Deep brain stimulation for treatment-resistant depression

Can neuroscience be integrated into the DSM-V?

To date, the diagnosis of mental disorders has been based on clinical observation, specifically: the identification of symptoms that tend to cluster together, the timing of the symptoms' appearance, and their tendency to resolve, recur or become chronic. The Diagnostic and Statistical Manual of Mental Disorders and the International Classification of Disease, the manuals that specify these diagnoses and the criteria for making them, are currently undergoing revision. It is thus timely to ask whether neuroscience has progressed to the point that the next editions of these manuals can usefully incorporate information about brain structure and function.

Dissociable neural systems resolve conflict from emotional versus nonemotional distracters

The human brain protects the processing of task-relevant stimuli from interference ("conflict") by task-irrelevant stimuli via attentional biasing mechanisms. The lateral prefrontal cortex has been implicated in resolving conflict between competing stimuli by selectively enhancing task-relevant stimulus representations in sensory cortices. Conversely, recent data suggest that conflict from emotional distracters may be resolved by an alternative route, wherein the rostral anterior cingulate cortex inhibits amygdalar responsiveness to task-irrelevant emotional stimuli. Here we tested the proposal of 2 dissociable, distracter-specific conflict resolution mechanisms, by acquiring functional magnetic resonance imaging data during resolution of conflict from either nonemotional or emotional distracters. The results revealed 2 distinct circuits: a lateral prefrontal "cognitive control" system that resolved nonemotional conflict and was associated with enhanced processing of task-relevant stimuli in sensory cortices, and a rostral anterior cingulate "emotional control" system that resolved emotional conflict and was associated with decreased amygdalar responses to emotional distracters. By contrast, activations related to both emotional and nonemotional conflict monitoring were observed in a common region of the dorsal anterior cingulate. These data suggest that the neuroanatomical networks recruited to overcome conflict vary systematically with the nature of the conflict, but that they may share a common conflict-detection mechanism.

Anatomical connectivity of the subgenual cingulate region targeted with deep brain stimulation for treatment-resistant depression

Chronic deep brain stimulation (DBS) of subgenual cingulate white matter results in dramatic remission of symptoms in some previously treatment-resistant depression patients. The effects of stimulation may be mediated locally or via corticocortical or corticosubcortical connections. We use tractography to define the likely connectivity of cingulate regions stimulated in DBS-responsive patients using diffusion imaging data acquired in healthy control subjects. We defined 2 distinct regions within anterior cingulate cortex based on anatomical connectivity: a pregenual region strongly connected to medial prefrontal and anterior midcingulate cortex and a subgenual region with strongest connections to nucleus accumbens, amygdala, hypothalamus, and orbitofrontal cortex. The location of electrode contact points from 9 patients successfully treated with DBS lies within this subgenual region. The anatomical connectivity of the subgenual cingulate region targeted with DBS for depression supports the hypothesis that treatment efficacy is mediated via effects on a distributed network of frontal, limbic, and visceromotor brain regions. At present, targeting of DBS for depression is based on landmarks visible in conventional magnetic resonance imaging. Preoperatively acquired diffusion imaging for connectivity-based cortical mapping could improve neurosurgical targeting. We hypothesize that the subgenual region with greatest connectivity across the distributed network described here may prove most effective.

A final common pathway for depression? Progress toward a general conceptual framework

Functional neuroimaging studies of depressed patients have converged with functional brain mapping studies of depressed animals in showing that depression is accompanied by a hypoactivity of brain regions involved in positively motivated behavior together with a hyperactivity in regions involved in stress responses. Both sets of changes are reversed by diverse antidepressant treatments. It has been proposed that this neural pattern underlies the symptoms common to most forms of the depression, which are the loss of positively motivated behavior and increased stress. The paper discusses how this framework can organize diverse findings ranging from effects of monoamine neurotransmitters, cytokines, corticosteroids and neurotrophins on depression. The hypothesis leads to new insights concerning the relationship between the prolonged inactivity of the positive motivational network during a depressive episode and the loss of neurotrophic support, the potential antidepressant action of corticosteroid treatment, and to the key question of whether antidepressants act by inhibiting the activity of the stress network or by enhancing the activity of the positive motivational system.

Neurostimulation therapies in depression: a review of new modalities

OBJECTIVE

In response to an increased understanding of the neurobiology of severe psychiatric disorders, new therapeutic modalities are entering clinical practice that involve the direct stimulation of the brain.

METHOD

We provide a review of published literature regarding the clinical use of vagus nerve stimulation (VNS) therapy, transcranial magnetic stimulation (TMS) and deep brain stimulation (DBS) in psychiatric disorders, with an emphasis on treatment-resistant depression (TRD).

RESULTS

Vagus nerve stimulation is approved for use in both the EU and US for TRD. TMS has been approved for TRD in Canada, Australia, New Zealand, the European Union and Israel, but not yet in the United States. DBS remains in the early stages of investigation.

CONCLUSION

While additional studies are clearly warranted, treatments that directly stimulate the brain appear to hold great therapeutic promise for severe psychiatric disorders.

Resting-state functional connectivity in major depression: abnormally increased contributions from subgenual cingulate cortex and thalamus

BACKGROUND

Positron emission tomography (PET) studies of major depression have revealed resting-state abnormalities in the prefrontal and cingulate cortices. Recently, fMRI has been adapted to examine connectivity within a specific resting-state neural network--the default-mode network--that includes medial prefrontal and anterior cingulate cortices. The goal of this study was to examine resting-state, default-mode network functional connectivity in subjects with major depression and in healthy controls.

METHODS

Twenty-eight subjects with major depression and 20 healthy controls underwent 5-min fMRI scans while resting quietly. Independent component analysis was used to isolate the default-mode network in each subject. Group maps of the default-mode network were compared. A within-group analysis was performed in the depressed group to explore effects of depression refractoriness on functional connectivity.

RESULTS

Resting-state subgenual cingulate and thalamic functional connectivity with the default-mode network were significantly greater in the depressed subjects. Within the depressed group, the length of the current depressive episode correlated positively with functional connectivity in the subgenual cingulate.

CONCLUSIONS

This is the first study to explore default-mode functional connectivity in major depression. The findings provide cross-modality confirmation of PET studies demonstrating increased thalamic and subgenual cingulate activity in major depression. Further, the within-subject connectivity analysis employed here brings these previously isolated regions of hypermetabolism into the context of a disordered neural network. The correlation between refractoriness and subgenual cingulate functional connectivity within the network suggests that a quantitative, resting-state fMRI measure could be used to guide therapy in individual subjects.

