Interhemispheric Transfer Of Information Research Articles

HEMAsNet: A Hemisphere Asymmetry Network Inspired by the Brain for Depression Recognition From Electroencephalogram Signals.

Depression is a prevalent mental disorder that affects a significant portion of the global population. Despite recent advancements in EEG-based depression recognition models rooted in machine learning and deep learning approaches, many lack comprehensive consideration of depression's pathogenesis, leading to limited neuroscientific interpretability. To address these issues, we propose a hemisphere asymmetry network (HEMAsNet) inspired by the brain for depression recognition from EEG signals. HEMAsNet employs a combination of multi-scale Convolutional Neural Network (CNN) and Long Short-Term Memory (LSTM) blocks to extract temporal features from both hemispheres of the brain. Moreover, the model introduces a unique 'Callosum-like' block, inspired by the corpus callosum's pivotal role in facilitating inter-hemispheric information transfer within the brain. This block enhances information exchange between hemispheres, potentially improving depression recognition accuracy. To validate the performance of HEMAsNet, we first confirmed the asymmetric features of frontal lobe EEG in the MODMA dataset. Subsequently, our method achieved a depression recognition accuracy of 0.8067, indicating its effectiveness in increasing classification performance. Furthermore, we conducted a comprehensive investigation from spatial and frequency perspectives, demonstrating HEMAsNet's innovation in explaining model decisions. The advantages of HEMAsNet lie in its ability to achieve more accurate and interpretable recognition of depression through the simulation of physiological processes, integration of spatial information, and incorporation of the Callosum-like block.

Interhemispheric transfer time correlates with white matter integrity of the corpus callosum in healthy older adults

The corpus callosum (CC) has been identified as an important structure in the context of cognitive aging (Fling et al., 2011). Interhemispheric transfer time (IHTT) is regularly used in order to estimate interhemispheric integration enabled by the CC (Marzi, 2010; Nowicka and Tacikowski, 2011). However, only little is known with regards to the relationship between IHTT and the structural properties of the CC with only few studies with specific samples and methods available (Whitford et al., 2011). Thus, the present study aimed at investigating this relationship applying an event-related potentials (ERP) based approach of estimating IHTT as well as diffusion weighted imaging (DWI) with fractional anisotropy (FA) as an indicator of white matter integrity (WMI) of the genu, corpus and splenium of the CC. 56 healthy older adults performed a Dimond Task while ERPs were recorded and underwent DWI scanning. IHTT derived from posterior electrode sites correlated significantly with FA of the splenium (r = −0.286*, p = .03) but not the corpus (r = −0.187, p = .08) or genu (r = −0.189, p = .18). The present results support the notion that IHTT is related to WMI of the posterior CC. It may be concluded that ERP based IHTT is a suitable indicator of CC structure and function, however, likely specific to the interhemispheric transfer of visual information. Future studies may wish to confirm these findings in a more divers sample further exploring the precise interrelation between IHTT and structural or functional properties of the CC.

Visual integration across fixation: automatic processes are split but conscious processes remain unified in the split-brain.

The classic view holds that when "split-brain" patients are presented with an object in the right visual field, they will correctly identify it verbally and with the right hand. However, when the object is presented in the left visual field, the patient verbally states that he saw nothing but nevertheless identifies it accurately with the left hand. This interaction suggests that perception, recognition and responding are separated in the two isolated hemispheres. However, there is now accumulating evidence that this interaction is not absolute; for instance, split-brain patients are able to detect and localise stimuli anywhere in the visual field verbally and with either hand. In this study we set out to explore this cross-hemifield interaction in more detail with the split-brain patient DDC and carried out two experiments. The aim of these experiments is to unveil the unity of deliberate and automatic processing in the context of visual integration across hemispheres. Experiment 1 suggests that automatic processing is split in this context. In contrast, when the patient is forced to adopt a conscious, deliberate, approach, processing seemed to be unified across visual fields (and thus across hemispheres). First, we looked at the confidence that DDC has in his responses. The experiment involved a simultaneous "same" versus "different" matching task with two shapes presented either within one hemifield or across fixation. The results showed that we replicated the observation that split brain patients cannot match across fixation, but more interesting, that DDC was very confident in the across-fixation condition while performing at chance-level. On the basis of this result, we hypothesised a two-route explanation. In healthy subjects, the visual information from the two hemifields is integrated in an automatic, unconscious fashion via the intact splenium, and this route has been severed in DDC. However, we know from previous experiments that some transfer of information remains possible. We proposed that this second route (perhaps less visual; more symbolic) may become apparent when he is forced to use a deliberate, consciously controlled approach. In an experiment where he is informed, by a second stimulus presented in one hemifield, what to do with the first stimulus that was presented in the same or the opposite hemifield, we showed that there was indeed interhemispheric transfer of information. We suggest that this two-route model may help in clarifying some of the controversial issues in split-brain research.

