The left intraparietal sulcus modulates the selection of low salient stimuli

Neuropsychological and functional imaging studies have suggested a general right hemisphere advantage for processing global visual information and a left hemisphere advantage for processing local information. In contrast, a recent transcranial magnetic stimulation study [Mevorach, C., Humphreys, G. W., & Shalev, L. Opposite biases in salience-based selection for the left and right posterior parietal cortex. Nature Neuroscience, 9, 740-742, 2006b] demonstrated that functional lateralization of selection in the parietal cortices on the basis of the relative salience of stimuli might provide an alternative explanation for previous results. In the present study, we applied a whole-brain analysis of the functional magnetic resonance signal when participants responded to either the local or the global levels of hierarchical figures. The task (respond to local or global) was crossed with the saliency of the target level (local salient, global salient) to provide, for the first time, a direct contrast between brain activation related to the stimulus level and that related to relative saliency. We found evidence for lateralization of salience-based selection but not for selection based on the level of processing. Activation along the left intraparietal sulcus (IPS) was found when a low saliency stimulus had to be selected irrespective of its level. A control task showed that this was not simply an effect of task difficulty. The data suggest a specific role for regions along the left IPS in salience-based selection, supporting the argument that previous reports of lateralized responses to local and global stimuli were contaminated by effects of saliency

Resting-State Functional Connectivity in Youth With Gender Dysphoria

Current developmental models of gender identity and gender dysphoria (GD) lack sex-specific profiles of brain function that differentiate between typically-developing and cross-gender identified youth, as postulated by models like the unified theory of the origins of sex differences (Arnold, 2009) and the neurobiological theory of the origins of transsexuality (Swaab & Garcia-Falgueras, 2009). Previously, investigators have used brain imaging modalities such as Resting-State functional Magnetic Resonance Imaging (R-fMRI) to demonstrate differences in resting-state functional connectivity (RSFC) between typically-developing male and female youth, and between typically-developing and GID-diagnosed youth. In the present pilot study, I used R-fMRI to investigate differences in RSFC between typically-developing and cross-gender identified male and female youth subgroups, with the hypothesis that GID-diagnosed subgroups would demonstrate connectivity patterns in between those of typically-developing males and females. Eleven youth diagnosed with gender identity disorder (four males, ages 9 to 20 years; seven females, ages 12 to 20 years) were matched on age and assigned gender with 11 typically-developing youth. All participants completed written informed consent to undergo the IRB-approved research procedures. R-fMRI were collected while the participants were lying down and resting, with their eyes closed. Primary analyses focused on 14 brain regions selected because they showed sex differences most frequently or reliably in previous studies of R-fMRI in typically-developing youth. Statistical analysis used a 2 x 2 mixed effects analysis (assigned female versus assigned male x typically-developing versus GID-diagnosed), with-individual level connectivity maps as the dependent variable. Results showed that significant interaction effects of functional connectivity patterns were associated with 6 of the 14 selected brain regions. GID-diagnosed assigned females exhibited connectivity patterns similar to those of typically-developing males associated with the right medial superior frontal gyrus, right supplementary motor area, left lingual gyrus, right lingual gyrus, left middle frontal gyrus, left medial superior frontal gyrus, left cuneus, right thalamus, left dorsolateral superior frontal gyrus, and left inferior frontal gyrus, triangular part. GID-diagnosed assigned males exhibited functional connectivity patterns similar to those of typically-developing females associated with the right medial superior frontal gyrus and right supplementary motor area; in between those of typically-developing females and males associated with left lingual gyrus, right lingual gyrus, left middle frontal gyrus, left medial superior frontal gyrus, right medial superior frontal gyrus, left dorsolateral superior frontal gyrus, and left inferior frontal gyrus, triangular part; and similar to typically-developing males associated with the right lingual gyrus and left middle frontal gyrus. The right precuneus, hypothesized to show robust findings, did not reveal any effects. In the current study, GID-diagnosed assigned males tended toward demasculinized effects (quantitative interactions showing differences of magnitude), whereas GID-diagnosed assigned females tended toward masculinized effects (qualitative interactions showing differences in direction of correlation). The current findings support the view that brain development associated with gender dysphoria proceeds along separate but overlapping sex-related regions for GID-diagnosed assigned females and males and provide further evidence of greater cross-gender brain differentiation in assigned females at an earlier age than in assigned males (possibly due to earlier onset of puberty in females). These data suggest that any future use of patterns of brain function for diagnosing gender dysphoria may require separate criteria (e.g., different sets of brain regions) for assigned males and assigned females but will require replication on larger samples

