Controllability of structural brain networks.

Cognitive function is driven by dynamic interactions between large-scale neural circuits or networks, enabling behaviour. However, fundamental principles constraining these dynamic network processes have remained elusive. Here we use tools from control and network theories to offer a mechanistic explanation for how the brain moves between cognitive states drawn from the network organization of white matter microstructure. Our results suggest that densely connected areas, particularly in the default mode system, facilitate the movement of the brain to many easily reachable states. Weakly connected areas, particularly in cognitive control systems, facilitate the movement of the brain to difficult-to-reach states. Areas located on the boundary between network communities, particularly in attentional control systems, facilitate the integration or segregation of diverse cognitive systems. Our results suggest that structural network differences between cognitive circuits dictate their distinct roles in controlling trajectories of brain network function

Identifying the causal mechanisms of the quiet eye

Scientists who have examined the gaze strategies employed by athletes have determined that longer quiet eye (QE) durations (QED) are characteristic of skilled compared to less-skilled performers. However, the cognitive mechanisms of the QE and, specifically, how the QED affects performance are not yet fully understood. We review research that has examined the functional mechanism underlying QE and discuss the neural networks that may be involved. We also highlight the limitations surrounding QE measurement and its definition and propose future research directions to address these shortcomings. Investigations into the behavioural and neural mechanisms of QE will aid the understanding of the perceptual and cognitive processes underlying expert performance and the factors that change as expertise develops

Pre-stimulus influences on auditory perception arising from sensory representations and decision processes

The qualities of perception depend not only on the sensory inputs but also on the brain state before stimulus presentation. Although the collective evidence from neuroimaging studies for a relation between prestimulus state and perception is strong, the interpretation in the context of sensory computations or decision processes has remained difficult. In the auditory system, for example, previous studies have reported a wide range of effects in terms of the perceptually relevant frequency bands and state parameters (phase/power). To dissociate influences of state on earlier sensory representations and higher-level decision processes, we collected behavioral and EEG data in human participants performing two auditory discrimination tasks relying on distinct acoustic features. Using single-trial decoding, we quantified the relation between prestimulus activity, relevant sensory evidence, and choice in different task-relevant EEG components. Within auditory networks, we found that phase had no direct influence on choice, whereas power in task-specific frequency bands affected the encoding of sensory evidence. Within later-activated frontoparietal regions, theta and alpha phase had a direct influence on choice, without involving sensory evidence. These results delineate two consistent mechanisms by which prestimulus activity shapes perception. However, the timescales of the relevant neural activity depend on the specific brain regions engaged by the respective task

Altered Alpha Oscillatory Power Dynamics Underlie Difficulties with Cognitive Flexibility

Cognitive flexibility is an important mental faculty, but there are certain populations that experience reduced flexibility, which may be associated with altered neural activity. Rumination is when an individual becomes mentally stuck on a thought, and they experience difficulty shifting their attention away from the ruminative thought demonstrating reduced cognitive flexibility. In a similar manner, individuals diagnosed with substance use disorder show varying degrees of attentional bias towards drug related stimuli. The drug cues capture attention, and it is difficult for these individuals to shift attention away from thoughts related to drug cues. Both populations experience difficulty shifting attention when they experience highly salient thoughts (high automatic constraints). Here we suggest and demonstrate that reduced cognitive flexibility in these populations is associated with altered activity of alpha oscillations, as alpha oscillations play an important role in supporting cognitive flexibility. In our first study, we assess the relationship between trait tendency to ruminate and resting state alpha power in left frontal and parietal located electrodes. Individuals higher in trait rumination exhibit higher alpha power in left frontal located electrodes. This finding suggests that higher alpha power may contribute to mental inflexibility associated with rumination. In our second study, we assess the relationship between attentional bias towards drug cues and alpha power while automatic constraints on thought are high during an emotional version of the Stroop task and when drug cues are not present and therefore automatic constraints are low, but flexibility is required during a probabilistic reversal learning task. The emotional version of the Stroop task includes traditional congruent and incongruent word meanings as well as drug related and neutral word meanings. Participants in this study were long-term nicotine smokers, therefore the emotional stimuli were smoking related. The probabilistic reversal learning task instructs participants to choose one of two presented stimuli on each trial. The stimuli have different probabilities of reward or punishment. If the participant chooses the stimulus with the higher probability of reward several trials in a row, the reward probabilities reverse, and the participant must adapt to the new reward contingencies. Participants demonstrate the traditional Stroop effect of lower accuracy and slower reaction time during incongruent trials compared to congruent trials. Additionally, participants show a slowed reaction time during drug trials compared to neutral trials suggesting attentional bias during drug trials. Greater attentional bias is associated with higher alpha power in left frontal electrodes during drug trials. No significant relationship between attentional bias and alpha power during the probabilistic reversal learning task was revealed. Together, these results suggest higher alpha power in left frontal regions may contribute to mental inflexibility prompted by attentional bias when automatic constraints are high, but when automatic constraints are low, flexibility may not be reduced. All together these results reveal a relationship between reduced cognitive flexibility when salient stimuli or thoughts are present and altered alpha power dynamics, which may offer new avenues for behavioral intervention to improve cognitive flexibility

