The functional organization of the intraparietal sulcus in humans and monkeys

In macaque monkeys, the posterior parietal cortex (PPC) is concerned with the integration of multimodal information for constructing a spatial representation of the external world (in relation to the macaque's body or parts thereof), and planning and executing object-centred movements. The areas within the intraparietal sulcus (IPS), in particular, serve as interfaces between the perceptive and motor systems for controlling arm and eye movements in space. We review here the latest evidence for the existence of the IPS areas AIP (anterior intraparietal area), VIP (ventral intraparietal area), MIP (medial intraparietal area), LIP (lateral intraparietal area) and CIP (caudal intraparietal area) in macaques, and discuss putative human equivalents as assessed with functional magnetic resonance imaging. The data suggest that anterior parts of the IPS comprising areas AIP and VIP are relatively well preserved across species. By contrast, posterior areas such as area LIP and CIP have been found more medially in humans, possibly reflecting differences in the evolution of the dorsal visual stream and the inferior parietal lobule. Despite interspecies differences in the precise functional anatomy of the IPS areas, the functional relevance of this sulcus for visuomotor tasks comprising target selections for arm and eye movements, object manipulation and visuospatial attention is similar in humans and macaques, as is also suggested by studies of neurological deficits (apraxia, neglect, Bálint's syndrome) resulting from lesions to this region.     

Human V5/MT+: comparison of functional and cytoarchitectonic data

To date, the delineation of the human visual “motion area” still relies on functional paradigms originally devised to identify monkey area MT. Using fMRI, we have identified putative human area V5/MT+ in normals by modelling the BOLD responses to alternating radially moving and stationary dot patterns. Functional activations were compared with cytoarchitectonic probability maps of its putative correlate area hOc5, which was calculated based upon data from histological sections of ten human post-mortem brains. Bilateral visual cortex activations were seen in the single subject dynamic versus stationary contrasts and in the group random-effects analysis. Comparison of group data with area hOc5 revealed that 19.0%/39.5% of the right/left functional activation was assigned to the right/left hOc5. Conversely, 83.2%/53.5% of the right/left hOc5 was functionally activated. Comparison of functional probability maps (fPM) with area hOc5 showed that 28.6%/18.1% of the fPM was assigned to hOc5. In turn, 84.9%/41.5% of the area hOc5 was covered by the respective fPM. Thus, random-effects data and fPMs yielded similar results. The present study shows for the first time the correspondence between the functionally defined human V5/MT+ and the post-mortem cytoarchitectonic area hOc5.     

Age-dependent changes in the neural substrates of empathy in autism spectrum disorder

In typical development, empathic abilities continue to refine during adolescence and early adulthood. Children and adolescents with autism spectrum disorders (ASD) show deficits in empathy, whereas adults with ASD may have developed compensatory strategies. We aimed at comparing developmental trajectories in the neural mechanisms underlying empathy in individuals with ASD and typically developing control (TDC) subjects. Using an explicit empathizing paradigm and functional magnetic resonance imaging, 27 participants with ASD and 27 TDC aged 12–31 years were investigated. Participants were asked to empathize with emotional faces and to either infer the face’s emotional state (other-task) or to judge their own emotional response (self-task). Differential age-dependent changes were evident during the self-task in the right dorsolateral prefrontal cortex, right medial prefrontal cortex, right inferior parietal cortex, right anterior insula and occipital cortex. Age-dependent decreases in neural activation in TDC were paralleled by either increasing or unchanged age-dependent activation in ASD. These data suggest ASD-associated deviations in the developmental trajectories of self-related processing during empathizing. In TDC, age-dependent modulations of brain areas may reflect the ‘fine-tuning’ of cortical networks by reduction of task-unspecific brain activity. Increased age-related activation in individuals with ASD may indicate the development of compensatory mechanisms.     

Cortical reorganization after motor stroke: A pilot study on differences between the upper and lower limbs

Stroke patients suffering from hemiparesis may show substantial recovery in the first months poststroke due to neural reorganization. While reorganization driving improvement of upper hand motor function has been frequently investigated, much less is known about the changes underlying recovery of lower limb function. We, therefore, investigated neural network dynamics giving rise to movements of both the hands and feet in 12 well‐recovered left‐hemispheric chronic stroke patients and 12 healthy participants using a functional magnetic resonance imaging sparse sampling design and dynamic causal modeling (DCM). We found that the level of neural activity underlying movements of the affected right hand and foot positively correlated with residual motor impairment, in both ipsilesional and contralesional premotor as well as left primary motor (M1) regions. Furthermore, M1 representations of the affected limb showed significantly stronger increase in BOLD activity compared to healthy controls and compared to the respective other limb. DCM revealed reduced endogenous connectivity of M1 of both limbs in patients compared to controls. However, when testing for the specific effect of movement on interregional connectivity, interhemispheric inhibition of the contralesional M1 during movements of the affected hand was not detected in patients whereas no differences in condition‐dependent connectivity were found for foot movements compared to controls. In contrast, both groups featured positive interhemispheric M1 coupling, that is, facilitation of neural activity, mediating movements of the affected foot. These exploratory findings help to explain why functional recovery of the upper and lower limbs often develops differently after stroke, supporting limb‐specific rehabilitative strategies.     

