Hemispheric Interaction Research Articles

ВПЛИВ БІНАУРАЛЬНОГО РИТМУ 10 ГЦ НА АКТИВНІСТЬ ГОЛОВНОГО МОЗКУ ТА ЕФЕКТИВНІСТЬ ПРОСТОЇ СЕНСОМОТОРНОЇ РЕАКЦІЇ ТА РЕАКЦІЇ ВИБОРУ В ЧОЛОВІКІВ ТА ЖІНОК

As a result of researches of 20 persons, aged 18-23 years, it was found that men under the influence of binaural beats 10 Hz, compared with binaural sound when testing a simple sensorimotor reaction was found greater activity in the frontal, central and occipital areas of both hemispheres and right temporal and parietal areas, which may be indicative about activation system imaginative and creative thinking, the need for which was absent for the implementation of a simple sensorimotor reaction. Differences in time as a simple sensorimotor reaction and choice reaction was observed. When testing, choice reaction was detected influence of binaural beats 10 Hz on the brain activity of men. In women under the influence of binaural beats 10 Hz were significantly higher speeds as a simple sensorimotor reaction and choice reaction and significantly smaller spread of latent periods of simple sensorimotor reaction. This was above the hemispheric interaction suppressed irrelevant zone and the high activity of the ascending process of attention that has provided highly specific data processing and high performance tasks compared with binaural sound.

Bilateral versus ipsilesional cortico-subcortical activity patterns in stroke show hemispheric dependence.

Background Understanding of interhemispheric interactions in stroke patients during motor control is an important clinical neuroscience quest that may provide important clues for neurorehabilitation. In stroke patients, bilateral overactivation in both hemispheres has been interpreted as a poor prognostic indicator of functional recovery. In contrast, ipsilesional patterns have been linked with better motor outcomes. Aim We investigated the pathophysiology of hemispheric interactions during limb movement without and with contralateral restraint, to mimic the effects of constraint-induced movement therapy. We used neuroimaging to probe brain activity with such a movement-dependent interhemispheric modulation paradigm. Methods We used an fMRI block design during which the plegic/paretic upper limb was recruited/mobilized to perform unilateral arm elevation, as a function of presence versus absence of contralateral limb restriction ( n = 20, with balanced left/right lesion sites). Results Analysis of 10 right-hemispheric stroke participants yielded bilateral sensorimotor cortex activation in all movement phases in contrast with the unilateral dominance seen in the 10 left-hemispheric stroke participants. Superimposition of contralateral restriction led to a prominent shift from activation to deactivation response patterns, in particular in cortical and basal ganglia motor areas in right-hemispheric stroke. Left-hemispheric stroke was in general characterized by reduced activation patterns, even in the absence of restriction, which induced additional cortical silencing. Conclusion The observed hemispheric-dependent activation/deactivation shifts are novel and these pathophysiological observations suggest short-term neuroplasticity that may be useful for hemisphere-tailored neurorehabilitation.

Abstract: Language Phoneme Discrimination in Infants with Sagittal Craniosynostosis: An ERP Study

PURPOSE: Neurocognitive deficits associated with craniosynostosis in infancy are poorly characterized. With school-age neurocognitive studies of craniosynostosis revealing impairments in language-related abilities (e.g., reading and spelling), early language processing is of particular interest. We compared neural response to speech sounds in infants with nonsyndromic sagittal craniosynostosis (NSC) using event-related potentials (ERPs) to characterize differences in language processing. Given its association with language impairments in infancy (e.g. dysphasia, cleft palate), we analyzed the mismatch negativity (MMN) component evoked by distinct speech sounds. Studying the MMN expands on our previous work examining other auditory ERPs in NSC infants. METHODS: EEG was recorded while 39 infants (12 NSC, 27 control; ages 2 to 8 months) listened to the Hindi dental /da/ and retroflex /da/ phonemes (non-native phonemic discrimination task). Frontal and central electrodes were used for analysis. The MMN was extracted as the peak amplitude of the largest negative deflection in the difference wave (retroflex minus dental) over 80-300ms post-stimulus. Differences in MMN were analyzed using repeated measures analysis of variance (group as between subjects factor; region, hemisphere as within subjects factors). RESULTS: MMN amplitude was lower in magnitude in the NSC infants compared to controls (p=0.047). A significant region by group interaction (p=0.045) was observed, and pairwise comparisons revealed that NSC infants displayed attenuated MMN in the frontal electrodes compared with controls (p=0.010). A significant region by hemisphere interaction (p=0.012) was also observed, and pairwise comparisons revealed a trend of higher magnitude MMN in the frontal region compared to central region in the left hemisphere (p=0.074). CONCLUSION: The MMN was significantly attenuated in NSC infants compared to controls. This finding suggests atypical neural response to language in NSC infants. Given the association of these brain responses with phoneme discrimination, our findings have important implications for the understanding the later language impairments observed in school-aged individuals with NSC.

