Activation In Parietal Lobe Research Articles

Complex partial non-convulsive status epilepticus masquerading as hepatic encephalopathy: a case report

IntroductionHepatic encephalopathy is usually suspected in patients who are cirrhotic with neuropsychiatric manifestations. We present a case of suspected hepatic encephalopathy that did not respond to standard empiric therapy and was eventually diagnosed as non-convulsive status epilepticus of complex partial type. Our patient responded dramatically to anti-convulsive therapy.Case presentationWe report the case of a 45-year-old African-American man with hepatitis C virus cirrhosis and human immunodeficiency virus who presented to our facility with a one-day history of confusion and a variable mental status. Our patient’s vital signs were stable and all his electrolytes were within normal range. A clinical diagnosis of hepatic encephalopathy was made and our patient was started on empiric therapy with lactulose and rifaximin. Our patient did not respond to therapy. After five days of treatment, alternative diagnoses were sought and a neurology consult was requested. An electroencephalogram was eventually performed which showed seizure activity in the right parietal lobe. A diagnosis of non-convulsive status epilepticus was made and our patient was started on oral levetiracetam. On day two of therapy, our patient was alert and oriented. He continues to do well on follow-up approximately one year after discharge.ConclusionsNon-convulsive status epilepticus should be considered in the differential diagnosis of patients with suspected hepatic encephalopathy who do not respond to empirical treatment. Further studies are needed to investigate the incidence of this entity in patients with persistent hepatic encephalopathy.

Age-related changes in parietal lobe activation during an episodic memory retrieval task

The crucial role of lateral parietal regions in episodic memory has been confirmed in previous studies. While aging has an influence on retrieval of episodic memory, it remains to be examined how the involvement of lateral parietal regions in episodic memory changes with age. We investigated episodic memory retrieval in two age groups, using faces as stimuli and retrieval success as a measure of episodic memory. Young and elderly participants showed activation within a similar network, including lateral and medial parietal as well as prefrontal regions, but elderly showed a higher level of brain activation regardless of condition. Furthermore, we examined functional connectivity in the two age groups and found a more extensive network in the young group, including correlations of parietal and prefrontal regions. In the elderly, the overall stronger activation related to memory performance may indicate a compensatory process for a less extensive functional network.

Functional Integration of Parietal Lobe Activity in Early Alzheimer’s Disease: Findings and Implications

Functional Integration of Parietal Lobe Activity in Early Alzheimer’s Disease: Findings and Implications

Interactions between Visual Attention and Episodic Retrieval: Dissociable Contributions of Parietal Regions during Gist-Based False Recognition

The interaction between episodic retrieval and visual attention is relatively unexplored. Given that systems mediating attention and episodic memory appear to be segregated, and perhaps even in competition, it is unclear how visual attention is recruited during episodic retrieval. We investigated the recruitment of visual attention during the suppression of gist-based false recognition, the tendency to falsely recognize items that are similar to previously encountered items. Recruitment of visual attention was associated with activity in the dorsal attention network. The inferior parietal lobule, often implicated in episodic retrieval, tracked veridical retrieval of perceptual detail and showed reduced activity during the engagement of visual attention, consistent with a competitive relationship with the dorsal attention network. These findings suggest that the contribution of the parietal cortex to interactions between visual attention and episodic retrieval entails distinct systems that contribute to different components of the task while also suppressing each other.

The Development of Brain Systems Associated with Successful Memory Retrieval of Scenes