Unlocking the symmetric transfer of irrelevant information: gene-environment interplay and enhanced interhemispheric cross-talk.

Hemispheric specialization influences stimulus processing and behavioural control, affecting responses to relevant stimuli. However, most sensory input is irrelevant and must be filtered out to prevent interference with task-relevant behaviour, a process known as habituation. Despite habituation's vital role, little is known about hemispheric specialization for this brain function. We conducted an experiment with domestic chicks, an elite animal model to study lateralization. They were exposed to distracting visual stimuli while feeding when using binocular or monocular vision. Switching the viewing eye after habituation, we examined if habituation was confined to the stimulated hemisphere or shared across hemispheres. We found that both hemispheres learned equally to ignore distracting stimuli. However, embryonic light stimulation, influencing hemispheric specialization, revealed an asymmetry in interhemispheric transfer of the irrelevant information discarded via habituation. Unstimulated chicks exhibited a directional bias, with the right hemisphere failing to transfer distracting stimulus information to the left hemisphere, while transfer from left to right was possible. Nevertheless, embryonic light stimulation counteracted this asymmetry, enhancing communication from the right to the left hemisphere and reducing the pre-existing imbalance. This sharing extends beyond hemisphere-specific functions and encompasses a broader representation of irrelevant events.

Development and Standardization of Low-Verbal Material for Assessment of Central Auditory Processing in Arabic Language

Development and Standardization of Low-Verbal Material for Assessment of Central Auditory Processing in Arabic Language

Interhemispheric transfer of visual information: Meaningfulness and response formation

We examined whether Redundancy Gain (RG) can be dissociated from the response stage of a go/nogo paradigm, and whether the meaningfulness of a stimulus modulates the stage at which interhemispheric transfer occurs. Experiment 1 used a lateralized match-to-category paradigm, taken from categories with varying meaningfulness. Experiment 2 presented a novel design, which separates the perceptual stage from response formation, in examination of RG. A sequence of two stimuli was presented. Participants responded by matching the category of the second stimulus to that of the first. The redundant stimulus could appear at the first or the second stage, thus redundancy gain could be separated from the response. Experiment 1 revealed that redundancy gain occurs earlier in the process of stimulus identification for highly meaningful stimuli than for less meaningful stimuli. The results of Experiment 2 support the hypothesis that redundancy gain results from interhemispheric integration of perceptual information, rather than response-formation. Results from both experiments suggest that redundancy gain arises from interhemispheric integration in the perceptual stage, and the efficiency of this integration depends on the meaningfulness of the stimulus. These results are relevant to current hypotheses about the physiological mechanisms underlying RG.

A single dose of hydrocortisone does not alter interhemispheric transfer of information or transcallosal integration.

Stress has been suggested as a factor that may explain the link between altered functional lateralization and psychopathology. Modulation of the function of the corpus callosum via stress hormones may be crucial in this regard. Interestingly, there is evidence that interhemispheric integration and hemispheric asymmetries are modifiable by endocrinological influences. In previous studies, our group could show an enhancing effect of acute stress on interhemispheric integration. To investigate if this effect can be attributed to an increase in the stress hormone cortisol, 50 male participants received 20 mg hydrocortisone or a placebo in a double-blind crossover design. In each test session, we collected EEG data while participants completed a lexical decision task and a Poffenberger paradigm. In the lexical decision task, we found shorter latencies of the N1 ERP component for contralateral compared to ipsilateral presentation of lexical stimuli. Similarly, we replicated the classical Poffenberger effect with shorter ERP latencies for stimuli presented in the contralateral visual field compared to the ipsilateral visual field. However, no effect of cortisol on latency differences between hemispheres could be detected. These results suggest that a temporary increase in cortisol alone might not be enough to affect the interhemispheric transfer of information via the corpus callosum. Together with previous results from our group, this suggests that chronically elevated stress hormone levels play a more central role in the relationship between altered hemispheric asymmetries and a variety of mental disorders.

