Hemispheric and gender related differences in the midcingulum bundle: a DTI study.

The midcingulate cortex and therefore the underlying midcingulum bundle (MCB) as well play a major role in attention. Although a specific structure's function does strongly depend on its neuroanatomical characteristics, research assessing the morphological variability of the midcingulate region is rather sparse. The present study examined the micro- and macrostructure of the MCB in both hemispheres by means of diffusion-tensor imaging. Besides, effects of gender (Female = 40, Male = 39) and handedness (Lefthanders = 45, Righthanders = 34) were assessed as well. Measures of fractional anisotropy, mean diffusion, as well as the white matter volumes of the MCBs were assessed. By integration of multi-modal images, the MCB was isolated and confounding with callosal fibers was avoided. Evidence was found indicating differences between hemispheres and gender regarding both volume and microstructural characteristics of the MCB. Interestingly, gender-related effects seem to be substantially associated with variations in individual brain volumes. Handedness did not emerge as relevant factor in the analyses. These findings might indicate a higher functional connectivity of the left MCB and in males as compared to females.

Effects of anterior cingulate fissurization on cognitive control during stroop interference.

The midcingulate cortex, as part of the more anteriorly located cingulate regions, is thought to play a major role in cognitive processes like conflict monitoring or response selection. Regarding midcingulate fissurization, the occurrence of a second or paracingulate sulcus is more common in the left than in the right hemisphere and has been shown to be associated with an advantageous performance on tests of executive functions. However, the cognitive mechanisms underlying such behavioral differences are completely unknown. The current study addressed this issue by comparing subjects with a low and a high degree of left hemispheric midcingulate fissurization while collecting behavioral as well as electrophysiological correlates of Stroop interference. A high degree of fissurization was associated with decreased behavioral Stroop interference accompanied by a stronger and prolonged frontal negative potential to incongruent trials starting around 320 ms. This increased frontal negativity is assumed to reflect an enhanced activity of a conflict monitoring system located in the midcingulate cortex. In contrast and starting around 400 ms, subjects with low fissurization revealed an increased positivity over parieto-occipital regions suggesting a compensatory need for enhanced effortful cognitive control in this group. These results contribute to the understanding of the neuronal implementation of individual differences regarding attentional mechanisms.

Altered tonic and phasic cortisol secretion following unilateral stroke.

Evidence is accumulating that cerebral laterality appears to be an important feature in the regulation of the stress response with the right hemisphere being closely linked to stress-regulatory systems, including the hypothalamic-pituitary-adrenal (HPA) axis. Although some animal and human data support this hypothesis, studies on brain damaged patients yet failed to substantiate laterality effects on cortisol secretion. The aim of this study was to examine whether unilateral stroke differentially affects tonic and phasic response characteristics of the HPA axis, and to evaluate the impact of intrahemispheric lesion location. Basal morning cortisol levels and phasic responses towards a mentally challenging task were examined in 32 stroke patients with left-sided (LH; n=18) or right-sided (RH; n=14) infarctions and 30 healthy controls matched for age and gender. Only LH, but not RH patients displayed increased morning cortisol levels when compared to controls. In contrast, phasic reactions were blunted in the combined patient group with RH patients showing the most distinct decline. More anterior located lesions were associated with reduced phasic, but not tonic cortisol measures. This relationship appeared to be particularly pronounced in RH patients. Results support the conclusion that the central regulation of cortisol secretion is under excitatory control of the right hemisphere and can be interpreted within a framework of asymmetrical regulation of the stress response. Left- and right-sided strokes may differentially affect response patterns of the HPA axis, a stress-regulatory system that is associated with effective protection against disease and external challenges.

Impaired performance on the Wisconsin Card Sorting Test under left- when compared to right-sided deep brain stimulation of the subthalamic nucleus in patients with Parkinson's disease.

Over the past decade, deep brain stimulation (DBS) has become an effective treatment option for managing severe Parkinson's disease (PD). However, evidence is accumulating that DBS of target sites like the subthalamic nucleus (STN) can result in unintended cognitive effects that lie beyond motor control. The aim of the present study was to evaluate whether changes in executive task performance after chronic DBS might be predominantly associated with the stimulation of only one hemisphere. Eight patients with PD who had undergone DBS treatment of the STN were selected to participate in the study. Using a repeated measurements design, they underwent a neuropsychological examination under unilateral left- and right-sided stimulation in order to investigate laterality effects in their performance on the Wisconsin Card Sorting Test. All patients showed a significant improvement in motor symptoms postoperatively. Selected aspects of executive task performance were compromised under left- when compared to right-sided stimulation. Performance measures were unrelated to demographic, neurological, and behavioral characteristics of the patients. Findings are consistent with the emerging evidence that the STN is not only involved in motor control, but also participates in functions of the cognitive domain. Moreover, results raise the possibility that the left and right hemisphere might differ in their vulnerability to tolerate side effects on executive functions of DBS treatment. Potential consequences for future research questions and the management of cognitive side effects are discussed.

