Steven G. Greening

Multiple Mechanisms of Consciousness: The Neural Correlates of Emotional Awareness

Emotional stimuli, including facial expressions, are thought to gain rapid and privileged access to processing resources in the brain. Despite this access, we are conscious of only a fraction of the myriad of emotion-related cues we face everyday. It remains unclear, therefore, what the relationship is between activity in neural regions associated with emotional representation and the phenomenological experience of emotional awareness. We used functional magnetic resonance imaging and binocular rivalry to delineate the neural correlates of awareness of conflicting emotional expressions in humans. Behaviorally, fearful faces were significantly more likely to be perceived than disgusted or neutral faces. Functionally, increased activity was observed in regions associated with facial expression processing, including the amygdala and fusiform gyrus during emotional awareness. In contrast, awareness of neutral faces and suppression of fearful faces were associated with increased activity in dorsolateral prefrontal and inferior parietal cortices. The amygdala showed increased functional connectivity with ventral visual system regions during fear awareness and increased connectivity with perigenual prefrontal cortex (pgPFC; Brodmanns area 32/10) when fear was suppressed. Despite being prioritized for awareness, emotional items were associated with reduced activity in areas considered critical for consciousness. Contributions to consciousness from bottom-up and top-down neural regions may be additive, such that increased activity in specialized regions within the extended ventral visual system may reduce demands on a frontoparietal system important for awareness. The possibility is raised that interactions between pgPFC and the amygdala, previously implicated in extinction, may also influence whether or not an emotional stimulus is accessible to consciousness.

Conscious Perception of Emotional Stimuli Brain Mechanisms

Emotional stimuli are thought to gain rapid and privileged access to processing resources in the brain. The structures involved in this enhanced access are thought to support subconscious, reflexive processes. Whether these pathways contribute to the phenomenological experience of emotional visual awareness (i.e., conscious perception) is unclear. In this review, it is argued that subcortical networks associated with the rapid detection of emotionally salient stimuli also play a key role in shaping awareness. This proposal is based on the idea that awareness of visual stimuli should be considered along a continuum, having intermediate levels, rather than as an all-or-none construct. It is also argued that awareness of emotional stimuli requires less input from frontoparietal structures that are often considered crucial for visual awareness. Evidence is also presented that implicates a region of the medial prefrontal cortex, involved in emotion regulation, in modulating amygdala output to determine awareness of emotional visual stimuli; when emotional stimuli are present, the conscious perception of alternative stimuli requires greater regulatory influences from cortical structures. Thus, emotional stimuli are privileged not only for neuronal representation and impact on subconscious processes, but also for awareness, allowing humans to deal flexibly rather than merely reflexively to biologically significant stimuli.

The neural correlates of regulating positive and negative emotions in medication-free major depression

Depressive cognitive schemas play an important role in the emergence and persistence of major depressive disorder (MDD). The current study adapted emotion regulation techniques to reflect elements of cognitive behavioural therapy (CBT) and related psychotherapies to delineate neurocognitive abnormalities associated with modulating the negative cognitive style in MDD. Nineteen non-medicated patients with MDD and 19 matched controls reduced negative or enhanced positive feelings elicited by emotional scenes while undergoing functional magnetic resonance imaging. Although both groups showed significant emotion regulation success as measured by subjective ratings of affect, the controls were significantly better at modulating both negative and positive emotion. Both groups recruited regions of dorsolateral prefrontal cortex and ventrolateral prefrontal cortex (VLPFC) when regulating negative emotions. Only in controls was this accompanied by reduced activity in sensory cortices and amygdala. Similarly, both groups showed enhanced activity in VLPFC and ventral striatum when enhancing positive affect; however, only in controls was ventral striatum activity correlated with regulation efficacy. The results suggest that depression is associated with both a reduced capacity to achieve relief from negative affect despite recruitment of ventral and dorsal prefrontal cortical regions implicated in emotion regulation, coupled with a disconnect between activity in reward-related regions and subjective positive affect.

Do fearful eyes activate empathy-related brain regions in individuals with callous traits?