Brain imaging correlates of depressive symptom severity and predictors of symptom improvement after antidepressant treatment

BACKGROUND

It would be therapeutically useful to predict clinical response to antidepressant drugs. We evaluated structural magnetic resonance imaging (MRI) and functional MRI (fMRI) data as predictors of symptom change in people with depression.

METHODS

Brain structure and function were measured with MRI in 17 patients with major depression immediately before 8 weeks treatment with fluoxetine 20 mg/day. For fMRI, patients were scanned during visual presentation of faces representing different intensities of sadness. Clinical response was measured by change in serial scores on the Hamilton Rating Scale for Depression. Symptom change scores (and baseline symptom severity) were regressed on structural and functional MRI data to map brain regions where grey matter volume, or activation by sad facial affect processing, was significantly associated with symptom change (or baseline severity).

RESULTS

Faster rates of symptom improvement were strongly associated with greater grey matter volume in anterior cingulate cortex, insula, and right temporo-parietal cortex. Patients with greater than median grey matter volume in this system had faster rates of improvement and significantly lower residual symptom scores after 8 weeks' treatment. Faster improvement was also predicted by greater functional activation of anterior cingulate cortex. Baseline symptom severity was negatively correlated with greater grey matter volume in dorsal prefrontal and anterior midcingulate regions anatomically distinct from the pregenual and subgenual cingulate regions predicting treatment response.

CONCLUSIONS

Structural MRI measurements of anterior cingulate cortex could provide a useful predictor of antidepressant treatment response.

Deep Brain Stimulation

BACKGROUND

Deep brain stimulation (DBS) for the treatment of neurologic diseases has markedly increased in popularity over the past 15 years. This review primarily focuses on movement disorder applications and efficacy of DBS, but also briefly reviews other promising new and old uses of DBS.

REVIEW SUMMARY

A multidisciplinary team consisting of a movement disorders neurologist, a functional neurosurgeon, and a neuropsychologist optimally selects patients for DBS. Patients must be significantly disabled despite optimal medical therapy and be cognitively healthy without significant psychiatric disorders. Although this surgery is elective, it should not be withheld until the patient suffers marked loss of quality of life. Patients must have support from caregivers and postoperatively multiple DBS programming visits may be required. DBS of the subthalamic nucleus (STN) and the globus pallidus pars interna (GPi) significantly improves motor performance, activities of daily living, and quality of life in advanced Parkinson disease. In addition, STN DBS allows for marked reductions of antiparkinson medication. Stimulation of the ventralis intermedius nucleus of the thalamus is an effective treatment for essential tremor with sustained long-term effects. The GPi may be the preferred site of stimulation for dystonia with movement scores typically improved by 75% in patients with primary dystonia.

CONCLUSIONS

DBS is an effective surgical treatment for movement disorders with sustained long-term benefits. Further research is ongoing to better understand the mechanism of DBS, refine the hardware to improve efficacy and reduce adverse effects, and identify additional applications and new anatomic targets.

Affective neuroscience and psychiatry

Affective neuroscience addresses the brain mechanisms underlying emotional behaviour. In psychiatry, affective neuroscience finds application not only in understanding the neurobiology of mood disorders, but also by providing a framework for understanding the neural control of interpersonal and social behaviour and processes that underlie psychopathology. By providing a coherent conceptual framework, affective neuroscience is increasingly able to provide a mechanistic explanatory understanding of current therapies and is driving the development of novel therapeutic approaches.

Psychiatric and neuropsychiatric adverse events associated with deep brain stimulation: A meta-analysis of ten years' experience

Deep brain stimulation (DBS) has been approved by the FDA for use in the treatment of Parkinson's disease, essential tremor, and dystonia. Case reports and case series have reported significant psychiatric side effects in some individuals. The goal of this meta-analysis is to characterize the risks and benefits of DBS and to assess its possible use within the psychiatric setting. A search was conducted on PubMed, EBSCO, and PsycInfo in January 2006 that covered the time period 1 Jan 1996-30 Dec 2005. All identified articles were reviewed and those describing adverse events were further examined with a structured instrument. The initial searches yielded 2667 citations; 808 articles met inclusion criteria for the meta-analysis; 98.2% of studies that specifically assessed motor function reported some level of improvement. Most reported side effects were device or procedure related (e.g., infection and lead fracture). The prevalence of depression was 2-4%, mania 0.9-1.7%, emotional changes 0.1-0.2%, and the prevalence of suicidal ideation/suicide attempt was 0.3-0.7%. The completed suicide rate was 0.16-0.32%. In conclusion, DBS is an effective treatment for Parkinson's disease, dystonia, and essential tremor, and case reports suggest that major depression and OCD may also respond to DBS. Reported rates of depression, cognitive impairment, mania, and behavior change are low, but there is a high rate of suicide in patients treated with DBS, particularly with thalamic and GPi stimulation. Because of the high suicide rate, patients should be prescreened for suicide risk prior to DBS surgery. Additionally, patients should be monitored closely for suicidal behavior post-operatively.

Reduced evoked fos expression in activity-related brain regions in animal models of behavioral depression

A previous study showed that two mouse models of behavioral depression, immune system activation and depletion of brain monoamines, are accompanied by marked reductions in stimulated neural activity in brain regions involved in motivated behavior. The present study tested whether this effect is common to other depression models by examining the effects of repeated forced swimming, chronic subordination stress or acute intraventricular galanin injection - three additional models - on baseline or stimulated c-fos expression in several brain regions known to be involved in motor or motivational processes (secondary motor, M2, anterior piriform cortex, APIR, posterior cingulate gyrus, CG, nucleus accumbens, NAC). Each of the depression models was found to reduce the fos response stimulated by exposure to a novel cage or a swim stress in all four of these brain areas but not to affect the response of a stress-sensitive region (paraventricular hypothalamus, PVH) that was included for control purposes. Baseline fos expression in these structures was either unaffected or affected in an opposite direction to the stimulated response. Pretreatment with either desmethylimipramine (DMI) or tranylcypromine (tranyl) attenuated these changes. It is concluded that the pattern of a reduced neural function of CNS motor/motivational regions with an increased function of stress areas is common to 5 models of behavioral depression in the mouse and is a potential experimental analog of the neural activity changes occurring in the clinical condition.

