Mental stress and sudden cardiac death: asymmetric midbrain activity as a linking mechanism

Patients with specific neurological, psychiatric or cardiovascular conditions are at enhanced risk of cardiac arrhythmia and sudden death. The neurogenic mechanisms are poorly understood. However, in many cases, stress may precipitate cardiac arrhythmia and sudden death in vulnerable patients, presumably via centrally driven autonomic nervous system responses. From a cardiological perspective, the likelihood of arrhythmia is strongly associated with abnormalities in electrical repolarization (recovery) of the heart muscle after each contraction. Inhomogeneous and asymmetric repolarization, reflected in ECG T-wave abnormalities, is associated with a greatly increased risk of arrhythmia, i.e. a proarrhythmic state. We therefore undertook a study to identify the brain mechanisms by which stress can induce cardiac arrhythmia through efferent autonomic drive. We recruited a typical group of 10 out-patients attending a cardiological clinic. We simultaneously measured brain activity, using H2(15)O PET, and the proarrhythmic state of the heart, using ECG, during mental and physical stress challenges and corresponding control conditions. Proarrhythmic changes in the heart were quantified from two ECG-derived measures of repolarization inhomogeneity and were related to changes in magnitude and lateralization of regional brain activity reflected in regional cerebral blood flow. Across the patient group, we observed a robust positive relationship between right-lateralized asymmetry in midbrain activity and proarrhythmic abnormalities of cardiac repolarization (apparent in two independent ECG measures) during stress. This association between stress-induced lateralization of midbrain activity and enhanced arrhythmic vulnerability provides empirical support for a putative mechanism for stress-induced sudden death, wherein lateralization of central autonomic drive during stress results in imbalanced activity in right and left cardiac sympathetic nerves. A right-left asymmetry in sympathetic drive across the surface of the heart disrupts the electrophysiological homogeneity of ventricular repolarization, predisposing to arrhythmia. Our findings highlight a proximal brain basis for stress-induced cardiac arrhythmic vulnerability.

Brain activity relating to the contingent negative variation: an fMRI investigation

The contingent negative variation (CNV) is a long-latency electroencephalography (EEG) surface negative potential with cognitive and motor components, observed during response anticipation. CNV is an index of cortical arousal during orienting and attention, yet its functional neuroanatomical basis is poorly understood. We used functional magnetic resonance imaging (fMRI) with simultaneous EEG and recording of galvanic skin response (GSR) to investigate CNV-related central neural activity and its relationship to peripheral autonomic arousal. In a group analysis, blood oxygenation level dependent (BOLD) activity during the period of CNV generation was enhanced in thalamus, somatomotor cortex, bilateral midcingulate, supplementary motor, and insular cortices. Enhancement of CNV-related activity in anterior and midcingulate, SMA, and insular cortices was associated with decreases in peripheral sympathetic arousal. In a subset of subjects in whom we acquired simultaneous EEG and fMRI data, we observed activity in bilateral thalamus, anterior cingulate, and supplementary motor cortex that was modulated by trial-by-trial amplitude of CNV. These findings provide a likely functional neuroanatomical substrate for the CNV and demonstrate modulation of components of this neural circuitry by peripheral autonomic arousal. Moreover, these data suggest a mechanistic model whereby thalamocortical interactions regulate CNV amplitude.

Activity in ventromedial prefrontal cortex covaries with sympathetic skin conductance level: a physiological account of a “default mode” of brain function

We examined neural activity related to modulation of skin conductance level (SCL), an index of sympathetic tone, using functional magnetic resonance imaging (fMRI) while subjects performed biofeedback arousal and relaxation tasks. Neural activity within the ventromedial prefrontal cortex (VMPFC) and the orbitofrontal cortex (OFC) covaried with skin conductance level (SCL), irrespective of task. Activity within striate and extrastriate cortices, anterior cingulate and insular cortices, thalamus, hypothalamus and lateral regions of prefrontal cortex reflected the rate of change in electrodermal activity, highlighting areas supporting transient skin conductance responses (SCRs). Successful performance of either biofeedback task (where SCL changed in the intended direction) was associated with enhanced activity in mid-OFC. The findings point to a dissociation between neural systems controlling basal sympathetic tone (SCL) and transient skin conductance responses (SCRs). The level of activity in VMPFC has been related to a default mode of brain function and our findings provide a physiological account of this state, indicating that activity within VMPFC and OFC reflects a dynamic between exteroceptive and interoceptive deployment of attention.

