Quantifying the attenuation of the ketamine pharmacological magnetic resonance imaging response in humans: a validation using antipsychotic and glutamatergic agents

Ketamine acts as an N-methyl-D-aspartate receptor antagonist and evokes psychotomimetic symptoms resembling schizophrenia in healthy humans. Imaging markers of acute ketamine challenge have the potential to provide a powerful assay of novel therapies for psychiatric illness, although to date this assay has not been fully validated in humans. Pharmacological magnetic resonance imaging (phMRI) was conducted in a randomized, placebo-controlled crossover design in healthy volunteers. The study comprised a control and three ketamine infusion sessions, two of which included pretreatment with lamotrigine or risperidone, compounds hypothesized to reduce ketamine-induced glutamate release. The modulation of the ketamine phMRI response was investigated using univariate analysis of prespecified regions and a novel application of multivariate analysis across the whole-brain response. Lamotrigine and risperidone resulted in widespread attenuation of the ketamine-induced increases in signal, including the frontal and thalamic regions. A contrasting effect across both pretreatments was observed only in the subgenual prefrontal cortex, in which ketamine produced a reduction in signal. Multivariate techniques proved successful in both classifying ketamine from placebo (100%) and identifying the probability of scans belonging to the ketamine class (ketamine pretreated with placebo: 0.89). Following pretreatment, these predictive probabilities were reduced to 0.58 and 0.49 for lamotrigine and risperidone, respectively. We have provided clear demonstration of a ketamine phMRI response and its attenuation with both lamotrigine and risperidone. The analytical methodology used could be readily applied to investigate the mechanistic action of novel compounds relevant for psychiatric disorders such as schizophrenia and depression.

A novel method for reducing the effect of tonic muscle activity on the gamma band of the scalp EEG

Neural oscillations in the gamma band are of increasing interest, but separating them from myogenic electrical activity has proved difficult. A novel algorithm has been developed to reduce the effect of tonic scalp and neck muscle activity on the gamma band of the EEG. This uses mathematical modelling to fit individual muscle spikes and then subtracts them from the data. The method was applied to the detection of motor associated gamma in two separate groups of eight subjects using different sampling rates. A reproducible increase in high gamma (65-85 Hz) magnitude occurred immediately after the motor action in the left central area (p = 0.02 and p = 0.0002 for the two cohorts with individually optimized algorithm parameters, compared to p = 0.03 and p = 0.16 before correction). Whilst the magnitude of this event-related gamma synchronisation was not reduced by the application of the EMG reduction algorithm, the baseline left central gamma magnitude was significantly reduced by an average of 23 % with a faster sampling rate (p < 0.05). In comparison, at left and right temporo-parietal locations the gamma amplitude was reduced by 60 and 54 % respectively (p < 0.05). The reduction of EMG contamination by fitting and subtraction of individual spikes shows promise as a method of improving the signal to noise ratio of high frequency neural oscillations in scalp EEG.

PROBABILISTIC PREDICTION OF NEUROLOGICAL DISORDERS WITH A STATISTICAL ASSESSMENT OF NEUROIMAGING DATA MODALITIES

For many neurological disorders, prediction of disease state is an important clinical aim. Neuroimaging provides detailed information about brain structure and function from which such predictions may be statistically derived. A multinomial logit model with Gaussian process priors is proposed to: (i) predict disease state based on whole-brain neuroimaging data and (ii) analyze the relative informativeness of different image modalities and brain regions. Advanced Markov chain Monte Carlo methods are employed to perform posterior inference over the model. This paper reports a statistical assessment of multiple neuroimaging modalities applied to the discrimination of three Parkinsonian neurological disorders from one another and healthy controls, showing promising predictive performance of disease states when compared to nonprobabilistic classifiers based on multiple modalities. The statistical analysis also quantifies the relative importance of different neuroimaging measures and brain regions in discriminating between these diseases and suggests that for prediction there is little benefit in acquiring multiple neuroimaging sequences. Finally, the predictive capability of different brain regions is found to be in accordance with the regional pathology of the diseases as reported in the clinical literature.