Mean Green operators and Eshelby tensors for hemispherical inclusions and hemisphere interactions in spheres. Application to bi-material spherical inclusions in isotropic spaces

This paper mainly presents an exact expression for the mean shape function of a hemispherical inclusion, from which are obtained analytical forms for the mean Green operator (GO) and Eshelby tensor of this hemi-sphere as well as for the related mean pair interaction Green operator (IGO) between the two hemi-spheres of a sphere, in media with isotropic (elastic or dielectric) properties. We secondly address the problem of bi-material inclusions, in the sense of a two-phase compact set of two or a few elementary domains, a particular inclusion pattern case for which we give an estimate of the mean stress and strain in each phase accounting for interactions. This estimate results from knowing the mean GO (or Eshelby tensor) for each pattern element plus the mean IGO between element pairs, what is rarely fulfilled analytically. The here solved case for bi-material spherical inclusions made of two different hemispherical elements adds to the recently made available solution for bi-material cylindrical inclusions made of piled coaxial finite cylinders. The obtained mean stress estimates are exemplified able to satisfactorily match with FEM calculations up to highly contrasted bi-material inclusions. Other types of bi-material spherical inclusions are mentioned for which the mean GOs for the sub-domains and their pair IGO can be obtained without calculation, owing to particular symmetries of the phase arrangement. Mean GOs and IGOs are also useful in certain homogenization frameworks yielding overall property estimates for inclusion-reinforced matrices. Further discussions and specific applications will be presented in forthcoming papers.

Selective increase in posterior corpus callosum thickness between the age of 4 and 11 years

Establishing an efficient functional and structural connectivity between the two cerebral hemispheres is an important developmental task during childhood, and alterations in this development have accordingly been linked to a series of neurodevelopmental and pediatric disorders. The corpus callosum, the major white-matter structure connecting the hemispheres, has been shown to increase in size throughout the three first decades of life. However, behavioral studies indicate that adult-like performance levels of functional hemispheric interaction are already reached during middle and late childhood. Thus, here we specifically examine the structural development of the corpus callosum during the functionally relevant time period by for the first time (a) selectively addressing prospective childhood development and (b) analyzing a sample in which also younger children are well represented. Corpus callosum anatomy was assessed from 732 T1-weighted MRI datasets acquired from 428 children (213 boys, 215 girls) aged of 4.1 and 10.9years, of which 304 were scanned at two time points. Regional callosal thickness was determined from an outline-based segmentation of the mid-sagittal cross-sectional surface area. Linear-mixed model analyses revealed a significant increase in thickness with age (effect size: up to 15% explained variance) equivalent to a growth in callosal thickness of up to 0.19mm per year in the posterior corpus callosum. The age effect was found to be stronger in posterior segments (i.e., splenium) than in other callosal subregions. Also, the age effect was found to be comparable between boys and girls, and was detected irrespective of whether developmental or individual differences in overall brain size where accounted for or not. Our results demonstrate a selective increase in posterior corpus-callosum thickness during middle and late childhood. Since axons crossing the midline in the splenium mainly connect occipital and parietal cortices, the accentuated posterior growth might reflect the onset of a posterior-to-anterior moving maturation wave in cortical development known to take place in the same time period.

The contributions of handedness and working memory to episodic memory.