Localization of Odors Can Be Learned

Chemicals selectively stimulating the olfactory nerve typically cannot be localized in a lateralization task. Purpose of this study was to investigate whether the ability of subjects to localize an olfactory stimulus delivered passively to 1 of the 2 nostrils would improve under training. Fifty-two young, normosmic women divided in 2 groups participated. One group performed olfactory lateralization training, whereas the other group performed cognitive tasks. Results showed that only subjects performing lateralization training significantly improved in their ability to lateralize olfactory stimuli compared with subjects who did not undergo such trainin

Topographic hub maps of the human structural neocortical network

Hubs within the neocortical structural network determined by graph theoretical analysis play a crucial role in brain function. We mapped neocortical hubs topographically, using a sample population of 63 young adults. Subjects were imaged with high resolution structural and diffusion weighted magnetic resonance imaging techniques. Multiple network configurations were then constructed per subject, using random parcellations to define the nodes and using fibre tractography to determine the connectivity between the nodes. The networks were analysed with graph theoretical measures. Our results give reference maps of hub distribution measured with betweenness centrality and node degree. The loci of the hubs correspond with key areas from known overlapping cognitive networks. Several hubs were asymmetrically organized across hemispheres. Furthermore, females have hubs with higher betweenness centrality and males have hubs with higher node degree. Female networks have higher small-world indices

Language Outcome after Left Anterior Temporal Lobectomy in Patients with Discordant Functional Magnetic Resonance Imaging and Intracarotid Sodium Amobarbital Testing Results

Language Outcome after Left Temporal Anterior Lobectomy in Patients with Discordant Functional Magnetic Resonance Imaging and Intracarotid Sodium Amobarbital Testing Results Rationale: Previous research has examined concordance rates between Wada and fMRI language lateralization indices (LIs) and has yielded variable results with limited post-surgical language outcome data. Therefore, additional evidence of the concurrent and predictive validity of fMRI LIs is needed. We will calculate Wada/fMRI LI concordance rates in the largest sample to date, investigate predictors of discordance and examine the ability of each procedure to predict language outcome in discordant cases. Methods: A consecutive series of 229 presurgical epilepsy patients who underwent Wada testing and fMRI will be included in the study. Wada LIs (% correct inject right –% correct inject left condition) were calculated based on performance on comprehension, naming, repetition and reading language tasks. fMRI LIs ((L-R)/(L+R) where L = number of activated left hemisphere voxels and R = number of activated right hemisphere voxels) were calculated for four ROIs using a published semantic decision/tone decision task. Discordance will be determined using a difference score of .50. Regression analyses will be performed to investigate factors that are predictive of discordance and the predictive value of Wada and fMRI in discordant cases. Results: Available by conference date. Conclusions: We hypothesize a discordance rate of approximately 1 in 10. We hypothesize predictors of discordance may be posterior cerebral artery filling, crossflow ratings, abnormal vasculature, duration of drug effect, fMRI behavioral performance and activation threshold, motion artifacts, MTS, and IQ

Language Outcome After Left Temporal Lobectomy in Patients with Discordant fMRI and Sodium Amobarbital Testing Results

The rationale for this study was to examine 1) language lateralization discordance rates between fMRI and the IAT in pre- surgical epilepsy patients and 2) naming outcome after left ATL in a group of patients for whom IAT and fMRI language LIs were discordant. Participants were 229 consecutive pre-surgical epilepsy patients who underwent the IAT and fMRI. IAT LIs (% correct inject right -% correct inject left condition) were calculated based on performance on comprehension, naming, repetition and reading language tasks. The fMRI LIs [(L-R)/(L+R) where L = number of activated left hemisphere voxels and R = number of activated right hemisphere voxels) were calculated for lateral, angular gyrus, temporal, and frontal regions of interest (ROIs) using a published semantic decision task. Discordance was determined using cut scores and difference scores for each method. Regression analyses were performed to investigate predictors of discordance. Additionally, regression formulas developed from a separate sample for predicting language outcome using fMRI and IAT LIs were applied to the discordant cases so that observed and predicted outcome scores could be compared with each method. Discordance rates ranged from 14-17%, depending on ROI. Atypical language dominance on fMRI was most predictive of discordance. Of discordant cases who underwent left ATL, language outcome was more accurately predicted by each method in approximately half the cases. When fMRI indicates left language dominance, IAT LI concordance is high. However, when fMRI indicates atypical language dominance, concordance rates with the IAT decrease. Post-operative language outcome data suggests that the IAT and fMRI each predict outcome in certain cases, suggesting some error variance with each mapping method