Corticospinal tract asymmetries at the level of the internal capsule: is there an association with handedness?

The functional integrity of the corticospinal tract (CST) is of crucial importance for fine and independent finger movement. Therefore, it has been frequently speculated that interhemispheric asymmetries in this tract might be associated with handedness. The objective of the present study was to examine this proposed relationship, by studying the effects of handedness on macro- and microstructural properties of the CST. For this purpose, 30 consistently left and 30 consistently right-handed participants of either sex were examined applying a combination of anatomical T1-weighted and diffusion-tensor (DTI) MR imaging. In an automated procedure and based on white matter probability maps as well as on DTI fibre direction information, the left and right hemispheric CST was segmented in the individual brain. Focussing the analysis on the posterior limb of the internal capsule, the size as well as two DTI parameters (mean diffusion and fractional anisotropy) was determined. Although the statistical analysis revealed substantial CST asymmetries regarding size, mean diffusion, and anisotropy, neither of these metrics showed a significant hemisphere-by-handedness interaction. From this it was concluded that handedness might be related to motorcortical asymmetries which seem not to be directly reflected in the corticospinal fibre tract characteristics.

Development of a short version of the Apathy Evaluation Scale specifically adapted for demented nursing home residents.

OBJECTIVE: Apathy is among the most frequent neuropsychiatric symptoms in dementia, particularly Alzheimer disease. The Apathy Evaluation Scale (AES) has been widely employed for assessing apathy in different patient groups. To further facilitate the usage of the AES, an abbreviated version was constructed. METHOD: On basis of a sample of 356 nursing home residents, a cross-validation procedure was carried out to develop a brief version of the AES. According to a thorough clinical examination, 85% of the residents were demented, 8% presented with mild cognitive impairment, whereas 7% did not present any cognitive deficits. After subdividing the patient group into two matched samples, the first subsample was used to identify problematic items due to defined psychometric and content-related criteria. The original 18-item scale was thus reduced to 10 items. Psychometric properties of the shortened version were subsequently reassessed in the second subsample. RESULTS: The short version demonstrated favorable psychometric properties that could be confirmed by cross-validation with the second sample. Correlations with the original full-length version were high (r = 0.97 for both subsamples); the shortened scale yielded no substantial losses regarding internal consistency or construct validity (correlations with the respective subscales of the Neuropsychiatric Inventory). CONCLUSION: The frequency of apathetic symptoms in the nursing home residents included confirms the clinical importance of apathy for understanding dementia. Given this specific patient population, setting, and mode of data collection, the short-version AES seems to be a valuable and time-efficient instrument for assessing apathy.

Morphologic asymmetry of the human anterior cingulate cortex.

The anterior cingulate cortex (ACC) is thought to play a major role in executive processes. Studies assessing neuroanatomical attributes of this region report a high degree of morphological variability. Recent theories consider the fissurization of the cortex to be a product of gross mechanical processes related to cortical growth and local cytoarchitectural characteristics. Hence, local sulcal patterning and gray matter volume are supposed to be associated. ACC fissurization was quantified in left- and right-handers of both sexes by recording the presence and extension of the paracingulate sulcus (PCS). Differences between groups regarding local gray matter volume were assessed by means of optimized voxel-based morphometry (oVBM) including additional modulation. Overall, the PCS occurred more often and was more pronounced in the left as compared to the right anterior cingulate region, although hemispheric differences were less pronounced in male left- and female right-handers. These discrepancies between groups seem to stem from variations of cingulate morphology in the left rather than the right hemisphere. The pattern of relevant comparisons in the oVBM analysis indicated a similar interaction. Therefore, evidence was found for discrepancies between groups and hemispheres on the macrostructural level.

Interhemispheric transfer time and structural properties of the corpus callosum.

The present study examined how interhemispheric transfer time (IHTT) is affected by interindividual differences in corpus callosum (CC) architecture. For this purpose the CC of 42 healthy male subjects was assessed by applying a combination of morphological and diffusion-tensor magnetic resonance imaging to characterize the CC on macro- (midsagittal area) and microstructural level (mean diffusion, fractional anisotropy). Following the so-called Poffenberger paradigm, IHTT was determined with both reaction time measures and event-related potentials recorded in response to stimuli briefly presented to either left or right visual hemifield. Statistical analysis revealed significant negative correlations between mean diffusion and IHTT estimates derived from the P100 component (at O1/O2 electrode pair), particularly in the posterior CC subregion. Interpreting mean diffusion as an index of microstructural tissue properties, IHTT appears to be directly related to the structural integrity of the posterior CC.

The role of the corpus callosum in dichotic listening: a combined morphological and diffusion tensor imaging study.

