• Cortical Reorganization
• Sensorimotor system
• Stroke

• R01 HD109157 NICHD NIH HHS

• Humans
• White Matter/physiopathology
• White Matter/diagnostic imaging
• White Matter/pathology
• Proprioception/physiology
• Male
• Female
• Middle Aged
• Stroke/physiopathology
• Stroke/complications
• Aged
• Adult
• Robotics

• Bilateral median nerve stimulation
• High-frequency oscillations
• Interhemispheric interactions
• Primary somatosensory cortex
• Somatosensory evoked potentials

• Humans
• Median Nerve/physiology
• Male
• Female
• Somatosensory Cortex/physiology
• Evoked Potentials, Somatosensory/physiology
• Adult
• Electric Stimulation/methods
• Neural Inhibition/physiology
• Young Adult
• Functional Laterality/physiology
• Electroencephalography/methods

• callosotomy
• functional connectivity
• interhemispheric connectivity
• lateralization
• resting-state

• corpus callosum
• diffusion tensor imaging
• infantile hydrocephalus
• macrostructure
• microstructural integrity

• Humans
• Corpus Callosum/diagnostic imaging
• Corpus Callosum/pathology
• Hydrocephalus/diagnostic imaging
• Hydrocephalus/pathology
• Male
• Female
• Diffusion Tensor Imaging/methods
• Child
• Magnetic Resonance Imaging/methods
• Child, Preschool
• Infant
• Image Processing, Computer-Assisted

• Academic Medical Organization of Southwestern Ontario
• Canada First Research Excellence Fund

• Callosotomy
• Corpus callosum
• Dichotic listening
• Laterality
• Selective attention
• Split brain

• Humans
• Dichotic Listening Tests
• Prohibitins
• Auditory Perception
• Attention
• Mental Recall
• Functional Laterality

• Callosotomized patients. interhemispheric transfer. brain imaging
• Corpus callosum
• Topographic organization

• EEG
• cortical reorganization
• hemiparetic stroke
• sensorimotor system
• somatosensory evoked potentials

• Interhemispheric inhibition
• musculoskeletal pain
• neuroplasticity
• primary sensory cortex
• sensorimotor function
• sensory evoked potentials

• Acute Pain
• Electromyography
• Evoked Potentials, Motor/physiology
• Functional Laterality/physiology
• Humans
• Motor Cortex
• Muscle, Skeletal
• Myalgia/chemically induced
• Neural Inhibition/physiology
• Transcranial Magnetic Stimulation

•

The functional characterization of callosal connections is informed by anatomical data.

The brain operates through the synaptic interaction of distant neurons within flexible, often heterogeneous, distributed systems. Histological studies have detailed the connections between distant neurons, but their functional characterization deserves further exploration. Studies performed on the corpus callosum in animals and humans are unique in that they capitalize on results obtained from several neuroscience disciplines. Such data inspire a new interpretation of the function of callosal connections and delineate a novel road map, thus paving the way toward a general theory of cortico-cortical connectivity. Here we suggest that callosal axons can drive their post-synaptic targets preferentially when coupled to other inputs endowing the cortical network with a high degree of conditionality. This might depend on several factors, such as their pattern of convergence-divergence, the excitatory and inhibitory operation mode, the range of conduction velocities, the variety of homotopic and heterotopic projections and, finally, the state-dependency of their firing. We propose that, in addition to direct stimulation of post-synaptic targets, callosal axons often play a conditional driving or modulatory role, which depends on task contingencies, as documented by several recent studies.

• Callosal axon diameter
• Callosal conduction velocity
• Callosal connections flexibility
• Callosal disconnection syndromes
• Callosal interhemispheric transfer
• Corpus callosum

• Corpus callosum
• Hemineglect
• Hemispheric asymmetry
• Laterality
• Spatial attention
• Split brain

• agency
• consciousness
• corpus callosum
• cross-cueing
• perception
• split-brain
• subcortical structures
• unity of consciousness

• Corpus Callosum
• Disconnection syndromes
• Haptics
• Interhemispheric transfer
• Stroke
• Tactile recognition

• Brain
• Corpus Callosum/diagnostic imaging
• Functional Laterality
• Humans
• Touch
• White Matter/diagnostic imaging