Alterations in white matter evident before the onset of psychosis

BACKGROUND

Psychotic disorders are associated with widespread reductions in white matter (WM) integrity. However, the stage at which these abnormalities first appear and whether they are correlates of psychotic illness, as opposed to an increased vulnerability to psychosis, is unclear. We addressed these issues by using diffusion tensor imaging (DTI) to study subjects at ultra high risk (UHR) of psychosis before and after the onset of illness.

METHODS

Thirty-two individuals at UHR for psychosis, 32 controls, and 15 patients with first-episode schizophrenia were studied using DTI. The UHR subjects and controls were re-scanned after 28 months. During this period, 8 UHR subjects had developed schizophrenia. Between-group differences in fractional anisotropy (FA) and diffusivity were evaluated cross sectionally and longitudinally using a nonparametric voxel-based analysis.

RESULTS

At baseline, WM DTI properties were significantly different between the 3 groups (P < .001). Relative to controls, first-episode patients showed widespread reductions in FA and increases in diffusivity. DTI indices in the UHR group were intermediate relative to those in the other 2 groups. Longitudinal analysis revealed a significant group by time interaction in the left frontal WM (P < .001). In this region, there was a progressive reduction in FA in UHR subjects who developed psychosis that was not evident in UHR subjects who did not make a transition.

CONCLUSIONS

People at UHR for psychosis show alterations in WM qualitatively similar to, but less severe than, those in patients with schizophrenia. The onset of schizophrenia may be associated with a progressive reduction in the integrity of the frontal WM.

Differential corticospinal tract degeneration in homozygous 'D90A' SOD-1 ALS and sporadic ALS

BACKGROUND

The homogeneous genotype and stereotyped phenotype of a unique familial form of amyotrophic lateral sclerosis (ALS) (patients homozygous for aspartate-to-alanine mutations in codon 90 (homD90A) superoxide dismutase 1) provides an ideal model for studying genotype/phenotype interactions and pathological features compared with heterogeneous apparently sporadic ALS. The authors aimed to use diffusion tensor tractography to quantify and compare changes in the intracerebral corticospinal tracts of patients with both forms of ALS, building on previous work using whole-brain voxelwise group analysis.

METHOD

21 sporadic ALS patients, seven homD90A patients and 20 healthy controls underwent 1.5&emsp14;T diffusion tensor MRI. Patients were assessed using 'upper motor neuron burden,' El Escorial and ALSFR-R scales. The intracranial corticospinal tract was assessed using diffusion tensor tractography measures of fractional anisotropy (FA), mean diffusivity, and radial and axial diffusivity obtained from its entire length.

RESULTS

Corticospinal tract FA was reduced in sporadic ALS patients compared with both homD90A ALS patients and controls. The diffusion measures in sporadic ALS patients were consistent with anterograde (Wallerian) degeneration of the corticospinal tracts. In sporadic ALS, corticospinal tract FA was related to clinical measures. Despite a similar degree of clinical upper motor neuron dysfunction and disability in homD90A ALS patients compared with sporadic ALS, there were no abnormalities in corticospinal tract diffusion measures compared with controls.

CONCLUSIONS

Diffusion tensor tractography has shown axonal degeneration within the intracerebral portion of the corticospinal tract in sporadic ALS patients, but not those with a homogeneous form of familial ALS. This suggests significant genotypic influences on the phenotype of ALS and may provide clues to slower progression of disease in homD90A patients.

Patient classification as an outlier detection problem: an application of the One-Class Support Vector Machine

Pattern recognition approaches, such as the Support Vector Machine (SVM), have been successfully used to classify groups of individuals based on their patterns of brain activity or structure. However these approaches focus on finding group differences and are not applicable to situations where one is interested in accessing deviations from a specific class or population. In the present work we propose an application of the one-class SVM (OC-SVM) to investigate if patterns of fMRI response to sad facial expressions in depressed patients would be classified as outliers in relation to patterns of healthy control subjects. We defined features based on whole brain voxels and anatomical regions. In both cases we found a significant correlation between the OC-SVM predictions and the patients' Hamilton Rating Scale for Depression (HRSD), i.e. the more depressed the patients were the more of an outlier they were. In addition the OC-SVM split the patient groups into two subgroups whose membership was associated with future response to treatment. When applied to region-based features the OC-SVM classified 52% of patients as outliers. However among the patients classified as outliers 70% did not respond to treatment and among those classified as non-outliers 89% responded to treatment. In addition 89% of the healthy controls were classified as non-outliers.