The objective of the present study was to examine the role of the corpus callosum (CC) in dichotic listening. For this purpose, 40 right-handed healthy male participants were assessed with morphological and diffusion tensor imaging, which yielded macrostructural (midsagittal area) and microstructural (mean diffusion, fractional anisotropy) measures of the total CC and predefined subregions. Applying the standard consonant-vowel Bergen Dichotic Listening Test (including 3 different attentional instructions), the authors found dichotic listening performance to be substantially related to the integrity of the CC at both macro- and microstructural levels. Results indicate a dual role of the CC; it is relevant not only for the stimulus-driven (bottom-up) transfer of left-ear input to the left hemisphere but also for its attentional (top-down) modulation.

The association of macro- and microstructure of the corpus callosum and language lateralisation.

The present study aimed to examine how differences in functional lateralisation of language are related to interindividual variations in interhemispheric connectivity. Utilising an fMRI silent word-generation paradigm, 89 left- and right-handed subjects were subdivided into four lateralisation subgroups. Applying morphological and diffusion-tensor MRI, midsagittal cross-sectional area as well as quantitative measures of molecular diffusion (anisotropy, mean diffusion) of the corpus callosum were determined to assess interhemispheric connectivity. Statistical analyses revealed group differences in molecular diffusion but not in callosal size, which may be interpreted to reflect a stronger and/or faster interhemispheric connection in strongly left-lateralised subjects as compared to moderately left-lateralised, bilateral, or moderately right-lateralised subjects.

Handedness, dichotic-listening ear advantage, and gender effects on planum temporale asymmetry--a volumetric investigation using structural magnetic resonance imaging.

Previous research has often examined whether the asymmetrical structure of the planum temporale (PT) represents an anatomical correlate of lateralized language-processing functions, gathering diverging empirical evidence by comparing PT asymmetry in subjects with differing handedness, gender, or speech lateralization. Apart from other methodological problems, direct comparisons between studies are hampered by insufficient assessment and consideration of all three potential determinants of structural cerebral asymmetry. Based on volumetric assessment of structural Magnetic Resonance Imaging (MRI) scans of 104 healthy subjects, the present study replicated earlier observations of an overall leftward PT asymmetry, which was found to prevail irrespective of handedness, gender, or dichotic-listening ear advantage. However, the mean magnitude of this leftward asymmetry was not determined by either one of these factors in itself, but varied depending on their specific combination. A clear correspondence between structural and functional asymmetry was only observed among right-handed males. In this particular subgroup, more pronounced structural asymmetry was associated with an enlarged PT on the left side, while the enhanced leftward asymmetry of female sinistrals resulted from smaller adjusted volumes of their right PT. The existence of such complex interactions suggests that future research in this area can only be expected to overcome past inconsistencies by adequately considering handedness, gender, and speech lateralization.

Effects of handedness and gender on macro- and microstructure of the corpus callosum and its subregions: a combined high-resolution and diffusion-tensor MRI study.

The corpus callosum (CC) represents the major commissural tract connecting the two cerebral hemispheres and is supposed to play crucial integrative role in functional hemispheric specialization. The present study examined whether interindividual variations in macro- and microstructure of the human CC are associated with handedness and gender. Therefore, a combined diffusion-tensor (DTI) and high-resolution morphological MRI study was performed on 34 right- and 33 left-handed subjects of both sexes. The mid-sagittal surface areas and quantitative measures of molecular diffusion (relative anisotropy, mean diffusion) of the total CC and its subregions (genu, truncus, posterior third) were determined. Analysis revealed a larger total callosal area in right- as compared to left-handed subjects and in males as compared to females. Throughout all callosal subregions, anisotropy was found to be increased in left-handed as well as in male subjects, while the mean diffusion was diminished only in left-handers. For the posterior third of the CC, a significant negative correlation (r=-0.34) between anisotropy and area was detected in right-handed subjects. Summarized, significant alterations in the molecular diffusion and in the size of the CC with respect to gender and handedness were revealed in the present study. These findings can be interpreted as handedness- and gender-related differences in macro- and microstructure of the callosal pathways. It was demonstrated that the inspection of the callosal microstructure using DTI yields empirical evidence on interhemispheric connectivity that goes well beyond the information revealed by anatomical measurements alone. Thus, DTI has proven to be a useful additional method in cognitive neuroscience.

The influence of handedness and gender on the microstructure of the human corpus callosum: a diffusion-tensor magnetic resonance imaging study.

The aim of the present study was to examine whether handedness and gender are associated with microstructural differences in human corpus callosum (CC). For this purpose, diffusion-tensor magnetic resonance imaging (DTI) was performed on 34 right- and 33 left-handed subjects of both sexes. Four quantitative variables (Mean Diffusion, Relative Anisotropy, parallel and orthogonal diffusion) were computed within the CC. A significantly increased anisotropy was found in left- as compared to right-handed subjects, and in men as compared to women. Additionally, both overall and orthogonal diffusion were significantly lower in left- than in right-handed subjects. Possible interpretations of these findings are discussed. The novel DTI technique promises to further advance current understanding of morphological structure in the living brain.