Past studies have independently shown associations of working memory and degree of handedness with episodic memory retrieval. The current study takes a step ahead by examining whether handedness and working memory independently predict episodic memory. In agreement with past studies, there was an inconsistent-handed advantage for episodic memory; however, this advantage was absent for working memory tasks. Furthermore, regression analyses showed handedness, and complex working memory predicted episodic memory performance at different times. Results are discussed in light of theories of episodic memory and hemispheric interaction.

Enhancing the ecological validity of tests of lateralization and hemispheric interaction: Evidence from fixated displays of letters or symbols of varying complexity

Two experiments expand upon behavioural evidence of interactions among lateralization, hemispheric interaction, and task complexity with findings from an ecologically valid procedure. Target displays of letters or symbols were presented at fixation in go/no-go matching tasks of physical or categorical identity. Simultaneously with the target, a distractor appeared in the left visual field or right visual field to weight processing of the target to the hemisphere ipsilateral to the distractor, or the distractor did not appear at all. Comparison of the respective distractor-present trials with distractor-absent trials measures the relative costs or benefits of hemispheric interaction.Both experiments found that 3-item displays were processed faster and more accurately than displays of 5 items, suggesting they are relatively simple. Accuracy to the simple tasks showed left-hemisphere lateralization in the lexical task, right-hemisphere lateralization in the spatial task, a cost of hemispheric interaction compared to the advantaged hemisphere, and a benefit of hemispheric interaction compared to the less-advantaged hemisphere, suggesting that the contributions of the less-advantaged hemisphere interfere with processing, and that the advantaged hemisphere controls the lion’s share. In contrast, 5-item displays for physical match in both experiments showed a significant benefit to accuracy of hemispheric interaction compared to the left hemisphere, an insignificant benefit compared to the right hemisphere, no lateralization, no cost of hemispheric interaction, and a consequence to performance that was more costly to the hemisphere that had been advantaged in simple tasks, suggesting that the advantaged hemisphere relinquishes control as tasks become more complex and complementary processing results from both increased collaboration and decreased lateralization between the hemispheres. The findings expand upon behavioural evidence, converge with imaging evidence, and suggest future directions for brain mapping.

Reading disability and enhanced dynamic spatial reasoning: A review of the literature

Previous research on reading disabilities (RD) has primarily focused on the cause and expression of the disability. The vast majority of this research has focused on the disorder itself, although it has been proposed that RD embodies other qualities not necessarily related to language or reading deficits. In fact, strengths in nonverbal processing and visual-spatial talents have been proposed to exist in persons with RD. However, the limited empirical data on this matter have yielded inconsistent results. The purpose of this review was to examine this literature, focusing on research concerning dynamic and complex spatial processing or reasoning in people with dyslexia. Our review suggests that there is little evidence in support of a spatial advantage in people with dyslexia, and, in fact, the data show that RD samples most often perform worse or equal to non-RD samples. An exception to this general conclusion may be performance on holistic visualization of complex figures, where RD samples have consistently demonstrated faster response times even though accuracy rates often do not exceed that of controls. The possibility of a unique spatial processing neurology that develops through right-left hemisphere interactions in persons with RD is discussed based on preliminary fMRI data.

Features of memory and intellectual activity among the elderly with different reading productivity

The aim of this work was the study of indicators of memory and intellectual activity among the elderly with different reading productivity. The results of the study showed that the elderly were distinguished by a greater number of errors when performing tasks on oral-aural, visual memory and visual-spatial activities. The mistakes made by subjects with low reading productivity may indicate dysfunction of tone and wakefulness, of receiving, processing and storing information, as well as weakening of hemispheric interaction.