Segmentation of the thalamus in MRI based on T1 and T2

Reliable identification of thalamic nuclei is required to improve positioning of electrodes in Deep Brain Stimulation (DBS), and to allow the role of individual thalamic nuclei in health and disease to be fully investigated. In this work, a previously proposed method for identifying sub-regions within the thalamus based on differences in their T1 and T2 values is explored in detail. The effect on the segmentation of T1 and T2 dependence weighted against priors for spatial position and extent was investigated. When T1 and T2 dependence was highly weighted, good distinction between identified regions was obtained in T1/T2 feature-space, but no contiguous anatomically distinct regions were identified within the thalamus. Incorporating spatial priors was necessary to ensure anatomically distinct regions were defined. Optimal values for segmentation parameters were obtained by assessing performance on a 'synthetic thalamus'. Using these optimum input parameters, within- and between-subjects reproducibility was assessed. Good reproducibility was obtained when six regions were specified to be identified in the thalamus. The six regions identified were similar in the majority of the normal subject group. However, intriguingly these regions were different from those obtained in the same subjects using a well-known connectivity-based segmentation technique. This method shows promise to identify intrathalamic structures on the basis of T1 and T2 signal. A comprehensive characterisation of thalamic nuclei may require a fully multi-modal approach.

Neural correlates of visuospatial working memory in the 'at-risk mental state'

BACKGROUND

Impaired spatial working memory (SWM) is a robust feature of schizophrenia and has been linked to the risk of developing psychosis in people with an at-risk mental state (ARMS). We used functional magnetic resonance imaging (fMRI) to examine the neural substrate of SWM in the ARMS and in patients who had just developed schizophrenia.

METHOD

fMRI was used to study 17 patients with an ARMS, 10 patients with a first episode of psychosis and 15 age-matched healthy comparison subjects. The blood oxygen level-dependent (BOLD) response was measured while subjects performed an object-location paired-associate memory task, with experimental manipulation of mnemonic load.

RESULTS

In all groups, increasing mnemonic load was associated with activation in the medial frontal and medial posterior parietal cortex. Significant between-group differences in activation were evident in a cluster spanning the medial frontal cortex and right precuneus, with the ARMS groups showing less activation than controls but greater activation than first-episode psychosis (FEP) patients. These group differences were more evident at the most demanding levels of the task than at the easy level. In all groups, task performance improved with repetition of the conditions. However, there was a significant group difference in the response of the right precuneus across repeated trials, with an attenuation of activation in controls but increased activation in FEP and little change in the ARMS.

CONCLUSIONS

Abnormal neural activity in the medial frontal cortex and posterior parietal cortex during an SWM task may be a neural correlate of increased vulnerability to psychosis.

Neural correlates of movement generation in the 'at-risk mental state'

OBJECTIVE

People with 'prodromal' symptoms have a very high risk of developing psychosis. We examined the neurocognitive basis of this vulnerability by using functional MRI to study subjects with an at-risk mental state (ARMS) while they performed a random movement generation task.

METHOD

Cross-sectional comparison of individuals with an ARMS (n = 17), patients with first episode schizophreniform psychosis (n = 10) and healthy volunteers (n = 15). Subjects were studied using functional MRI while they performed a random movement generation paradigm.

RESULTS

During random movement generation, the ARMS group showed less activation in the left inferior parietal cortex than controls, but greater activation than in the first episode group.

CONCLUSION

The ARMS is associated with abnormalities of regional brain function that are qualitatively similar to those in patients who have recently presented with psychosis but less severe.

Association of Neuregulin 1 rs3924999 genotype with antisaccades and smooth pursuit eye movements

