Defining the Temporal and Occipital Lobes: Cadaveric Study with Application to Neurosurgery of the Inferior Brain.

BACKGROUND: For surgical interventions, a precise understanding of the anatomical variations of the brain and defined anatomical landmarks to demarcate the regions of the temporal lobe is essential. Many anatomical studies have facilitated important surgical approaches to the temporobasal region. Because there is considerable sulcal variability, morphological analysis of the brain is imperative. The aim of this study was to define the boundaries of the temporal and occipital lobes and to define the variations in sulci and gyri in the inferior aspect. METHODS: In 110 cerebral hemispheres variations were identified and the major landmarks of the gyral-sulcal pattern at the inferior aspect of the brain were defined. RESULTS: The anatomy of the inferior aspect of the brain is defined in detail by morphological analysis of formalin-fixed hemispheres with a view to informing important surgical approaches. CONCLUSIONS: Since the literature defines no clear separation between the temporal and occipital lobes, certain landmarks such as the preoccipital notch and a basal temporo-occipital line were suggested as ways of making the distinction. The parahippocampal ramus is a constant structure that can be used as a reliable landmark for the posterior end of the hippocampus.

The influence of age and sex on the absolute cell numbers of the human brain cerebral cortex.

The human cerebral cortex is one of the most evolved regions of the brain, responsible for most higher-order neural functions. Since nerve cells (together with synapses) are the processing units underlying cortical physiology and morphology, we studied how the human neocortex is composed regarding the number of cells as a function of sex and age. We used the isotropic fractionator for cell quantification of immunocytochemically labeled nuclei from the cerebral cortex donated by 43 cognitively healthy subjects aged 25-87 years old. In addition to previously reported sexual dimorphism in the medial temporal lobe, we found more neurons in the occipital lobe of men, higher neuronal density in women's frontal lobe, but no sex differences in the number and density of cells in the other lobes and the whole neocortex. On average, the neocortex has ~10.2 billion neurons, 34% in the frontal lobe and the remaining 66% uniformly distributed among the other 3 lobes. Along typical aging, there is a loss of non-neuronal cells in the frontal lobe and the preservation of the number of neurons in the cortex. Our study made possible to determine the different degrees of modulation that sex and age evoke on cortical cellularity.

Anatomy of the occipital lobe using lateral and posterior approaches: a neuroanatomical study with a neurosurgical perspective on intraoperative brain mapping.

BACKGROUND: A major concern of occipital lobe surgery is the risk of visual field deficits. Extending anatomical occipital lobectomy to the functional requires awake conditions because the anterior resection border comprises language-, motor- and visuospatial function-related areas within the temporal and parietal lobes. This study investigated the lateral and posterior perspectives of the occipital lobe anatomy when approaching intraaxial occipital lobe lesions. MATERIALS AND METHODS: Ten adult cadaveric cerebral hemispheres were dissected after being prepared following the concept described by Klingler for the first time. RESULTS: The occipital lobe was located posteriorly to the parietotemporal line. Within the occipital lobe, the occipital horn of the lateral ventricle represented the only anatomical landmark. Laterally, optic radiation was identified as a part of the sagittal stratum. None of the intraoperatively identifiable tracts was found medial to the occipital horn. Language- and motor-related areas were identified anteriorly and should be actively identified when lobectomy based on function is planned. Subcortically, from a posterior perspective, the anterolateral border constituted the arcuate fascicle/superior longitudinal fascicle complex and was anteromedial to the thalamocortical tract. Remaining posterior to the line connecting the preoccipital notch with the superior Rolandic point avoided the cortical and white matter tracts related to language, motor and visuospatial function. CONCLUSIONS: Knowledge of occipital lobe anatomy and surrounding structures is essential to preoperatively assess the risk of the procedure and proper consultation of a patient in terms of the extent of resection, primarily concerning visual field deficits.

The Topography of the Frontal Terminations of the Uncinate Fasciculus Revisited Through Focused Fiber Dissections: Shedding Light on a Current Controversy and Introducing the Insular Apex as a Key Anatomoclinical Area.

