Objective: To examine relationships between sleep, alcohol consumption, and a physiological and behavioral marker of cognitive function in college students. College students are in a high risk category for high alcohol consumption and poor sleep quality, two unhealthful behaviors which can lead to poor mental health outcomes and compromised academic performance. Participants: Thirty college students from a large midwestern institution. Methods: Participants performed an interhemispheric transfer task while their electroencephalography was recorded for later examination of event-related potentials. They were also administered the Pittsburgh Sleep Quality Index, the Alcohol Use Disorders Identification Test, and the Alcohol Timeline Follow-Back. Results: Results demonstrate that increased alcohol consumption is associated with poor right-to-left interhemispheric transfer performance, and increased frontal P1 ERP amplitudes to neuro-ipsilateral targets requiring an interhemispheric-transfer. Conclusions: These findings assist in furthering explorations into the impacts of unhealthy behaviors in college students and underlying markers of simple cognitive and behavioral function.

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.

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.

In nonhuman primates, major input to the striatum originates from ipsilateral cortex and thalamus. The striatum is a target also of crossed corticostriatal (CSt) projections from the contralateral hemisphere, which have been so far somewhat neglected. In the present study, based on neural tracer injections in different parts of the striatum in macaques of either sex, we analyzed and compared qualitatively and quantitatively the distribution of labeled CSt cells in the two hemispheres. The results showed that crossed CSt projections to the caudate and the putamen can be relatively robust (up to 30% of total labeled cells). The origin of the direct and the crossed CSt projections was not symmetrical as the crossed ones originated almost exclusively from motor, prefrontal, and cingulate areas and not from parietal and temporal areas. Furthermore, there were several cases in which the contribution of contralateral areas tended to equal that of the ipsilateral ones. The present study is the first detailed description of this anatomic pathway of the macaque brain and provides the substrate for bilateral distribution of motor, motivational, and cognitive signals for reinforcement learning and selection of actions or action sequences, and for learning compensatory motor strategies after cortical stroke.SIGNIFICANCE STATEMENT In nonhuman primates the striatum is a target of projections originating from the contralateral hemisphere (crossed CSt projections), which have been so far poorly investigated. The present study analyzed qualitatively and quantitatively in the macaque brain the origin of the crossed CSt projections compared with those originating from the ipsilateral hemisphere. The results showed that crossed CSt projections originate mostly from frontal and rostral cingulate areas and in some cases their contribution tended to equal that from ipsilateral areas. These projections could provide the substrate for bilateral distribution of motor, motivational, and cognitive signals for reinforcement learning and action selection, and for learning compensatory motor strategies after cortical stroke.

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 17 years, 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 12 years 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.

The role of white matter pathways in cognition is a topic of active investigation that is vital to both the fields of clinical neurology and cognitive neuroscience. White matter pathways provide critical connectivity amongst numerous specialized brain regions thereby enabling higher level cognition. While the effects of dissections and lesions of the corpus callosum have been reported, it is less understood how unilateral focal white matter lesions may impact cognitive processes. Here, we report a unique case study in which a small left lateralized stroke in the white matter adjacent to the body of the corpus callosum selectively impaired the ability to name letters and numbers presented to the ipsilesional, left hand. Naming of letters, numbers and objects was tested in both the visual and tactile modalities in both hands. Diffusion-weighted imaging showed a marked reduction in white matter pathway integrity through the body of the corpus callosum. Clinically, this case highlights the significant impact that a focal white matter lesion can have on higher-level cognition, specifically the integration of verbal and tactile information. Moreover, this case adds to prior reports on tactile agnosia by including DTI imaging data and emphasizing the role that white matter pathways through the body of the corpus callosum play in integrating tactile input from the right hemisphere with verbal naming capabilities of the left hemisphere. Finally, the findings also provoke fresh insight into alternative strategies for rehabilitating cognitive functioning when structural connectivity may be compromised.