Influence of sympathetic autonomic arousal on cortical arousal: implications for a therapeutic behavioural intervention in epilepsy

Negative amplitude shifts of cortical potential are related to seizure activity in epilepsy. Regulation of the cortical potential with biofeedback has been successfully used to reduce the frequency of some patients' seizures. Although such behavioural treatments are increasingly popular as an alternative to pharmacotherapy, there has been no investigation of the mechanisms that might bridge the behavioural index of peripheral autonomic activity and the central regulation of arousal. Galvanic Skin Response (GSR) is a sensitive measurement of autonomic arousal and physiological state which reflects one's behaviour. Thus we investigated the effect of peripheral autonomic modulation on cortical arousal with the future intention of using GSR biofeedback as a therapeutic treatment for epilepsy. The cortical negative potential was induced using the paradigm called Contingent Negative Variation (CNV) and measured in different physiological states. A high skin resistance state (reflecting a state of relaxation) and a low skin resistance state (reflecting a state of arousal), were engendered by two opposing procedures of GSR biofeedback. The CNV negative potential, acting as an index of cortical excitation, was significantly greater in amplitude at high levels of skin resistance (relaxed state) than at low levels of skin resistance (aroused state). Our results suggest an inverse relationship between a peripheral measure of autonomic arousal and an index of cortical arousal, the CNV. Moreover, we demonstrate modulation of this arousal-related potential by a behavioural intervention, indicating a potential therapeutic use of arousal biofeedback using GSR in the management of treatment-resistant epilepsy.

Neural systems supporting interoceptive awareness

Influential theories of human emotion argue that subjective feeling states involve representation of bodily responses elicited by emotional events. Within this framework, individual differences in intensity of emotional experience reflect variation in sensitivity to internal bodily responses. We measured regional brain activity by functional magnetic resonance imaging (fMRI) during an interoceptive task wherein subjects judged the timing of their own heartbeats. We observed enhanced activity in insula, somatomotor and cingulate cortices. In right anterior insular/opercular cortex, neural activity predicted subjects' accuracy in the heartbeat detection task. Furthermore, local gray matter volume in the same region correlated with both interoceptive accuracy and subjective ratings of visceral awareness. Indices of negative emotional experience correlated with interoceptive accuracy across subjects. These findings indicate that right anterior insula supports a representation of visceral responses accessible to awareness, providing a substrate for subjective feeling states.

Social and motivational functioning is not critically dependent on feedback of autonomic responses: neuropsychological evidence from patients with pure autonomic failure

Social, emotional and motivational behaviours are associated with production of automatic bodily responses. Re-representation in the brain through feedback of autonomic and skeletomuscular arousal is proposed to underlie "feeling states". These influence emotional judgments and bias motivational decision-making and guide social interactions. Consistent with this hypothesis, dissocial behaviour and deficits on emotional and motivation tasks are associated with blunted bodily responses in patients with orbitofrontal brain lesions or developmental psychopathy. To determine the critical dependence of social and emotional behaviours on bodily responses mediated by the autonomic nervous system, we examined patients with pure autonomic failure (PAF), a peripheral denervation of autonomic neurons with onset in middle age. Compared to healthy subjects, PAF patients were unimpaired on tests of motivational decision-making (Iowa Gambling Task), recognition of emotional facial expressions, Theory of Mind Tasks and tests of social cognition. Only on a test of emotional attribution, which is perhaps more sensitive to subjective feeling states, did PAF patients score worse than the comparison group, though there was no evidence that this deficit was specific to a discrete emotion and requires further validation. These findings suggest that emotional and social functioning is not critically tied to on-going experience of autonomic arousal state, Acquisition of autonomic failure late in life may protect against maladaptive social behaviour through established behavioural responses that may be associated with central "as if" representations.