BACKGROUND: Recent studies advocate a connectivity pattern wider than previously believed of the uncinate fasciculus that extends to the ventrolateral and dorsolateral prefrontal cortices. These new percepts on the connectivity of the tract suggest a more expansive role for the uncinate fasciculus. Our aim was to shed light on this controversy through fiber dissections. METHODS: Twenty normal adult human formalin-fixed cerebral hemispheres were used. Focused dissections on the insular, orbitofrontal, ventromedial, ventrolateral, and dorsolateral prefrontal areas were performed to record the topography of the frontal terminations of the uncinate fasciculus. RESULTS: Three discrete fiber layers were consistently disclosed: the first layer was recorded to terminate at the posterior orbital gyrus and pars orbitalis, the second layer at the posterior two thirds of the gyrus rectus, and the last layer at the posterior one third of the paraolfactory gyrus. The insular apex was documented as a crucial landmark regarding the topographic differentiation of the uncinate and occipitofrontal fasciculi (i.e., fibers that travel ventrally belong to the uncinate fasciculus whereas those traveling dorsally are occipitofrontal fibers). CONCLUSIONS: The frontal terminations of the uncinate fasciculus were consistently documented to project to the posterior orbitofrontal area. The area of the insular apex is introduced for the first time as a crucial surface landmark to effectively distinguish the stems of the uncinate and occipitofrontal fasciculi. This finding could refine the spatial resolution of awake subcortical mapping, especially for insular lesions, and improve the accuracy of in vivo diffusion tensor imaging protocols.

The morphometry of left cuneus mediating the genetic regulation on working memory.

Working memory is a basic human cognitive function. However, the genetic signatures and their biological pathway remain poorly understood. In the present study, we tried to clarify this issue by exploring the potential associations and pathways among genetic variants, brain morphometry and working memory performance. We first carried out association analyses between 2-back accuracy and 212 image-derived phenotypes from 1141 Human Connectome Project (HCP) subjects using a linear mixed model (LMM). We found a significantly positive correlation between the left cuneus volume and 2-back accuracy (T = 3.615, p = 3.150e-4, Cohen's d = 0.226, corrected using family-wise error [FWE] method). Based on the LMM-based genome-wide association study (GWAS) on the HCP dataset and UK Biobank 33 k GWAS summary statistics, we identified eight independent single nucleotide polymorphisms (SNPs) that were reliably associated with left cuneus volume in both UKB and HCP dataset. Within the eight SNPs, we found a negative correlation between the rs76119478 polymorphism and 2-back accuracy accuracy (T = -2.045, p = .041, Cohen's d = -0.129). Finally, an LMM-based mediation analysis elucidated a significant effect of left cuneus volume in mediating rs76119478 polymorphism on the 2-back accuracy (indirect effect = -0.007, 95% BCa CI = [-0.045, -0.003]). These results were also replicated in a subgroup of Caucasians in the HCP population. Further fine mapping demonstrated that rs76119478 maps on intergene CTD-2315A10.2 adjacent to protein-encoding gene DAAM1, and is significantly associated with L3HYPDH mRNA expression. Our study suggested this new variant rs76119478 may regulate the working memory through exerting influence on the left cuneus volume.

Occipital Intralobar fasciculi: a description, through tractography, of three forgotten tracts.

Diffusion MRI paired with tractography has facilitated a non-invasive exploration of many association, projection, and commissural fiber tracts. However, there is still a scarcity of research studies related to intralobar association fibers. The Dejerines' (two of the most notable neurologists of 19th century France) gave an in-depth description of the intralobar fibers of the occipital lobe. Unfortunately, their exquisite work has since been sparsely cited in the modern literature. This work gives a modern description of many of the occipital intralobar lobe fibers described by the Dejerines. We perform a virtual dissection and reconstruct the tracts using diffusion MRI tractography. The dissection is guided by the Dejerines' treatise, Anatomie des Centres Nerveux. As an accompaniment to this article, we provided a French-to-English translation of the treatise portion concerning five intra-occipital tracts, namely: the stratum calcarinum, the stratum proprium cunei, the vertical occipital fasciculus of Wernicke, the transverse fasciculus of the cuneus and the transverse fasciculus of the lingual lobule of Vialet. It was possible to reconstruct all but one of these tracts. For completeness, the recently described sledge runner fasciculus, although not one of the Dejerines' tracts, was identified and successfully reconstructed.

Mapping the superficial morphology of the occipital lobe: proposal of a universal nomenclature for clinical and anatomical use.