Hemispheric functional segregation facilitates target detection during sustained visuospatial attention.

Visuospatial attention is strongly lateralized, with the right hemisphere commonly exhibiting stronger activation and connectivity patterns than the left hemisphere during attentive processes. However, whether such asymmetry influences inter‐hemispheric information transfer and behavioral performance is not known. Here we used a region of interest (ROI) and network‐based approach to determine steady‐state fMRI functional connectivity (FC) in the whole cerebral cortex during a leftward/rightward covert visuospatial attention task. We found that the global FC topology between either ROIs or networks was independent on the attended side. The side of attention significantly modulated FC strength between brain networks, with leftward attention primarily involving the connections of the right visual network with dorsal and ventral attention networks in both the left and right hemisphere. High hemispheric functional segregation significantly correlated with faster target detection response times (i.e., better performance). Our findings suggest that the dominance of the right hemisphere in visuospatial attention is associated with an hemispheric functional segregation that is beneficial for behavioral performance.

Compromised interhemispheric transfer of information partially mediates cognitive function deficits in adolescents with fetal alcohol syndrome.

Prenatal alcohol exposure (PAE) has been associated with compromised interhemispheric transfer of tactile stimuli in childhood and structural changes to the corpus callosum (CC). In this study, we used a finger localization task (FLT) to investigate whether interhemispheric transfer deficits persist in adolescence; whether effects of PAE on perceptual reasoning, working memory, and executive function are mediated by deficits in interhemispheric transfer of information; and whether CC size in childhood predicts FLT performance in adolescence. Participants, aged 16 to 17years, were from the Cape Town Longitudinal Cohort, whose mothers were recruited during pregnancy and interviewed regarding their alcohol use using the timeline follow-back method. Diagnoses of fetal alcohol syndrome (FAS) and partial FAS (PFAS) were determined by two expert dysmorphologists; nonsyndromal exposed children were designated as heavily exposed (HE); those born to abstainers or light drinkers, as controls. The FLT was administered to 74 participants (12 FAS, 16 PFAS, 14 HE and 32 controls). CC size at age 9 to 12years was available for 35 participants (7 FAS, 13 PFAS, 5 HE and 10 control). Although the degree of PAE was similar in the FAS, PFAS, and HE groups, only the adolescents with FAS showed more transfer-related errors than controls in conditions in which one finger was stimulated. FLT performance mediated the effects of FAS on perceptual reasoning and executive function. In the subsample for which neuroimaging data from childhood were available, there was an association among adolescents with PAE of smaller CC volumes with more transfer-related errors on the one-finger/hand hidden condition, suggesting that CC damage previously seen in childhood continues to impact function through adolescence. This study provides evidence of compromised interhemispheric transfer of information in adolescents with FAS, while those with PFAS or heavy exposed nonsyndromal individuals are apparently spared. It is the first to show that PAE effects on important aspects of cognitive function are partially mediated by deficits in the interhemispheric transfer of information.

Distinguishing transient from persistent tactile agnosia after partial anterior circulation infarcts – Behavioral and neuroimaging evidence for white matter disconnection