Psychopathy, a developmental disorder characterized by profound social disturbance, is associated with impaired recognition of distress cues. Since distress processing and moral socialization are closely linked, uncovering techniques to improve distress recognition could have positive treatment implications for developmental disorders that feature empathy impairments. Previous studies demonstrate that fear-recognition deficits can be remedied by redirecting attention to critical cues (the eyes for fearful faces). However, it remains unclear whether this manipulation increases activity in empathy-related brain regions, or has an alternate compensatory effect that may not promote prosocial behaviours. In this fMRI study, a community sample of individuals with high vs low callous traits completed an emotion recognition task that varied whether the most or least socially meaningful facial features were visible (the eyes were isolated or occluded). For fearful faces, individuals with high callous traits showed significantly less amygdala and medial prefrontal cortex activity than those with low callous traits when the eyes were occluded, but not when they were isolated. Consistent with recent models of the amygdala that emphasize orientation to disambiguate stimuli rather than represent distress, individuals with low trait empathy showed greater amygdala activity to the least vs most socially meaningful features of fearful faces.

Parsing decision making processes in prefrontal cortex: response inhibition, overcoming learned avoidance, and reversal learning.

Reversal learning refers to the ability to inhibit or switch responding to an object when the object-reward contingency changes. Deficits in this process are related to social abnormalities, impulsiveness, and a number of psychiatric disorders. A range of neural regions play a role in this process, including dorsolateral prefrontal cortex (dlPFC), dorsomedial prefrontal cortex (dmPFC), and inferior frontal gyrus (IFG). However, determining the specific functional contribution of each region has proved difficult, in part because reversal learning involves multiple cognitive subprocesses such as error detection, inhibiting responding to formerly rewarded stimuli, and overcoming avoidance of previously punished stimuli. We used fMRI and an experimental task adapted from a recent neurochemical study in marmosets to parse neural responding to subprocesses of reversal learning during choice and feedback trial components. Error-feedback processing was associated with increased activity in dmPFC, dlPFC, and IFG whether participants were overcoming avoidance, inhibiting responding, or performing classic response reversal. Reduced activity in medial prefrontal cortex (mPFC) was associated with error-feedback processing for response inhibition but not overcoming avoidance. Conversely, there was significantly greater activity in anterior dmPFC during error-feedback processing in overcoming avoidance compared to response inhibition. A conjunction analysis confirmed that a striking overlap in activity was observed across the three conditions in IFG, dlPFC, and dmPFC. The results are consistent with conceptualizations of IFG function that emphasize modulating stimulus-response maps rather than purely response inhibition. The approach has implications for models of prefrontal function and neurocognitive perspectives on a range of behavioural abnormalities associated with impairments in decision making.

Multivariate cross-classification: applying machine learning techniques to characterize abstraction in neural representations

Here we highlight an emerging trend in the use of machine learning classifiers to test for abstraction across patterns of neural activity. When a classifier algorithm is trained on data from one cognitive context, and tested on data from another, conclusions can be drawn about the role of a given brain region in representing information that abstracts across those cognitive contexts. We call this kind of analysis Multivariate Cross-Classification (MVCC), and review several domains where it has recently made an impact. MVCC has been important in establishing correspondences among neural patterns across cognitive domains, including motor-perception matching and cross-sensory matching. It has been used to test for similarity between neural patterns evoked by perception and those generated from memory. Other work has used MVCC to investigate the similarity of representations for semantic categories across different kinds of stimulus presentation, and in the presence of different cognitive demands. We use these examples to demonstrate the power of MVCC as a tool for investigating neural abstraction and discuss some important methodological issues related to its application.

Exploring the Construct Validity of the Transtheoretical Model to Structure Physical Activity Interventions for Individuals with Serious Mental Illness

OBJECTIVE Physical activity intervention research involving individuals with serious mental illness are often not based on any theoretical framework. This study examined the construct validity of the Transtheoretical Model (TTM) in individuals with serious mental illness to guide future physical activity interventions. METHODS Fifty-four individuals completed surveys that asked about their current stage of change for physical activity, self-efficacy, and perceived advantages and disadvantages of being more physically active. RESULTS Most individuals reported being in the preparation stage of the TTM. As individuals approached the action and maintenance stages, self-efficacy and perceived benefits of physical activity increased significantly. Although perceived disadvantages decreased with each successive stage, this change was not significant. CONCLUSIONS This studys findings support the TTMs application in this population to structure physical activity interventions given that self-efficacy, perceived benefits of and barriers to physical activity differed across stages and changes were in the direction predicted by theory.