The superficial anatomy of the occipital lobe has been described as irregular and highly complex. This notion mainly arises from the variability of the regional sulco-gyral architecture. Our aim was to investigate the prevalence, morphology, and correlative anatomy of the sulci and gyri of the occipital region in cadaveric specimens and to summarize the nomenclature used in the literature to describe these structures. To this end, 33 normal, adult, formalin-fixed hemispheres were studied. In addition, a review of the relevant literature was conducted with the aim to compare our findings with data from previous studies. Hence, in the lateral occipital surface, we recorded the lateral occipital sulcus and the intraoccipital sulcus in 100%, the anterior occipital sulcus in 24%, and the inferior occipital sulcus in 15% of cases. In the area of the occipital pole, we found the transverse occipital sulcus in 88% of cases, the lunate sulcus in 64%, the occipitopolar sulcus in 24%, and the retrocalcarine sulcus in 12% of specimens. In the medial occipital surface, the calcarine fissure and parieto-occipital sulcus were always present. Finally, the basal occipital surface was always indented by the posterior occipitotemporal and posterior collateral sulci. A sulcus not previously described in the literature was identified on the supero-lateral aspect of the occipital surface in 85% of cases. We named this sulcus "marginal occipital sulcus" after its specific topography. In this study, we offer a clear description of the occipital surface anatomy and further propose a standardized taxonomy for clinical and anatomical use.

Association of Poor Family Functioning From Pregnancy Onward With Preadolescent Behavior and Subcortical Brain Development.

Importance: The association of poor family functioning, a potent stressor, with child behavior is potentially long term and relevant for a person's well-being later in life. Whether changes in brain development underlie the associations with preadolescent behavior and help identify periods of vulnerability is unclear. Objective: To assess the associations of poor family functioning from pregnancy onward with cortical, white matter, and subcortical volumes, and to examine the extent to which, in particular, hippocampal volume mediates the association of prenatal parental environmental exposures with child problem behavior in preadolescence. Design, Setting, and Participants: This population-based cohort study, conducted from April 2002 to January 2006, was embedded in Generation R, a multiethnic population-based cohort from fetal life onward. All pregnant women living in Rotterdam, the Netherlands, with an expected delivery date between April 2002 and January 2006 were invited to participate. Of the 8879 pregnant women enrolled during pregnancy, 1266 mothers with no partner data and 490 with missing family functioning data were excluded, as well as 1 sibling of 32 twin pairs. After excluding an additional 657 children with poor imaging data quality or incidental findings, the final sample consisted of 2583 mother-child pairs. Data analysis was performed from March 1, 2019, to June 28, 2019. Exposures: Mother- and father-rated poor family functioning was repeatedly measured by the General Functioning subscale of the Family Assessment Device. Main Outcomes and Measures: Our primary hypothesis, formulated after data collection but before analysis, was that poor prenatal family functioning would be associated with smaller hippocampal and amygdala volumes in late childhood. High-resolution structural neuroimaging data of children aged 10 years were collected with a single 3-T magnetic resonance imaging system. Child emotional and behavioral problems were assessed with the Child Behavior Checklist. Results: Data were available for 2583 children (mean [SD] age, 10.1 [0.6] years; 1315 girls [50.9%]). Data for parents included 2583 mothers (mean [SD] age, 31.1 [4.7] years; 1617 Dutch race/ethnicity [62.6%]) and 1788 fathers (mean [SD] age, 33.5 [5.3] years; 1239 Dutch race/ethnicity [69.3%]). Children exposed to prenatal maternal-reported poor family functioning had smaller hippocampal (B = -0.08; 95% CI, -0.13 to -0.02) and occipital lobe (B = -0.70; 95% CI, -1.19 to -0.21) volumes in preadolescence. There was no evidence for an association of exposure to poor family functioning at mid- or late childhood with brain morphology. Hippocampal volumes partially mediated the association of prenatal maternal-reported poor family functioning with preadolescent problem behavior (B = 0.08; 95% CI, 0.03-0.13), even after adjusting for prior child problems at age 1.5 years. Analyses of combined maternal and paternal family functioning ratings showed similar results, but associations were largely driven by maternal family functioning reports. Conclusions and Relevance: In this population-based cohort study, prenatal maternal-reported poor family functioning was associated with a smaller hippocampus in preadolescents. This difference in brain structure may underlie behavioral problems and is a possible neurodevelopmental manifestation of the long-term consequences of poor family functioning for the child.