From a cohort of 36 patients presenting apperceptive tactile agnosia after first cortical ischemic stroke, 14 showed temporary impairment at admission. A previous multi-voxel analysis of the cortical lesions, using as explanatory variable the course of tactile object recognition performance over the recovery period of 9 months, partitioned the cohort into three subgroups. Of the 14 patients constituting two of the subgroups, 7 recovered from their impairment whereas 7 did not. These two subgroups could not be distinguished at admission. The primary aim of the present study is to present two assessments that can do so.The first assessment comprises a pattern of behavioral measures, determined via principal component analysis, encoded in three tests: picking small objects, macrogeometrical discrimination and tactile object recognition. The receiver operating characteristic curve derived from permutation of the behavioral test scores yielded an 80% probability of correct identification of the patient subgroup and an 8% probability for false identification. As done with the permuted scores, the pattern could predict the persistence of affliction of new stroke patients with tactile agnosia.The second predictive assessment extends our previous evaluation of cortical MRI lesion maps to include subcortical regions. Confirming our previous study, the lesions of the persistently impaired subgroup disrupted significantly the anterior arcuatus fasciculus and associated superior longitudinal fasciculus III in the ipsilesional hemisphere, impeding reciprocal information transfer between supramarginal gyrus and both the ventral premotor cortex and Brodmann area 44. Due to the importance of interhemispheric information transfer in tactile agnosia, we performed a supplementary analysis of tactile object recognition scores. It showed that haptic information transfer from the non-affected to the affected hands in the persistent cases partly restored function during the nine months, possibly following restoration of functional interhemispheric haptic information transfer at the border of posterior corpus callosum and splenium.In conclusion, the combined findings of the cortical lesion at subarea PFt of the inferior parietal lobule and the associated subcortical tract lesions permit almost perfect prediction of persistent impairment of tactile object recognition. The study substantiates the need for combined analysis of both cortical lesions and white matter tract disconnections.

Neurobiology of Neuronal Network Alteration in Intellectual Disability Related to Fetal Alcohol Spectrum Disorders

The molecular and cellular mechanisms by which alcohol produces its deleterious effects on neuronal networks are only now beginning to be understood. This review focused on alcohol-induced neurobiological alterations on neuronal network components underlying information processing, for further understanding of intellectual disability related to FASD. Abnormal neurodevelopmental events related to alcohol-damaged fetal brain included neurogenesis inhibition, aberrant migration, impaired differentiation, exacerbated apoptosis, impaired axon outgrowth and branching altering synaptogenesis and synaptic plasticity, abnormal GABAergic interneurons triggering synaptic inhibitory/excitatory imbalance, reduced myelinogenesis causing injured white matter in prefrontal lobe and atrophied corpus callosum compromising interhemispheric information transfer, the whole compromising neuronal network scaffolding which may lead to biased information processing with deficits in executive function. What added to these abnormalities are smaller gray matter and reduced hippocampus, resulting in cognition and memory failures. As a whole, these developmental disorders may underlie intellectual disability related to FASD. In rodents, these neuronal network components matured mainly during the second and third trimesters equivalents of human gestation. Transferability of results from animal to human was also discussed. It was hoped that the understanding of alcohol-induced neuronal networks failure mechanisms during the developing brain may lay a foundation for prospective new treatments and interventions.

Callosal Transfer Test Performance in Patient with Multiple Sclerosis: A Case Report

Patient (P) female, 23, consistent right-hander was diagnosed as having multiple sclerosis at the onset of clinical symptoms (loss of sensation in the left limb and left part of the face). MRI revealed demyelination in cerebellar region, intratentorial white matter and tissue adjacent to the fourth ventricle, as well as demyelinated plagues localized in the rostrum, truncus and splenium of corpus callosum. One year after, aggravation of clinical symptoms (loss of sensation in the right limb and in the right part of the face, difficulty in holding as well as recognizing things, discoordination of movements and occasional diplopia) was registered. Patient was tested on callosal interhemispheric transfer of information after the spontaneous resolve of most of symptoms. At that period, patient experienced paresthesia in the upper limb when bending the neck. Tests on finger cross- localization, crossmatching of objects, drawing to dictation, simultaneous drawing with both hands, reading words perceived by “non-verbal” right hemisphere and line bisection were administered. Patient was found successful in performing all tests on interhemispheric transfer of information, suggesting the callosal system of study participant efficient in interhemispheric communication.

Connectivity-Based Topographical Changes of the Corpus Callosum During Aging.