MUSIC CLASSES INFLUENCE ON THE COGNITIVE DEVELOPMENT OF PRIMARY SCHOOL CHILDREN

The aim of the study is to determine the influence of music classes on the cognitive functions formation in children of primary school age with regulatory development and children with attention deficit hyperactivity disorder (ADHD). Methods. The complex pediatric neuropsychological method by T. V. Akhutina is used in the presented study. This method was developed at the Laboratory of Neuropsychology in Moscow State University under the direction of T. V. Akhutina. Results. The quantitative and qualitative analysis of the results obtained during the neuropsychological research reveals that music classes within one year significantly influence on the increase in the rate of cognitive development of children with regulatory development. This is manifested in a more rapid formation of their kinetic and kinesthetic functions, hemispheric interaction and the ability to perceive and reproduce rhythmic structures. Research of influence of learning to play musical instruments within two years on the cognitive development of children with attention deficit hyperactivity disorder showed significantly greater development of the programming functions and voluntary activity control, the kinetic functions, hemispheric interaction, the ability to perceive and reproduce rhythms per sample, verbal memory of children involved in music. This demonstrates more rapid flow of their compensatory processes and forming a number of cognitive functions. Scientific novelty. The statistically confirmed data on correctional-developing influence of music classes on cognitive development of children with attention deficit hyperactivity disorder are achieved. Practical significance. The research materials may be applied by practical psychologists in preparation of complex correctional care programs for children with attention deficit hyperactivity disorder.

Connectivity measures in the Poffenberger paradigm indicate hemispheric asymmetries.

The Poffenberger paradigm is a well-known measure of interhemispheric transfer delays, calculated on the basis of the crossed vs uncrossed reaction time difference (CUD). However, the proper interpretation of CUD is extensively debated in the literature. In this study we used connectivity measures in an attempt to interpret CUD from the perspective of functional connectivity. Accordingly, we tried to define functional couplings in the Poffenberger paradigm; we used a simple choice version of the paradigm, and included a stimulation only (SO) condition for comparison. As an index of functional coupling we employed partial directed coherence, exploiting bilateral grouping of the electrodes to compute intra-and interhemispheric connection weight ratios (CWRs). Our findings indicated modulations in functional weights in relation to the SO condition, rather than the crossed and uncrossed conditions, such that the response executed by the right hemisphere yielded a decrease in intra-, yet an increase in interhemispheric CWRs, whereas the left hemisphere interactions showed connectivity patterns similar to the SO condition irrespective of the side of movement. Overall, our results suggest modulation of connectivity in the same/similar system, which was found to be optimized, in terms of hemispheric asymmetries, to different tasks.

Interim results of neuropsychological analysis of the development of children with perinatal risks

This article presents a brief description of the normative mental development of the elder preschool children: features hemispheric interaction between the cerebral hemispheres, dynamic, spatial and motor praxis, memory, visual-objective, visual-spatial and acoustic-verbal gnosis and originality of speech, thought and attention. Besides, this article illuminates analysis of the interim data obtained in the course of neuropsychological investigation of cerebral organization of mental functions among preschoolers whose mothers have an anamnesis of various risk factors of perinatal pathology of the fetus. The analysis of the data illustrates that very often agenda had difficulties in carrying out tests for visual gnosis, audio-verbal memory, dynamic and spatial praxis. Also it was hard for children to compile stories for narrative paintings and series of narrative pictures. Besides, it was recorded that the majority of children have shown attention fatigue and instability of attention and the high level of exhaustion. So the interim results received on this level of experimental research illustrate the existence of tendency of defection in the process of formation of high psychic functions among children with different risk of development of perinatal pathology in their anamnesis. But in the cause of the insufficiency of experimental data it is to early to make strict conclusions concerning the concrete consequences of the different perinatal risks for brain organization of child’s psychic activity.

Антагонист глутаматных NMDA-рецепторов (амантадина сульфат) в интенсивной терапии тяжелой черепно-мозговой травмы