• I01 CX000254 CSRD VA
• R01 DC016345 NIDCD NIH HHS

• Aging
• Brain plasticity
• Connectivity
• Corpus callosum
• Musical training
• Neuroprotection

Due to anticipated postoperative neuropsychological sequelae, patients with gliomas infiltrating the corpus callosum rarely undergo tumor resection and mostly present in a poor neurological state. We aimed at investigating the benefit of glioma resection in the corpus callosum, hypothesizing neuropsychological deficits were mainly caused by tumor presence. Between 01/2017 and 1/2020, 21 patients who underwent glioma resection in the corpus callosum were prospectively enrolled into this study. Neuropsychological function was assessed preoperatively, before discharge and after 6 months. Gross total tumor resection was possible in 15 patients, and in 6 patients subtotal tumor resection with a tumor reduction of 97.7% could be achieved. During a median observation time of 12.6 months 9 patients died from glioblastoma after a median of 17 months. Preoperatively, all cognitive domains were affected in up to two thirds of patients, who presented a median KPS of 100% (range 60–100%). After surgery, the proportion of impaired patients increased in all neurocognitive domains. Most interestingly, after 6 months, significantly fewer patients showed impairments in attention, executive functioning, memory and depression, which are domains considered crucial for everyday functionality. Thus, the results of our study strongly support our hypothesis that in patients with gliomas infiltrating the corpus callosum the benefit of tumor resection might outweigh morbidity.

Recently, the discussion regarding the consequences of cutting the corpus callosum (“split-brain”) has regained momentum (Corballis, Corballis, Berlucchi, & Marzi, Brain, 141(6), e46, 2018; Pinto et al., Brain, 140(5), 1231–1237, 2017a; Pinto, Lamme, & de Haan, Brain, 140(11), e68, 2017; Volz & Gazzaniga, Brain, 140(7), 2051–2060, 2017; Volz, Hillyard, Miller, & Gazzaniga, Brain, 141(3), e15, 2018). This collective review paper aims to summarize the empirical common ground, to delineate the different interpretations, and to identify the remaining questions. In short, callosotomy leads to a broad breakdown of functional integration ranging from perception to attention. However, the breakdown is not absolute as several processes, such as action control, seem to remain unified. Disagreement exists about the responsible mechanisms for this remaining unity. The main issue concerns the first-person perspective of a split-brain patient. Does a split-brain harbor a split consciousness or is consciousness unified? The current consensus is that the body of evidence is insufficient to answer this question, and different suggestions are made with respect to how future studies might address this paucity. In addition, it is suggested that the answers might not be a simple yes or no but that intermediate conceptualizations need to be considered.

• Consciousness agents
• Epilepsy
• Lateralization
• Split-brain
• Visual perception

• Voice gender categorization
• gender bias
• hemispheric asymmetries
• split-brain patient
• temporal voice area (TVA)

• Consciousness
• Epilepsy
• Lateralisation
• Split-brain
• Tactile perception

• Corpus Callosum
• Functional Laterality
• Hand
• Humans
• Male
• Split-Brain Procedure
• Touch

The paradoxical absence of a split-brain syndrome in most cases of callosal dysgenesis has originated three main hypotheses, namely, (i) bilateral cortical representation of language, (ii) bilateral thalamocortical projections of somatosensory pathways conveyed by the spinothalamic-medial lemniscus system, and (iii) a variable combination of (i) and (ii). We used functional neuroimaging to investigate the cortical representation and lateralization of somatosensory information from the palm of each hand in six cases of callosal dysgenesis (hypothesis [ii]). Cortical regions of interest were contralateral and ipsilateral S1 (areas 3a and 3b, 1 and 2 in the central sulcus and postcentral gyrus) and S2 (parts of areas 40 and 43 in the parietal operculum). The degree of cortical asymmetry was expressed by a laterality index (LI), which may assume values from −1 (fully left-lateralized) to +1 (fully right-lateralized). In callosal dysgenesis, LI values for the right and the left hands were, respectively, −1 and + 1 for both S1 and S2, indicating absence of engagement of ipsilateral S1 and S2. In controls, LI values were − 0.70 (S1) and − 0.51 (S2) for right hand stimulation, and 0.82 (S1) and 0.36 (S2) for left hand stimulation, reflecting bilateral asymmetric activations, which were significantly higher in the hemisphere contralateral to the stimulated hand. Therefore, none of the main hypotheses so far entertained to account for the callosal dysgenesis-split-brain paradox have succeeded. We conclude that the preserved interhemispheric transfer of somatosensory tactile information in callosal dysgenesis must be mediated by a fourth alternative, such as aberrant interhemispheric bundles, reorganization of subcortical commissures, or both.