Delay-period activity in frontal, parietal, and occipital cortex tracks noise and biases in visual working memory.

Working memory is imprecise, and these imprecisions can be explained by the combined influences of random diffusive error and systematic drift toward a set of stable states ("attractors"). However, the neural correlates of diffusion and drift remain unknown. Here, we investigated how delay-period activity in frontal and parietal cortex, which is known to correlate with the decline in behavioral memory precision observed with increasing memory load, might relate to diffusion and drift. We analyzed data from an existing experiment in which subjects performed delayed recall for line orientation, at different loads, during functional magnetic resonance imaging (fMRI) scanning. To quantify the influence of drift and diffusion, we modeled subjects' behavior using a discrete attractor model and calculated within-subject correlation between frontal and parietal delay-period activity and whole-trial estimates of drift and diffusion. We found that although increases in frontal and parietal activity were associated with increases in both diffusion and drift, diffusion explained the most variance in frontal and parietal delay-period activity. In comparison, a subsequent whole-brain regression analysis showed that drift, rather than diffusion, explained the most variance in delay-period activity in lateral occipital cortex. These results are consistent with a model of the differential recruitment of general frontoparietal mechanisms in response to diffusive noise and of stimulus-specific biases in occipital cortex.

The Relationships Between Cortical Activity while Observing Images Featuring Different Degrees of Ambiguity and Ambiguity Tolerance.

We performed a fMRI study during which 18 healthy subjects passively viewed abstract images and tried to name them. The images were geometric primitives, impossible images (Penrose images), and ambiguous images (Rorschach inkblots). Activation and deactivation areas were revealed for each task. The results of psychological assessment of ambiguity tolerance according to MSTAT-I inventory were used as regressors. Deactivation of the precuneus (Brodmann area 7) and neighboring structures (especially when observing geometric primitives and inventing names for them) and in the fronto-temporal areas was associated with high ambiguity tolerance. Similar links were observed for both activation and deactivation (depending on the certain contrast) of the occipito-cerebellar area.

Anatomy and white matter connections of the fusiform gyrus.

The fusiform gyrus is understood to be involved in the processing of high-order visual information, particularly related to faces, bodies, and stimuli characterized by high spatial frequencies. A detailed understanding of the exact location and nature of associated white-tracts could significantly improve post-operative morbidity related to declining capacity. Through generalized q-sampling imaging (GQI) validated by gross dissection as a direct anatomical method of identifying white matter tracts, we have characterized these connections based on relationships to other well-known structures. We created the white matter tracts using GQI and confirmed the tracts using gross dissection. These dissections demonstrated connections to the occipital lobe from the fusiform gyrus along with longer association fibers that course through this gyrus. The fusiform gyrus is an important region implicated in such tasks as the visual processing of human faces and bodies, as well as the perception of stimuli with high spatial frequencies. Post-surgical outcomes related to this region may be better understood in the context of the fiber-bundle anatomy highlighted by this study.

The visual white matter connecting human area prostriata and the thalamus is retinotopically organized.

The human visual system is capable of processing visual information from fovea to the far peripheral visual field. Recent fMRI studies have shown a full and detailed retinotopic map in area prostriata, located ventro-dorsally and anterior to the calcarine sulcus along the parieto-occipital sulcus with strong preference for peripheral and wide-field stimulation. Here, we report the anatomical pattern of white matter connections between area prostriata and the thalamus encompassing the lateral geniculate nucleus (LGN). To this end, we developed and utilized an automated pipeline comprising a series of Apps that run openly on the cloud computing platform brainlife.io to analyse 139 subjects of the Human Connectome Project (HCP). We observe a continuous and extended bundle of white matter fibers from which two subcomponents can be extracted: one passing ventrally parallel to the optic radiations (OR) and another passing dorsally circumventing the lateral ventricle. Interestingly, the loop travelling dorsally connects the thalamus with the central visual field representation of prostriata located anteriorly, while the other loop travelling more ventrally connects the LGN with the more peripheral visual field representation located posteriorly. We then analyse an additional cohort of 10 HCP subjects using a manual plane extraction method outside brainlife.io to study the relationship between the two extracted white matter subcomponents and eccentricity, myelin and cortical thickness gradients within prostriata. Our results are consistent with a retinotopic segregation recently demonstrated in the OR, connecting the LGN and V1 in humans and reveal for the first time a retinotopic segregation regarding the trajectory of a fiber bundle between the thalamus and an associative visual area.