Neuromelanin marks the spot: identifying a locus coeruleus biomarker of cognitive reserve in healthy aging

Leading a mentally stimulating life may build up a reserve of neural and mental resources that preserve cognitive abilities in late life. Recent autopsy evidence links neuronal density in the locus coeruleus (LC), the brains main source of norepinephrine, to slower cognitive decline before death, inspiring the idea that the noradrenergic system is a key component of reserve (Robertson, I. H. 2013. A noradrenergic theory of cognitive reserve: implications for Alzheimers disease. Neurobiol. Aging. 34, 298-308). Here, we tested this hypothesis using neuromelanin-sensitive magnetic resonance imaging to visualize and measure LC signal intensity in healthy younger and older adults. Established proxies of reserve, including education, occupational attainment, and verbal intelligence, were linearly correlated with LC signal intensity in both age groups. Results indicated that LC signal intensity was significantly higher in older than younger adults and significantly lower in women than in men. Consistent with the LC-reserve hypothesis, both verbal intelligence and a composite reserve score were positively associated with LC signal intensity in older adults. LC signal intensity was also more strongly associated with attentional shifting ability in older adults with lower cognitive reserve. Together these findings link in vivo estimates of LC neuromelanin signal intensity to cognitive reserve in normal aging.

A network of amygdala connections predict individual differences in trait anxiety

In this study we demonstrate that the pattern of an amygdala‐centric network contributes to individual differences in trait anxiety. Individual differences in trait anxiety were predicted using maximum likelihood estimates of amygdala structural connectivity to multiple brain targets derived from diffusion‐tensor imaging (DTI) and probabilistic tractography on 72 participants. The prediction was performed using a stratified sixfold cross validation procedure using a regularized least square regression model. The analysis revealed a reliable network of regions predicting individual differences in trait anxiety. Higher trait anxiety was associated with stronger connections between the amygdala and dorsal anterior cingulate cortex, an area implicated in the generation of emotional reactions, and inferior temporal gyrus and paracentral lobule, areas associated with perceptual and sensory processing. In contrast, higher trait anxiety was associated with weaker connections between amygdala and regions implicated in extinction learning such as medial orbitofrontal cortex, and memory encoding and environmental context recognition, including posterior cingulate cortex and parahippocampal gyrus. Thus, trait anxiety is not only associated with reduced amygdala connectivity with prefrontal areas associated with emotion modulation, but also enhanced connectivity with sensory areas. This work provides novel anatomical insight into potential mechanisms behind information processing biases observed in disorders of emotion. Hum Brain Mapp 36:4819–4830, 2015.

Higher locus coeruleus MRI contrast is associated with lower parasympathetic influence over heart rate variability

Abstract The locus coeruleus (LC) is a key node of the sympathetic nervous system and suppresses parasympathetic activity that would otherwise increase heart rate variability. In the current study, we examined whether LC‐MRI contrast reflecting neuromelanin accumulation in the LC was associated with high‐frequency heart rate variability (HF‐HRV), a measure reflecting parasympathetic influences on the heart. Recent evidence indicates that neuromelanin, a byproduct of catecholamine metabolism, accumulates in the LC through young and mid adulthood, suggesting that LC‐MRI contrast may be a useful biomarker of individual differences in habitual LC activation. We found that, across younger and older adults, greater LC‐MRI contrast was negatively associated with HF‐HRV during fear conditioning and spatial detection tasks. This correlation was not accounted for by individual differences in age or anxiety. These findings indicate that individual differences in LC structure relate to key cardiovascular parameters. HighlightsWe measured locus coeruleus neuromelanin MRI contrast (LC‐MRI).Participants with higher LC‐MRI had lower high‐frequency heart rate variability.This relationship was not due to individual differences in age or anxiety.