Human cingulate cortex and autonomic control: converging neuroimaging and clinical evidence

Human anterior cingulate function has been explained primarily within a cognitive framework. We used functional MRI experiments with simultaneous electrocardiography to examine regional brain activity associated with autonomic cardiovascular control during performance of cognitive and motor tasks. Using indices of heart rate variability, and high- and low-frequency power in the cardiac rhythm, we observed activity in the dorsal anterior cingulate cortex (ACC) related to sympathetic modulation of heart rate that was dissociable from cognitive and motor-related activity. The findings predict that during effortful cognitive and motor behaviour the dorsal ACC supports the generation of associated autonomic states of cardiovascular arousal. We subsequently tested this prediction by studying three patients with focal damage involving the ACC while they performed effortful cognitive and motor tests. Each showed abnormalities in autonomic cardiovascular responses with blunted autonomic arousal to mental stress when compared with 147 normal subjects tested in identical fashion. Thus, converging neuroimaging and clinical findings suggest that ACC function mediates context-driven modulation of bodily arousal states.

Mood-dependent memory

Have you ever noticed that when you are in a bad mood the whole world seems to be against you? More negative things seem to happen, and you even remember past episodes of your life in a more negative way than usual. Most of us have experienced this phenomenon, but few will have thought about how this mood might interact with our ability to remember. In a recent paper, Susanne Erk et al. shed light on a possible neural basis for this phenomena.

Impaired olfactory identification in Asperger's syndrome

The authors measured odor detection threshold and odor identification in 12 males with Asperger's syndrome and 12 matched control subjects. Relative to control subjects, Asperger's syndrome subjects were not impaired at odor detection but were significantly impaired at olfactory identification.

Changes in cerebral morphology consequent to peripheral autonomic denervation

Pure autonomic failure (PAF) is characterized by an acquired, selective, peripheral denervation of the autonomic nervous system. Patients with PAF fail to generate bodily states of arousal via the autonomic nervous system in response to physical or cognitive effort. We used voxel-based morphometry to test the hypothesis that changes in the morphology of brain regions involved in autonomic control would arise as a consequence to the longstanding absence of peripheral autonomic responses in PAF patients. Optimized voxel-based morphometry of structural magnetic resonance scans was used to test for regional differences in grey and white matter in 15 PAF patients and matched controls. There were no group differences observed in global measures of grey matter, white matter, or cerebrospinal fluid (CSF). We identified morphometric differences reflecting regional decreases in grey matter volume and concentration in anterior cingulate and insular cortices in PAF patients relative to controls. Morphometric differences in brainstem and subcortical regions did not reach statistical significance. Our findings suggest that peripheral autonomic denervation is associated with grey matter loss in cortical regions encompassing areas that we have previously shown are functionally involved in generation and representation of bodily states of autonomic arousal. The nature of these changes cannot be determined from morphometric analysis alone, but we suggest that they reflect experience-dependent change consequent upon loss of afferent input to brain regions involved in representation of autonomic states.

Asperger syndrome: a proton magnetic resonance spectroscopy study of brain

BACKGROUND

Asperger syndrome (AS; an autistic disorder) is associated with impaired social skills and obsessional/repetitive behavior. Patients with autism have significant abnormalities in the frontal lobe and frontoparietal connectivity. Nobody has examined the relationship between abnormalities in the frontal and parietal lobes and clinical symptoms in people with AS.

METHODS

We used in vivo proton magnetic resonance spectroscopy to examine neuronal integrity of the medial prefrontal and parietal lobes in 14 non-learning-disabled adults with AS and 18 control subjects (of similar sex, age, and IQ). We obtained measures of the prefrontal lobe in 11, the parietal lobe in 13, and both lobes in 10 subjects with AS. We measured concentrations and ratios of N-acetylaspartate (NAA), creatine and phosphocreatine (Cr + PCr), and choline (Cho). Levels of NAA, Cr + PCr, and Cho are indicators of neuronal density and mitochondrial metabolism, phosphate metabolism, and membrane turnover. Frontal metabolite levels were correlated with scores on the Yale-Brown Obsessive Compulsive Scale and the Autism Diagnostic Interview.