Целью настоящего исследования было изучение эффективности препарата амантадина сульфат (ПК-Мерц) на госпитальном этапе у пациентов с тяжелой черепно-мозговой травмой (ЧМТ) с целью ранней нейропротекции за счет коррекции глутаматной эксайтотоксичности.Материал и методы исследования. Исследование проводилось в 2012–2014 годах в ДОКТМО на базе кафедры анестезиологии и интенсивной терапии ФПО Донецкого национального медицинского университета им. М. Горького. Обследовано 60 пациентов с диагнозом «тяжелая черепно-мозговая травма».Дизайн исследования. Открытое проспективное исследование по типу «случай — контроль», которое проводится в группе пациентов с тяжелой ЧМТ. Уровень нарушения сознания при поступлении в стационар от 4 до 8 баллов по шкале комы Глазго (ШКГ); возраст от 20 до 50 лет; 1-я группа состояла из 30 пациентов, получавших терапию по стандартному протоколу, 2-я группа — из 30 больных, получавших, кроме терапии по протоколу, препарат амантадин (ПК-Мерц), который применяли с первых суток после получения травмы в виде инфузионного раствора в дозе 500 мл (200 мг) 2 раза в сутки внутривенно медленно капельно в течение 7 суток. Изучали цереброкардиальные взаимоотношения у больных с тяжелой ЧМТ методами количественной электроэнцефалографии и кросс-корреляционного анализа вариабельности сердечного ритма, исследовали мозговой кровоток с помощью транскраниальной допплерографии, компьютерной томографии головного мозга.Результаты и обсуждение. Установлены высокие прямые корреляционные связи между повышением уровня сознания по шкале комы Глазго и снижением уровня абсолютной спектральной мощности дельта-диапазона, которые свидетельствовали о том, что после включения в терапию амантадина (ПК-Мерца) именно снижение глутаматергической активности (снижение δ-, рост α- и β1- и β2-ритмов) у пациентов с тяжелой ЧМТ приводит к повышению уровня сознания. Это сочеталось с ростом мощности низкочастотного спектра вариабельности сердечного ритма, что отражало значимую активацию стрессреализующих механизмов адаптации. Снижение глутаматергической активности с помощью амантадина (ПК-Мерца) сопровождалось активацией холинергической активности и умеренной активацией дофаминергической активности, преимущественно в проекции стволовых структур, что способствовало восстановлению уровня сознания. Уже на 3-и сутки терапии шанс восстановления сознания на 5 и более баллов по ШКГ был выше в группе, где применяли дополнительно к стандартному протоколу лечения амантадин (ПК-Мерц).У больных установлено резкое ослабление межполушарного взаимодействия большинства когерентных связей в основных частотных диапазонах электроэнцефалограммы (ЭЭГ), отражающее степень торможения коры головного мозга. В динамике терапии с применением амантадина происходит усиление межполушарных когерентных связей фоновой ЭЭГ, выход из тормозного состояния коры.При исследовании реактивности мозга в динамике терапии амантадином во второй группе исследования, в отличие от 1-й, отмечено статистически значимое (χ2, W-W, кКУ — p ≤ 0,05) снижение kfc-1 = = (δ + θ + β1)/(α + β2) на обеих половинах мозга, свидетельствующее об уменьшении дезорганизации ЭЭГ-паттерна более чем на 30 %.По данным транскраниальной допплерографии, на 7-е сутки интенсивной терапии при благоприятном течении заболевания отмечен достоверный (р ≤ 0,05, χ2; Т-W) рост скорости венозного оттока, симметричное снижение линейной скорости кровотока, уменьшение вазоконстрикции интракраниальных сосудов практически до нормальных значений в обеих группах больных без четкой разницы.Выводы. Уже на 3-и сутки терапии шанс восстановления сознания на 5 и более баллов по ШКГ был выше в группе, в которой применяли дополнительно к стандартному протоколу лечения амантадин ­(ПК-Мерц) (ОR ± 95% ДИ = 6,5 (1,8–23,2) при S = 0,649).Риск летального исхода на 7-е сутки был выше в группе, в которой использовали только стандартный комплекс лечения по протоколу (RR ± 95% ДИ = 0,273 (0,084–0,881) при S = 0,598).Применение амантадина (ПК-Мерца) в острейшем периоде тяжелой ЧМТ обусловливало статистически значимое снижение риска смерти (р = 0,050).

