Gary R. Turner

Intrinsic architecture underlying the relations among the default, dorsal attention, and frontoparietal control networks of the human brain

Human cognition is increasingly characterized as an emergent property of interactions among distributed, functionally specialized brain networks. We recently demonstrated that the antagonistic “default” and “dorsal attention” networks—subserving internally and externally directed cognition, respectively—are modulated by a third “frontoparietal control” network that flexibly couples with either network depending on task domain. However, little is known about the intrinsic functional architecture underlying this relationship. We used graph theory to analyze network properties of intrinsic functional connectivity within and between these three large-scale networks. Task-based activation from three independent studies were used to identify reliable brain regions (“nodes”) of each network. We then examined pairwise connections (“edges”) between nodes, as defined by resting-state functional connectivity MRI. Importantly, we used a novel bootstrap resampling procedure to determine the reliability of graph edges. Furthermore, we examined both full and partial correlations. As predicted, there was a higher degree of integration within each network than between networks. Critically, whereas the default and dorsal attention networks shared little positive connectivity with one another, the frontoparietal control network showed a high degree of between-network interconnectivity with each of these networks. Furthermore, we identified nodes within the frontoparietal control network of three different types—default-aligned, dorsal attention-aligned, and dual-aligned—that we propose play dissociable roles in mediating internetwork communication. The results provide evidence consistent with the idea that the frontoparietal control network plays a pivotal gate-keeping role in goal-directed cognition, mediating the dynamic balance between default and dorsal attention networks.

The Functional Neuroanatomy of Episodic and Semantic Autobiographical Remembering: A Prospective Functional MRI Study

Autobiographical memory comprises episodic and semantic components mediated by dissociable states of consciousness, one promoting the experience of the self at a specific moment in the past, and the other involving self-knowledge that does not require mental time travel. These components can be difficult to dissociate using retrospective autobiographical stimuli collection. In this study, we manipulated the episodic/semantic distinction within prospectively collected autobiographical stimuli. Over several months, participants made recordings documenting specific episodes, repeated episodes, and world knowledge. These recordings were later played back to participants during scanning with functional MRI. The results indicated overlapping but distinct patterns of brain activity corresponding to episodic and semantic autobiographical memory. Both episodic and semantic autobiographical memory engaged the left anteromedial prefrontal cortex associated with self-reference, but the episodic condition did so to a greater degree. The episodic condition uniquely engaged the medial temporal, posterior cingulate, and diencephalic regions associated with remote memory recovery. Whereas the episodic condition engaged the right temporo-parietal cortex involved in reconstruction of spatial context and attentional orienting, the semantic condition engaged the left temporo-parietal and parieto-frontal systems involved in egocentric spatial processing and top-down attentional control. Episodic recollection was also associated with suppression of emotional paralimbic regions. These findings support a functional neuroanatomical dissociation between episodic and semantic autobiographical memory, providing concordance to amnesic syndromes with disproportionate impairment in one of these two forms of autobiographical memory.

Executive functions and neurocognitive aging: dissociable patterns of brain activity.

Studies of neurocognitive aging report altered patterns of brain activity in older versus younger adults performing executive function tasks. We review the extant literature, using activation likelihood estimation meta-analytic methods, to compare age-related differences in the pattern of brain activity across studies examining 2 categories of tasks associated with executive control processing: working memory and inhibition. In a direct contrast of young and older adult activations, older adults engaged bilateral regions of dorsolateral prefrontal cortex as well as supplementary motor cortex and left inferior parietal lobule during working memory. In contrast, age-related changes during inhibitory control were observed in right inferior frontal gyrus and presupplementary motor area. Additionally, when we examined task-related differences within each age group we observed the predicted pattern of differentiated neural response in the younger subjects: lateral prefrontal cortex activity associated with working memory versus right anterior insula/frontal opercular activity associated with inhibition. This separation was largely maintained in older subjects. These data provide the first quantitative meta-analytic evidence that age-related patterns of functional brain change during executive functioning depend on the specific control process being challenged.