Neuroanatomical and psychological evidence suggests prolonged maturation of declarative memory systems in the human brain from childhood into young adulthood. Here, we examine functional brain development during successful memory retrieval of scenes in children, adolescents, and young adults ages 8-21 via functional magnetic resonance imaging. Recognition memory improved with age, specifically for accurate identification of studied scenes (hits). Successful retrieval (correct old-new decisions for studied vs unstudied scenes) was associated with activations in frontal, parietal, and medial temporal lobe (MTL) regions. Activations associated with successful retrieval increased with age in left parietal cortex (BA7), bilateral prefrontal, and bilateral caudate regions. In contrast, activations associated with successful retrieval did not change with age in the MTL. Psychophysiological interaction analysis revealed that there were, however, age-relate changes in differential connectivity for successful retrieval between MTL and prefrontal regions. These results suggest that neocortical regions related to attentional or strategic control show the greatest developmental changes for memory retrieval of scenes. Furthermore, these results suggest that functional interactions between MTL and prefrontal regions during memory retrieval also develop into young adulthood. The developmental increase of memory-related activations in frontal and parietal regions for retrieval of scenes and the absence of such an increase in MTL regions parallels what has been observed for memory encoding of scenes.

Variants in the DYX2 locus are associated with altered brain activation in reading-related brain regions in subjects with reading disability

Reading disability (RD) is a complex genetic disorder with unknown etiology. Genes on chromosome 6p22, including DCDC2, KIAA0319, and TTRAP, have been identified as RD associated genes. Imaging studies have shown both functional and structural differences between brains of individuals with and without RD. There are limited association studies performed between RD genes, specifically genes on 6p22, and regional brain activation during reading tasks. Using fourteen variants in DCDC2, KIAA0319, and TTRAP and exhaustive reading measures, we first tested for association with reading performance in 82 parent-offspring families (326 individuals). Next, we determined the association of these variants with activation of sixteen brain regions of interest during four functional magnetic resonance imaging-reading tasks. We nominally replicated associations between reading performance and variants of DCDC2 and KIAA0319. Furthermore, we observed a number of associations with brain activation patterns during imaging-reading tasks with all three genes. The strongest association occurred between activation of the left anterior inferior parietal lobe and complex tandem repeat BV677278 in DCDC2 (uncorrected p=0.00003, q=0.0442). Our results show that activation patterns across regions of interest in the brain are influenced by variants in the DYX2 locus. The combination of genetic and functional imaging data show a link between genes and brain functioning during reading tasks in subjects with RD. This study highlights the many advantages of imaging data as an endophenotype for discerning genetic risk factors for RD and other communication disorders and underscores the importance of integrating neurocognitive, imaging, and genetic data in future investigations.

What is the parietal lobe contribution to long-term memory?

Until relatively recently, the lateral parietal lobe (PL) was not considered an important region for long-term memory, typically associated instead with functions such as visuospatial attention and visually-guided reaching. Scientific interest in a possible link with episodic memory was fuelled by the realisation of an intriguing discrepancy between functional imaging studies of episodic memory retrieval, which showed consistent PL activation, and the seemingly unaffected memory performance in patients with PL lesions. Shallice and Cooper dedicated a section in their book The Organisation of Mind to this newly emerged topic, reflecting how it has rapidly become an established research focus in the cognitive neurosciences.

Frontal and parietal activity after sleep deprivation is dependent on task difficulty and can be predicted by the fMRI response after normal sleep

Sleep disturbance in neurological and psychiatric disorders is common and associated with diminished cognitive functioning. Whilst these deficits can be localised predominantly to frontal and parietal regions, there have been reported inconsistencies which may be due to differences in the difficulty and type of task. In the present study we examined the effects of sleep deprivation (SD) whilst parametrically varying working memory load using an n-back task. 20 right-handed males performed the n-back task after a night of normal sleep (RW: rested wakefulness) and after approximately 31h of SD. Comparison of load responsive cerebral activation identified two clusters where the parametric response was altered after SD. In the right ventrolateral prefrontal cortex activity was reduced at the most difficult working memory load, whereas in the right inferior parietal lobe activity was increased at the simplest working memory load. The strength of activation in both of these regions during RW predicted the response of those same regions to SD. While the ability to predict signal change has previously been demonstrated using behavioural measures, to our knowledge this is the first study to show that the neuronal effects of SD can be predicted based upon activation during a normal rested condition.

