Observations, reflections and speculations on the cerebral determinants of mood and on the bilaterally asymmetrical distributions of the major neurotransmitter systems

Sex differences in neuronal systems function and behaviour: beyond a single diagnosis in autism spectrum disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that is associated with functional brain alterations that underlie the expression of behaviour. Males are diagnosed up to four times more than females, and sex differences have been identified in memory, cognitive flexibility, verbal fluency, and social communication. Unfortunately, there exists a lack of information on the sex-dependent mechanisms of ASD, as well as biological markers to distinguish sex-specific symptoms in ASD. This can often result in a standardized diagnosis for individuals across the spectrum, despite significant differences in the various ASD subtypes. Alterations in neuronal connectivity and oscillatory activity, such as is observed in ASD, are highly coupled to behavioural states. Yet, despite the well-identified sexual dimorphisms that exist in ASD, these functional patterns have rarely been analyzed in the context of sex differences or symptomology. This review summarizes alterations in neuronal oscillatory function in ASD, discusses the age, region, symptom and sex-specific differences that are currently observed across the spectrum, and potential targets for regulating neuronal oscillatory activity in ASD. The need to identify sex-specific biomarkers, in order to facilitate specific diagnostic criteria and allow for more targeted therapeutic approaches for ASD will also be discussed.

Neural effective connectivity explains subjective fatigue in stroke

Persistent fatigue is a major debilitating symptom in many psychiatric and neurological conditions, including stroke. Post-stroke fatigue has been linked to low corticomotor excitability. Yet, it remains elusive as to what the neuronal mechanisms are that underlie motor cortex excitability and chronic persistence of fatigue.

In this cross-sectional observational study, in two experiments we examined a total of 59 non-depressed stroke survivors with minimal motoric and cognitive impairments using ‘resting-state’ MRI and single- and paired-pulse transcranial magnetic stimulation.

In the first session of Experiment 1, we assessed resting motor thresholds—a typical measure of cortical excitability—by applying transcranial magnetic stimulation to the primary motor cortex (M1) and measuring motor-evoked potentials in the hand affected by stroke. In the second session, we measured their brain activity with resting-state MRI to assess effective connectivity interactions at rest. In Experiment 2 we examined effective inter-hemispheric connectivity in an independent sample of patients using paired-pulse transcranial magnetic stimulation. We also assessed the levels of non-exercise induced, persistent fatigue using Fatigue Severity Scale (FSS-7), a self-report questionnaire that has been widely applied and validated across different conditions. We used spectral dynamic causal modelling in Experiment 1 and paired-pulse transcranial magnetic stimulation in Experiment 2 to characterize how neuronal effective connectivity relates to self-reported post-stroke fatigue. In a multiple regression analysis, we used the balance in inhibitory connectivity between homologue regions in M1 as the main predictor, and have included lesioned hemisphere, resting motor threshold and levels of depression as additional predictors.

Our novel index of inter-hemispheric inhibition balance was a significant predictor of post-stroke fatigue in Experiment 1 (β = 1.524, P = 7.56 × 10⁻⁵, confidence interval: 0.921 to 2.127) and in Experiment 2 (β = 0.541, P = 0.049, confidence interval: 0.002 to 1.080). In Experiment 2, depression scores and corticospinal excitability, a measure associated with subjective fatigue, also significantly accounted for variability in fatigue.

We suggest that the balance in inter-hemispheric inhibitory effects between primary motor regions can explain subjective post-stroke fatigue. Findings provide novel insights into neural mechanisms that underlie persistent fatigue.

Hormonal regulation of circuit function: sex, systems and depression

Major depressive disorder (MDD) is a debilitating chronic illness that is two times more prevalent in women than in men. The mechanisms associated with the increased female susceptibility to depression remain poorly characterized. Aberrant neuronal oscillatory activity within the putative depression network is an emerging mechanism underlying MDD. However, innate sex differences in network activity and its contribution to depression vulnerability have not been well described. In this review, current evidence of sex differences in neuronal oscillatory activity, including the influence of sex hormones and female cycling, will first be described followed by evidence of disrupted neuronal circuit function in MDD and the effects of antidepressant treatment. Lastly, current knowledge of sex differences in MDD-associated aberrant circuit function and oscillatory activity will be highlighted, with an emphasis on the role of sex steroids and female cycling. Collectively, it is clear that there are significant gaps in the literature regarding innate and pathologically associated sex differences in network activity and that the elucidation of these differences is invaluable to our understanding of sex-specific vulnerabilities and therapies for MDD.