Rehabilitation of Executive Functioning in Patients with Frontal Lobe Brain Damage with Goal Management Training

Executive functioning deficits due to brain disease affecting frontal lobe functions cause significant real-life disability, yet solid evidence in support of executive functioning interventions is lacking. Goal Management Training (GMT), an executive functioning intervention that draws upon theories concerning goal processing and sustained attention, has received empirical support in studies of patients with traumatic brain injury, normal aging, and case studies. GMT promotes a mindful approach to complex real-life tasks that pose problems for patients with executive functioning deficits, with a main goal of periodically stopping ongoing behavior to monitor and adjust goals. In this controlled trial, an expanded version of GMT was compared to an alternative intervention, Brain Health Workshop that was matched to GMT on non-specific characteristics that can affect intervention outcome. Participants included 19 individuals in the chronic phase of recovery from brain disease (predominantly stroke) affecting frontal lobe function. Outcome data indicated specific effects of GMT on the Sustained Attention to Response Task as well as the Tower Test, a visuospatial problem-solving measure that reflected far transfer of training effects. There were no significant effects on self-report questionnaires, likely owing to the complexity of these measures in this heterogeneous patient sample. Overall, these data support the efficacy of GMT in the rehabilitation of executive functioning deficits.

Deficits in facial emotion perception in adults with recent traumatic brain injury

UNLABELLED We examined whether facial emotion perception was compromised in adults with recent traumatic brain injury (TBI). Few studies have examined emotion perception in TBI; those that have, examined chronic patients only. Recent and chronic TBI populations differ according to degree of functional reorganization of the brain, use of compensatory strategies, and severity of cognitive impairments--any of which might differentially affect presentation of emotion perception deficits. A secondary aim of the study was to utilize the TBI population--in whom diffuse axonal injury (DAI) is a cardinal neurological feature--to examine the suggestion of Adolphs et al. [Journal of Neuroscience 20(7) (2000) 2683] that damage to white matter tracts should give rise to emotion perception deficits. METHODS Thirty TBI participants and 30 age-matched controls were tested. A 2 x 3 mixed design was employed. The dependent variable was accuracy on neutral and emotional face perception tests. RESULTS (1) The TBI group performed significantly less accurately than the matched controls on the facial emotion perception tasks, whereas the groups performed equivalently on a non-emotional face perception control task. (2) A sub-group of TBI participants without evidence of focal injury to areas of the brain most commonly implicated in facial emotion perception was as impaired on the emotion perception tasks as a second sub-group who had sustained focal lesions to these areas. This suggests an alternative neurological mechanism for deficits in the first sub-group, such as DAI. CONCLUSIONS Patients with recently acquired TBI are impaired in their ability to perceive emotions in faces. DAI alone may cause facial emotion perception deficits.

Augmented neural activity during executive control processing following diffuse axonal injury

Background: Deficits in working memory are commonly observed after traumatic brain injury (TBI), with executive control processes preferentially impacted relative to storage and rehearsal. Previous activation functional neuroimaging investigations of working memory in patients with TBI have reported altered functional recruitment, but methodologic issues including sample heterogeneity (e.g., variability in injury mechanism, severity, neuropathology or chronicity), underspecified definitions of “working memory,” and behavioral differences between TBI and control groups have hindered interpretation of these changes. Methods: Executive control processing in working memory was explicitly engaged during fMRI in a sample of carefully selected chronic-stage, moderate-to-severe TBI patients with diffuse axonal injury (DAI) but without focal lesions. Results: Despite equivalent task performance, we observed a pattern of greater recruitment of interhemispheric and intrahemispheric regions of prefrontal cortex (PFC) and posterior cortices in our DAI sample. Enhanced activations were recorded in the left dorsolateral PFC (middle frontal gyrus), right ventrolateral PFC (inferior frontal gyrus), bilateral posterior parietal cortices, and left temporo-occipital junction. Region-of-interest analyses confirmed that these effects were robust across individual patients and could not be attributed to load factors or slowed speed of processing. Conclusions: Augmented functional recruitment in the context of normal behavioral performance may be a neural marker of capacity or efficiency limits that can affect functional outcome after traumatic brain injury with diffuse injury.

Training of goal-directed attention regulation enhances control over neural processing for individuals with brain injury

Deficits in attention and executive control are some of the most common, debilitating and persistent consequences of brain injuries. Understanding neural mechanisms that support clinically significant improvements, when they do occur, may help advance treatment development. Intervening via rehabilitation provides an opportunity to probe such mechanisms. Our objective was to identify neural mechanisms that underlie improvements in attention and executive control with rehabilitation training. We tested the hypothesis that intensive training enhances modulatory control of neural processing of perceptual information in patients with acquired brain injuries. Patients (n=12) participated either in standardized training designed to target goal-directed attention regulation, or a comparison condition (brief education). Training resulted in significant improvements on behavioural measures of attention and executive control. Functional magnetic resonance imaging methods adapted for testing the effects of intervention for patients with varied injury pathology were used to index modulatory control of neural processing. Pattern classification was utilized to decode individual functional magnetic resonance imaging data acquired during a visual selective attention task. Results showed that modulation of neural processing in extrastriate cortex was significantly enhanced by attention regulation training. Neural changes in prefrontal cortex, a candidate mediator for attention regulation, appeared to depend on individual baseline state. These behavioural and neural effects did not occur with the comparison condition. These results suggest that enhanced modulatory control over visual processing and a rebalancing of prefrontal functioning may underlie improvements in attention and executive control.