Stimulus transformation into motor action: Dynamic graph analysis reveals a posterior‐to‐anterior shift in brain network communication of older subjects

Cognitive performance slows down with increasing age. This includes cognitive processes that are essential for the performance of a motor act, such as the slowing down in response to an external stimulus. The objective of this study was to identify aging‐associated functional changes in the brain networks that are involved in the transformation of external stimuli into motor action. To investigate this topic, we employed dynamic graphs based on phase‐locking of Electroencephalography signals recorded from healthy younger and older subjects while performing a simple visually‐cued finger‐tapping task. The network analysis yielded specific age‐related network structures varying in time in the low frequencies (2–7 Hz), which are closely connected to stimulus processing, movement initiation and execution in both age groups. The networks in older subjects, however, contained several additional, particularly interhemispheric, connections and showed an overall increased coupling density. Cluster analyses revealed reduced variability of the subnetworks in older subjects, particularly during movement preparation. In younger subjects, occipital, parietal, sensorimotor and central regions were—temporally arranged in this order—heavily involved in hub nodes. Whereas in older subjects, a hub in frontal regions preceded the noticeably delayed occurrence of sensorimotor hubs, indicating different neural information processing in older subjects. All observed changes in brain network organization, which are based on neural synchronization in the low frequencies, provide a possible neural mechanism underlying previous fMRI data, which report an overactivation, especially in the prefrontal and pre‐motor areas, associated with a loss of hemispheric lateralization in older subjects.     

Are Dyspeptic Symptoms in Patients with Campylobacter pylori-Associated Type B Gastritis Linked to Delayed Gastric Emptying?

In this paper, the association of gastric Campylobacter pylori (CP) colonization with histologic findings and gastric emptying of a mixed solid-liquid meal was prospectively investigated in 43 consecutive patients with essential non-ulcer dyspepsia (ENUD). Gastric emptying was also measured in 30 symptom-free control subjects. The frequency of CP infection in patients with ENUD was 44.2%. We found a strong association between gastric CP colonization and chronic antral type B gastritis. Although gastric emptying was significantly prolonged in patients with ENUD, compared with the control group (p less than 0.05), we could not detect significant differences of gastric emptying between CP-negative and CP-positive ENUD patients, both groups disclosing a similar proportion of patients with significantly delayed gastric emptying (29.2% vs 31.6%). We therefore conclude that delayed gastric emptying of a mixed solid-liquid meal is not correlated with CP-positive chronic antral type B gastritis, and does not help to explain dyspeptic symptoms, which may possibly arise in relation to gastric CP colonization.     

Differential roles of inferior frontal and inferior parietal cortex in task switching: Evidence from stimulus‐categorization switching and response‐modality switching

We used fMRI to investigate both common and differential neural mechanisms underlying two distinct types of switching requirements, namely switching between stimulus categorizations (color vs. form) and switching between response modalities (hand vs. foot responses). Both types of switching induced similar behavioral shift costs. However, at the neural level, switching between stimulus categorizations led to left‐hemispheric activations including the inferior frontal gyrus as well as the intraparietal sulcus extending to the superior parietal gyrus and the supramarginal gyrus. In contrast, switching between response modalities was associated mainly with left‐hemispheric activation of the intraparietal sulcus and the supramarginal gyrus. A conjunction analysis indicated common activation of the left intraparietal sulcus and the supramarginal gyrus for both types of switching. Together, these results qualify previous claims about a general role of the left prefrontal cortex in task control by suggesting that the left inferior frontal gyrus is specifically involved in switching between stimulus categorizations, whereas parietal cortex is more generally implicated in the selection of action rules. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.     

Absolute serum neurofilament light chain levels and its early kinetics predict brain injury after out-of-hospital cardiac arrest

Journal of Neurology - To test if the early kinetics of neurofilament light (NFL) in blood adds to the absolute values of NFL in the prediction of outcome, and to evaluate if NFL can discriminate...