Functionally distinct contributions of parietal cortex to a numerical landmark task: An fMRI study

A meta-analysis of functional neuroimaging tasks associated with pseudoneglect

Major evidence for a right-hemisphere dominance of the brain in spatial and/or attentional tasks comes from lesion studies in patients with spatial neglect. However, the neuroanatomy of the different forms of neglect remains a matter of debate, and it remains unclear how dysfunctions in neglect relate to intact processes. In the healthy brain, perceptual pseudoneglect has been considered to be a phenomenon complementary to specific subtypes of neglect as observed in paradigms such as the line bisection task. Therefore, the current study investigated the intact functional anatomy of perceptual pseudoneglect using a meta-analysis to compensate for some of the limitations of individual imaging studies. We collated the data from 24 articles that tested 952 participants with a range of paradigms (landmark task, line bisection, grating-scales task, and number line task) obtaining 337 foci. Using Activation Likelihood Estimation (ALE) we identified a right-hemisphere biased network of cortical areas, including superior and intraparietal regions, the intraoccipital sulcus together with other occipital regions, as well as inferior frontal areas that were associated with perceptual pseudoneglect in partial agreement with lesion studies in patients with neglect. Our study is the first meta-analysis on the mechanisms underlying perceptual judgments which have been shown to give rise to perceptual pseudoneglect.

Assessing the impact of infantile hydrocephalus on visuomotor integration through behavioural and neuroimaging studies

Infantile hydrocephalus considerably impacts neurodevelopment, warranting attention to potential long-term consequences on visuomotor functions. The current study investigated the impact of infantile hydrocephalus on functional connectivity within the posterior cortex. Fourteen patients, who were treated for infantile hydrocephalus, were matched for age and sex with 14 typically-developing controls. Both groups had a mean age of 9 years old. Resting-state functional MRI was used to conduct a functional connectivity analysis within the visuomotor integration network, including the inferior frontal occipital fasciculus, superior longitudinal fasciculus, and frontal aslant tract. Patients had reduced functional connectivity in visuomotor pathways compared to typically-developing children with notable impact on the left and right fusiform gyrus and precuneus. Children with infantile hydrocephalus also performed significantly lower in tasks involving visuomotor integration, visual processing, visuospatial skills, motor coordination, and fine motor manipulation. This study enhances our understanding of the multifaceted impact of infantile hydrocephalus on both neural connectivity and considering behavioral outcomes.

Sign-tracking modulates reward-related neural activation to reward cues, but not reward feedback

Research shows cognitive and neurobiological overlap between sign-tracking [value-modulated attentional capture (VMAC) by response-irrelevant, discrete cues] and maladaptive behaviour (e.g. substance abuse). We investigated the neural correlates of sign-tracking in 20 adults using an additional singleton task (AST) and functional magnetic resonance imaging (fMRI). Participants responded to a target to win monetary reward, the amount of which was signalled by singleton type (reward cue: high value vs. low value). Singleton responses resulted in monetary deductions. Sign-tracking-greater distraction by high-value vs. low-value singletons (H > L)-was observed, with high-value singletons producing slower responses to the target than low-value singletons. Controlling for age and sex, analyses revealed no differential brain activity across H > L singletons. Including sign-tracking as a regressor of interest revealed increased activity (H > L singletons) in cortico-subcortical loops, regions associated with Pavlovian conditioning, reward processing, attention shifts and relative value coding. Further analyses investigated responses to reward feedback (H > L). Controlling for age and sex, increased activity (H > L reward feedback) was found in regions associated with reward anticipation, attentional control, success monitoring and emotion regulation. Including sign-tracking as a regressor of interest revealed increased activity in the temporal pole, a region related to value discrimination. Results suggest sign-tracking is associated with activation of the 'attention and salience network' in response to reward cues but not reward feedback, suggesting parcellation between the two at the level of the brain. Results add to the literature showing considerable overlap in neural systems implicated in reward processing, learning, habit formation, emotion regulation and substance craving.

