Sex differences in brain homotopic co-activations: a meta-analytic study

An element of great interest in functional connectivity is ‘homotopic connectivity’ (HC), namely the connectivity between two mirrored areas of the two hemispheres, mainly mediated by the fibers of the corpus callosum. Despite a long tradition of studying sexual dimorphism in the human brain, to our knowledge only one study has addressed the influence of sex on HC. We investigated the issue of homotopic co-activations in women and men using a coordinate-based meta-analytic method and data from the BrainMap database. A first unexpected observation was that the database was affected by a sex bias: women-only groups are investigated less often than men-only ones, and they are more often studied in certain domains such as emotion compared to men, and less in cognition. Implementing a series of sampling procedures to equalize the size and proportion of the datasets, our results indicated that females exhibit stronger interhemispheric co-activation than males, suggesting that the female brain is less lateralized and more integrated than that of males. In addition, males appear to show less intense but more extensive co-activation than females. Some local differences also appeared. In particular, it appears that primary motor and perceptual areas are more co-activated in males, in contrast to the opposite trend in the rest of the brain. This argues for a multidimensional view of sex brain differences and suggests that the issue should be approached with more complex models than previously thought. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00429-022-02572-0

Fronto-parietal homotopy in resting-state functional connectivity predicts task-switching performance

Homotopic functional connectivity reflects the degree of synchrony in spontaneous activity between homologous voxels in the two hemispheres. Previous studies have associated increased brain homotopy and decreased white matter integrity with performance decrements on different cognitive tasks across the life-span. Here, we correlated functional homotopy, both at the whole-brain level and specifically in fronto-parietal network nodes, with task-switching performance in young adults. Cue-to-target intervals (CTI: 300 vs. 1200 ms) were manipulated on a trial-by-trial basis to modulate cognitive demands and strategic control. We found that mixing costs, a measure of task-set maintenance and monitoring, were significantly correlated to homotopy in different nodes of the fronto-parietal network depending on CTI. In particular, mixing costs for short CTI trials were smaller with lower homotopy in the superior frontal gyrus, whereas mixing costs for long CTI trials were smaller with lower homotopy in the supramarginal gyrus. These results were specific to the fronto-parietal network, as similar voxel-wise analyses within a control language network did not yield significant correlations with behavior. These findings extend previous literature on the relationship between homotopy and cognitive performance to task-switching, and show a dissociable role of homotopy in different fronto-parietal nodes depending on task-demands

The homotopic connectivity of the functional brain: a meta-analytic approach

Abstract Homotopic connectivity (HC) is the connectivity between mirror areas of the brain hemispheres. It can exhibit a marked and functionally relevant spatial variability, and can be perturbed by several pathological conditions. The voxel-mirrored homotopic connectivity (VMHC) is a technique devised to enquire this pattern of brain organization, based on resting state functional connectivity. Since functional connectivity can be revealed also in a meta-analytical fashion using co-activations, here we propose to calculate the meta-analytic homotopic connectivity (MHC) as the meta-analytic counterpart of the VMHC. The comparison between the two techniques reveals their general similarity, but also highlights regional differences associated with how HC varies from task to rest. Two main differences were found from rest to task: (i) regions known to be characterized by global hubness are more similar than regions displaying local hubness; and (ii) medial areas are characterized by a higher degree of homotopic connectivity, while lateral areas appear to decrease their degree of homotopic connectivity during task performance. These findings show that MHC can be an insightful tool to study how the hemispheres functionally interact during task and rest conditions

Cerebral lateralization of language in deaf children and adults with cochlear implant (CI): a neurofunctional study with transcranial doppler ultrasound (fTCD)

Severe to profound sensorineural hearing loss (SNHL) is a pathological condition, that affects about 1-3/1000 newborns, but as shown by several studies on humans and animals, can be considered a scientific opportunity for understanding the role of auditory stimuli in neuroplasticity. In the late decades the advent of Cochlear Implantation (CI) has also permitted further investigation on how stimuli restoration can affect neuroplasticity in previously deprived subjects. This issue has been studied in terms of timing of restoration (age of implantation) and side of stimulation (afferented ear), and effects on auditory perception and language development in the case of humans. Within this theoretical frame, the present study focuses on language lateralization, measured through functional Transcranial Doppler ultrasonography (fTCD), a non invasive technique, that quantifies a Lateralization Index (LI) detecting blood flow during language performance. At this aim, 3 different groups of subjects were evaluated by fTCD: (i) 36 children with prelingual profound bilateral SNHL with monolateral CI (and 24 control subjects with normal hearing); they were also evaluated in language achievement (PPVT, TCGB, Inpe high and low frequencies, GASS and language composite score); (ii) 11 children with profound congenital unilateral hearing loss (UHL) (and 11 control subjects with normal hearing bilaterally); they were evaluated on verbal and non verbal development (PPVT, TROG2, IQ, PRI, WMI, PSI, VCI, VMI); (iii) 6 adults with preverbal profound bilateral SNHL, evaluated before and after CI. The results show that (i) left dominance is maintained, even if bilateral representation for language appears more frequent in children with monolateral CI; children with right ear implanted or left LI show better language performance. (ii) left activation was confirmed in children with right UHL while it was not confirmed in those with left UHL. Performance on verbal test were significantly better in children with right hearing. (iii) No significant changes LI were observed in adults, after implantation. On the basis of the present study neuroplasticity of auditory and language circuits appears to be a complex phenomenon in which some biological constraints for left dominance for language are confirmed, but other factors, such as age of reafferentation, and side of afference can play roles, that have still to be clearly understood. Furthermore the present study brings some support to the right ear advantage hypothesis and this should be taken into account while choosing the ear to be implanted, in the case of unilateral CI. From this point of view the right implant could be considered the first choice in monolateral or sequenced implantation. fTDC for LI evaluation can be considered in the case of late diagnosed deafness before implantation