High-Speed Imaging Reveals Neurophysiological Links to Behavior in an Animal Model of Depression

The hippocampus is one of several brain areas thought to play a central role in affective behaviors, but the underlying local network dynamics are not understood. We used quantitative voltage-sensitive dye imaging to probe hippocampal dynamics with millisecond resolution in brain slices after bidirectional modulation of affective state in rat models of depression. We found that a simple measure of real-time activity-stimulus-evoked percolation of activity through the dentate gyrus relative to the hippocampal output subfield-accounted for induced changes in animal behavior independent of the underlying mechanism of action of the treatments. Our results define a circuit-level neurophysiological endophenotype for affective behavior and suggest an approach to understanding circuit-level substrates underlying psychiatric disease symptoms.

Deep brain stimulation for treatment-refractory obsessive-compulsive disorder: the search for a valid target

Obsessive-compulsive disorder (OCD) is a common psychiatric disease that is marked by recurring, anxiety-provoking thoughts (obsessions) accompanied by repetitive and time-consuming behaviors (compulsions). Among the controversies in the OCD literature is the issue of the origin of the disease and whether brain changes observed with modern imaging techniques are the causes or results of OCD behaviors and thoughts. These issues remain unresolved; however, significant strides have been made in understanding the illness from both phenomenological and pathophysiological perspectives. The current staple of OCD management remains pharmacological in nature and often occurs in conjunction with cognitive behavioral therapy. Refractory cases, however, are occasionally referred for neurosurgical consultation, and several procedures have been examined. Success in the treatment of Parkinson's disease, the reversibility of the therapy, and a relatively safe side-effect profile have allowed deep brain stimulation (DBS) to be examined as an alternative treatment for some psychiatric conditions. Here we assess the possibility of applying DBS to the treatment of OCD. Morphological, functional metabolic, and volumetric data point to several brain regions that are important to the etiology and maintenance of OCD. Converging evidence from the genetics and neurocircuitry literature suggests that several subcortical structures play prominent roles in the disease. The functional modification of these structures could potentially provide symptom relief. Here, we review the ablative and DBS procedures for refractory OCD, and provide a research-driven hypothesis that highlights the ventromedial head of the caudate nucleus, and structures up- and downstream from it, as potential DBS targets for treatment-resistant disease. We hope that a research-driven approach, premised on converging evidence and previous experience, will lead to a safe and effective DBS procedure that will benefit patients who remain disabled despite presently available therapies.

Anatomy and physiology of the basal ganglia: implications for DBS in psychiatry

The basal ganglia have been a target for neuromodulation surgery since Russell Meyers' pioneering works in the late 1930s. Contemporary movement disorder surgery on the brain has evolved from empiric observations on movement behavior after neurological lesions. So too has the development of psychiatric surgical procedures followed the observation of lesions in the brain on cognitive and affective behavior. Just as deep brain stimulation (DBS) has revolutionized the practice of movement disorder surgery, its application to psychiatric illness has become the cutting edge of functional and restorative neurosurgery. The fundamental concept of the cortico-striatal-pallido-thalamocortical loop will be explored in the context of psychiatric disorders. DBS targeting this circuitry appears from initial evidence in obsessive-compulsive disorder (OCD) to be a promising option for patients with neuropsychiatric illness resistant to conventional therapies. Further exploring the anatomic interconnectivity of the physiologically relevant cortical and subcortical areas will inevitably lead to better applications of DBS for the treatment of OCD, major depression (MD) and potentially for other psychiatric disorders. Implementing such therapies optimally will require the creation of treatment centers with specialized expertise in the psychiatric, neurosurgical, and ethical issues that arise with these populations.

Increased left prefrontal activation in patients with unipolar depression: an event-related, parametric, performance-controlled fMRI study

BACKGROUND

Executive deficits associated with frontal lobe dysfunction are prominent in depression. We applied a newly developed WM task to investigate the neural correlates of executive processes with functional magnetic resonance imaging (fMRI) at comparable performance levels analyzing correct trials only.

METHODS

We studied 12 partially remitted, medicated inpatients meeting DSM-IV criteria for major depressive disorder and 17 healthy controls. We used a parametric version of a delayed match-to-sample WM task requiring manipulation of verbal material during a delay period in an event-related fMRI design.

RESULTS

Depressed patients were generally slower and load-dependently less accurate than healthy controls. Patients showed significantly more activation of left dorsolateral prefrontal cortex with highest cognitive load. Additionally, they showed higher activation in ventromedial prefrontal cortex during the control condition.

LIMITATIONS

The fact that patients were taking different antidepressant drugs could limit the explanatory power of the present results.

CONCLUSIONS

Increased lateral prefrontal activation despite comparably successful performance - when only correct trials were analyzed - in patients with depression can be interpreted as evidence for compensatory recruitment of prefrontal cortical resources.

Translational principles of deep brain stimulation

Deep brain stimulation (DBS) has shown remarkable therapeutic benefits for patients with otherwise treatment-resistant movement and affective disorders. This technique is not only clinically useful, but it can also provide new insights into fundamental brain functions through direct manipulation of both local and distributed brain networks in many different species. In particular, DBS can be used in conjunction with non-invasive neuroimaging methods such as magnetoencephalography to map the fundamental mechanisms of normal and abnormal oscillatory synchronization that underlie human brain function. The precise mechanisms of action for DBS remain uncertain, but here we give an up-to-date overview of the principles of DBS, its neural mechanisms and its potential future applications.

Circuit-breakers: optical technologies for probing neural signals and systems

Neuropsychiatric disorders, which arise from a combination of genetic, epigenetic and environmental influences, epitomize the challenges faced in understanding the mammalian brain. Elucidation and treatment of these diseases will benefit from understanding how specific brain cell types are interconnected and signal in neural circuits. Newly developed neuroengineering tools based on two microbial opsins, channelrhodopsin-2 (ChR2) and halorhodopsin (NpHR), enable the investigation of neural circuit function with cell-type-specific, temporally accurate and reversible neuromodulation. These tools could lead to the development of precise neuromodulation technologies for animal models of disease and clinical neuropsychiatry.

