visual processing speed were significantly related to lower right fronto-parietal network iFC. This result supports a particular role of the right fronto-parietal network in maintaining phasic alerting capabilities in aging. We then compared healthy older participants to a previously reported sample of healthy younger participants to assess whether behaviour-iFC relationships are age group specific. The comparison revealed that the association between phasic alerting and cingulo-opercular network iFC is significantly lower in older than in younger adults.
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The superior colliculus is sensitive to gestalt-like stimulus configuration in hemispherectomy patients.
Georgy, L, Celeghin, A, Marzi, CA, Tamietto, M, Ptito, A
Cortex; a journal devoted to the study of the nervous system and behavior. 2016;:151-61
Abstract
Patients with cortical blindness following a lesion to the primary visual cortex (V1) may retain nonconscious visual abilities (blindsight). One intriguing, though largely unexplored question, is whether nonconscious vision in the blind hemifield of hemianopic patients can be sensitive to higher-order perceptual organization, and which V1-independent structure underlies such effect. To answer this question, we tested two rare hemianopic patients who had undergone hemispherectomy, and in whom the only post-chiasmatic visual structure left intact in the same side of the otherwise damaged hemisphere was the superior colliculus (SC). By using a variant of the redundant target effect (RTE), we presented single dots, patterns composed by the same dots organized in quadruple gestalt-like configurations, or patterns of four dots arranged in random configurations, either singly to the intact visual hemifield or bilaterally to both hemifields. As reported in a number of prior studies on blindsight patients, we found that bilateral stimulation yielded faster reaction times (RTs) than single stimulation of the intact field for all conditions (i.e., there was an implicit RTE). In addition to this effect, both patients showed a further speeding up of RTs when the gestalt-like, but not the random shape, quadruple patterns were projected to their blind hemifield during bilateral stimulation. Because other retino-recipient subcortical and cortical structures in the damaged hemisphere are absent, the SC on the lesioned side seems solely responsible for such an effect. The present results provide initial support to the notion that nonconscious vision might be sensitive to perceptual organization and stimulus configuration through the pivotal contribution of the SC, which can enhance the processing of gestalt-like or structured stimuli over meaningless or randomly assembled ones and translate them into facilitatory motor outputs.
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Induction of cortical plasticity and improved motor performance following unilateral and bilateral transcranial direct current stimulation of the primary motor cortex.
Kidgell, DJ, Goodwill, AM, Frazer, AK, Daly, RM
BMC neuroscience. 2013;:64
Abstract
BACKGROUND Transcranial direct current stimulation (tDCS) is a non-invasive technique that modulates the excitability of neurons within the primary motor cortex (M1). Research shows that anodal-tDCS applied over the non-dominant M1 (i.e. unilateral stimulation) improves motor function of the non-dominant hand. Similarly, previous studies also show that applying cathodal tDCS over the dominant M1 improves motor function of the non-dominant hand, presumably by reducing interhemispheric inhibition. In the present study, one condition involved anodal-tDCS over the non-dominant M1 (unilateral stimulation) whilst a second condition involved applying cathodal-tDCS over the dominant M1 and anodal-tDCS over non-dominant M1 (bilateral stimulation) to determine if unilateral or bilateral stimulation differentially modulates motor function of the non-dominant hand. Using a randomized, cross-over design, 11 right-handed participants underwent three stimulation conditions: 1) unilateral stimulation, that involved anodal-tDCS applied over the non-dominant M1, 2) bilateral stimulation, whereby anodal-tDCS was applied over the non-dominant M1, and cathodal-tDCS over the dominant M1, and 3) sham stimulation. Transcranial magnetic stimulation (TMS) was performed before, immediately after, 30 and 60 minutes after stimulation to elucidate the neural mechanisms underlying any potential after-effects on motor performance. Motor function was evaluated by the Purdue pegboard test. RESULTS There were significant improvements in motor function following unilateral and bilateral stimulation when compared to sham stimulation at all-time points (all P < 0.05); however there was no difference across time points between unilateral and bilateral stimulation. There was also a similar significant increase in corticomotor excitability with both unilateral and bilateral stimulation immediately post, 30 minutes and 60 minutes compared to sham stimulation (all P < 0.05). Unilateral and bilateral stimulation reduced short-interval intracortical inhibition (SICI) immediately post and at 30 minutes (all P < 0.05), but returned to baseline in both conditions at 60 minutes. There was no difference between unilateral and bilateral stimulation for SICI (P > 0.05). Furthermore, changes in corticomotor plasticity were not related to changes in motor performance. CONCLUSION These results indicate that tDCS induced behavioural changes in the non-dominant hand as a consequence of mechanisms associated with use-dependant cortical plasticity that is independent of the electrode arrangement.