•

We studied the cortical sensory representation of the hands in callosal dysgenesis.

• Callosal dysgenesis
• Somatosensory cortical lateralization
• fMRI callosal agenesis

• Adolescent
• Adult
• Agenesis of Corpus Callosum/physiopathology
• Brain Mapping
• Female
• Functional Laterality
• Humans
• Magnetic Resonance Imaging
• Male
• Physical Stimulation
• Somatosensory Cortex/physiopathology
• Touch Perception/physiology
• Young Adult

To understand the neural mechanisms underlying the therapeutic effects of crossing nerve transfer for brachial plexus injuries in human patients, we investigated the cortical responses after crossing nerve transfer in mice using conventional and tomographic optical imaging. The distal cut ends of the left median and ulnar nerves were connected to the central cut ends of the right median and ulnar nerves with a sciatic nerve graft at 8 weeks of age. Eight weeks after the operation, the responses in the primary somatosensory cortex (S1) elicited by vibratory stimulation applied to the left forepaw were visualized based on activity-dependent flavoprotein fluorescence changes. In untreated mice, the cortical responses to left forepaw stimulation were mainly observed in the right S1. In mice with nerve crossing transfer, cortical responses to left forepaw stimulation were observed in the left S1 together with clear cortical responses in the right S1. We expected that the right S1 responses in the untreated mice were produced by thalamic inputs to layer IV, whereas those in the operated mice were mediated by callosal inputs from the left S1 to layer II/III of the right S1. To confirm this hypothesis, we performed tomographic imaging of flavoprotein fluorescence responses by macroconfocal microscopy. Flavoprotein fluorescence responses in layer IV were dominant compared to those in layer II/III in untreated mice. In contrast, responses in layer II/III were dominant compared to those in layer IV in operated mice. The peak latency of the cortical responses in the operated mice was longer than that in the untreated mice. These results confirmed our expectation that drastic reorganization in the cortical circuits was induced after crossing nerve transfer in mice.

• Animals
• Brachial Plexus/injuries
• Brachial Plexus/surgery
• Flavoproteins/metabolism
• Humans
• Male
• Median Nerve/surgery
• Mice
• Mice, Inbred C57BL
• Microscopy, Confocal
• Mitochondrial Proteins/metabolism
• Nerve Transfer
• Physical Stimulation
• Sciatic Nerve/transplantation
• Somatosensory Cortex/physiology
• Tomography, Optical/methods
• Ulnar Nerve/surgery
• Vibration

• KAKENHI

• diagnosis
• mTBI
• neuropsychiatric tests
• peripheral vision
• reaction time

• Touch
• bilateral integration
• body parts
• body side
• primary somatosensory cortex

In simple detection tasks, reaction times (RTs) are faster when stimuli are presented to the visual field or side of the body ipsilateral to the body part used to respond. This advantage, the crossed-uncrossed difference (CUD), is thought to reflect inter-hemispheric interactions needed for sensorimotor information to be integrated between the two cerebral hemispheres. However, it is unknown whether the tactile CUD is invariant when different body parts are stimulated. The most likely structure mediating such processing is thought to be the corpus callosum (CC). Neurophysiological studies have shown that there are denser callosal connections between regions that represent proximal parts of the body near the body midline and more sparse connections for regions representing distal extremities. Therefore, if the information transfer between the two hemispheres is affected by the density of callosal connections, stimuli presented on more distal regions of the body should produce a greater CUD compared to stimuli presented on more proximal regions. This is because interhemispheric transfer of information from regions with sparse callosal connections will be less efficient, and hence slower. Here, we investigated whether the CUD is modulated as a function of the different body parts stimulated by presenting tactile stimuli unpredictably on body parts at different distances from the body midline (i.e., Middle Finger, Forearm, or Forehead of each side of the body). Participants detected the stimulus and responded as fast as possible using either their left or right foot. Results showed that the magnitude of the CUD was larger on the finger (~2.6 ms) and forearm (~1.8 ms) than on the forehead (≃0.9 ms). This result suggests that the interhemispheric transfer of tactile stimuli varies as a function of the strength of callosal connections of the body parts.