Serial vagus nerve stimulation functional MRI in treatment-resistant depression

Vagus nerve stimulation (VNS) therapy has shown antidepressant effects in open acute and long-term studies of treatment-resistant major depression. Mechanisms of action are not fully understood, although clinical data suggest slower onset therapeutic benefit than conventional psychotropic interventions. We set out to map brain systems activated by VNS and to identify serial brain functional correlates of antidepressant treatment and symptomatic response. Nine adults, satisfying DSM-IV criteria for unipolar or bipolar disorder, severe depressed type, were implanted with adjunctive VNS therapy (MRI-compatible technique) and enrolled in a 3-month, double-blind, placebo-controlled, serial-interleaved VNS/functional MRI (fMRI) study and open 20-month follow-up. A multiple regression mixed model with blood oxygenation level dependent (BOLD) signal as the dependent variable revealed that over time, VNS therapy was associated with ventro-medial prefrontal cortex deactivation. Controlling for other variables, acute VNS produced greater right insula activation among the participants with a greater degree of depression. These results suggest that similar to other antidepressant treatments, BOLD deactivation in the ventro-medial prefrontal cortex correlates with the antidepressant response to VNS therapy. The increased acute VNS insula effects among actively depressed participants may also account for the lower dosing observed in VNS clinical trials of depression compared with epilepsy. Future interleaved VNS/fMRI studies to confirm these findings and further clarify the regional neurobiological effects of VNS.

A final common pathway for depression: implications for therapy

Depression in humans and animal models has been found to be accompanied by a hypoactivity of brain regions involved in positively motivated behavior together with a hyperactivity in regions involved in stress responses. Both sets of changes are reversed by diverse antidepressant treatments. It has been proposed that this neural pattern underlies the symptoms common to most forms of depression, which are the loss of positively motivated behavior and the increase in stress. The present paper discusses how this framework can organize diverse findings on the multiple factors associated with this disorder. The hypothesis suggests new therapeutic strategies involving treatment with low-dose corticosteroids to suppress the stress network or with antagonists of alpha(1A)- and agonists of alpha(1B)-adrenoceptors to disinhibit or activate the positive motivational network, respectively.

High frequency stimulation or elevated K+ depresses neuronal activity in the rat entopeduncular nucleus

High frequency stimulation (HFS) is applied to many brain regions to treat a variety of neurological disorders/diseases, yet the mechanism(s) underlying its effects remains unclear. While some studies showed that HFS inhibits the stimulated nucleus, others report excitation. In this in vitro study, we stimulated the rat globus pallidus interna (entopeduncular nucleus, EP), a commonly stimulated area for Parkinson's disease, to investigate the effect of HFS-induced elevation of extracellular potassium (K(+)(e)) on rat EP neuronal activity. Whole-cell patch-clamp recordings and [K(+)](e) measurements were obtained in rat EP brain slices before, during and after HFS. After HFS (150 Hz, 10 s), [K(+)](e) increased from 2.5-9.6+/-1.4 mM, the resting membrane potential of EP neurons depolarized by 11.1+/-2.5 mV, spiking activity was significantly depressed, and input resistance decreased by 25+/-6%. The GABA(A) receptor blocker, gabazine, did not prevent these effects. The bath perfusion of 6 or 10 mM K(+), with or without synaptic blockers, mimicked the HFS-mediated effects: inhibition of spike activity, a 20+/-9% decrease in input resistance and a 17.4+/-3.0 mV depolarization. This depolarization exceeded predicted values of elevated [K(+)](e) on the resting membrane potential. A depolarization block did not fully account for the K(+)-induced inhibition of EP neuronal activity. Taken together, our results show that HFS-induced elevation of [K(+)](e) decreased EP neuronal activity by the activation of an ion conductance resulting in membrane depolarization, independent of synaptic involvement. These findings could explain the inhibitory effects of HFS on neurons of the stimulated nucleus.

Anatomical analysis of afferent projections to the medial prefrontal cortex in the rat

The medial prefrontal cortex (mPFC) has been associated with diverse functions including attentional processes, visceromotor activity, decision making, goal directed behavior, and working memory. Using retrograde tracing techniques, we examined, compared, and contrasted afferent projections to the four divisions of the mPFC in the rat: the medial (frontal) agranular (AGm), anterior cingulate (AC), prelimbic (PL), and infralimbic (IL) cortices. Each division of the mPFC receives a unique set of afferent projections. There is a shift dorsoventrally along the mPFC from predominantly sensorimotor input to the dorsal mPFC (AGm and dorsal AC) to primarily 'limbic' input to the ventral mPFC (PL and IL). The AGm and dorsal AC receive afferent projections from widespread areas of the cortex (and associated thalamic nuclei) representing all sensory modalities. This information is presumably integrated at, and utilized by, the dorsal mPFC in goal directed actions. In contrast with the dorsal mPFC, the ventral mPFC receives significantly less cortical input overall and afferents from limbic as opposed to sensorimotor regions of cortex. The main sources of afferent projections to PL/IL are from the orbitomedial prefrontal, agranular insular, perirhinal and entorhinal cortices, the hippocampus, the claustrum, the medial basal forebrain, the basal nuclei of amygdala, the midline thalamus and monoaminergic nuclei of the brainstem. With a few exceptions, there are few projections from the hypothalamus to the dorsal or ventral mPFC. Accordingly, subcortical limbic information mainly reaches the mPFC via the midline thalamus and basal nuclei of amygdala. As discussed herein, based on patterns of afferent (as well as efferent) projections, PL is positioned to serve a direct role in cognitive functions homologous to dorsolateral PFC of primates, whereas IL appears to represent a visceromotor center homologous to the orbitomedial PFC of primates.

Pulse-to-pulse changes in the frequency of deep brain stimulation affect tremor and modeled neuronal activity

The effectiveness of deep brain stimulation (DBS) in relieving the symptoms of movement disorders is dependent on the average frequency of stimulation. However, no one has yet examined whether the effectiveness of DBS in relieving tremor is dependent on the pulse-to-pulse (instantaneous) frequency of DBS. We examined the effects of paired-pulse thalamic DBS on tremor in subjects with essential tremor and on the firing of model neurons in a biophysically based computational model of DBS. DBS with an average rate of 130 Hz was more effective at reducing tremor when pulses were evenly spaced than when there were large differences between intrapair and interpair pulse intervals. Similar correlations were observed in the firing patterns of model neurons: increasing the difference between the intrapair and interpair intervals rendered model neurons more likely to fire synchronous bursts, more likely to fire irregularly, and less likely to entrain to the stimulus. The tremor responses provide evidence that the pulse-to-pulse frequency of DBS, not just its average rate, plays an important role in DBS function. Modeling results also suggest that effective DBS overrides oscillatory pathological activity and replaces it with more regularized neuronal firing patterns.