Fluctuations of attention network activation during the resting state reflect fluctuations in subjective attentional state.

peer reviewe

Neural correlates of phonological processing in Polish-English bilinguals: An fMRI study

Wydział AnglistykiNiniejsza dysertacja bada problem neuronalnych korelatów przetwarzania fonologicznego języka ojczystego i języka obcego u polskich użytkowników języka angielskiego. W celu wskazania struktur i funkcji mózgu odpowiedzialnych za przetwarzanie fonologiczne stworzono zestaw eksperymentów, które przeprowadzono na grupie średniozaawansowanych polskich użytkowników języka angielskiego. Korzystając z metody rezonansu magnetycznego sprawdzono hipotezę zakładającą zrózżnicowanie w reprezentacji procesów fonologicznych w mózgu, w zależności od przetwarzanego języka oraz stopnia zaawansowania użytkownika. Zestaw zawierał cztery eksperymenty z zadaniami w języku polskim i angielskim, takimi jak słuchanie pasywne, Test Pamięci Roboczej Sternberga, test fluencji słownej, oraz Test Leksykalny dla Zaawansowanych Uczniów Języka Angielskiego. Na eksperymenty złożyły się również trzy eksperymenty nie oparte na żadnych zadaniach. Wyniki wraz z dokładną dyskusją sugerują model przetwarzania drugiego języka, który składa się z modułów związanych z zadaniami językowymi zbudowanych ze współgrających ze sobą sieci mózgowych. W związku z tym, niniejsza dysertacja wnosi nowe odkrycia do dziedzin językoznawstwa i neuronauki, poszerzając nasze zrozumienie procesów przetwarzania języka w mózgu.The present thesis investigates the issue of neural basis for phonological processing of native and non-native speech in Polish-English bilinguals. In order to pinpoint the structures and functions that are relevant to phonological processing, a set of experiments was devised on a group of moderately proficient Polish-English bilinguals. Using the method of Magnetic Resonance Imaging, and hypothesizing that there will be differences in the representation of phonological processes in the brain, dependent on the language and the level of proficiency in the language, four task-based experiments in both Polish and English, including listening to stories, Sternberg Working Memory Task, Verbal Fluency Task, and Lexical Test for Advanced Learners of English, and three task-independent experiments were conducted. The results of the thesis, along with the detailed discussion suggest a model of phonological processing in L2, which consists of different task-related modules of interacting brain networks. As such, the present thesis contributes to both fields of linguistics and neuroscience, broadening the understanding of how the brain processes language

Functional connectivity of the ageing brain

This thesis investigated the impact of advancing age on modifying the functional connectivity (FC) of both typical cortical resting-state networks and subcortical structures in the human brain. Furthermore, it explored how any differences in FC may be associated with changes in sleep quality, also thought to be affected by age, and how such interactions may contribute to typical cognitive disruption associated with older age. The results suggest that older age is associated with the heterogeneous, spatially specific re-organisation of resting-state networks (RSNs), as well as indicating gender-specific spatial re-organisation. Investigation of thalamic FC revealed that older adults exhibited greater thalamo-sensory and thalamo-hippocampal FC, which was related to cognitive performance on RT and memory tasks, respectively. Investigation into participant’s sleep patterns provided evidence that sleep quality was more variable amongst the older participants. Furthermore, older adults that slept the longest each night were found to exhibit patterns of thalamic FC which were associated with better cognitive performance, than seen in older shorter sleepers. These results provide preliminary evidence that sleep may be associated with more ‘preferable’ patterns of FC in older adults which may be beneficial for cognitive function

Cognition in prostate cancer patients before undergoing androgen deprivation therapy and elderly males

Deleterious cognitive effects of testosterone deprivation in prostate cancer (PC) patients undergoing androgen deprivation therapy have been reported. However, due to methodological limitations of past research, there is mixed consensus of the cognitive domains affected. The current study therefore aimed to assess cognition before ADT through a comprehensive battery of cognitive and neuroimaging investigations which previous undertakings have lacked. A cross sectional study of 30 ageing PC patients before ADT and 29 age and intelligence matched healthy controls underwent neuropsychological and neuroimaging investigations. While there were generally no differences, some significant differences were revealed where patients had higher testosterone levels and better spatial reasoning accuracy compared to controls suggesting some compensatory effect of testosterone in patients. A second study was conducted to assess the reliability of cognition in controls in a longitudinal six month study. Controls were confirmed to have reliable and stable cognition with intact underlying neural correlates confirming their appropriateness for future longitudinal assessments in PC patients. In conclusion, this research facilitated development and management of cognition in PC patients before therapy. If side-effects can be resolved before therapy, then they may be prevented during ADT. Moreover, it provides a basis for a longitudinal future research