Neuregulin 1 (NRG1) has been identified as one of the leading candidate genes for schizophrenia. However, its functional mechanisms and its effects on neurocognition remain unclear. In this study, we used two well-established oculomotor endophenotypes, the antisaccade (AS) and smooth pursuit eye movement (SPEM) tasks, to investigate the functional mechanisms of a single nucleotide polymorphism (SNP) in NRG1 (rs3924999) at the neurocognitive level in a healthy volunteer sample. A total of 114 healthy Caucasian volunteers completed genotyping for NRG1 rs3924999 and infrared oculographic assessment of AS and SPEM (at target velocities of 12 degrees , 24 degrees and 36 degrees per second). Additionally, self-report questionnaires of schizotypy, neuroticism, attention deficit hyperactivity and obsessive-compulsive traits were included. A significant effect of rs3924999 genotype, with gender as a covariate, was found for AS amplitude gain (P < 0.01), with an increasing number of A alleles being associated with increasingly hypermetric performance. No statistically significant associations were found for other AS and SPEM variables or questionnaire scores. These findings indicate that NRG1 rs3924999 affects spatial accuracy on the AS task, suggesting an influence of the gene on the neural mechanisms underlying visuospatial sensorimotor transformations, a mechanism that has been previously found to be impaired in patients with schizophrenia and their relatives.

Neither in vivo MRI nor behavioural assessment indicate therapeutic efficacy for a novel 5HT(1A) agonist in rat models of ischaemic stroke

Background

5HT_1A agonists have previously been shown to promote recovery in animal models of stroke using ex vivo outcome measures which have raised the hopes for a potential clinical implementation. The purpose of this study was to evaluate the potential neuroprotective properties of a novel 5HT_1A agonist DU123015 in 2 different models of transient focal ischaemic stroke of varying severities using both in vivo neuroimaging and behavioural techniques as primary outcome measures. For these studies, the NMDA receptor antagonist MK-801 was also utilized as a positive control to further assess the effectiveness of the stroke models and techniques used.

Results

In contrast to MK-801, no significant therapeutic effect of DU123015 on lesion volume in either the distal MCAo or intraluminal thread model of stroke was found. MK-801 significantly reduced lesion volume in both models; the mild distal MCAo condition (60 min ischaemia) and the intraluminal thread model, although it had no significant impact upon the lesion size in the severe distal MCAo condition (120 min ischaemia). These therapeutic effects on lesion size were mirrored on a behavioural test for sensory neglect and neurological deficit score in the intraluminal thread model.

Conclusion

This study highlights the need for a thorough experimental design to test novel neuroprotective compounds in experimental stroke investigations incorporating: a positive reference compound, different models of focal ischaemia, varying the duration of ischaemia, and objective in vivo assessments within a single study. This procedure will help us to minimise the translation of less efficacious compounds.

Functional coupling of the amygdala in depressed patients treated with antidepressant medication

The amygdala plays a central role in various aspects of affect processing and mood regulation by its rich anatomical connections to other limbic and cortical regions. It is plausible that depressive disorders, and response to antidepressant drugs, may reflect changes in the physiological coupling between the amygdala and other components of affect-related large-scale brain systems. We explored this hypothesis by mapping the functional coupling of right and left amygdalae in functional magnetic resonance imaging data acquired from 19 patients with major depressive disorder and 19 healthy volunteers, each scanned twice (at baseline and 8 weeks later) during performance of an implicit facial affect processing task. Between scanning sessions, the patients received treatment with an antidepressant drug, fluoxetine 20 mg/day. We found that the amygdala was positively coupled bilaterally with medial temporal and ventral occipital regions, and negatively coupled with the anterior cingulate cortex. Antidepressant treatment was associated with significantly increased coupling between the amygdala and right frontal and cingulate cortex, striatum, and thalamus. Treatment-related increases in functional coupling to frontal and other regions were greater for the left amygdala than for the right amygdala. These results indicate that antidepressant drug effects can be measured in terms of altered coupling between components of cortico-limbic systems and that these effects were most clearly demonstrated by enhanced functional coupling of the left amygdala.

AMPA receptor potentiation can prevent ethanol-induced intoxication

We present a substantial series of behavioral and imaging experiments, which demonstrate, for the first time, that increasing AMPA receptor-mediated neurotransmission via administration of potent and selective biarylsulfonamide AMPA potentiators LY404187 and LY451395 reverses the central effects of an acutely intoxicating dose of ethanol in the rat. Using pharmacological magnetic resonance imaging (phMRI), we observed that LY404187 attenuated ethanol-induced reductions in blood oxygenation level dependent (BOLD) in the anesthetized rat brain. A similar attenuation was apparent when measuring local cerebral glucose utilization (LCGU) via C14-2-deoxyglucose autoradiography in freely moving conscious rats. Both LY404187 and LY451395 significantly and dose-dependently reversed ethanol-induced deficits in both motor coordination and disruptions in an operant task where animals were trained to press a lever for food reward. Both prophylactic and acute intervention treatment with LY404187 reversed ethanol-induced deficits in motor coordination. Given that LY451395 and related AMPA receptor potentiators/ampakines are tolerated in both healthy volunteers and elderly patients, these data suggest that such compounds may form a potential management strategy for acute alcohol intoxication.