The predictive role of eye movements in mental arithmetic

Behavioural studies have suggested that number manipulation involves shifting attention along a left-to-right oriented continuum. However, these studies provide little evidence about the time course of attention shifts during number processing. We used an eye-tracker with high spatio-temporal resolution to measure eye movements during the mental solving of addition (e.g., 43 + 4) and subtraction problems (e.g., 53 - 6), as a proxy for the rightward and leftward attention shifts that accompany these operations. A first difference in eye position was observed as soon as the operator was heard: the hearing of "plus" shifted the eye rightward compared to "minus". A second difference was observed later between problem offset and response onset: addition shifted the eye rightward and upward compared to subtraction, suggesting that the space used to represent the problem is bidimensional. Further analyses confirmed the fast deployment of spatial attention and evidenced its relationship with the carrying and borrowing procedures triggered by the problem presentation. The predictive role of horizontal eye movements, in particular, is essential to understand how attention contributes to narrow down the range of plausible answers. We propose that attention illuminates significant portions of the numerical continuum anticipatively to guide the search of the answer and facilitate the implementation of solving procedures in verbal working memory.

Response inhibition and memory updating in the count/nocount task: an ERP study

The present study aimed to separate the neural activities between response inhibition and memory updating processes in the Count/Nocount task. Memory load was manipulated to investigate the memory updating process. Within each trial, participants were asked to count/withhold counting the number of O/X letters in the Count/Nocount task. The participants were asked to silently add 1 if a Count letter was presented in the low load condition, and add 2 in the high load condition. Data from 28 healthy participants showed that: (1) in both high load and low load conditions, the latencies of P2 and N2 components were shorter for the Nocount than Count trials, indicating faster attentional orienting and conflict monitoring processes for the Nocount stimuli (i.e., inhibition processes triggered by the Nocount stimuli against those response execution processes triggered by Count stimuli); (2) more positive frontal P3 amplitudes were evoked for the Nocount relative to the Count stimuli, indicating a more intensive response inhibition process for the Nocount trials; (3) a more positive parietal P3 component was evoked for the low load relative to high load condition, indicating a more intensive working memory updating process for the high load condition. This load effect was absent for the frontal P3 component, suggesting that the frontal P3 might not be associated with the memory updating process. In sum, both the cognitive inhibition process (reflected by the frontal P3 component) and working memory updating process (reflected by the parietal P3 component) appear to be involved in the Count/Nocount task.

The relation between parietal GABA concentration and numerical skills

Several scientific, engineering, and medical advancements are based on breakthroughs made by people who excel in mathematics. Our current understanding of the underlying brain networks stems primarily from anatomical and functional investigations, but our knowledge of how neurotransmitters subserve numerical skills, the building block of mathematics, is scarce. Using 1H magnetic resonance spectroscopy (N = 54, 3T, semi-LASER sequence, TE = 32 ms, TR = 3.5 s), the study examined the relation between numerical skills and the brain's major inhibitory (GABA) and excitatory (glutamate) neurotransmitters. A negative association was found between the performance in a number sequences task and the resting concentration of GABA within the left intraparietal sulcus (IPS), a key region supporting numeracy. The relation between GABA in the IPS and number sequences was specific to (1) parietal but not frontal regions and to (2) GABA but not glutamate. It was additionally found that the resting functional connectivity of the left IPS and the left superior frontal gyrus was positively associated with number sequences performance. However, resting GABA concentration within the IPS explained number sequences performance above and beyond the resting frontoparietal connectivity measure. Our findings further motivate the study of inhibition mechanisms in the human brain and significantly contribute to our current understanding of numerical cognition's biological bases.

The fronto-central N2 but not parietal P3 reflects response inhibition in the count/no-count task

This study aimed to investigate whether the N2 or P3 component in the count/no-count task reflects response inhibition. The participants were asked to count/withhold counting the number of O/X letters in the count/no-count task, and to calculate the sum of all digits (i.e., 1/0) in the digital accumulation task. Therefore, four conditions were obtained in this study: count, no-count, Add 1, and Add 0. In the count and Add 1 conditions, the counting/calculation number need to be updated. In both no-count and Add 0 conditions, the memory of counting/calculation number need not to be updated; a No-go (withhold) instruction was given in the no-count condition, but a Go instruction was given in the Add 0 condition. Results showed that an enhanced fronto-central N2 was evoked in the no-count than in the Add 0 condition, indicating that a stronger response conflict or stronger inhibition might be triggered in the No-count condition. The frontocentral P3 showed no differences between no-count and Add 0 conditions, however, an enhanced centro-parietal P3 component was observed for the count relative to the no-count condition and for the Add 1 relative to the Add 0 condition, indicating that a greater amount of attentional resources might be consumed during memory updating process. Taken together, in the count/no-count task, the fronto-central N2 might reflect response inhibition or conflict and the parietal P3 might reflect attentional resource allocation but not response inhibition.