Background: The corpus callosum (CC) is the most prominent white matter connection for interhemispheric information transfer. It is implicated in a variety of cognitive functions, which tend to decline with age. The region-specific projections of the fiber bundles with microstructural heterogeneity of the CC are associated with cognitive functions and diseases. However, how the CC is associated with the information transfer within functional networks and the connectivity changes during aging remain unclear. Studying the CC topography helps to understand the functional specialization and age-related changes of CC subregions.Methods: Diffusion tractography was used to subdivide the CC into seven subregions from 1,086 healthy volunteers within a wide age range (21–90 years), based on the connections to the cortical parcellations of the functional networks. Quantitative diffusion indices and connection probability were calculated to study the microstructure differences and age-related changes in the CC subregions.Results: According to the population-based probabilistic topography of the CC, part of the default mode network (DMN) and limbic network (LN) projected fibers through the genu and rostrum; the frontoparietal network (FPN), ventral attention network (VA) and somatomotor networks (SM) were interconnected by the CC body; callosal fibers arising from the part of the default mode network (DMN), dorsal attention network (DA) and visual network (VIS) passed through the splenium. Anterior CC subregions interconnecting DMN, LN, FPN, VA, and SM showed lower fractional anisotropy (FA) and higher mean diffusivity (MD) and radial diffusivity (RD) than posterior CC subregions interconnecting DA and VIS. All the CC subregions showed slightly increasing FA and decreasing MD, RD, and axial diffusivity (AD) at younger ages and opposite trends at older ages. Besides, the anterior CC subregions exhibited larger microstructural and connectivity changes compared with the posterior CC subregions during aging.Conclusion: This study revealed the callosal subregions related to functional networks and uncovered an overall “anterior-to-posterior” region-specific changing trend during aging, which provides a baseline to identify the presence and timing of callosal connection states.

Morphology and Morphometry of Foetal Corpus Callosum Using MRI – A Retrospective Study

Introduction: Corpus callosum (CC) is the largest commissural white fibres interconnecting cerebral hemispheres. The corpus callosum is responsible for interhemispheric transfer of information which is essential for cognitive function. The foetal corpus callosum serves as sensitive indicator for normal brain development and maturation. As the corpus callosum is a part of the highest order latest maturing mental network of the brain, its measurements are important to assess normal brain development and to locate structural changes. A comprehensive evaluation of normal human foetal corpus callosal development is essential to detect and understand the congenital anomalies of the brain. Thus, the prenatal diagnosis of partial or complete agenesis of the corpus callosum is important for predicting the normal development of the foetus. Foetal neural anomalies that are suspected on prenatal ultrasonography (USG) can be detected in early stage using foetal MRI. This imaging technique is highly useful for detailed visualization of normal neural development. Certain conditions like colpocephaly and widening of interhemispheric fissure can be clearly visualized using foetal MRI when compared to prenatal ultrasonography. Aim and objective: Was to establish the normal reference values for the measurement of foetal corpus callosum. The length and thickness of the foetal CC was measured corresponding to gestational age (GA) between 18-36weeks. Materials and methods: A retrospective MRI study was carried out in Radiology department of Sri Ramachandra Hospital. The study was conducted on 50 pregnant women with GA of 18-32 weeks and morphology of foetal corpus callosum was measured using MRI. The corpus callosum was visualized in a mid-sagittal plane as an anechoic structure, delimited by two echogenic lines superiorly by sulcus of the corpus callosum and inferiorly by the septum pellucidum. The length of corpus callosum was measured from the anterior most aspect of genu to the posterior most aspect of the splenium and the width of individual parts were measured and correlated with gestational age. The values obtained from the study were statistically calculated using regression coefficient method. Results: In the present study following parameters were observed such as length and width of diverse parts of Corpus callosum. The length of foetal CC ranged from 25.96 to 47.2 mm in 18 to 32 weeks of gestational age. The range of width of rostrum, genu, body and splenium were 1.2 to 2.2 mm, 1.2-2.8mm, 1.3-3.1mm and 1.36-3.2mm respectively. Conclusion: The periodic development of nervous system can be calculated more effectively with the morphometric measurement of foetal CC and its correlation with BPD. It is considered to be accurate than using BPD measurement of head circumference in USG. Hence, with the normative data of foetal CC measurements correlated with gestational age would give us accurate details of neuronal growth rather than measuring biparietal diameter (BPD) alone using USG. This knowledge will be highly helpful for the gynaecologists to predict the abnormal development of the foetus and it is advised to include foetal CC parameters as a one of the tools for early detection of CNS anomalies.

Interlimb Transfer of Reach Adaptation Does Not Require an Intact Corpus Callosum: Evidence from Patients with Callosal Lesions and Agenesis.