RESULTS

Subjects with AS had a significantly higher prefrontal lobe concentration of NAA (z = -3.1; P =.002), Cr + PCr (z = -2.2; P =.03), and Cho (z = -2.9; P =.003). Increased prefrontal NAA concentration was significantly correlated with obsessional behavior (tau = 0.67; P =.005); increased prefrontal concentration of Cho, with social function (tau = 0.72; P =.02). We found no significant differences in parietal lobe metabolite concentrations.

CONCLUSION

Subjects with AS have abnormalities in neuronal integrity of the prefrontal lobe, which is related to severity of clinical symptoms.

Cortical and subcortical gray matter abnormalities in schizophrenia determined through structural magnetic resonance imaging with optimized volumetric voxel-based morphometry

OBJECTIVE

Structural neuroimaging studies have suggested an association between schizophrenia and abnormalities in brain morphology such as ventricular enlargement and differences in gray matter distribution. Less consistently reported are findings of regional abnormalities such as selective differences in thalamic volume. The authors applied an unbiased technique to test for differences in cerebral morphometry between patients with schizophrenia and matched comparison subjects.

METHOD

T(1)-weighted images from 20 schizophrenic patients and matched comparison subjects were processed by using optimized automated voxel-based morphometry within multiple linear regression analyses.

RESULTS

Global differences in gray matter volume were seen between the schizophrenic and comparison subjects, with selective regional gray matter differences noted in the mediodorsal thalamus and across cortical regions, including the ventral and medial prefrontal cortices. Within the schizophrenic subjects, a relationship was observed between gray matter volume loss in the medial prefrontal cortex and a positive family history of schizophrenia. There was no significant difference between patients and comparison subjects in rates of proportional gray matter reduction with age.

CONCLUSIONS

These observations confirm an association between thalamocortical morphometric abnormalities and schizophrenia, consistent with theoretical models of primary pathoetiological dysfunction in filtering, integration, and information transfer processes in patients with schizophrenia.

Volitional control of autonomic arousal: a functional magnetic resonance study

Electrodermal activity reflects autonomic sympathetic innervation of dermal sweat glands providing an index of emotion-related bodily states of arousal. Relaxation techniques, which are facilitated by external (bio)feedback of electrodermal activity, can be used by trained subjects to actively control bodily and emotional arousal. Biofeedback relaxation provides an experimental model to explore neural mechanisms contributing to emotional representations and intentional autonomic control. We used functional magnetic resonance imaging (fMRI) to explore neural mechanisms contributing to integration of volitional intent, self-representation, and autonomic states of arousal, embodied within performance of a biofeedback relaxation exercise. Data were obtained from 17 subjects to assess brain activity during relaxation in which a visual index of electrodermal arousal was modulated by accuracy (addition of random "noise") or sensitivity (by scalar adjustments of feedback). A central matrix of cortical, subcortical and brainstem autonomic centres was activated during biofeedback relaxation, as well as regions that mediate visual and somatesthetic representations and executive control. Anterior cingulate, amygdala, and insula activity was modulated by task manipulations that increased demand on processing interoceptive representations, while variation in anterior insula activity reflected an interaction between accuracy and sensitivity of feedback. These findings identify neural substrates that support integration of perceptual processing, interoception, and intentional modulation of bodily states of arousal.

Brain anatomy and sensorimotor gating in Asperger's syndrome

Asperger's syndrome (an autistic disorder) is characterized by stereotyped and obsessional behaviours, and pervasive abnormalities in socio-emotional and communicative behaviour. These symptoms lead to social exclusion and a significant healthcare burden; however, their neurobiological basis is poorly understood. There are few studies on brain anatomy of Asperger's syndrome, and no focal anatomical abnormality has been reliably reported from brain imaging studies of autism, although there is increasing evidence for differences in limbic circuits. These brain regions are important in sensorimotor gating, and impaired 'gating' may partly explain the failure of people with autistic disorders to inhibit repetitive thoughts and actions. Thus, we compared brain anatomy and sensorimotor gating in healthy people with Asperger's syndrome and controls. We included 21 adults with Asperger's syndrome and 24 controls. All had normal IQ and were aged 18-49 years. We studied brain anatomy using quantitative MRI, and sensorimotor gating using prepulse inhibition of startle in a subset of 12 individuals with Asperger's syndrome and 14 controls. We found significant age-related differences in volume of cerebral hemispheres and caudate nuclei (controls, but not people with Asperger's syndrome, had age-related reductions in volume). Also, people with Asperger's syndrome had significantly less grey matter in fronto-striatal and cerebellar regions than controls, and widespread differences in white matter. Moreover, sensorimotor gating was significantly impaired in Asperger's syndrome. People with Asperger's syndrome most likely have generalized alterations in brain development, but this is associated with significant differences from controls in the anatomy and function of specific brain regions implicated in behaviours characterizing the disorder. We hypothesize that Asperger's syndrome is associated with abnormalities in fronto-striatal pathways resulting in defective sensorimotor gating, and consequently characteristic difficulties inhibiting repetitive thoughts, speech and actions.