Drug-specific laterality effects on frontal lobe activation of atomoxetine and methylphenidate in attention deficit hyperactivity disorder boys during working memory

BACKGROUND

The catecholamine reuptake inhibitors methylphenidate (MPH) and atomoxetine (ATX) are the most common treatments for attention deficit hyperactivity disorder (ADHD). This study compares the neurofunctional modulation and normalization effects of acute doses of MPH and ATX within medication-naive ADHD boys during working memory (WM).

METHOD

A total of 20 medication-naive ADHD boys underwent functional magnetic resonance imaging during a parametric WM n-back task three times, under a single clinical dose of either MPH, ATX or placebo in a randomized, double-blind, placebo-controlled, cross-over design. To test for normalization effects, brain activations in ADHD under each drug condition were compared with that of 20 age-matched healthy control boys.

RESULTS

Relative to healthy boys, ADHD boys under placebo showed impaired performance only under high WM load together with significant underactivation in the bilateral dorsolateral prefrontal cortex (DLPFC). Both drugs normalized the performance deficits relative to controls. ATX significantly enhanced right DLPFC activation relative to MPH within patients, and significantly normalized its underactivation relative to controls. MPH, by contrast, both relative to placebo and ATX, as well as relative to controls, upregulated the left inferior frontal cortex (IFC), but only during 2-back. Both drugs enhanced fronto-temporo-striatal activation in ADHD relative to control boys and deactivated the default-mode network, which were negatively associated with the reduced DLPFC activation and performance deficits, suggesting compensation effects.

CONCLUSIONS

The study shows both shared and drug-specific effects. ATX upregulated and normalized right DLPFC underactivation, while MPH upregulated left IFC activation, suggesting drug-specific laterality effects on prefrontal regions mediating WM.

Comparison of two models of hemispheric specialization with unilaterally lesioned patients: material-specific impairment vs response-bias distortion

Validity of two models of hemispheric specialization was compared. The "material-specific impairment" model was radicalized as postulating that left hemisphere (LH) lesions impair processing of verbal material and that right hemisphere (RH) lesions impair processing of visuospatial material, independently of response-bias distortions. The "response-bias distortion" model was radicalized as postulating that LH lesions distort response style toward omissiveness and that RH lesions distort response style toward commissiveness, regardless of material-specific impairments. Participants had comparable left (N=27) or right (N=24) hemisphere cortical lesions having occurred between birth and early adolescence. Four cognitive neuropsychological tests were adjusted to optimize applicability and comparability of the two theoretical models: Rey Complex Figure, Kimura's Recurring Figures, the Story Recall subtest of the Children's Memory Scale, and the California Verbal Learning Test. Both models significantly, independently, and equally distinguished the LH from the RH patients. Both these forms of hemispheric specialization seemed to be implemented very early in life and very rigidly. Intrahemispheric lesion sites, e.g., frontal vs nonfrontal, held no significant relation to the effects described above.

Autistic spectrum disorders as functional disconnection syndrome

We outline the basis of how functional disconnection with reduced activity and coherence in the right hemisphere would explain all of the symptoms of autistic spectrum disorder as well as the observed increases in sympathetic activation. If the problem of autistic spectrum disorder is primarily one of desynchronization and ineffective interhemispheric communication, then the best way to address the symptoms is to improve coordination between areas of the brain. To do that the best approach would include multimodal therapeusis that would include a combination of somatosensory, cognitive, behavioral, and biochemical interventions all directed at improving overall health, reducing inflammation and increasing right hemisphere activity to the level that it becomes temporally coherent with the left hemisphere. We hypothesize that the unilateral increased hemispheric stimulation has the effect of increasing the temporal oscillations within the thalamocortical pathways bringing it closer to the oscillation rate of the adequately functioning hemisphere. We propose that increasing the baseline oscillation speed of one entire hemisphere will enhance the coordination and coherence between the two hemispheres allowing for enhanced motor and cognitive binding.