It wasn’t me! Motor activation from irrelevant spatial information in the absence of a response

Embodied cognition postulates that perceptual and motor processes serve higher-order cognitive faculties like language. A major challenge for embodied cognition concerns the grounding of abstract concepts. Here we zoom in on abstract spatial concepts and ask the question to what extent the sensorimotor system is involved in processing these. Most of the empirical support in favor of an embodied perspective on (abstract) spatial information has derived from so-called compatibility effects in which a task-irrelevant feature either facilitates (for compatible trials) or hinders (in incompatible trials) responding to the task-relevant feature. This type of effect has been interpreted in terms of (task-irrelevant) feature-induced response activation. The problem with such approach is that incompatible features generate an array of task-relevant and –irrelevant activations [e.g., in primary motor cortex (M1)], and lateral hemispheric interactions render it difficult to assign credit to the task-irrelevant feature per se in driving these activations. Here, we aim to obtain a cleaner indication of response activation on the basis of abstract spatial information. We employed transcranial magnetic stimulation (TMS) to probe response activation of effectors in response to semantic, task-irrelevant stimuli (i.e., the words left and right) that did not require an overt response. Results revealed larger motor evoked potentials (MEPs) for the right (left) index finger when the word right (left) was presented. Our findings provide support for the grounding of abstract spatial concepts in the sensorimotor system.

МНОГОПАРАМЕТРИЧЕСКИЙ АНАЛИЗ ЭЭГ У ПАЦИЕНТОВ С ПРАВОСТОРОННЕЙ ЛОКАЛИЗАЦИЕЙ ЭПИЛЕПТИЧЕСКОГО ОЧАГА

The article considers the peculiarities of the spatial organization of brain potentials in epileptic patients with a lesion in the right hemisphere. We identified violations of the spatial organization of brain potentials, which allow you to objectify violations of structural-functional relationships in epileptic patients with a lesion in the right hemisphere with the formation of multilevel pathological neural networks involving intact neural populations. Specific changes of hemispheric interactions characterized by a significant decrease in average levels of coherence in the occipital, parietal and anterio temporal areas in most frequency bands. The obtained data allow to suppose the specificity of the changes in alpha activity, characterized by the reciprocity of changes in the alpha rhythm in the range of 9-10 and 11-12 number`s.

Hemispheric bases for emotion and memory.

Hemispheric bases for emotion and memory.

List constituency and orthographic and phonological processing: A shift to high familiarity words from low familiarity words

Two lexical decision experiments build on established patterns of laterality and hemispheric interaction to test whether the presence of low familiarity words dynamically affects the use of an orthographic or phonological strategy for high familiarity words; and, if so, whether the hemispheres are similarly flexible in adapting to the constituency change. Experiment 1 restricted word strings to the highly familiar. Experiment 2 presented the same high familiarity words, along with an equal number of low familiarity words. Targets for lexical decision were presented at fixation to approximate normal viewing behaviour, either with or without a non-lexical distractor lateralized left visual field (LVF) or right visual field (RVF). Response time and accuracy were measured. Responses were faster in Experiment 1 than Experiment 2 to high familiarity words, pseudowords (orthographically correct), and non-words (orthographically incorrect), suggesting that a different strategy was used. A main effect of distractor location in Experiment 1 was due to more accurate responses to letter strings accompanied by a RVF distractor than no distractor, revealing a cost from hemispheric interaction compared to the right hemisphere when a task is simple. Experiment 2 found an interaction between distractor location and string type in both the response time and accuracy data. Separate analyses of word strings revealed a shift to a left hemisphere advantage: Accuracy to low familiarity words and speed to high familiarity words was better when accompanied by a LVF than a RVF distractor. Critical to a dynamic effect of list constituency is that the right hemisphere slowed to the same high familiarity words that had provoked speedier responses in Experiment 1. The findings are consistent with the use of an orthographic strategy in Experiment 1 and a phonological strategy in Experiment 2, and support the idea that right hemisphere access to familiar phonology is slower than the left hemisphere. Taken together, the findings suggest that the strategy used by both hemispheres is flexible, that both adapt to list constituency by adopting a strategy that is optimal for the task as a whole, and that there are different timelines of phonological activation in the two cerebral hemispheres.

Functional specialization in the human brain estimated by intrinsic hemispheric interaction.