Dorsal and ventral attention systems underlie social and symbolic cueing

none3siEye gaze is a powerful cue for orienting attention in space. Studies examining whether gaze and symbolic cues recruit the same neural mechanisms have found mixed results. We tested whether there is a specialized attentional mechanism for social cues. We separately measured BOLD activity during orienting and reorienting attention following predictive gaze and symbolic cues. Results showed that gaze and symbolic cues exerted their influence through the same neural networks but also produced some differential modulations. Dorsal frontoparietal regions in left intraparietal sulcus (IPS) and bilateral MT+/lateral occipital cortex only showed orienting effects for symbolic cues, whereas right posterior IPS showed larger validity effects following gaze cues. Both exceptions may reflect the greater automaticity of gaze cues: Symbolic orienting may require more effort, while disengaging attention during reorienting may be more difficult following gaze cues. Face-selective regions, identified with a face localizer, showed selective activations for gaze cues reflecting sensory processing but no attentional modulations. Therefore, no evidence was found linking face-selective regions to a hypothetical, specialized mechanism for orienting attention to gaze cues. However, a functional connectivity analysis showed greater connectivity between face-selective regions and right posterior IPS, posterior STS, and inferior frontal gyrus during gaze cueing, consistent with proposals that face-selective regions may send gaze signals to parts of the dorsal and ventral frontoparietal attention networks. Finally, although the default-mode network is thought to be involved in social cognition, this role does not extend to gaze orienting as these regions were more deactivated following gaze cues and showed less functional connectivity with face-selective regions during gaze cues.mixedCallejas, Alicia; Shulman, Gordon L.; Corbetta, MaurizioCallejas, Alicia; Shulman, Gordon L.; Corbetta, Maurizi

Structural and Functional Neuroimaging of Restricted and Repetitive Behavior in Autism Spectrum Disorder

A prominent symptom of Autism Spectrum Disorder includes restricted and repetitive behaviours. This symptom has been divided into three subtypes: repetitive motor behaviour, insistence on sameness and circumscribed interests. In the past, the neural correlates of these behaviours have been largely understudied. More recently, neuroimaging studies have pointed to a number of neural networks that may underlay these behaviours. However, results from this work have been varied and remain difficult to integrate. The purpose of this review is to summarize recent neuroimaging studies on restricted and repetitive behaviours in autism, and to provide an organized framework that will permit a clearer understanding of the neural correlates of these behaviours. Using a developmental perspective, this review will identify that there are distinct and overlapping neural networks that are associated with repetitive motor behaviour, insistence on sameness and circumscribed interests. In addition, this review will identify a series of executive and affective function tasks that have proven efficacious in the study of repetitive behaviour

Functional Brain Differences Predict Challenging Auditory Speech Comprehension in Older Adults

abstract: Older adults often experience communication difficulties, including poorer comprehension of auditory speech when it contains complex sentence structures or occurs in noisy environments. Previous work has linked cognitive abilities and the engagement of domain-general cognitive resources, such as the cingulo-opercular and frontoparietal brain networks, in response to challenging speech. However, the degree to which these networks can support comprehension remains unclear. Furthermore, how hearing loss may be related to the cognitive resources recruited during challenging speech comprehension is unknown. This dissertation investigated how hearing, cognitive performance, and functional brain networks contribute to challenging auditory speech comprehension in older adults. Experiment 1 characterized how age and hearing loss modulate resting-state functional connectivity between Heschl’s gyrus and several sensory and cognitive brain networks. The results indicate that older adults exhibit decreased functional connectivity between Heschl’s gyrus and sensory and attention networks compared to younger adults. Within older adults, greater hearing loss was associated with increased functional connectivity between right Heschl’s gyrus and the cingulo-opercular and language networks. Experiments 2 and 3 investigated how hearing, working memory, attentional control, and fMRI measures predict comprehension of complex sentence structures and speech in noisy environments. Experiment 2 utilized resting-state functional magnetic resonance imaging (fMRI) and behavioral measures of working memory and attentional control. Experiment 3 used activation-based fMRI to examine the brain regions recruited in response to sentences with both complex structures and in noisy background environments as a function of hearing and cognitive abilities. The results suggest that working memory abilities and the functionality of the frontoparietal and language networks support the comprehension of speech in multi-speaker environments. Conversely, attentional control and the cingulo-opercular network were shown to support comprehension of complex sentence structures. Hearing loss was shown to decrease activation within right Heschl’s gyrus in response to all sentence conditions and increase activation within frontoparietal and cingulo-opercular regions. Hearing loss also was associated with poorer sentence comprehension in energetic, but not informational, masking. Together, these three experiments identify the unique contributions of cognition and brain networks that support challenging auditory speech comprehension in older adults, further probing how hearing loss affects these relationships.Dissertation/ThesisDoctoral Dissertation Neuroscience 201