Prenatal influences on brain dopamine and their relevance to the rising incidence of autism

The incidence of autism has risen 10-fold since the early 1980s, with most of this rise not explainable by changing diagnostic criteria. The rise in autism is paradoxical in that autism is considered to be one of the most genetically determined of the major neurodevelopmental disorders and should accordingly either be stable or even declining. Because a variety of epigenetic influences, particularly those occurring during the prenatal period, can override or masquerade as genetic influences, these should be considered as prime contributors to the recent increase of autism. Prenatal influences on dopamine activity are especially well-documented, including the effects of maternal psychosocial stress, maternal fever, maternal genetic and hormonal status, use of certain medications, urban birth, and fetal hypoxia. All of these factors have been implicated in the genesis of autism, which is characterized by a "hyperdopaminergic" state based on evidence from monkey and human behavioral studies, pharmacological studies in humans, and a left-hemispheric predominance of both dopamine and autistic-like symptoms. Chronically high maternal levels of dopamine caused by the pressures of increasingly urbanized societies and by changing maternal demographics such as increased workforce participation, educational achievement level, and age at first birth, may be especially significant epigenetic contributors to the recent autism rise.

Amygdala volume and depressive symptoms in patients with borderline personality disorder

BACKGROUND

Borderline personality disorder (BPD) is characterized by a high prevalence of comorbid psychiatric disorders, including major depression (MD). The aim of this study was to examine whether a co-occurrence of MD is associated with structural changes in the amygdala of BPD patients.

METHODS

Twenty-five right-handed, female patients with BPD and 25 matched healthy control subjects were examined. Diagnoses of BPD and MD were made according to DSM IV. Depressive symptomatology was determined with the Hamilton Depression Scale (HAMD). Magnetic resonance imaging scans were performed with 1.5 T Magnetom Vision (Siemens, Erlangen, Germany). The software program "BRAINS" was applied for brain volumetry and segmentation. The amygdala was delineated as "region of interest."

RESULTS

Comparison of amygdala volumes between the whole group of BPD patients and control subjects revealed no significant difference. Amygdala volumes in both hemispheres were significantly larger in BPD patients with MD compared with those without MD. There was a significant correlation in BPD patients between left amygdala volume and depressive symptoms as measured by HAMD.

CONCLUSIONS

Correlation of amygdala volume with depression in BPD patients might indicate a causal relationship. Future studies should clarify whether amygdala enlargement is a risk factor for MD in BPD patients or a consequence of the affective disorder.

The role of the extrapersonal brain systems in religious activity

The neuropsychology of religious activity in normal and selected clinical populations is reviewed. Religious activity includes beliefs, experiences, and practice. Neuropsychological and functional imaging findings, many of which have derived from studies of experienced meditators, point to a ventral cortical axis for religious behavior, involving primarily the ventromedial temporal and frontal regions. Neuropharmacological studies generally point to dopaminergic activation as the leading neurochemical feature associated with religious activity. The ventral dopaminergic pathways involved in religious behavior most closely align with the action-extrapersonal system in the model of 3-D perceptual-motor interactions proposed by . These pathways are biased toward distant (especially upper) space and also mediate related extrapersonally dominated brain functions such as dreaming and hallucinations. Hyperreligiosity is a major feature of mania, obsessive-compulsive disorder, schizophrenia, temporal-lobe epilepsy and related disorders, in which the ventromedial dopaminergic systems are highly activated and exaggerated attentional or goal-directed behavior toward extrapersonal space occurs. The evolution of religion is linked to an expansion of dopaminergic systems in humans, brought about by changes in diet and other physiological influences.