Neural correlates supporting sensory discrimination after left hemisphere stroke

Background: Nearly half of stroke patients have impaired sensory discrimination, however, the neural structures that support post-stroke sensory function have not been described. Objectives: 1) To evaluate the role of the primary somatosensory (S1) cortex in post-stroke sensory discrimination and 2) To determine the relationship between post-stroke sensory discrimination and structural integrity of the sensory component of the superior thalamic radiation (sSTR). Methods: 10 healthy adults and 10 individuals with left hemisphere stroke participated. Stroke participants completed sensory discrimination testing. An fMRI was conducted during right, impaired hand sensory discrimination. Fractional anisotropy and volume of the sSTR were quantified using diffusion tensor tractography. Results: Sensory discrimination was impaired in 60% of participants with left stroke. Peak activation in the left (S1) did not correlate with sensory discrimination ability, rather a more distributed pattern of activation was evident in post-stroke subjects with a positive correlation between peak activation in the parietal cortex and discrimination ability (r=.70, p=.023). The only brain region in which stroke participants had significantly different cortical activation than control participants was the precuneus. Region of interest analysis of the precuneus across stroke participants revealed a positive correlation between peak activation and sensory discrimination ability (r=.77, p=.008). The L/R ratio of sSTR fractional anisotropy also correlated with right hand sensory discrimination (r=.69, p=.027). Conclusions: Precuneus cortex, distributed parietal lobe activity, and microstructure of the sSTR support sensory discrimination after left hemisphere stroke.

Functional integration of parietal lobe activity in early Alzheimer's disease

Objectives: Parietal lobe dysfunction is an important characteristic of early Alzheimer’s disease (AD). Functional studies have shown conflicting parietal activation patterns indicative of either compensatory or dysfunctional mechanisms. This study aimed at examining activation differences in early AD using a visuospatial task. We focused on functional characteristics of the parietal lobe and examined compensation or disconnection mechanisms by combining a fMRI task with effective connectivity measures from Granger Causality Mapping (GCM). Methods: Eighteen male patients with amnestic mild cognitive impairment (aMCI) and 18 male cognitively healthy older individuals were given a mental rotation task with different rotation angles. Results: There were no behavioral group differences on the fMRI task. Separate measurements at each angle revealed widespread activation group differences. More temporal and parietal activation in the higher angle condition was observed in aMCI patients. The parametric modulation, which identifies regions associated with increasing angle, confirmed these results. The GCM showed increased connectivity within the parietal lobe and between parietal and temporal regions in aMCI patients. Decreased connectivity was found between the inferior parietal lobule and posterior cingulate gyrus. Connectivity patterns correlated with memory performance scores in aMCI patients. Conclusions: Our results demonstrate increased effective temporo-parietal connectivity in aMCI patients, while maintaining intact behavioral performance. This might be a compensational mechanism to counteract a parietal-posterior cingulate gyrus disconnection. These findings highlight the importance of connectivity changes in the pathophysiology of AD. In addition, effective connectivity may be a promising method for evaluating interventions aimed at the promotion of compensatory mechanisms.

Pouring or chilling a bottle of wine: an fMRI study on the prospective planning of object-directed actions

This fMRI study investigates the neural mechanisms supporting the retrieval of action semantics. A novel motor imagery task was used in which participants were required to imagine planning actions with a familiar object (e.g. a toothbrush) or with an unfamiliar object (e.g. a pair of pliers) based on either goal-related information (i.e. where to move the object) or grip-related information (i.e. how to grasp the object). Planning actions with unfamiliar compared to familiar objects was slower and was associated with increased activation in the bilateral superior parietal lobe, the right inferior parietal lobe and the right insula. The stronger activation in parietal areas for unfamiliar objects fits well with the idea that parietal areas are involved in motor imagery and suggests that this process takes more effort in the case of novel or unfamiliar actions. In contrast, the planning of familiar actions resulted in increased activation in the anterior prefrontal cortex, suggesting that subjects maintained a stronger goal-representation when planning actions with familiar compared to unfamiliar objects. These findings provide further insight into the neural structures that support action semantic knowledge for the functional use of real-world objects and suggest that action semantic knowledge is activated most readily when actions are planned in a goal-directed manner.