• CUD
• body parts
• interhemispheric transfer
• sensory-motor integration
• tactile

This short review examines the most recent functional studies of the topographic organization of the human corpus callosum, the main interhemispheric commissure. After a brief description of its anatomy, development, microstructure, and function, it examines and discusses the latest findings obtained using diffusion tensor imaging (DTI) and tractography (DTT) and functional magnetic resonance imaging (fMRI), three recently developed imaging techniques that have significantly expanded and refined our knowledge of the commissure. While DTI and DTT have been providing insights into its microstructure, integrity and level of myelination, fMRI has been the key technique in documenting the activation of white matter fibers, particularly in the corpus callosum. By combining DTT and fMRI it has been possible to describe the trajectory of the callosal fibers interconnecting the primary olfactory, gustatory, motor, somatic sensory, auditory and visual cortices at sites where the activation elicited by peripheral stimulation was detected by fMRI. These studies have demonstrated the presence of callosal fiber tracts that cross the commissure at the level of the genu, body, and splenium, at sites showing fMRI activation. Altogether such findings lend further support to the notion that the corpus callosum displays a functional topographic organization that can be explored with fMRI.

• Corpus callosum
• Interhemispheric transfer
• Functional magnetic resonance imaging and diffusion tensor imaging
• Brain imaging
• Topographic organization

• MEG
• SI
• bilateral integration
• touch at the fingers

• Callosal commissure
• DTI
• functional brain imaging
• interhemispheric transfer
• split-brain patients

• Audio-visual integration
• Chimeric face
• Dichotic stimulation
• Hemispheric asymmetry
• Split-brain

• Acute Disease
• Adult
• Antimalarials/administration & dosage
• Artemisinins/administration & dosage
• Chloroquine/administration & dosage
• Corpus Callosum/parasitology
• Corpus Callosum/pathology
• Drug Therapy, Combination
• Follow-Up Studies
• Hemolysis
• Humans
• Magnetic Resonance Imaging
• Malaria, Falciparum/diagnostic imaging
• Malaria, Falciparum/drug therapy
• Malaria, Falciparum/pathology
• Male
• Middle Aged
• Parasitemia
• Primaquine/administration & dosage
• Prospective Studies
• Radiography
• Thailand
• Thrombocytopenia
• Young Adult

• R21 NS055348 NINDS NIH HHS
• U01 HD061233 NICHD NIH HHS

• callosal agenesis
• callosal plasticity
• human connectome

• Emotional valence
• divided visual field
• hybrid faces
• split-brain
• subliminal processing

Several experimental studies in the literature have shown that even when performing purely kinesthetic tasks, such as reaching for a kinesthetically felt target with a hidden hand, the brain reconstructs a visual representation of the movement. In our previous studies, however, we did not observe any role of a visual representation of the movement in a purely kinesthetic task. This apparent contradiction could be related to a fundamental difference between the studied tasks. In our study subjects used the same hand to both feel the target and to perform the movement, whereas in most other studies, pointing to a kinesthetic target consisted of pointing with one hand to the finger of the other, or to some other body part. We hypothesize, therefore, that it is the necessity of performing inter-limb transformations that induces a visual representation of purely kinesthetic tasks. To test this hypothesis we asked subjects to perform the same purely kinesthetic task in two conditions: INTRA and INTER. In the former they used the right hand to both perceive the target and to reproduce its orientation. In the latter, subjects perceived the target with the left hand and responded with the right. To quantify the use of a visual representation of the movement we measured deviations induced by an imperceptible conflict that was generated between visual and kinesthetic reference frames. Our hypothesis was confirmed by the observed deviations of responses due to the conflict in the INTER, but not in the INTRA, condition. To reconcile these observations with recent theories of sensori-motor integration based on maximum likelihood estimation, we propose here a new model formulation that explicitly considers the effects of covariance between sensory signals that are directly available and internal representations that are ‘reconstructed’ from those inputs through sensori-motor transformations.