Spatial organization of occipital white matter tracts in the common marmoset.

The primate brain contains a large number of interconnected visual areas, whose spatial organization and intracortical projections show a high level of conservation across species. One fiber pathway of recent interest is the vertical occipital fasciculus (VOF), which is thought to support communication between dorsal and ventral visual areas in the occipital lobe. A recent comparative diffusion MRI (dMRI) study reported that the VOF in the macaque brain bears a similar topology to that of the human, running superficial and roughly perpendicular to the optic radiation. The present study reports a comparative investigation of the VOF in the common marmoset, a small New World monkey whose lissencephalic brain is approximately tenfold smaller than the macaque and 150-fold smaller than the human. High-resolution ex vivo dMRI of two marmoset brains revealed an occipital white matter structure that closely resembles that of the larger primate species, with one notable difference. Namely, unlike in the macaque and the human, the VOF in the marmoset is spatially fused with other, more anterior vertical tracts, extending anteriorly between the parietal and temporal cortices. We compare several aspects of this continuous structure, which we term the VOF complex (VOF +), and neighboring fasciculi to those of macaques and humans. We hypothesize that the essential topology of the VOF+ is a conserved feature of the posterior cortex in anthropoid primates, with a clearer fragmentation into multiple named fasciculi in larger, more gyrified brains.

Functional, anatomical and diffusion tensor MRI study of radiology expertise.

BACKGROUND: Repeated practice to acquire expertise could result in the structural and functional changes in relevant brain circuits as a result of long-term potentiation, neurogenesis, glial genesis, and remodeling. PURPOSE: The goal of this study is to use task fMRI to study the brain of expert radiologists performing a diagnosis task where a series of medical images were presented during fMRI acquisition for 12s and participants were asked to choose a diagnosis. Structural and diffusion-tensor MRI were also acquired. METHODS: Radiologists (N = 12, 11M, 38.2±10.3 years old) and non-radiologists (N = 17, 15M, 30.6±5.5 years old) were recruited with informed consent. Medical images were presented for 12 s and three multiple choices were displayed and the participants were asked to choose a diagnosis. fMRI, structural and diffusion-tensor MRI were acquired. fMRI analysis used FSL to determine differences in fMRI responses between groups. Voxel-wise analysis was performed to determine if subcortical volume, cortical thickness and fractional anisotropy differed between groups. Correction for multiple comparisons used false discovery rate. RESULTS: Radiologists showed overall lower task-related brain activation than non-radiologists. Radiologists showed significantly lower activation in the left lateral occipital cortex, left superior parietal lobule, occipital pole, right superior frontal and precentral gyri, lingual gyrus, and the left intraparietal sulcus (p<0.05). There were no significant differences between groups in cortical thickness, subcortical volume and fractional anisotropy (p>0.05). CONCLUSIONS: Radiologists and non-radiologists had no significant difference in structural metrics. However, in diagnosis tasks, radiologists showed markedly lower task-related brain activations overall as well as a number of high-order visual and non-visual brain regions than non-radiologists. Some brain circuits appear to be uniquely associated with differential-diagnosis paradigm expertise that are not involved in simpler object-recognition cases. Improved understanding of the brain circuitry involved in acquisition of expertise might be used to design optimal training paradigms.

Fractional amplitude of low frequency fluctuation in drug-naïve first-episode patients with anorexia nervosa: A resting-state fMRI study.

To characterize the fractional amplitude of low-frequency fluctuation (fALFF) in drug-naïve first-episode female patients with anorexia nervosa (AN) using resting-state functional magnetic resonance imaging (rs-fMRI).Whole brain rs-fMRI data were collected from 7 drug-naïve first-episode female patients with DSM-5 AN and 14 age-matched healthy female controls. fALFF values were calculated and compared between the two groups using a two-sample t test. Correlation analysis between the fALFF values in the entire brain and body mass index (BMI) was performed.Compared with the healthy controls, increased fALFF values were observed in the AN patients in their right hippocampus and left superior frontal gyrus, while decreased fALFF values were observed in their left rectus and left middle occipital gyrus. Moreover, low BMI was significantly associated with decreased fALFF in the left inferior frontal gyrus but increased fALFF in the left calcarine. In particular, the z-standardized fALFF (zfALFF) value of the left rectus was positive associated with BMI.Our findings suggest that spontaneous brain activity in the frontal region, hippocampus and rectus, characterized by fALFF values, was altered in drug-naïve, first-episode female patients with AN.