Differential Activation of Frontoparietal Attention Networks by Social and Symbolic Spatial Cues

Perception of both gaze-direction and symbolic directional cues (e.g. arrows) orient an observer’s attention toward the indicated location. It is unclear, however, whether these similar behavioral effects are examples of the same attentional phenomenon and, therefore, subserved by the same neural substrate. It has been proposed that gaze, given its evolutionary significance, constitutes a ‘special’ category of spatial cue. As such, it is predicted that the neural systems supporting spatial reorienting will be different for gaze than for non-biological symbols. We tested this prediction using functional magnetic resonance imaging to measure the brain’s response during target localization in which laterally presented targets were preceded by uninformative gaze or arrow cues. Reaction times were faster during valid than invalid trials for both arrow and gaze cues. However, differential patterns of activity were evoked in the brain. Trials including invalid rather than valid arrow cues resulted in a stronger hemodynamic response in the ventral attention network. No such difference was seen during trials including valid and invalid gaze cues. This differential engagement of the ventral reorienting network is consistent with the notion that the facilitation of target detection by gaze cues and arrow cues is subserved by different neural substrates

On Control Systems of the Brain: A Study of Their Connections, Activations, and Interactions

Implementation of daily functions in humans crucially relies on both the bottom-up moment-to- moment processing of relevant input and output information as well as the top-down controls that instantiate and regulate goal-directed strategies. The current dissertation focuses on different systems of brain regions related to task control. We are interested in investigating, in detail, some of the basic activity patterns that different control systems carry during simple tasks, and how differences in activity patterns may shed new insight onto the distinctions among the systems\u27 functional roles. In addition, carefully coordinated interactions between brain regions specialized for control-related activity and regions specialized for bottom-up information processing are essential for humans to adeptly undertake various goal-directed tasks. Hence, another goal is to explore how the relationships among regions related to control and regions related to processing will change as result of top-down control signals during tasks. In Chapter 2, we applied the graph theory method of link communities onto the brain\u27s resting-state intrinsic connectivity structure to identify possible points of interactions among the previously defined functional systems, including various control systems. In Chapter 3, we conducted a meta-analysis of tasks to examine the distinct functional characteristics of control systems in task activation. Using a data-driven clustering analysis, we identified two distinct trial-related response profiles that divided the regions of control systems into a right frontoparietal and cinguloopercular cluster, which may be engaged in fine-tuning task parameters and evaluating performance, and a left frontoparietal and dorsal attention cluster, which may be involved in timely updates of trial-wise parameters as well as information processing. In Chapter 4, we explored the changes in functional relationships among selected systems during individual trials of a goal-direct task and found the presence of complex and dynamic relationships that suggest changes among the various functional systems across a trial reflect both continuous as well as momentary effects of top-down signals. Collectively, the studies presented here both contributed to as well as challenged previous frameworks of task control in an effort to build better understanding of the basic organization and interactions among the brain\u27s functional systems

Anxiety and attention to threat: cognitive mechanisms and treatment with attention bias modification

Anxiety disorders are common and difficult to treat. Some cognitive models of anxiety propose that attention bias to threat causes and maintains anxiety. This view led to the development of a computer-delivered treatment: attention bias modification (ABM) which predominantly trains attention avoidance of threat. However, meta-analyses indicate disappointing effectiveness of ABM-threat-avoidance training in reducing anxiety. This article considers how ABM may be improved, based on a review of key ideas from models of anxiety, attention and cognitive control. These are combined into an integrative framework of cognitive functions which support automatic threat evaluation/detection and goal-directed thought and action, which reciprocally influence each other. It considers roles of bottom-up and top-down processes involved in threat-evaluation, orienting and inhibitory control in different manifestations of attention bias (initial orienting, attention maintenance, threat avoidance, threat-distractor interference) and different ABM methods (e.g., ABM-threat-avoidance, ABM-positive-search). The framework has implications for computer-delivered treatments for anxiety. ABM methods which encourage active goal-focused attention-search for positive/nonthreat information and flexible cognitive control across multiple processes (particularly inhibitory control, which supports a positive goal-engagement mode over processing of minor threat cues) may prove more effective in reducing anxiety than ABM-threat-avoidance training which targets a specific bias in spatial orienting to threat