Bispectral index monitoring does not improve anesthesia performance in patients with movement disorders undergoing deep brain stimulating electrode implantation

BACKGROUND

Deep brain stimulation (DBS) has emerged as a promising therapy for movement disorders. During the implantation procedure for the electrodes, the patient emerges from anesthesia repeatedly to facilitate neurological testing. We investigated whether Bispectral Index (BIS) monitoring would be beneficial in patients receiving "sleep-awake-sleep" anesthesia with respect to time of arousal, consumption of propofol, and cardiopulmonary stability (i.e., heart rate, arterial blood pressure, and end-tidal carbon dioxide).

METHODS

We investigated 21 patients scheduled for implantation of DBS electrodes. Depth of propofol anesthesia was controlled either with BIS guidance in 10 patients (BIS group) or without in 11 patients (non-BIS group). In the BIS group, a BIS score of 40-60 was targeted during sleep periods, whereas in the non-BIS group, a value of 1 (= no response to tactile stimulation [unconsciousness]) on the Observers' Assessment of Alertness/Sedation Scale was targeted. For analgesia, the sites for the burr holes and for the pins of the stereotactic ring were infiltrated with 2% lidocaine; no opioids were used. For periods during which an awake patient required neurological testing, propofol was discontinued.

RESULTS

We found no difference between groups with respect to times of arousal, total amount of propofol consumption, and cardiopulmonary stability. However, significantly more propofol boluses had to be administered in the BIS group (30 +/- 11.6 vs 17 +/- 4.6) to maintain the BIS score within the target range (P < 0.05).

CONCLUSION

BIS monitoring does not improve anesthesia management for DBS electrode implantation in patients with movement disorders.

Studies of caloric vestibular stimulation: implications for the cognitive neurosciences, the clinical neurosciences and neurophilosophy

OBJECTIVE

Caloric vestibular stimulation (CVS) has traditionally been used as a tool for neurological diagnosis. More recently, however, it has been applied to a range of phenomena within the cognitive neurosciences. Here, we provide an overview of such studies and review our work using CVS to investigate the neural mechanisms of a visual phenomenon - binocular rivalry. We outline the interhemispheric switch model of rivalry supported by this work and its extension to a metarivalry model of interocular-grouping phenomena. In addition, studies showing a slow rate of binocular rivalry in bipolar disorder are discussed, and the relationship between this finding and the interhemispheric switch model is described. We also review the effects of CVS in various clinical contexts, explain how the technique is performed and discuss methodological issues in its application.

METHODS

A review of CVS and related literature was conducted.

RESULTS

Despite CVS being employed with surprising effect in a wide variety of cognitive and clinical contexts, it has been a largely underutilized brain stimulation method for both exploratory and therapeutic purposes. This is particularly so given that it is well tolerated, safe, inexpensive and easy to administer.

CONCLUSION

CVS can be used to investigate various cognitive phenomena including perceptual rivalry, attention and mood, as well as somatosensory representation, belief, hemispheric laterality and pain. The technique can also be used to investigate clinical conditions related to these phenomena and may indeed have therapeutic utility, especially with respect to postlesional disorders, mania, depression and chronic pain states. Furthermore, we propose that based on existing reports of the phenomenological effects of CVS and the brain regions it is known to activate, the technique could be used to investigate and potentially treat a range of other clinical disorders. Finally, the effects of CVS (and its potential effects) on several phenomena of interest to philosophy suggest that it is also likely to become a useful tool in experimental neurophilosophy.

An optical neural interface:in vivocontrol of rodent motor cortex with integrated fiberoptic and optogenetic technology

Neural interface technology has made enormous strides in recent years but stimulating electrodes remain incapable of reliably targeting specific cell types (e.g. excitatory or inhibitory neurons) within neural tissue. This obstacle has major scientific and clinical implications. For example, there is intense debate among physicians, neuroengineers and neuroscientists regarding the relevant cell types recruited during deep brain stimulation (DBS); moreover, many debilitating side effects of DBS likely result from lack of cell-type specificity. We describe here a novel optical neural interface technology that will allow neuroengineers to optically address specific cell types in vivo with millisecond temporal precision. Channelrhodopsin-2 (ChR2), an algal light-activated ion channel we developed for use in mammals, can give rise to safe, light-driven stimulation of CNS neurons on a timescale of milliseconds. Because ChR2 is genetically targetable, specific populations of neurons even sparsely embedded within intact circuitry can be stimulated with high temporal precision. Here we report the first in vivo behavioral demonstration of a functional optical neural interface (ONI) in intact animals, involving integrated fiberoptic and optogenetic technology. We developed a solid-state laser diode system that can be pulsed with millisecond precision, outputs 20 mW of power at 473 nm, and is coupled to a lightweight, flexible multimode optical fiber, approximately 200 microm in diameter. To capitalize on the unique advantages of this system, we specifically targeted ChR2 to excitatory cells in vivo with the CaMKIIalpha promoter. Under these conditions, the intensity of light exiting the fiber ( approximately 380 mW mm(-2)) was sufficient to drive excitatory neurons in vivo and control motor cortex function with behavioral output in intact rodents. No exogenous chemical cofactor was needed at any point, a crucial finding for in vivo work in large mammals. Achieving modulation of behavior with optical control of neuronal subtypes may give rise to fundamental network-level insights complementary to what electrode methodologies have taught us, and the emerging optogenetic toolkit may find application across a broad range of neuroscience, neuroengineering and clinical questions.

The Economo-Koskinas Atlas Revisited: Cytoarchitectonics and Functional Context

The monumental Atlas of Cytoarchitectonics of the Adult Human Cerebral Cortex of Economo and Koskinas represents a gigantic intellectual and technical effort, never sufficiently recognized. One reason might have been the limited number of copies produced; another, the complex (albeit logical and precise) symbol notation, which comprises a Roman capital (from the initial of the respective lobe), a calligraphic capital (the sequence of a gyrus within a lobe), and a Latin or Greek subscript (for microscopic features). Economo and Koskinas defined 107 cortical areas, as opposed to Brodmann's 44 areas for the human brain. Their cytoarchitectonic criteria confer the advantage of a more detailed parcellation scheme, despite the traditional familiarity of neuroscientists with Brodmann numbers. The system of 107 areas of Economo and Koskinas may be especially useful for modern studies on functional localization.