Neural correlates of working memory in Temporal Lobe Epilepsy — An fMRI study

It has traditionally been held that the hippocampus is not part of the neural substrate of working memory (WM), and that WM is preserved in Temporal Lobe Epilepsy (TLE). Recent imaging and neuropsychological data suggest this view may need revision. The aim of this study was to investigate the neural correlates of WM in TLE using functional MRI (fMRI). We used a visuo-spatial ‘n-back’ paradigm to compare WM network activity in 38 unilateral hippocampal sclerosis (HS) patients (19 left) and 15 healthy controls. WM performance was impaired in both left and right HS groups compared to controls. The TLE groups showed reduced right superior parietal lobe activity during single- and multiple-item WM. No significant hippocampal activation was found during the active task in any group, but the hippocampi progressively deactivated as the task demand increased. This effect was bilateral for controls, whereas the TLE patients showed progressive unilateral deactivation only contralateral to the side of the hippocampal sclerosis and seizure focus. Progressive deactivation of the posterior medial temporal lobe was associated with better performance in all groups. Our results suggest that WM is impaired in unilateral HS and the underlying neural correlates of WM are disrupted. Our findings suggest that hippocampal activity is progressively suppressed as the WM load increases, with maintenance of good performance. Implications for understanding the role of the hippocampus in WM are discussed.

Functional integration of parietal lobe activity in early Alzheimer disease

Parietal lobe dysfunction is an important characteristic of early Alzheimer disease (AD). Functional studies have shown conflicting parietal activation patterns indicative of either compensatory or dysfunctional mechanisms. This study aimed at examining activation differences in early AD using a visuospatial task. We focused on functional characteristics of the parietal lobe and examined compensation or disconnection mechanisms by combining a fMRI task with effective connectivity measures from Granger causality mapping (GCM). Eighteen male patients with amnestic mild cognitive impairment (aMCI) and 18 male cognitively healthy older individuals were given a mental rotation task with different rotation angles. There were no behavioral group differences on the fMRI task. Separate measurements at each angle revealed widespread activation group differences. More temporal and parietal activation in the higher angle condition was observed in patients with aMCI. The parametric modulation, which identifies regions associated with increasing angle, confirmed these results. The GCM showed increased connectivity within the parietal lobe and between parietal and temporal regions in patients with aMCI. Decreased connectivity was found between the inferior parietal lobule and posterior cingulate gyrus. Connectivity patterns correlated with memory performance scores in patients with aMCI. Our results demonstrate increased effective temporoparietal connectivity in patients with aMCI, while maintaining intact behavioral performance. This might be a compensational mechanism to counteract a parietal-posterior cingulate gyrus disconnection. These findings highlight the importance of connectivity changes in the pathophysiology of AD. In addition, effective connectivity may be a promising method for evaluating interventions aimed at the promotion of compensatory mechanisms.

Spontaneous brain activity in mild cognitive impairment revealed by amplitude of low-frequency fluctuation analysis: a resting-state fMRI study

Spontaneous low-frequency fluctuations (LFF) in the blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal have been shown to reflect cerebral spontaneous neural activity. The objective of this study was to explore brain functional changes in patients with mild cognitive impairment (MCI) by measuring the amplitude of the BOLD signals. Eighteen amnestic MCI patients and 20 healthy elderly individuals underwent the fMRI scan. The amplitude of LFF (ALFF) was calculated using REST software. MCI patients showed decreased ALFF in the right hippocampus and parahippocampal cortex, left lateral temporal cortex and right ventral medial prefrontal cortex and increased ALFF in the left temporal-parietal joint (TPJ) and inferior parietal lobule. The ALFF value in the right hippocampus and parahippocampal cortex was positively correlated with the scores of Mini-Mental State Exam. Reduced medial temporal lobe activity may implicate the underlying memory impairment mechanisms in MCI. Increased TPJ and inferior parietal lobule activity may indicate the compensatory mechanism in MCI patients. These findings suggest that ALFF analysis could provide a useful tool in the fMRI study of MCI.