Rehabilitation of Executive Functioning After Focal Damage to the Cerebellum

Executive dysfunction accounts for significant disability in patients with many types of brain injury in many locations. Clinical reports have described impaired executive functioning after damage to the cerebellum, and anatomical and neuroimaging studies have identified the likely basis for this effect: a cortico—ponto—cerebellar network through which the cerebellum is densely connected to areas of frontal cortex. The patterns of executive impairment attributable to cerebellar damage have been extensively described in the past 15 years, but there has been no assessment of the efficacy of rehabilitation in this patient population. Here, the use of a cognitive rehabilitation technique, Goal Management Training, in a patient with persisting executive dysfunction after a right cerebellar hemorrhage is described. The patient made and maintained modest gains on measures of sustained attention, planning, and organization that translated into significant improvement in real-life functioning. This is the first report on the rehabilitation of impaired executive functioning following focal damage to the cerebellum and in the presence of intact frontal cortex.

Reconstructing the Past: Personal Memory Technologies Are Not Just Personal and Not Just for Memory

Research has shown that personal memory technologies are a promising way to address the needs of older adults with memory impairments. In this article, we review three recently completed studies that evaluated technologies for personal memories intended for persons with Alzheimers disease (AD) or mild cognitive impairment (MCI). In the first study, we worked with 12 participants with AD or MCI and their families to construct DVD-based Multimedia Biographies that depicted prominent events, people, and places from the participants past. We then evaluated over a period of 6 months psychosocial effects that viewing the biographies had on the participants and their family members. These effects included stimulating reminiscence of past events, triggering predominantly positive emotions of happiness and occasional moments of sadness, and engaging conversations with family members. In our second study, we designed a home-based ambient display that allowed a man with AD to similarly review his past life, in combination with recent photos automatically captured by a lifelogging device called SenseCam. Psychometric tests and semistructured interviews revealed how the intervention appeared to improve the participants sense of self and lower apathy. In our final study of 5 cognitively impaired participants we compared representations of recent experiences captured with SenseCam in 3 ways: with the raw image stream, with a slide show consisting of a selected number of SenseCam images narrated by a family member, and with a control reviewing no images. Results included evidence that reviewing SenseCam images improved episodic recall for personal events depicted in the images for 4 of the 5 participants. Based on lessons learned from this research, we suggest that personal memory technologies should not just be framed as systems for augmenting an individual users capacity for accurate recall of personal events, but instead should support groups of people such as members of a family in telling their life stories. This conception yields benefits beyond the support of memory, such as fostering a sense of self and strengthening interpersonal relationships with family members. We conclude the article by presenting design considerations to help guide and inform the development and evaluation of future “personal memory” technologies.

Prefrontal compensatory engagement in TBI is due to altered functional engagement of existing networks and not functional reorganization

Functional neuroimaging studies of traumatic brain injury (TBI) have demonstrated altered neural recruitment, specifically within prefrontal cortex (PFC). This is manifest typically as increased recruitment of homologous regions of PFC (e.g., right ventrolateral PFC during performance of a verbal working memory task, possibly in response to damage involving the left PFC). The behavioral correlates of these functional changes are poorly understood. We used fMRI and multivariate analytic methods to investigate changes in spatially distributed activity patterns and their behavioral correlates in a sample of TBI patients with diffuse axonal injury (DAI, but without focal injury) and matched healthy controls. Participants performed working memory tasks with varying memory load and executive demand. We identified networks within left and right PFC that uniquely and positively correlated with performance in our control and TBI samples respectively, providing evidence of compensatory functional recruitment. Next we combined brain–behavior and functional connectivity analyses to investigate whether compensatory brain changes were facilitated by functional reorganization (i.e., recruitment of brain regions not engaged by our control sample) or altered functional engagement (i.e., differential recruitment of similar brain regions between the two groups based on task demands). In other words, does altered recruitment represent the instantiation of novel neural networks to support working memory performance after injury or the unmasking of extant, but behaviorally latent, functional connectivity? Our results support an altered functional engagement hypothesis. Areas within PFC that are normally coactivated during working memory are behaviorally relevant at an earlier stage of difficulty for TBI patients as compared to controls. This altered functional engagement, also evident in the aging literature, is attributable to distributed changes owing to significant DAI.