Neuroethical responsibilities

Neuroscience represents a dynamic area of biomedical research where neuroethical responsibilities for researchers are emerging. This paper is the companion piece to the French-language one also published in this issue of the Canadian Journal of Neurological Sciences. It serves as a review of recent advances in neuroethics through the lens of three cases: (1) incidental finding of anomalies in neuroimaging research; (2) creation of neurotechnologies that can lead to cognitive enhancement, and (3) responsible communication of research results. We propose and discuss a multidimensional framework of neuroethical responsibilities to help tackle these issues. The framework reiterates the fundamental role of scientific integrity, puts in the foreground social responsibilities pertaining to the eventual use of neuroscience knowledge, and highlights self-reflection in research and training of researchers.

Proportional Feedback Stimulation for Seizure Control in Rats

PURPOSE

A responsive electrical brain stimulation system using control feedback was investigated for the treatment of seizures.

METHODS

A proportional feedback stimulation system was designed. Penicillin-induced episodic seizures were created in rat primary motor cortex. Both intracranial (proximal to seizure focus) and extracranial EEGs were monitored. Current stimulation was applied at the seizure focus by using the intracranial EEG as the current-stimulus template. Different gains (H) for determining feedback stimulus amplitudes were tested.

RESULTS

The effect of feedback stimulation on seizures was initially assessed by measuring change in variance of the amplitude histogram of the intracranial EEG before and during stimulation. Mean reduction in amplitude variance during seizure activity was significant, with variance during stimulation progressively reduced as feedback gain was increased, indicating that overall suppression of seizure amplitude depended on H. Further increases in feedback gain typically produced saturating oscillations, indicating that this level of H resulted in instability. Frequency analysis of seizure and stimulation periods for each of the effective levels of H demonstrated close correlation across a large frequency domain, suggesting that the reduction in EEG seizure amplitude during feedback stimulation was possibly because of shunting of neuronal currents near electrodes as opposed to an alteration of neuronal dynamics. Although the frequency and energy responses during seizures before or during feedback stimulation remained well correlated in the delta band, this correlation progressively decreased across the theta, alpha, and beta bands.

CONCLUSIONS

These results demonstrate that proportional feedback stimulation holds the promise of suppressing seizure activity. More-complicated control algorithms for generating feedback stimulation may provide further improvements in seizure suppression.

How can drug discovery for psychiatric disorders be improved?

Psychiatric disorders such as depression, anxiety and schizophrenia are leading causes of disability worldwide, and have a huge societal impact. However, despite the clear need for better therapies, and major advances in the understanding of the molecular basis of these disorders in recent years, efforts to discover and develop new drugs for neuropsychiatric disorders, particularly those that might revolutionize disease treatment, have been relatively unsuccessful. A multidisciplinary approach will be crucial in addressing this problem, and in the first Advances in Neuroscience for Medical Innovation symposium, experts in multiple areas of neuroscience considered key questions in the field, in particular those related to the importance of neuronal plasticity. The discussions were used as a basis to propose steps that can be taken to improve the effectiveness of drug discovery for psychiatric disorders.

Identification of arm movements using correlation of electrocorticographic spectral components and kinematic recordings

The purpose of this study was to explore the possibility of using electrocorticographic (ECoG) recordings from subdural electrodes placed over the motor cortex to identify the upper limb motion performed by a human subject. More specifically, we were trying to identify features in the ECoG signals that could help us determine the type of movement performed by an individual. Two subjects who had subdural electrodes implanted over the motor cortex were asked to perform various motor tasks with the upper limb contralateral to the site of electrode implantation. ECoG signals and upper limb kinematics were recorded while the participants were performing the movements. ECoG frequency components were identified that correlated well with the performed movements measured along 6D coordinates (X, Y, Z, roll, yaw and pitch). These frequencies were grouped using histograms. The resulting histograms had consistent and unique shapes that were representative of individual upper limb movements performed by the participants. Thus, it was possible to identify which movement was performed by the participant without prior knowledge of the arm and hand kinematics. To confirm these findings, a nearest neighbour classifier was applied to identify the specific movement that each participant had performed. The achieved classification accuracy was 89%.

Is deep brain stimulation a form of psychosurgery?

OBJECTIVE

To examine the potential for the experimental treatment of deep brain stimulation for neuropsychiatric disorders, and to debate the argument that it should be considered another form of psychosurgery.

CONCLUSIONS

Psychosurgery is an old term with considerable pejorative connotations. It should be replaced with the more descriptive and accurate 'neurosurgery for psychiatric disorders'. Moreover, neurosurgery should reflect ablative neurosurgery, and surgery for brain stimulation should be categorised as brain stimulation rather than neurosurgery, or indeed psychosurgery. This will prevent legislative restrictions on the development of brain stimulation techniques and not tar them with the lobotomy brush.

Deep brain stimulation in movement and psychiatric disorders

Deep brain stimulation (DBS) is the most focal and invasive of the electromagnetic brain stimulation therapies. A subcutaneous pulse generator provides continuous stimulation of circumscribed brain tissue via a multicontact microelectrode that terminates within its target. The result is an adjustable, reversible, and specific therapy. Despite limited understanding of its mechanisms of action, DBS efficacy has been established in several movement disorders, and promising reports have emerged for Tourette syndrome, obsessive-compulsive disorder, and major depression. Deep brain stimulation may prove to be a reasonable option for severely ill and treatment-resistant patients who otherwise have limited therapeutic options and a poor prognosis.

Transcranial and deep brain stimulation approaches as treatment for depression

Given that a considerable portion of depressed patients does not respond to or remit during pharmacotherapy, there is increasing interest in non-pharmacological strategies to treat depressive disorders. Several brain stimulation approaches are currently being investigated as novel therapeutic interventions beside electroconvulsive therapy (ECT), a prototypic method in this field with proven effectiveness. These neurostimulation methods include repetitive transcranial magnetic stimulation (rTMS), magnetic seizure therapy (MST), vagus nerve stimulation (VNS), deep brain stimulation (DBS) and transcranial direct current stimulation (tDCS). It is via different neuroanatomically defined "windows" that the various approaches access the neuronal networks showing an altered function in depression. Also, the methods vary regarding their degree of invasiveness. One or the other method may finally achieve antidepressant effectiveness with minimized side effects and constitute a new effective treatment for major depression.