Pattern classification of sad facial processing: toward the development of neurobiological markers in depression

BACKGROUND

Methods of analysis that examine the pattern of cerebral activity over the whole brain have been used to identify and predict neurocognitive states in healthy individuals. Such methods may be applied to functional neuroimaging data in patient groups to aid in the diagnosis of psychiatric disorders and the prediction of treatment response. We sought to examine the sensitivity and specificity of whole brain pattern classification of implicit processing of sad facial expressions in depression.

METHODS

Nineteen medication-free patients with depression and 19 healthy volunteers had been recruited for a functional magnetic resonance imaging (fMRI) study involving serial scans. The fMRI paradigm entailed incidental affective processing of sad facial stimuli with modulation of the intensity of the emotional expression (low, medium, and high intensity). The fMRI data were analyzed at each level of affective intensity with a support vector machine pattern classification method.

RESULTS

The pattern of brain activity during sad facial processing correctly classified up to 84% of patients (sensitivity) and 89% of control subjects (specificity), corresponding to an accuracy of 86% (p < .0001). Classification of patients' clinical response at baseline, prior to the initiation of treatment, showed a trend toward significance.

CONCLUSIONS

Significant classification of patients in an acute depressive episode was achieved with whole brain pattern analysis of fMRI data. The prediction of treatment response showed a trend toward significance due to the reduced power of the subsample. Such methods may provide the first steps toward developing neurobiological markers in psychiatry.

Neural basis of the emotional Stroop interference effect in major depression

BACKGROUND

A mood-congruent sensitivity towards negative stimuli has been associated with development and maintenance of major depressive disorder (MDD). The emotional Stroop task assesses interference effects arising from the conflict of emotional expressions consistent with disorder-specific self-schemata and cognitive colour-naming instructions. Functional neuroimaging studies of the emotional Stroop effect advocate a critical involvement of the anterior cingulate cortex (ACC) during these processes.

METHOD

Subjects were 17 medication-free individuals with unipolar MDD in an acute depressive episode (mean age 39 years), and 17 age-, gender- and IQ-matched healthy volunteers. In an emotional Stroop task, sad and neutral words were presented in various colours, and subjects were required to name the colour of words whilst undergoing functional magnetic resonance imaging (fMRI). Overt verbal responses were acquired with a clustered fMRI acquisition sequence.

RESULTS

Individuals with depression showed greater increases in response time from neutral to sad words relative to controls. fMRI data showed a significant engagement of left rostral ACC (BA 32) and right precuneus during sad words in patients relative to controls. Additionally, rostral ACC activation was positively correlated with latencies of negative words in MDD patients. Healthy controls did not have any regions of increased activation compared to MDD patients.

CONCLUSIONS

These findings provide evidence for a behavioural and neural emotional Stroop effect in MDD and highlight the importance of the ACC during monitoring of conflicting cognitive processes and mood-congruent processing in depression.

A method for removing global effects in small-animal functional MRI

Global effects in functional MRI are temporal modulations in signal intensity resulting from various scanner and subject phenomena. These effects contribute to the overall variance, reducing the effect size associated with an experimental paradigm. Statistical estimations that include an approximation for concurrent global effects will reduce the residual error within the model and so improve statistical power of the study. Conventionally, estimates of global effects are derived from mean intracerebral signal intensities, but these may be prone to contributions from localised experimentally evoked signal changes. In such cases, inaccurate estimates of global effects may result in erroneous inferences of neural modulations based on statistical artefact. A novel, computationally simple, method of estimating global effects is proposed using muscle tissue acquired within the same acquisition volume. Quantitative improvements in sensitivity are reported for a somatosensory stimulation paradigm using global muscle signal intensities as a covariate of no-interest. The method is independent of local neurogenic signal changes and, under particular experimental conditions, may be more representative of true global effects. The utility of this strategy to applications in small-animal functional MRI that evoke systemic physiological changes as a result of the experimental manipulation is critically discussed.