General and specific responsiveness of the amygdala during explicit emotion recognition in females and males

<p>Abstract</p> <p>Background</p> <p>The ability to recognize emotions in facial expressions relies on an extensive neural network with the amygdala as the key node as has typically been demonstrated for the processing of fearful stimuli. A sufficient characterization of the factors influencing and modulating amygdala function, however, has not been reached now. Due to lacking or diverging results on its involvement in recognizing all or only certain negative emotions, the influence of gender or ethnicity is still under debate.</p> <p>This high-resolution fMRI study addresses some of the relevant parameters, such as emotional valence, gender and poser ethnicity on amygdala activation during facial emotion recognition in 50 Caucasian subjects. Stimuli were color photographs of emotional Caucasian and African American faces.</p> <p>Results</p> <p>Bilateral amygdala activation was obtained to all emotional expressions (anger, disgust, fear, happy, and sad) and neutral faces across all subjects. However, only in males a significant correlation of amygdala activation and behavioral response to fearful stimuli was observed, indicating higher amygdala responses with better fear recognition, thus pointing to subtle gender differences. No significant influence of poser ethnicity on amygdala activation occurred, but analysis of recognition accuracy revealed a significant impact of poser ethnicity that was emotion-dependent.</p> <p>Conclusion</p> <p>Applying high-resolution fMRI while subjects were performing an explicit emotion recognition task revealed bilateral amygdala activation to all emotions presented and neutral expressions. This mechanism seems to operate similarly in healthy females and males and for both in-group and out-group ethnicities. Our results support the assumption that an intact amygdala response is fundamental in the processing of these salient stimuli due to its relevance detecting function.</p

Temporal lobe white matter asymmetry and language laterality in epilepsy patients.

Recent studies using diffusion tensor imaging (DTI) have advanced our knowledge of the organization of white matter subserving language function. It remains unclear, however, how DTI may be used to predict accurately a key feature of language organization: its asymmetric representation in one cerebral hemisphere. In this study of epilepsy patients with unambiguous lateralization on Wada testing (19 left and 4 right lateralized subjects; no bilateral subjects), the predictive value of DTI for classifying the dominant hemisphere for language was assessed relative to the existing standard-the intra-carotid Amytal (Wada) procedure. Our specific hypothesis is that language laterality in both unilateral left- and right-hemisphere language dominant subjects may be predicted by hemispheric asymmetry in the relative density of three white matter pathways terminating in the temporal lobe implicated in different aspects of language function: the arcuate (AF), uncinate (UF), and inferior longitudinal fasciculi (ILF). Laterality indices computed from asymmetry of high anisotropy AF pathways, but not the other pathways, classified the majority (19 of 23) of patients using the Wada results as the standard. A logistic regression model incorporating information from DTI of the AF, fMRI activity in Broca\u27s area, and handedness was able to classify 22 of 23 (95.6%) patients correctly according to their Wada score. We conclude that evaluation of highly anisotropic components of the AF alone has significant predictive power for determining language laterality, and that this markedly asymmetric distribution in the dominant hemisphere may reflect enhanced connectivity between frontal and temporal sites to support fluent language processes. Given the small sample reported in this preliminary study, future research should assess this method on a larger group of patients, including subjects with bi-hemispheric dominance

Right Structural and Functional Reorganization in Four-Year-Old Children with Perinatal Arterial Ischemic Stroke Predict Language Production

Brain imaging methods have contributed to shed light on the mechanisms of recovery after early brain insult. The assumption that the unaffected right hemisphere can take over language functions after left perinatal stroke is still under debate. Here, we report how patterns of brain structural and functional reorganization were associated with language outcomes in a group of 4-year-old children with left perinatal arterial ischemic stroke. Specifically, we gathered specific fine-grained developmental measures of receptive and productive aspects of language as well as standardized measures of cognitive development. We also collected structural neuroimaging data as well as functional activations during a passive listening story-telling fMRI task and a resting state session (rs-fMRI). Children with a left perinatal stroke showed larger lateralization indices of both structural and functional connectivity of the dorsal language pathway towards the right hemisphere that, in turn, were associated with better language outcomes. Importantly, the pattern of structural asymmetry was significantly more right-lateralized in children with a left perinatal brain insult than in a group of matched healthy controls. These results strongly suggest that early lesions of the left dorsal pathway and the associated perisylvian regions can induce the inter-hemispheric transfer of language functions to right homolog regions. This study provides combined evidence of structural and functional brain reorganization of language networks after early stroke with strong implications for neurobiological models of language development