The burden of severe depression: a review of diagnostic challenges and treatment alternatives

Among the factors making recognition of severe depression problematic for clinicians are the heterogeneous nature of the condition, lack of standardized definitions, and concomitant comorbidities that confound differential diagnosis of symptoms. The spectrum of severity in depressive disorders is extraordinarily broad, and severity assessment is comprised of several metrics including symptom intensity, diagnostic subtypes, suicidality risk, and hospitalization status. The overall diagnosis is achieved through consideration of symptom types and severities together with the degree of functional impairment as assessed by the psychiatric interview. It is likely that no single fundamental neurobiological defect underlies severe depression. The chronicity and heterogeneity of this disorder lead to frequent clinic visits and a longer course of treatment; therefore, successful approaches may require an arsenal of treatments with numerous mechanisms of action. The categories of drugs used to treat severe depression are detailed herein, as are several non-pharmacologic options including a number of experimental treatments. Pharmacotherapies include tricyclic antidepressants, selective serotonin reuptake inhibitors, atypical antidepressants such as serotonin-norepinephrine reuptake inhibitors and monoamine oxidase inhibitors, and combination and augmentation therapies. Drugs within each class are not equivalent, and efficacy may vary with symptom severity. Patient adherence makes tolerability another critical consideration in antidepressant choice. The role of non-pharmacological treatments such as electroconvulsive therapy, vagus nerve stimulation, transcranial magnetic stimulation, and deep brain stimulation remain active avenues of investigation. Improved knowledge and treatment approaches for severe depression are necessary to facilitate remission, the ideal treatment goal.

Changes in QEEG prefrontal cordance as a predictor of response to antidepressants in patients with treatment resistant depressive disorder: a pilot study

INTRODUCTION

Previous studies of patients with unipolar depression have shown that early decreases of EEG cordance (a new quantitative EEG method) can predict clinical response. We examined whether early QEEG decrease represents a phenomenon associated with response to treatment with different antidepressants in patients with treatment resistant depression.

METHOD

The subjects were 17 inpatients with treatment resistant depression. EEG data and response to treatment were monitored at baseline and after 1 and 4 weeks on an antidepressant treatment. QEEG cordance was computed at three frontal electrodes in theta frequency band. The prefrontal cordance combines complementary information from absolute and relative power of EEG spectra. Recent studies have shown that cordance correlates with cortical perfusion. Depressive symptoms were assessed using Montgomery-Asberg Depression Rating Scale (MADRS).

RESULTS

All 17 patients completed the 4-week study. All five responders showed decreases in prefrontal cordance after the first week of treatment. Only 2 of the 12 nonresponders showed early prefrontal cordance decrease. The decrease of prefrontal QEEG cordance after week 1 in responders as well as the increase in nonresponders were both statistically significant (p-value 0.03 and 0.01, respectively) and the changes of prefrontal cordance values were different between both groups (p-value 0.001).

CONCLUSION

Our results suggest that decrease in prefrontal cordance may indicate early changes of prefrontal activity in responders to antidepressants. QEEG cordance may become a useful tool in the prediction of response to antidepressants.

Rostral anterior cingulate cortex activity in the theta band predicts response to antidepressive medication

During the last 10 years the knowledge about rostral anterior cingulate cortex (ACC) activity in major depression has substantially increased. Several groups have independently described a relationship between resting activity in this area and response to antidepressant treatment. We have recently confirmed a relationship between resting activity of rostral ACC activity and response in a group of 20 patients with major depression using resting theta activity. In this earlier study regions of interest (ROI) were defined in order to establish regional specificity. Differences between responders and nonresponders were only found in the ACC-ROI, but not in the posterior cingulate region. We have now reanalyzed our data using a whole brain voxelwise approach, in order not to miss any other relevant functional differences. In addition to major differences between responders and nonresponders in the rostral ACC, we have identified a nearby region in the midline orbito-frontal region.

A biopsychosocial model as a guide for psychoeducation and treatment of depression

Effective treatment of severe or chronic unipolar depression requires the combination of pharmacological and psychotherapeutic interventions, and demands a theoretical paradigm integrating biological and psychosocial aspects of depression. Supported by recent research, we propose in our article a biopsychosocial diathesis-stress model of depression. Its basic aim is psychoeducational: to provide therapists, patients, and their environment a constructive conceptual framework to understand depressive complaints, vulnerability, and stress. The core of the model consists of the concept of psychobiological vulnerability, which is determined by risk factors-of a biogenetic, psychological, somatic, and societal nature-and by protective factors. Life events with an idiosyncratic, stress-inducing value interact with this vulnerability, triggering severe or chronic distress that affects the individual's resilience and leads to symptoms of depression. The pathogenesis of depression is symbolized by a negative downward loop, in which interactions among symptoms, vulnerability, and stressors drive the patient toward a depressive condition. Moreover, experiencing recurrent depression influences psychobiological vulnerability, the occurrence of stressors, and tremendously increases the risk of further relapse. The model stresses the self-evident integration of biological and psychological therapeutic interventions that need to focus on symptom reduction and on relapse prevention. Moreover, it offers the patient and therapist a psychoeducational context in which the individual's vulnerability and depressive symptoms can be treated. Finally, applications of the depression model as a therapeutic approach to severe depression in the phases of remoralization, symptom reduction, and relapse prevention are presented.

Context-dependent effects of substantia nigra stimulation on eye movements

In a series of now classic experiments, an output structure of the basal ganglia (BG)--the substantia nigra pars reticulata (SNr)--was shown to be involved in the generation of saccades made in particular behavioral contexts, such as when memory was required for guidance. Recent electrophysiological experiments, however, call this original hypothesis into question. Here we test the hypothesis that the SNr is involved preferentially in nonvisually guided saccades using electrical stimulation. Monkeys performed visually guided and memory-guided saccades to locations throughout the visual field. On 50% of the trials, electrical stimulation of the SNr occurred. Stimulation of the SNr altered the direction, amplitude, latency, and probability of saccades. Visually guided saccades tended to be rotated toward the field contralateral to the side of stimulation, whereas memory-guided saccades tended to be rotated toward the hemifield ipsilateral to the side of stimulation. Overall, the changes in saccade vector direction were larger for memory-guided than for visually guided saccades. Both memory- and visually guided saccades were hypometric during stimulation trials, but the stimulation preferentially affected the length of memory-guided saccades. Electrical stimulation of the SNr produced decreases in visually guided saccades bilaterally. In contrast, memory-guided saccades often had increases in saccade latency bilaterally. Finally, we found approximately 10% reduction in the probability of memory-guided saccades bilaterally. Visually guided saccade probability was unaltered. Taken together the results are consistent with the hypothesis that SNr primarily influences nonvisually guided saccades. The pattern of stimulation effects suggests that SNr influence is widespread, altering the pattern of activity bilaterally across the superior colliculus map of saccades.