I’m not as slim as that girl: Neural bases of body shape self-comparison to media images

The aim of the present study was to assess the impact of images of slim female fashion models on healthy young women. Brain responses to images of slim-idealized bodies (active condition) and interior designs (control condition) were measured using functional neuroimaging in 18 healthy young women. Instructions encouraged the participants to compare their own body shape/own home with the one in the images. Participants rated the level of anxiety that they experienced while exposed to the images. In the active relative to the control condition, participants activated body shape processing networks, including the lateral fusiform gyrus on both sides, the right inferior parietal lobule, the right lateral prefrontal cortex and the left anterior cingulate. The level of reported anxiety during the exposure to slim bodies correlated with established measures of shape and weight concern and with brain activations in bilateral basal ganglia, left amygdala, bilateral dorsal anterior cingulate, and left inferior lateral prefrontal cortex. Brain networks associated with anxiety induced by self-comparison to slim images may be involved in the genesis of body dissatisfaction and hence with vulnerability to eating disorders.

Caffeine restores regional brain activation in acute hypoglycaemia in healthy volunteers

AIMS

Caffeine enhances counterregulatory responses to acute hypoglycaemia. Our aim was to explore its effects on cortical function, which are not known at present.

METHODS

Regional brain activation during performance of the four-choice reaction time (4CRT) at different levels of complexity was measured using functional magnetic resonance imaging (fMRI) at euglycaemia (5 mmol/l) and hypoglycaemia (2.6 mmol/l) in the presence and absence of caffeine in six healthy right-handed men.

RESULTS

During hypoglycaemia, caffeine enhanced adrenaline responses to hypoglycaemia (2.5 +/- 0.7 nmol/l to 4.0 +/- 1.0 nmol/l, P = 0.01) and restored the brain activation response to the non-cued 4CRT, the linear increases in regional brain activation associated with increased task complexity and the ability to respond to a cue that were lost in hypoglycaemia alone.

CONCLUSIONS

Caffeine can sustain regional brain activation patterns lost in acute hypoglycaemia, with some restoration of cortical function and enhanced adrenaline responsiveness. A methodology has been established that may help in the development of therapies to protect against severe hypoglycaemia in insulin therapy for patients with diabetes and problematic hypoglycaemia.

The nature of abnormal language processing in euthymic bipolar I disorder: evidence for a relationship between task demand and prefrontal function

OBJECTIVES

Abnormal language processing is a consistent finding in bipolar disorder (BD). We used functional magnetic resonance imaging (fMRI) to investigate the core components of language processing as well as the impact of task demand in a group of bipolar subjects.

METHODS

Twelve euthymic dextral male BD I participants receiving lithium monotherapy were matched with 12 controls. Groups were matched for age, years of education and estimated premorbid IQ. We employed a factorial design manipulating task demand (decision versus fluency) and task domain (phonetic versus semantic) to investigate differences in language processing between groups and across different task domains and requirements. Data were fitted to haemodynamic response models convolved to the experimental design. Group and task difference maps were generated.

RESULTS

During the scanning session bipolar patients demonstrated significantly slower reaction times. However, groups demonstrated the same task accuracy except for one domain (phonetic decision). All participants activated regions known to be engaged by language tasks, but compared to controls the bipolar patients showed altered patterns of prefrontal activation which were related to the nature of the task, language processing, and increasing task demand.

CONCLUSIONS

We have demonstrated abnormal prefrontal activation in bipolar patients across a range of language tasks with varying task demands.

Effects of acute antipsychotic treatment on brain activation in first episode psychosis: an fMRI study

This study aimed to assess the neurophysiological effects of acute atypical antipsychotic treatment on cognitive functioning in subjects presenting with a first episode of psychosis. We used functional MRI to examine the modulatory effects of acute psychopharmacological intervention on brain activation during four different cognitive tasks: overt verbal fluency, random movement generation, n-back and a spatial object memory task. Treatment with atypical antipsychotics was associated with alterations in regional activation during each task and also when task demands were manipulated within paradigms. The initial treatment of psychosis with atypical antipsychotics thus appears to be associated with modifications of the neurofunctional correlates of executive and mnemonic functions. These effects need to be considered when interpreting group differences in activation between medicated patients and controls.