Defense mechanisms are mental functions which facilitate coping when real or imagined events challenge personal wishes, needs, and feelings. Whether defense mechanisms have a specific neural basis is unknown. The present research tested the hypothesis that interhemispheric integration plays a critical role in defense mechanism development, by studying a unique sample of patients born without the corpus callosum (agenesis of the corpus callosum; AgCC). Adults with AgCC (N = 27) and matched healthy volunteers (N = 30) were compared on defense mechanism use across increasing levels of developmental maturity (denial, least; projection, intermediate; identification, most). Narratives generated in response to Thematic Apperception Test images were scored according to the Defense Mechanism Manual. Greater use of denial and less identification was found in persons with AgCC, compared to healthy comparisons. This difference emerged after age 18 when full maturation of defenses among healthy individuals was expected. The findings provide clinically important characterization of social and emotional processing in persons with AgCC. More broadly, the results support the hypothesis that functional integration across the hemispheres is important for the development of defense mechanisms.

Alexithymia is a personality construct that could occur in up to 53 % of patients with multiple sclerosis (MS). It entails difficulties in identifying and describing one\'s feelings and an externally oriented thinking. The current work aims to assess the neural underpinnings of alexithymia in this population.
Forty-five patients with MS filled in the Toronto Alexithymia Scale (n = 17 with high alexithymia and n = 28 with low alexithymia). Brain magnetic resonance imaging was obtained for each patient and a morphometry algorithm (MorphoBox) was applied to calculate regional brain volumes. All patients underwent a clinical and neuropsychological evaluation which included measures for anxiety, depression, fatigue, daytime sleepiness, and basic and social cognition.
Compared to patients with low alexithymia, patients with high alexithymia had significantly higher fatigue and depression ratings, and lower empathy scores. In addition, they had lower volumes of corpus callosum, deep white matter, pallidum bilaterally, and left thalamus. In the whole cohort, alexithymia scores were inversely correlated with gray matter (thalamus and pallidum bilaterally) and white matter volumes (corpus callosum and bilateral deep white matter) after controlling for covariates (ps<0.05).
This study offers insights on the neuropsychological and neural substrates of alexithymia in MS. The current findings are consistent with alexithymia reports in other clinical populations, and suggest an association between alexithymia and atrophy of thalami, pallidum, corpus callosum and deep white matter in MS. Further research is needed to enhance the understanding of alexithymia mechanisms in this clinical context.

A deficit in interhemispheric transfer has been proposed as a neuropsychological theory of dyslexia. Interactions between the hemispheres during word recognition can be studied using the visual half-field paradigm. The well-established recognition advantage for right visual field (RVF) words over left visual field (LVF) words is thought to reflect the additional processing costs associated with callosal transfer of LVF word representations to the language-specialised left hemisphere. In addition, a further gain in recognition for bilateral presentation of a word has been attributed to cooperative interactions between the hemispheres. These recognition advantages can therefore be seen as behavioural indices of the efficiency of callosal transfer. This study aimed to replicate the finding of an absence of the bilateral advantage in developmental dyslexia, previously reported by Henderson et al. In all, 47 dyslexic and 43 control adult participants were tested, and no significant difference was found in the size of the bilateral advantage between the two groups. Our data did however replicate the previous finding of an increased RVF-LVF difference in dyslexic participants caused by poorer accuracy for LVF words (i.e., a greater LVF cost). This evidence is compatible with the interhemispheric deficit theory of dyslexia, suggesting an impairment in the transfer of visual word information from the right to the left hemisphere during reading.

The integrity of white matter architecture in the human brain is related to cognitive processing abilities. The corpus callosum is the largest white matter bundle interconnecting the two cerebral hemispheres. \"Split-brain\" patients in whom all cortical commissures have been severed to alleviate intractable epilepsy demonstrate remarkably intact cognitive abilities despite the lack of this important interhemispheric pathway. While it has often been speculated that there are compensatory alterations in the remaining interhemispheric fibers in split-brain patients several years post-commissurotomy, this has never been directly shown. Here we examined extra-callosal pathways for interhemispheric communication in the brain of a patient who underwent complete cerebral commissurotomy using diffusion weighted imaging tractography. We found that compared with a healthy age-matched comparison group, the split-brain patient exhibited increased fractional anisotropy (FA) of the dorsal and ventral pontine decussations of the cortico-cerebellar interhemispheric pathways. Few differences were observed between the patient and the comparison group with respect to FA of other long-range intrahemispheric fibers. These results point to specific cerebellar anatomical substrates that may account for the spared interhemispheric coordination and intact cognitive abilities that have been extensively documented in this unique patient.