A source-imaging (low-resolution electromagnetic tomography) study of the EEGs from unmedicated males with depression

Imaging studies and quantitative EEG have often, but not consistently, implicated the right hemisphere and the left prefrontal cortex in depression. To help clarify this picture, a spatial filter shown to be effective for enhancing differences between EEG populations was combined with an electrical tomographic approach called low-resolution electromagnetic tomography and used to compare the source-current densities from a group of 25 male subjects with depression and a group of 65 matched controls. To elicit differences, comparisons were made during resting conditions and during verbal and spatial cognitive challenges to the subjects. Estimates of the source-current density were derived from 43-electrode recordings of the EEG reduced to the delta, alpha and beta frequency bands. The depressed subjects were unmedicated and selected according to DSM IV criteria. Regions of significantly increased current density in depression compared to controls were generally right hemispheric, while regions of significantly decreased current density were generally frontal and left hemispheric. A within-group comparison of the depressed subjects during the two cognitive challenges suggested a left anterior functional hypoactivation in depression. Retrospective classification of the two groups indicated that the spatial challenge best separated the groups irrespective of frequency band.

Narrow and broad definition of mixed-handedness in male psychiatric patients

Differences in assessment and classification procedures of many mixed-handedness studies have made comparison of findings difficult. In the present study, "narrow" and "broad" definitions of mixed-handedness were investigated using the Annett Handedness Questionnaire in patients with schizophrenia (n=68), panic disorder (n=62), borderline personality disorder (n=35), heroin addiction (n=54), and mental retardation (n=33) in comparison with 944 controls. According to the "narrow" definition of mixed-handedness, an excess of mixed-handedness was observed in patients with borderline personality disorder and mental retardation. An excess of nonmixed-handedness was found in patients with panic disorder. According to the "broad" definition of mixed-handedness, an excess of mixed-handedness was observed in patients with mental retardation, in the total sample of psychiatric patients (n=252), and in the schizophrenic patients. Thus, we can conclude that different mixed-handedness definitions can be associated with different results. Furthermore, we suggest that the neurotic part of the present psychopathology spectrum tends to be related to an excess of normal or nonmixed-handedness, and the psychotic as well as the organic portion is associated with an excess of mixed-handedness, regardless of the definition of mixed-handedness used.

Emotion and immunity

Earlier studies have suggested that depression is associated with decreased immune function, but a recent literature review has revealed that a majority of studies reached inconsistent or conflicting conclusions. On the other hand, studies on immune function in anxiety disorders are sparse, and their findings are also inconsistent. Despite a few contradictory results, a clinical level of anxiety seems to reduce immune function, whereas a subclinical level of anxiety seems to enhance immunity. The latter may be a transient phenomenon occurring prior to the downregulation of immune function, reflecting the body's defense to a stressor. Thus, research needs to be conducted to elucidate the relationship between those hormones related to hypothalamic-pituitary-adrenal axis and a variety of immune measures at the subclinical level of anxiety. In addition, to confirm the interaction between emotion and immune function, the effectiveness of treatment with medication and psychotherapy on immunity should be investigated.

Muscarinic elicitation of EEG asymmetry in freely moving rats

Averaged frequency spectra (0.5-30 Hz) of electroencephalogram (EEG) were studied in six freely moving rats with chronically implanted electrodes in symmetrical areas of somatosensory cortex. Hemispheric asymmetry in spectra of an ongoing EEG was expressed as a power decrease in 15.6-17.2 Hz band on the left hemisphere and as that in 25.2-27.8 Hz band on the right one. Physostigmine subcutaneous (s.c.) injection (0.25 mg/kg) provoked appearance of the significant left brain bias in 4.7-8.6 Hz range of EEG spectra and the right brain bias in 19.3-21.3 Hz band. These physostigmine effects were counteracted by scopolamine (1.5 mg/kg, s.c.) injected 30 min before. It is suggested that a muscarinic component may be involved in the interhemispheric cooperation associated with cortical theta activity in rats.