Electrodermal responses: what happens in the brain

Electrodermal activity (EDA) is now the preferred term for changes in electrical conductance of the skin, including phasic changes that have been referred to as galvanic skin responses (GSR), that result from sympathetic neuronal activity. EDA is a sensitive psychophysiological index of changes in autonomic sympathetic arousal that are integrated with emotional and cognitive states. Until recently there was little direct knowledge of brain mechanisms governing generation and control of EDA in humans. However, studies of patients with discrete brain lesions and, more recently, functional imaging techniques have clarified the contribution of brain regions implicated in emotion, attention, and cognition to peripheral EDA responses. Moreover, such studies enable an understanding of mechanisms by which states of bodily arousal, indexed by EDA, influence cognition and bias motivational behavior.

Neural responses during anticipation of a primary taste reward

The aim of this study was to determine the brain regions involved in anticipation of a primary taste reward and to compare these regions to those responding to the receipt of a taste reward. Using fMRI, we scanned human subjects who were presented with visual cues that signaled subsequent reinforcement with a pleasant sweet taste (1 M glucose), a moderately unpleasant salt taste (0.2 M saline), or a neutral taste. Expectation of a pleasant taste produced activation in dopaminergic midbrain, posterior dorsal amygdala, striatum, and orbitofrontal cortex (OFC). Apart from OFC, these regions were not activated by reward receipt. The findings indicate that when rewards are predictable, brain regions recruited during expectation are, in part, dissociable from areas responding to reward receipt.

Fear conditioning in humans: the influence of awareness and autonomic arousal on functional neuroanatomy

The degree to which perceptual awareness of threat stimuli and bodily states of arousal modulates neural activity associated with fear conditioning is unknown. We used functional magnetic neuroimaging (fMRI) to study healthy subjects and patients with peripheral autonomic denervation to examine how the expression of conditioning-related activity is modulated by stimulus awareness and autonomic arousal. In controls, enhanced amygdala activity was evident during conditioning to both "seen" (unmasked) and "unseen" (backward masked) stimuli, whereas insula activity was modulated by perceptual awareness of a threat stimulus. Absent peripheral autonomic arousal, in patients with autonomic denervation, was associated with decreased conditioning-related activity in insula and amygdala. The findings indicate that the expression of conditioning-related neural activity is modulated by both awareness and representations of bodily states of autonomic arousal.

Functional magnetic resonance imaging of odor identification: the effect of aging

BACKGROUND

Sense of smell declines with age and impairment in olfaction has been observed in some neurodegenerative disorders such as Alzheimer's disease. Functional neuroimaging techniques enable researchers to observe brain regions activated by olfactory stimuli.

METHODS

We gave three mainly olfactory-mediated odors (limonene, methylsalicylate, and eugenol) to six young and six elderly subjects and observed the areas activated by using blood oxygen level dependent contrast functional magnetic resonance imaging.

RESULTS

The group mapping of young subjects showed extensive activation in the orbitofrontal cortex, commonly believed to be the olfactory cortex, some limbic areas (the hippocampus and the thalamus), regions involved with gustatory sensation (the anterior insula and the inferior postcentral gyrus), superior and inferior temporal gyri, and cerebellum. In the elderly group, only the left inferior temporal gyrus and the primary visual cortex reached accepted significance levels.

CONCLUSIONS

We have therefore confirmed previous reports of brain regions involved in olfactory processing in young volunteers and demonstrated decreased activation in elderly volunteers.