The human brain demonstrates functional specialization, including strong hemispheric asymmetries. Here specialization was explored using fMRI by examining the degree to which brain networks preferentially interact with ipsilateral as opposed to contralateral networks. Preferential within-hemisphere interaction was prominent in the heteromodal association cortices and minimal in the sensorimotor cortices. The frontoparietal control network exhibited strong within-hemisphere interactions but with distinct patterns in each hemisphere. The frontoparietal control network preferentially coupled to the default network and language-related regions in the left hemisphere but to attention networks in the right hemisphere. This arrangement may facilitate control of processing functions that are lateralized. Moreover, the regions most linked to asymmetric specialization also display the highest degree of evolutionary cortical expansion. Functional specialization that emphasizes processing within a hemisphere may allow the expanded hominin brain to minimize between-hemisphere connectivity and distribute domain-specific processing functions.

Rigidity, chaos and integration: hemispheric interaction and individual differences in metaphor comprehension.

Neurotypical individuals cope flexibly with the full range of semantic relations expressed in human language, including metaphoric relations. This impressive semantic ability may be associated with distinct and flexible patterns of hemispheric interaction, including higher right hemisphere (RH) involvement for processing novel metaphors. However, this ability may be impaired in specific clinical conditions, such as Asperger syndrome (AS) and schizophrenia. The impaired semantic processing is accompanied by different patterns of hemispheric interaction during semantic processing, showing either reduced (in Asperger syndrome) or excessive (in schizophrenia) RH involvement. This paper interprets these individual differences using the terms Rigidity, Chaos and Integration, which describe patterns of semantic memory network states that either lead to semantic well-being or are disruptive of it. We argue that these semantic network states lie on a rigidity-chaos semantic continuum. We define these terms via network science terminology and provide network, cognitive and neural evidence to support our claim. This continuum includes left hemisphere (LH) hyper-rigid semantic memory state on one end (e.g., in persons with AS), and RH chaotic and over-flexible semantic memory state on the other end (e.g., in persons with schizophrenia). In between these two extremes lie different states of semantic memory structure which are related to individual differences in semantic creativity. We suggest that efficient semantic processing is achieved by semantic integration, a balance between semantic rigidity and semantic chaos. Such integration is achieved via intra-hemispheric communication. However, impairments to this well-balanced and integrated pattern of hemispheric interaction, e.g., when one hemisphere dominates the other, may lead to either semantic rigidity or semantic chaos, moving away from semantic integration and thus impairing the processing of metaphoric language.

Causal evidence supporting functional dissociation of verbal and spatial working memory in the human dorsolateral prefrontal cortex

The human dorsolateral prefrontal cortex (dlPFC) is crucial for monitoring and manipulating information in working memory, but whether such contributions are domain-specific remains unsettled. Neuroimaging studies have shown bilateral dlPFC activity associated with working memory independent of the stimulus domain, but the causality of this relationship cannot be inferred. Repetitive transcranial magnetic stimulation (rTMS) has the potential to test whether the left and right dlPFC contribute equally to verbal and spatial domains; however, this is the first study to investigate the interaction of task domain and hemisphere using offline rTMS to temporarily modulate dlPFC activity. In separate sessions, 20 healthy right-handed adults received 1Hz rTMS to the left dlPFC and right dlPFC, plus the vertex as a control site. The working memory performance was assessed pre-rTMS and post-rTMS using both verbal-'letter' and spatial-'location' versions of the 3-back task. The response times were faster post-rTMS, independent of the task domain or stimulation condition, indicating the influence of practice or other nonspecific effects. For accuracy, rTMS of the right dlPFC, but not the left dlPFC or vertex, led to a transient dissociation, reducing spatial, but increasing verbal accuracy. A post-hoc correlation analysis found no relationship between these changes, indicating that the substrates underlying the verbal and spatial domains are functionally independent. Collapsing across time, there was a trend towards a double dissociation, suggesting a potential laterality in the functional organisation of verbal and spatial working memory. At a minimum, these findings provide human evidence for domain-specific contributions of the dlPFC to working memory and reinforce the potential of rTMS to ameliorate cognition.