Neural Bases of a Specific Strategy for Visuospatial Processing in Rugby Players

Rugby is one of the most tactically complex sports. Rugby coaching theory suggests that rugby players need to possess various cognitive abilities. A previous study claimed that rugby players have high visuospatial awareness, which is induced by a strategy described as taking a "bird's eye view." To examine if there were differential cortical networks related to visuospatial processing tasks among top-level rugby players and control novices, we compared brain activities during a visuospatial processing task between 20 male top-level rugby players (Top) and 20 control novice males (Novice) using functional magnetic resonance imaging (fMRI). To avoid the effect of differential behavioral performances on brain activation, we recruited novices whose visuospatial ability was expected to match that of the rugby players. We adopted a 3-D mental rotation task during fMRI scanning as a visuospatial processing task. Significantly greater activations from baseline were observed for the Top group than for the Novice group in the right superior parietal lobe and lateral occipital cortex. Significantly greater deactivations from baseline were observed for the Top group than for the Novice group in the right medial prefrontal cortex. The discrepancy between psychobehavioral outputs and the fMRI results suggested the existence of a cognitive strategy among top-level rugby players that differs from that among control novices. The greater activation of the right superior parietal lobe and lateral occipital cortex in top-level rugby players suggested a strategy involving visuospatial cognitive processing with respect to the bird's eye view. In addition, the right medial prefrontal cortex is known to be a part of the default mode networks, suggesting an additional cognitive load for the Top group when using the bird's-eye-view strategy. This further supported the existence of a specific cognitive strategy among top-level rugby players.

How the Human Brain Goes Virtual: Distinct Cortical Regions of the Person-Processing Network Are Involved in Self-Identification with Virtual Agents

Millions of people worldwide engage in online role-playing with their avatar, a virtual agent that represents the self. Previous behavioral studies have indicated that many gamers identify more strongly with their avatar than with their biological self. Through their avatar, gamers develop social networks and learn new social-cognitive skills. The cognitive neurosciences have yet to identify the neural processes that underlie self-identification with these virtual agents. We applied functional neuroimaging to 22 long-term online gamers and 21 nongaming controls, while they rated personality traits of self, avatar, and familiar others. Strikingly, neuroimaging data revealed greater avatar-referential cortical activity in the left inferior parietal lobe, a region associated with self-identification from a third-person perspective. The magnitude of this brain activity correlated positively with the propensity to incorporate external body enhancements into one's bodily identity. Avatar-referencing furthermore recruited greater activity in the rostral anterior cingulate gyrus, suggesting relatively greater emotional self-involvement with one's avatar. Post-scanning behavioral data revealed superior recognition memory for avatar relative to others. Interestingly, memory for avatar positively covaried with play duration. These findings significantly advance our knowledge about the brain's plasticity to self-identify with virtual agents and the human cognitive-affective potential to live and learn in virtual worlds.

Brain Areas Consistently Linked to Individual Differences in Perceptual Decision-making in Younger as well as Older Adults before and after Training

Perceptual decision-making performance depends on several cognitive and neural processes. Here, we fit Ratcliff's diffusion model to accuracy data and reaction-time distributions from one numerical and one verbal two-choice perceptual-decision task to deconstruct these performance measures into the rate of evidence accumulation (i.e., drift rate), response criterion setting (i.e., boundary separation), and peripheral aspects of performance (i.e., nondecision time). These theoretical processes are then related to individual differences in brain activation by means of multiple regression. The sample consisted of 24 younger and 15 older adults performing the task in fMRI before and after 100 daily 1-hr behavioral training sessions in a multitude of cognitive tasks. Results showed that individual differences in boundary separation were related to striatal activity, whereas differences in drift rate were related to activity in the inferior parietal lobe. These associations were not significantly modified by adult age or perceptual expertise. We conclude that the striatum is involved in regulating response thresholds, whereas the inferior parietal lobe might represent decision-making evidence related to letters and numbers.