Does the superior fronto-occipital fascicle exist in the human brain? Fiber dissection and brain functional mapping in 90 patients with gliomas.

The presence of the superior fronto-occipital fascicle (SFOF) has been reported in the Rhesus monkey; however, it is a subject of controversy in humans. The aim of this study is to identify the SFOF using both in vitro and in vivo anatomo-functional analyses. This study consisted of two approaches. First, one acallosal brain and 12 normal postmortem hemispheres (five left and seven right sides) were dissected under a microscope using Klingler's fiber dissection technique. We focused on the medial subcallosal area superior to the Muratoff bundle, which has been indicated as a principal target area of the SFOF in previous studies. Second, 90 patients underwent awake craniotomy for gliomas with direct electrical stimulations. Functional examinations for visual, ataxic, and cognitive tasks were performed and 453 positive mapping sites were investigated by voxel-based morphometry analysis to establish the functions of the SFOF. The corticostriatal fibers, or the Muratoff bundle, and thalamic peduncle fibers joined in the area of the caudate nucleus, making thalamic peduncle/ corticostriatal bundles, which ran antero-posteriorly in the anterior subcallosal area and radiated from the caudate superior margin in the posterior subcallosal area. However, no SFOF fiber bundle crossed perpendicular to the thalamic peduncle/ corticostriatal bundles in the posterior subcallosal area. In the acallosal hemispheres, Probst bundles were confirmed and the subcallosal areas did not show a specific organization different from the normal brain. Hence, we could not detect a long and continuous association fascicle connecting the frontal lobe and occipital or parietal lobe in the target areas. Furthermore, in the in vivo functional mappings of awake surgery and voxel-based morphometry analysis, eight positive points on the SFOF were selected from the total 453 positive points, but their functions were not related with visual processing and spatial awareness, as has been reported in previous studies. In conclusion, in the present study we attempted to investigate the existence of the SFOF using an anatomical and functional approach. According to our results, the SFOF may not exist in the human brain.

White matter dissection and structural connectivity of the human vertical occipital fasciculus to link vision-associated brain cortex.

The vertical occipital fasciculus (VOF) is an association fiber tract coursing vertically at the posterolateral corner of the brain. It is re-evaluated as a major fiber tract to link the dorsal and ventral visual stream. Although previous tractography studies showed the VOF's cortical projections fall in the dorsal and ventral visual areas, the post-mortem dissection study for the validation remains limited. First, to validate the previous tractography data, we here performed the white matter dissection in post-mortem brains and demonstrated the VOF's fiber bundles coursing between the V3A/B areas and the posterior fusiform gyrus. Secondly, we analyzed the VOF's structural connectivity with diffusion tractography to link vision-associated cortical areas of the HCP MMP1.0 atlas, an updated map of the human cerebral cortex. Based on the criteria the VOF courses laterally to the inferior longitudinal fasciculus (ILF) and craniocaudally at the posterolateral corner of the brain, we reconstructed the VOF's fiber tracts and found the widespread projections to the visual cortex. These findings could suggest a crucial role of VOF in integrating visual information to link the broad visual cortex as well as in connecting the dual visual stream.

Linking the impact of aging on visual short-term memory capacity with changes in the structural connectivity of posterior thalamus to occipital cortices.