Generalization of sensorimotor adaptation across limbs, known as interlimb transfer, is a well-demonstrated phenomenon in humans, yet the underlying neural mechanisms remain unclear. Theoretical models suggest that interlimb transfer is mediated by interhemispheric transfer of information via the corpus callosum. We thus hypothesized that lesions of the corpus callosum, especially to its midbody connecting motor, supplementary motor, and premotor areas of the two cerebral hemispheres, would impair interlimb transfer of sensorimotor adaptation. To test this hypothesis, we recruited three patients: two rare stroke patients with recent, extensive callosal lesions including the midbody and one patient with complete agenesis. A prismatic adaptation paradigm involving unconstrained arm reaching movements was designed to assess interlimb transfer from the prism-exposed dominant arm (DA) to the unexposed non-dominant arm (NDA) for each participant. Baseline results showed that spatial performance of each patient did not significantly differ from controls, for both limbs. Further, each patient adapted to the prismatic perturbation, with no significant difference in error reduction compared with controls. Crucially, interlimb transfer was found in each patient. The absolute magnitude of each patient’s transfer did not significantly differ from controls. These findings show that sensorimotor adaptation can transfer across limbs despite extensive lesions or complete absence of the corpus callosum. Therefore, callosal pathways connecting homologous motor, premotor, and supplementary motor areas are not necessary for interlimb transfer of prismatic reach adaptation. Such interlimb transfer could be mediated by transcallosal splenium pathways (connecting parietal, temporal and visual areas), ipsilateral cortico-spinal pathways or subcortical structures such as the cerebellum.

Stroke-related alterations in inter-areal communication

Beyond causing local ischemia and cell damage at the site of injury, stroke strongly affects long-range anatomical connections, perturbing the functional organization of brain networks. Several studies reported functional connectivity abnormalities parallelling both behavioral deficits and functional recovery across different cognitive domains. FC alterations suggest that long-range communication in the brain is altered after stroke. However, standard FC analyses cannot reveal the directionality and time scale of inter-areal information transfer. We used resting-state fMRI and covariance-based Granger causality analysis to quantify network-level information transfer and its alteration in stroke. Two main large-scale anomalies were observed in stroke patients. First, inter-hemispheric information transfer was significantly decreased with respect to healthy controls. Second, stroke caused inter-hemispheric asymmetries, as information transfer within the affected hemisphere and from the affected to the intact hemisphere was significantly reduced. Both anomalies were more prominent in resting-state networks related to attention and language, and they correlated with impaired performance in several behavioral domains. Overall, our findings support the hypothesis that stroke provokes asymmetries between the affected and spared hemisphere, with different functional consequences depending on which hemisphere is lesioned.

A microstructural neural network biomarker for dystonia diagnosis identified by a DystoniaNet deep learning platform

Isolated dystonia is a neurological disorder of heterogeneous pathophysiology, which causes involuntary muscle contractions leading to abnormal movements and postures. Its diagnosis is remarkably challenging due to the absence of a biomarker or gold standard diagnostic test. This leads to a low agreement between clinicians, with up to 50% of cases being misdiagnosed and diagnostic delays extending up to 10.1 y. We developed a deep learning algorithmic platform, DystoniaNet, to automatically identify and validate a microstructural neural network biomarker for dystonia diagnosis from raw structural brain MRIs of 612 subjects, including 392 patients with three different forms of isolated focal dystonia and 220 healthy controls. DystoniaNet identified clusters in corpus callosum, anterior and posterior thalamic radiations, inferior fronto-occipital fasciculus, and inferior temporal and superior orbital gyri as the biomarker components. These regions are known to contribute to abnormal interhemispheric information transfer, heteromodal sensorimotor processing, and executive control of motor commands in dystonia pathophysiology. The DystoniaNet-based biomarker showed an overall accuracy of 98.8% in diagnosing dystonia, with a referral of 3.5% of cases due to diagnostic uncertainty. The diagnostic decision by DystoniaNet was computed in 0.36 s per subject. DystoniaNet significantly outperformed shallow machine-learning algorithms in benchmark comparisons, showing nearly a 20% increase in its diagnostic performance. Importantly, the microstructural neural network biomarker and its DystoniaNet platform showed substantial improvement over the current 34% agreement on dystonia diagnosis between clinicians. The translational potential of this biomarker is in its highly accurate, interpretable, and generalizable performance for enhanced clinical decision-making.