Changes in frontal-parietal activation and math skills performance following adaptive number sense training: Preliminary results from a pilot study

Number sense is believed to be critical for math development. It is putatively an implicitly learned skill and may therefore have limitations in terms of being explicitly trained, particularly in individuals with altered neurodevelopment. A case series study was conducted using an adaptive, computerised programme that focused on number sense and general problem-solving skills. The study was designed to investigate training effects on performance as well as brain function in a group of children with Turner syndrome who are at risk for math difficulties and altered development of math-related brain networks. Standardised measurements of math and math-related cognitive skills as well as functional magnetic resonance imaging (fMRI) were used to assess behavioural and neurobiological outcomes following training. Participants demonstrated significantly increased basic math skills, including number sense, and calculation as well as processing speed, cognitive flexibility and visual-spatial processing skills. With the exception of calculation, increased scores also were clinically significant (i.e., recovered) based on reliable change analysis. Participants additionally demonstrated significantly increased bilateral parietal lobe activation and decreased frontal-striatal and mesial temporal activation following the training programme. These findings show proof of concept for an accessible training approach that may be potentially associated with improved number sense, math and related skills, as well as functional changes in math-related neural systems, even among individuals at risk for altered brain development.

Impact of Marijuana on Response Inhibition: an fMRI Study in Young Adults

Rationale: Marijuana use in adolescence is prevalent and increasing. Understanding the neural correlates of the impact of this use is critical for policy making and for youth awareness. Objectives The effects of marijuana use on response inhibition were investigated in 19–21-year-olds using functional magnetic resonance imaging (fMRI). Methods: Participants were members of the Ottawa Prenatal Prospective Study, a longitudinal study that collected a unique body of information on participants from infancy to young adulthood including: prenatal drug history, detailed cognitive/behavioral performance, and current and past drug use. This information allowed for the control of an unparalleled number of potentially confounding variables including: prenatal marijuana, nicotine, alcohol, and caffeine exposure and offspring alcohol, marijuana, and nicotine use. Ten marijuana users and 14 nonusers that served as controls performed a Go/No-Go task while fMRI blood oxygen level-dependent response was examined. Results: Despite similar task performance, there was a positive relationship between amount of marijuana smoked and activation in right thalamus, premotor cortex and middle frontal gyrus. These regions form part of the neural network responsible for inhibition control. There was also a positive dose dependent relationship with marijuana and activation in inferior parietal lobe and precuneus, also parts of response inhibition pathways. Conclusions: These results suggest a dose dependent alteration in neural functioning during response inhibition after controlling for other prenatal and current drug use. These alterations may be necessary in order to compensate for neural changes in response inhibition circuits caused by long term marijuana use that began during adolescence/young adulthood.

Dissociating mental states related to doing nothing by means of fMRI pattern classification

Most juridical systems recognize intentional non-actions – the failure to render assistance – as intentional acts by regarding them as in principle culpable. This raises the fundamental question whether intentional non-actions can be distinguished from simply not doing anything. Classical GLM analysis on functional magnetic resonance imaging (fMRI) data reveals that not doing anything is associated with resting state brain areas whereas intentionally non-acting is associated with brain activity in left inferior parietal lobe and left dorsal premotor cortex. By means of pattern classification we quantify the accuracy with which we can distinguish these two mental states on the basis of brain activity. In order to identify brain regions that harbour a distributed, overlapping representation of voluntary non-actions and the decision not to act we performed pattern classification on brain areas that did not appear in the GLM contrasts. The prediction rate is not reduced and we show that the prediction relies mostly on brain areas that have been associated with action production and motor imagery as supplementary motor area, right inferior frontal gyrus and right middle temporal area (V5/MT). Hence our data support the implicit assumption of legal practice that voluntary non-action shares important features with overt voluntary action.