Shifting cerebral dominance in a woman with schizoaffective psychosis: a case study

We describe a case of an intelligent, artistic 50-year-old woman with schizoaffective disorder with a long history of delusional preoccupation with laterality and episodes of reported shifts in handedness. Investigations including dichotic listening and lateralised visual imagery tasks indicated unusual patterns of asymmetry. Executive functions were found to be intact, and EEG and CT scan were normal. Interview schedules revealed high scores for schizotypy, and no evidence of a dissociative disorder, whereas psychotic symptoms with mood lability were evident on mental status examination. The subject's preoccupations are illustrated with a selection of her artistic productions. The case is discussed in the context of reports of a relationship between schizophrenia and ambiguous handedness. A cognitive neuropsychiatric formulation briefly explores the possibility of alternative cerebral hemispheres affecting cognitive-perceptual operations.

Neurochemical predisposition to self-administer cocaine in rats: individual differences in dopamine and its metabolites

Using in vivo microdialysis, this study attempted to determine whether a neurochemical predisposition to self-administer cocaine could be identified. Estimated extracellular levels of dopamine and its metabolites were measured bilaterally in the mesocorticolimbic and nigrostriatal systems of naive rats that were subsequently trained to self-administer cocaine intravenously. There were several significant relationships between dopamine and dopamine metabolite (3,4-dihydroxyphenylacetic acid and homovanillic acid) levels and rates of cocaine self-administration during both acquisition and asymptotic phases of testing. Dopamine levels in the nucleus accumbens were non-monotonically related to rates of self-administration during both phases: low to moderate dopamine levels were positively correlated with self-administration rates whereas moderate to high dopamine levels were negative correlated with self-administration rates. Dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) levels in the striatum were inversely correlated with self-administration rates during the acquisition phase. DOPAC and HVA levels in the left and right sides of the medial prefrontal cortex were positively and negatively correlated, respectively, with self-administration rates during the asymptotic phase; left/right asymmetrics in cortical metabolite levels were also correlated with asymptotic rates. There were no significant relationships between any neurochemical indices and rates of bar-pressing for water. These results suggest that the normal variability in drug seeking behavior is at least in part attributable to individual differences in the activity of brain dopamine systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Emotional behavior as an agenda in neuropsychological evaluation

In an effort to objectify neuropsychologic evaluations, consideration of a patient's emotional behavior has often been neglected. An extensive literature review is undertaken in an effort to document lateralized emotional behaviors commonly found in brain injury populations. This evidence is contrasted with the psychiatric symptoms and lateralized neuropsychologic impairments seen in major depression and schizophrenia. A theoretical model is then proposed that attempts to integrate these "functional" vs. "organic" symptoms based upon reciprocal inhibition of lateralized emotional functioning in brain injury and psychiatric disorders. This opponent process model not only seems to account for some of the discrepant findings in the literature, but additionally provides a cogent and useful marker to neurophychologically differentiate "neuronal" vs. "metabolic" disorders. The model further suggests new ways of envisioning treatment and recovery from both psychiatric illness and brain injury.

Do the organs of the labyrinth differentially influence the sympathetic and parasympathetic systems?

It has long been recognized that the vestibular system plays a major role in autonomic control. The nature of this control remains in dispute, however, as some evidence points to a vestibularly mediated parasympathetic activation, whereas other evidence points to a sympatho-excitatory role for labyrinthine outputs. A theoretical explanation is offered that attempts to resolve this issue by postulating that the utricles exert a predominantly sympatho-excitatory influence via their interactions with brain noradrenergic pathways, while the semicircular canals (and possibly saccules) increase parasympathetic tone via their cholinergic brain stem and cerebellar projections. This explanation is relevant for understanding the vestibular role in orthostatic regulation, motion sickness, oculomotor control, and in many disorders or situations associated with neurochemical or autonomic imbalances.

[Depression and temporal epilepsy. The possible role of laterality of the epileptic foci and of gender]

From a prospective study of 47 epileptic patients (26 men and 21 women) 25 with a left and 22 with a right temporal epileptic focus, the authors show that depression measured by the HARD score, is more severe in males, with a left epileptic focus. These results and the vulnerability to depression of left temporal lobe epileptic patients are analyzed.