Music Playing and Interhemispheric Communication: Older Professional Musicians Outperform Age-Matched Non-Musicians in Fingertip Cross-Localization Test.

Numerous investigations have documented that age-related changes in the integrity of the corpus callosum are associated with age-related decline in the interhemispheric transfer of information. Conversely, there is accumulating evidence for more efficient white matter organization of the corpus callosum in individuals with extensive musical training. However, the relationship between making music and accuracy in interhemispheric transfer remains poorly explored. To test the hypothesis that musicians show enhanced functional connectivity between the two hemispheres, 65 professional musicians (aged 56-90 years) and 65 age- and sex-matched non-musicians performed the fingertip cross-localization test. In this task, subjects must respond to a tactile stimulus presented to one hand using the ipsilateral (intra-hemispheric test) or contralateral (inter-hemispheric test) hand. Because the transfer of information from one hemisphere to another may imply a loss of accuracy, the value of the difference between the intrahemispheric and interhemispheric tests can be utilized as a reliable measure of the effectiveness of hemispheric interactions. Older professional musicians show significantly greater accuracy in tactile interhemispheric transfer than non-musicians who suffer from age-related decline. Musicians have more efficient interhemispheric communication than age-matched non-musicians. This finding is in keeping with studies showing that individuals with extensive musical training have a larger corpus callosum. The results are discussed in relation to relevant data suggesting that music positively influences aging brain plasticity.

Light‐dependent development of the tectorotundal projection in pigeons

Left-right differences in the structural and functional organization of the brain are widespread in the animal kingdom and develop in close gene-environment interactions. The visual system of birds like chicks and pigeons exemplifies how sensory experience shapes lateralized visual processing. Owing to an asymmetrical posture of the embryo in the egg, the right eye/ left brain side is more strongly light-stimulated what triggers asymmetrical differentiation processes leading to a left-hemispheric dominance for visuomotor control. In pigeons (Columba livia), a critical neuroanatomical element is the asymmetrically organized tectofugal pathway. Here, more fibres cross from the right tectum to the left rotundus than vice versa. In the current study, we tested whether the emergence of this projection asymmetry depends on embryonic light stimulation by tracing tectorotundal neurons in pigeons with and without lateralized embryonic light experience. The quantitative tracing pattern confirmed higher bilateral innervation of the left rotundus in light-exposed and thus, asymmetrically light-stimulated pigeons. This was the same in light-deprived pigeons. Here, however, also the right rotundus received an equally strong bilateral input. This suggests that embryonic light stimulation does not increase bilateral tectal innervation of the stronger stimulated left but rather decreases such an input pattern to the right brain side. Combined with a morphometric analysis, our data indicate that embryonic photic stimulation specifically affects differentiation of the contralateral cell population. Differential modification of ipsi- and contralateral tectorotundal connections could have important impact on the regulation of intra- and interhemispheric information transfer and ultimately on hemispheric dominance pattern during visual processing.

Transcallosal approach for intraventricular gliomas: neuropsychological outcome and functionality of the corpus callosum.

The transcallosal approach is commonly used for surgery of lateral and third ventricle lesions. Cognitive deficits due to the transcallosal approach still remain controversial. Even if enormous efforts have been made in order to understand specific functions of the corpus callosum, still little is known. The present study was aimed to evaluate the neuropsychological results and the functionality of the corpus callosum in transferring visual, auditory and tactile information between the two hemispheres in a group of patients who were treated using the transcallosal approach. The study evaluated the neuropsychological status of five selected patients presenting low-grade lesions of lateral ventricles that had not previously undergone surgical treatments and that did not receive radiotherapy and chemotherapy. All patients were administered an extensive neuropsychological testing postoperatively and the interhemispheric transfer of visual, auditory and tactile information was also evaluated. Two patients were tested preoperatively. Incisions of 2.4 cm maximum of the corpus callosum length were operated. The postoperative cognitive profile was normal. In some patients, a postoperative subnormal performance in memory functions was found but it cannot be attributable to the surgical approach given that it was altered even pre-surgically. Small incisions of the corpus callosum preserved the integrity of this anatomical structure in transferring lateralized information between the two hemispheres. The transcallosal approach is a safe surgical route to lateral ventricles lesions and the neuropsychological evaluation of these cases could give new insights in the comprehension of corpus callosum functions.