Aging impacts both visual short-term memory (vSTM) capacity and thalamo-cortical connectivity. According to the Neural Theory of Visual Attention, vSTM depends on the structural connectivity between posterior thalamus and visual occipital cortices (PT-OC). We tested whether aging modifies the association between vSTM capacity and PT-OC structural connectivity. To do so, 66 individuals aged 20-77 years were assessed by diffusion-weighted imaging used for probabilistic tractography and performed a psychophysical whole-report task of briefly presented letter arrays, from which vSTM capacity estimates were derived. We found reduced vSTM capacity, and aberrant PT-OC connection probability in aging. Critically, age modified the relationship between vSTM capacity and PT-OC connection probability: in younger adults, vSTM capacity was negatively correlated with PT-OC connection probability while in older adults, this association was positive. Furthermore, age modified the microstructure of PT-OC tracts suggesting that the inversion of the association between PT-OC connection probability and vSTM capacity with aging might reflect age-related changes in white-matter properties. Accordingly, our results demonstrate that age-related differences in vSTM capacity links with the microstructure and connectivity of PT-OC tracts.

Attention Networks in the Parietooccipital Cortex Modulate Activity of the Human Vestibular Cortex during Attentive Visual Processing.

Previous studies in human subjects reported that the parieto-insular vestibular cortex (PIVC), a core area of the vestibular cortex, is inhibited when visual processing is prioritized. However, it has remained unclear which networks in the brain modulate this inhibition of PIVC. Based on previous results showing that the inhibition of PIVC is strongly influenced by visual attention, we here examined whether attention networks in the parietooccipital cortex modulate the inhibition of PIVC. Using diffusion-weighted and resting-state fMRI in a group of female and male subjects, we found structural and functional connections between PIVC and the posterior parietal cortex (PPC), a major brain region of the cortical attention network. We then temporarily inhibited PPC by repetitive transcranial magnetic stimulation (rTMS) and hypothesized that the modulatory influence of PPC over PIVC would be reduced; and, as a result, PIVC would be less inhibited. Subjects performed a visual attentional tracking task immediately after rTMS, and the inhibition of PIVC during attentive tracking was measured with fMRI. The results showed that the inhibition of PIVC during attentive tracking was less pronounced compared with sham rTMS. We also examined the effects of inhibitory rTMS over the occipital cortex and found that the visual-vestibular posterior insular cortex area was less activated during attentive tracking compared with sham rTMS or rTMS over PPC. Together, these results suggest that attention networks in the parietooccipital cortex modulate activity in core areas of the vestibular cortex during attentive visual processing.SIGNIFICANCE STATEMENT Although multisensory integration is generally considered beneficial, it can become detrimental when cues from different senses are in conflict. The occurrence of such multisensory conflicts can be minimized by inhibiting core cortical areas of the subordinate sensory system (e.g., vestibular), thus reducing potential conflict with ongoing processing of the prevailing sensory (e.g., visual) cues. However, it has remained unclear which networks in the brain modulate the magnitude of inhibition of the subordinate sensory system. Here, by investigating the inhibition of the vestibular sensory system when visual processing is prioritized, we show that attention networks in the parietooccipital cortex modulate the magnitude of inhibition of the vestibular cortex.

Mapping the human middle longitudinal fasciculus through a focused anatomo-imaging study: shifting the paradigm of its segmentation and connectivity pattern.

Τhe middle longitudinal fasciculus (MdLF) was initially identified in humans as a discrete subcortical pathway connecting the superior temporal gyrus (STG) to the angular gyrus (AG). Further anatomo-imaging studies, however, proposed more sophisticated but conflicting connectivity patterns and have created a vague perception on its functional anatomy. Our aim was, therefore, to investigate the ambiguous structural architecture of this tract through focused cadaveric dissections augmented by a tailored DTI protocol in healthy participants from the Human Connectome dataset. Three segments and connectivity patterns were consistently recorded: the MdLF-I, connecting the dorsolateral Temporal Pole (TP) and STG to the Superior Parietal Lobule/Precuneus, through the Heschl's gyrus; the MdLF-II, connecting the dorsolateral TP and the STG with the Parieto-occipital area through the posterior transverse gyri and the MdLF-III connecting the most anterior part of the TP to the posterior border of the occipital lobe through the AG. The lack of an established termination pattern to the AG and the fact that no significant leftward asymmetry is disclosed tend to shift the paradigm away from language function. Conversely, the theory of "where" and "what" auditory pathways, the essential relationship of the MdLF with the auditory cortex and the functional role of the cortical areas implicated in its connectivity tend to shift the paradigm towards auditory function. Allegedly, the MdLF-I and MdLF-II segments could underpin the perception of auditory representations; whereas, the MdLF-III could potentially subserve the integration of auditory and visual information.