Multiple-color optical activation, silencing, and desynchronization of neural activity, with single-spike temporal resolution

The quest to determine how precise neural activity patterns mediate computation, behavior, and pathology would be greatly aided by a set of tools for reliably activating and inactivating genetically targeted neurons, in a temporally precise and rapidly reversible fashion. Having earlier adapted a light-activated cation channel, channelrhodopsin-2 (ChR2), for allowing neurons to be stimulated by blue light, we searched for a complementary tool that would enable optical neuronal inhibition, driven by light of a second color. Here we report that targeting the codon-optimized form of the light-driven chloride pump halorhodopsin from the archaebacterium Natronomas pharaonis (hereafter abbreviated Halo) to genetically-specified neurons enables them to be silenced reliably, and reversibly, by millisecond-timescale pulses of yellow light. We show that trains of yellow and blue light pulses can drive high-fidelity sequences of hyperpolarizations and depolarizations in neurons simultaneously expressing yellow light-driven Halo and blue light-driven ChR2, allowing for the first time manipulations of neural synchrony without perturbation of other parameters such as spiking rates. The Halo/ChR2 system thus constitutes a powerful toolbox for multichannel photoinhibition and photostimulation of virally or transgenically targeted neural circuits without need for exogenous chemicals, enabling systematic analysis and engineering of the brain, and quantitative bioengineering of excitable cells.

Somatic therapies for treatment-resistant depression: new neurotherapeutic interventions

This brief review provides an overview of neurotherapeutic interventions for major depression that are available currently or are being studied in clinical trials. The growing utility of surgical and device-related treatments for psychiatric conditions may represent a sea change in the field of psychiatry comparable to that seen in other clinical disciplines. For example, for many years the overwhelming majority of cardiac conditions were treated with medications and behavioral interventions. With the advent of cardiac surgical procedures such as ablation and cardiac bypass surgery and the use of devices such as cardiac stents and pacemakers, the ability to treat cardiac disease has improved dramatically. The hope is that the use of neurotherapeutic interventions will lead to a similar improvement in the treatment of psychiatric illness. The future of neurotherpeutic interventions in psychiatry may include the use of neuroimaging technology to predict with patients may respond to which procedures or to guide the placement of DBS electrodes on an individual basis. DBS electrodes also could be placed in multiple brain regions. Clinical trials of cortical stimulation using surgically implanted electrodes on the brain surface are underway. These cortical-surface electrodes could provide cortical stimulation comparable to that induced by rTMS at the same location, obviating the need for visits to a physician for rTMS treatments and providing cortical stimulation of a greater magnitude and for an extended duration. Also, one can foresee surgical interventions in which neurotransmitter release is potentiated either by stimulating appropriate nuclei in the brain or by releasing neurotransmitters or neurotransmitter precursors into target brain regions using cannulae or an implanted device. Neurotrophic factors also could be introduced into target brain regions using analogous techniques. Although the future of neurotherapeutic interventions in psychiatry is hard to predict, it is clear that these treatments will have a growing role in the field.

Prediction of treatment response in major depression: integration of concepts

BACKGROUND

Two promising approaches have been introduced for the prediction of treatment response in major depression: one concept is based on the activity in the rostral anterior cingulate cortex (rACC). Subjects with higher metabolic rates respond better to sleep deprivation or antidepressive medication. Another approach is the investigation of the loudness dependence of the auditory evoked potential (LDAEP). Here, a high LDAEP is supposed to reflect low central serotonergic activity. We present the first study comparing both approaches in the same group of patients.

METHODS

Patients with major depression (n=20) were investigated using both resting EEG and LDAEP before treatment with either citalopram or reboxetine.

RESULTS

We found significant differences between responders and non-responders in the rACC in the theta-frequency range (6.5-8 Hz, p<0.05). In the subgroup of patients, treated with citalopram we found higher LDAEP-values in responders versus non-responders (p<0.05) and a significant correlation between pre-treatment-LDAEP and improvement in the Hamilton score after treatment (r=0.71, p<0.05).

CONCLUSIONS

In combining both methods a prediction whether a patient with major depression might be at risk for non-response to a standard therapy as well as a suggestion for a pharmacological approach of choice seems to be possible.

Deep brain stimulation for chronic pain investigated with magnetoencephalography

Deep brain stimulation has shown remarkable potential in alleviating otherwise treatment-resistant chronic pain, but little is currently known about the underlying neural mechanisms. Here for the first time, we used noninvasive neuroimaging by magnetoencephalography to map changes in neural activity induced by deep brain stimulation in a patient with severe phantom limb pain. When the stimulator was turned off, the patient reported significant increases in subjective pain. Corresponding significant changes in neural activity were found in a network including the mid-anterior orbitofrontal and subgenual cingulate cortices; these areas are known to be involved in pain relief. Hence, they could potentially serve as future surgical targets to relieve chronic pain.

Deep brain stimulation in neurologic disorders

Deep brain stimulation (DBS) is an effective surgical therapy for well-selected patients with medically intractable Parkinson's disease (PD) and essential tremor (ET). The purpose of this review is to describe the success of DBS in these two disorders and its promising application in dystonia, Tourette Syndrome (TS) and epilepsy. In the last 10 years, numerous short- and intermediate-term outcome studies have demonstrated significant relief to patients with PD and ET. A few long-term follow-up studies have also reported sustained benefits. When successful, DBS greatly reduces most of parkinsonian motor symptoms and drug-induced dyskinesia, and it frequently improves patients' ability to perform activities of daily living with less encumbrance from motor fluctuations. Quality of life is enhanced and many patients are able to significantly reduce the amount of antiparkinsonian medications required to still get good pharmacological benefit. Overall, adverse effects associated with DBS tend to be transient, although device-related and other postoperative complications do occur. DBS should be considered the surgical procedure of choice for patients who meet strict criteria with medically intractable PD, ET and selected cases of dystonia.