Neurochemical predisposition to self-administer morphine in rats

Using in vivo microdialysis, this study attempted to determine whether a neurochemical predisposition to self-administer morphine could be identified. Extracellular levels of dopamine and its metabolites were measured bilaterally in the mesocorticolimbic and nigrostriatal systems of naive rats that were subsequently trained to self-administer morphine intravenously. There were several significant relationships between dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels and rates of morphine self-administration during both acquisition and asymptotic phases of testing. DOPAC and HVA levels in the striatum were inversely correlated with self-administration rates during the asymptotic phase whereas hemispheric asymmetries in striatal metabolite levels were inversely correlated with self-administration during the acquisition phase. DOPAC and HVA levels in in the right but not in the left side of the medial prefrontal cortex were positively correlated with self-administration rates during the acquisition phase; right/left asymmetries in cortical metabolite levels were also correlated with acquisition rates. There were no significant relationships between neurochemical indices and rates of bar-pressing for water. These results suggest that the normal variability in drug seeking behavior is at least in part attributable to individual differences in the organization and activity of brain dopamine systems. Furthermore, different mechanisms appear to be responsible for the initiation and maintenance of morphine intake: DA release in the nucleus accumbens appears to be a critical component of both mechanisms; DA release in the striatum appears to modulate maintenance and, in relationship to striatal lateralization, modulate initiation; DA release in the right but not in the left medial prefrontal cortex appears to be an important predictor of initiation.

Side and region dependent changes in dopamine activation with various durations of restraint stress

Exposure to various mild stressors has been shown to result in the activation of dopamine containing neuronal systems projecting to the medial prefrontal cortex (PFC), to a lesser extent the nucleus accumbens septi/olfactory tubercle (NAS) and, in a few studies, the striatum. It has also been shown that dopamine (DA) systems on different sides of the PFC are successively activated as stressors are prolonged. We have therefore examined the effects of variation in the duration of a restraint stressor (15, 30 and 60 min) on region and side dependent alterations in DA utilization in the PFC, NAS and striatum. Increases in the concentrations of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and/or homovanillic acid (HVA) or in their ratios with DA were seen in all regions examined with the largest effects occurring in the PFC and lesser effects in the NAS and striatum. In each region, the magnitude of these effects varied with time of restraint exposure. In the PFC, lateralized alterations in HVA and DA were seen over time with effects progressing from a left greater than right involvement at 15 min to a right greater than left involvement at 60 min. These results are discussed with reference to side and region dependent effects on brain DA systems as stressors are prolonged and the implications they may have for lateralized regional brain activity associated with stressor precipitated psychiatric disease.

Affect, affective disorder and schizophrenia. A neuropsychological investigation of right hemisphere function

Performance on a happy-sad chimeric face test was used to examine the role of right hemisphere activation in positive and negative affect, both normal and abnormal, as well as in schizophrenia. This test is known to elicit a left-sided perceptual bias in right-handed normal subjects. Happy and sad mood in normals did not influence the perceptual bias. Depression and mania were associated with reduced and increased biases respectively, while schizophrenics showed no bias to either side. Possible explanations are right hemisphere hyperfunction in mania, moderate relative hypofunction in depression, and severe relative hypofunction in schizophrenia. The marked difference between mania and schizophrenia supports distinct pathophysiologies underlying the two conditions.

Psychosocial effects on immune function: neuroendocrine pathways

Psychoneuroimmunology represents the newest interdisciplinary endeavor relevant to psychosomatic medicine. Work in this area is particularly exciting because it promises to reveal a more unified view of the individual and the complex interactions between social, psychological, neural, endocrinological, immunological, and genetic factors that contribute to disease. This article reviews the major biological pathways implicated in the psychosocial modulation of immune function and disease resistance.

Effect of antemortem and postmortem factors on [3H]MK-801 binding in the human brain: transient elevation during early childhood

The effect of a number of antemortem and postmortem factors on [3H]MK-801 binding was investigated under equilibrium conditions in the frontal cortex of human brains of 38 controls. Binding values transiently increased during the early postnatal period reaching a maximum at the age of about 2 years. After age 10 years [3H]MK-801 binding sites disappeared at 5.7% per decade. The storage time of brain tissue had a reducing effect on these binding sites. There was no effect of gender, brain weight or postmortem time interval and the binding sites were bilaterally symmetrically distributed in the frontal cortex.