• Adult
• Algorithms
• Analysis of Variance
• Female
• Humans
• Kinesthesis/physiology
• Male
• Models, Theoretical
• Psychomotor Performance/physiology
• Visual Perception/physiology
• Young Adult

• Adult
• Auditory Perception/physiology
• Brain Mapping/methods
• Corpus Callosum/physiology
• Female
• Humans
• Magnetic Resonance Imaging/methods
• Male
• Middle Aged
• Psychomotor Performance/physiology
• Taste/physiology
• Touch/physiology
• Visual Perception/physiology
• Young Adult

• Age Factors
• Aged
• Aging/physiology
• Brain Mapping
• Evoked Potentials, Somatosensory/physiology
• Female
• Humans
• Magnetic Resonance Imaging
• Male
• Somatosensory Cortex/physiology
• Young Adult

• Animals
• Brachial Plexus/surgery
• Cadherins/genetics
• Cadherins/metabolism
• Male
• Mechanotransduction, Cellular
• Median Nerve/physiology
• Median Nerve/surgery
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Nerve Regeneration
• Nerve Transfer
• Receptors, N-Methyl-D-Aspartate/physiology
• Sciatic Nerve/transplantation
• Somatosensory Cortex/anatomy & histology
• Somatosensory Cortex/physiology
• Ulnar Nerve/physiology
• Ulnar Nerve/surgery

In the somatosensory domain it is still unclear at which processing stage information reaches the opposite hemispheres. Due to dense transcallosal connections, the secondary somatosensory cortex (S2) has been proposed to be the key candidate for interhemispheric information transfer. However, recent animal studies showed that the primary somatosensory cortex (S1) might as well account for interhemispheric information transfer. Using paired median nerve somatosensory evoked potential recordings in humans we tested the hypothesis that interhemispheric inhibitory interactions in the somatosensory system occur already in an early cortical processing stage such as S1. Conditioning right S1 by electrical median nerve (MN) stimulation of the left MN (CS) resulted in a significant reduction of the N20 response in the target (left) S1 relative to a test stimulus (TS) to the right MN alone when the interstimulus interval between CS and TS was between 20 and 25 ms. No such changes were observed for later cortical components such as the N20/P25, N30, P40 and N60 amplitude. Additionally, the subcortically generated P14 response in left S1 was also not affected. These results document the existence of interhemispheric inhibitory interactions between S1 in human subjects in the critical time interval of 20–25 ms after median nerve stimulation.

• Adult
• Electroencephalography
• Evoked Potentials, Somatosensory/physiology
• Female
• Humans
• Male
• Median Nerve/physiology
• Somatosensory Cortex/physiology
• Young Adult

• fetal alcohol spectrum disorder
• interhemispheric transfer
• fetal alcohol syndrome
• corpus callosum
• pregnancy binge drinking
• finger localization test

• Abnormalities, Drug-Induced/pathology
• Abnormalities, Drug-Induced/psychology
• Adult
• Agenesis of Corpus Callosum
• Central Nervous System Depressants/adverse effects
• Child
• Cohort Studies
• Corpus Callosum/physiology
• Ethanol/adverse effects
• Female
• Fingers/innervation
• Fingers/physiology
• Functional Laterality/drug effects
• Humans
• Magnetic Resonance Imaging
• Male
• Maternal Age
• Michigan
• Neural Pathways/drug effects
• Neural Pathways/physiology
• Pregnancy
• Prenatal Exposure Delayed Effects/pathology
• Prenatal Exposure Delayed Effects/psychology
• Psychomotor Performance/drug effects
• South Africa
• Touch/physiology

• R01 AA006966 NIAAA NIH HHS
• R01 AA09524 NIAAA NIH HHS
• U24 AA014815 NIAAA NIH HHS
• R01 AA016781 NIAAA NIH HHS
• R01 AA009524 NIAAA NIH HHS
• R03 TW007030 FIC NIH HHS
• U01 AA014790 NIAAA NIH HHS
• R21 DA021034 NIDA NIH HHS
• P50 AA0706 NIAAA NIH HHS
• R01 AA06966 NIAAA NIH HHS