Brain activity during biofeedback relaxation: a functional neuroimaging investigation

The mechanisms by which cognitive processes influence states of bodily arousal are important for understanding the pathogenesis and maintenance of stress-related morbidity. We used PET to investigate cerebral activity relating to the cognitively driven modulation of sympathetic activity. Subjects were trained to perform a biofeedback relaxation exercise that reflected electrodermal activity and were subsequently scanned performing repetitions of four tasks: biofeedback relaxation, relaxation without biofeedback and two corresponding control conditions in which the subjects were instructed not to relax. Relaxation was associated with significant increases in left anterior cingulate and globus pallidus activity, whereas no significant increases in activity were associated with biofeedback compared with random feedback. The interaction between biofeedback and relaxation, highlighting activity unique to biofeedback relaxation, was associated with enhanced anterior cingulate and cerebellar vermal activity. These data implicate the anterior cingulate cortex in the intentional modulation of bodily arousal and suggest a functional neuroanatomy of how cognitive states are integrated with bodily responses. The findings have potential implications for a mechanistic account of how therapeutic interventions, such as relaxation training in stress-related disorders, mediate their effects.

Neuroanatomical basis for first- and second-order representations of bodily states

Changes in bodily states, particularly those mediated by the autonomic nervous system, are crucial to ongoing emotional experience. A theoretical model proposes a first-order autoregulatory representation of bodily state at the level of dorsal pons, and a second-order experience-dependent re-mapping of changes in bodily state within structures such as cingulate and medial parietal cortices. We tested these anatomical predictions using positron emission tomography and a human neurological model (pure autonomic failure), in which peripheral autonomic denervation prevents the emergence of autonomic responses. Compared to controls, we observed task-independent differences in activity of dorsal pons and context-induced differences in cingulate and medial parietal activity in PAF patients. An absence of afferent feedback concerning autonomically generated bodily states was associated with subtle impairments of emotional responses in PAF patients. Our findings provide empirical support for a theory proposing a hierarchical representation of bodily states.

Neural activity in the human brain relating to uncertainty and arousal during anticipation

We used functional magnetic resonance neuroimaging to measure brain activity during delay between reward-related decisions and their outcomes, and the modulation of this delay activity by uncertainty and arousal. Feedback, indicating financial gain or loss, was given following a fixed delay. Anticipatory arousal was indexed by galvanic skin conductance. Delay-period activity was associated with bilateral activation in orbital and medial prefrontal, temporal, and right parietal cortices. During delay, activity in anterior cingulate and orbitofrontal cortices was modulated by outcome uncertainty, whereas anterior cingulate, dorsolateral prefrontal, and parietal cortices activity was modulated by degree of anticipatory arousal. A distinct region of anterior cingulate was commonly activated by both uncertainty and arousal. Our findings highlight distinct contributions of cognitive uncertainty and autonomic arousal to anticipatory neural activity in prefrontal cortex.

The functional neuroanatomy of social behaviour: changes in cerebral blood flow when people with autistic disorder process facial expressions

Although high-functioning individuals with autistic disorder (i.e. autism and Asperger syndrome) are of normal intelligence, they have life-long abnormalities in social communication and emotional behaviour. However, the biological basis of social difficulties in autism is poorly understood. Facial expressions help shape behaviour, and we investigated if high-functioning people with autistic disorder show neurobiological differences from controls when processing emotional facial expressions. We used functional MRI to investigate brain activity in nine adults with autistic disorder (mean age +/- standard deviation 37 +/- 7 years; IQ 102 +/- 15) and nine controls (27 +/- 7 years; IQ 116 +/- 10) when explicitly (consciously) and implicitly (unconsciously) processing emotional facial expressions. Subjects with autistic disorder differed significantly from controls in the activity of cerebellar, mesolimbic and temporal lobe cortical regions of the brain when processing facial expressions. Notably, they did not activate a cortical 'face area' when explicitly appraising expressions, or the left amygdala region and left cerebellum when implicitly processing emotional facial expressions. High-functioning people with autistic disorder have biological differences from controls when consciously and unconsciously processing facial emotions, and these differences are most likely to be neurodevelopmental in origin. This may account for some of the abnormalities in social behaviour associated with autism.