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Evidence for developmental programming of cerebral laterality in humans.
Jones, A, Osmond, C, Godfrey, KM, Phillips, DI
PloS one. 2011;(2):e17071
Abstract
Adverse fetal environments are associated with depression, reduced cognitive ability and increased stress responsiveness in later life, but underlying mechanisms are unknown. Environmental pressures on the fetus, resulting from variations in placental function and maternal nutrition, health and stress might alter neurodevelopment, promoting the development of some brain regions over others. As asymmetry of cerebral activity, with greater right hemisphere activity, has been associated with psychopathology, we hypothesized that regional specialization during fetal life might be reflected persistently in the relative activity of the cerebral hemispheres. We tested this hypothesis in 140 healthy 8-9 year-old children, using tympanic membrane temperature to assess relative blood flow to the cerebral hemispheres at rest and following psychosocial stress (Trier Social Stress Test for Children). Their birth weight and placental weight had already been measured when their mothers took part in a previous study of pregnancy outcomes. We found that children who had a smaller weight at birth had evidence of greater blood flow to the right hemisphere than to the left hemisphere (r = -.09, P = .29 at rest; r = -.18, P = .04 following stress). This finding was strengthened if the children had a relatively low birth weight for their placental weight (r = -.17, P = .05 at rest; r = -.31, P = .0005 following stress). Our findings suggest that lateralization of cerebral activity is influenced persistently by early developmental experiences, with possible consequences for long-term neurocognitive function.
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6.
Diagnostic methods for extra-temporal neocortical focal epilepsies: present and future.
Leite, RA, Otaduy, MC, Silva, GE, Ferreira, ML, Aragão, Mde F
Arquivos de neuro-psiquiatria. 2010;(1):119-26
Abstract
The progress of epilepsies diagnosis has been great, but, amongst the diagnostic detailing that demand research, one of the most important is the essential lateralization and localization of epileptogenic zone, considered as the cerebral cortex region, that removed, will result in a free state of seizures. The present study aims to analyze the possible uses of proton spectroscopy for clinical and pre-surgical evaluation of focal extratemporal epilepsies, since this group presents the highest difficulty degree for lateralizing and locating epileptogenic zones. In almost all cases, a non invasive diagnosis can be performed using routine electroencephalography, video-electroencephalography - considered as gold standard, and magnetic resonance imaging. However, when the results of these exams are contradictory, some patients need invasive techniques, as the intra-cranial video-EEG, using deep electrodes, sub-dural strip and grid, that are associated with increased diagnostic cost and risk of complications, as cerebral hemorrhages and intra-cranial infections. Proton spectroscopy appears as a possibility, given its capacity to evaluate cerebral metabolism, by N-acetyl-aspartate (NAA), creatine (Cre) and choline (Cho) concentrations, amongst other metabolites. This non invasive method may provide time reduction of this evaluation and reliable level improvement for this topographical diagnosis.
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7.
Bilateral capacity for speech sound processing in auditory comprehension: evidence from Wada procedures.
Hickok, G, Okada, K, Barr, W, Pa, J, Rogalsky, C, Donnelly, K, Barde, L, Grant, A
Brain and language. 2008;(3):179-84
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Abstract
Data from lesion studies suggest that the ability to perceive speech sounds, as measured by auditory comprehension tasks, is supported by temporal lobe systems in both the left and right hemisphere. For example, patients with left temporal lobe damage and auditory comprehension deficits (i.e., Wernicke's aphasics), nonetheless comprehend isolated words better than one would expect if their speech perception system had been largely destroyed (70-80% accuracy). Further, when comprehension fails in such patients their errors are more often semantically-based, than-phonemically based. The question addressed by the present study is whether this ability of the right hemisphere to process speech sounds is a result of plastic reorganization following chronic left hemisphere damage, or whether the ability exists in undamaged language systems. We sought to test these possibilities by studying auditory comprehension in acute left versus right hemisphere deactivation during Wada procedures. A series of 20 patients undergoing clinically indicated Wada procedures were asked to listen to an auditorily presented stimulus word, and then point to its matching picture on a card that contained the target picture, a semantic foil, a phonemic foil, and an unrelated foil. This task was performed under three conditions, baseline, during left carotid injection of sodium amytal, and during right carotid injection of sodium amytal. Overall, left hemisphere injection led to a significantly higher error rate than right hemisphere injection. However, consistent with lesion work, the majority (75%) of these errors were semantic in nature. These findings suggest that auditory comprehension deficits are predominantly semantic in nature, even following acute left hemisphere disruption. This, in turn, supports the hypothesis that the right hemisphere is capable of speech sound processing in the intact brain.