Ventromedial prefrontal cortex modulates fatigue after penetrating traumatic brain injury

Dynamic Prevalence of and Factors Associated With Fatigue Following Traumatic Brain Injury: A Systematic Review and Meta-analysis of Observational Studies

OBJECTIVE

To implement a systematic review and meta-analysis to comprehensively synthesize the prevalence of and factors associated with fatigue following traumatic brain injury (TBI).

METHODS

We systematically searched the PubMed, EMBASE, Cochrane Library, Cumulated Index to Nursing and Allied Health Literature, PsycINFO, and ProQuest Dissertations and Theses A&I databases in all fields from their inception to March 31, 2021. We included observational studies investigating fatigue at specific time points following TBI or factors associated with post-TBI fatigue. All data were analyzed using a random-effects model.

RESULTS

This meta-analysis included 29 studies that involved 12 662 patients with TBI and estimated the prevalence of post-TBI fatigue (mean age = 41.09 years); the meta-analysis also included 23 studies that involved 6681 patients (mean age = 39.95 years) and investigated factors associated with post-TBI fatigue. In patients with mild-to-severe TBI, the fatigue prevalence rates at 2 weeks or less, 1 to 3 months, 6 months, 1 year, and 2 years or more after TBI were 52.2%, 34.6%, 36.0%, 36.1%, and 48.8%, respectively. Depression (r = 0.48), anxiety (r = 0.49), sleep disturbance (r = 0.57), and pain (r = 0.46) were significantly associated with post-TBI fatigue. No publication bias was identified among the studies, except for those assessing fatigue prevalence at 6 months after TBI.

CONCLUSION

The pooled prevalence rates of post-TBI fatigue exhibited a U-shaped pattern, with the lowest prevalence rates occurring at 1 to 3 months after TBI. Depression, anxiety, sleep disturbance, and pain were associated with post-TBI fatigue. Younger patients and male patients were more likely to experience post-TBI fatigue. Our findings can assist healthcare providers with identifying appropriate and effective interventions targeting post-TBI fatigue at specific periods.

Self-reported Fatigue was Associated with Increased White-matter Alterations in Long-term Traumatic Brain Injury and Posttraumatic Stress Disorder Patients

Fatigue is a long-lasting problem in traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD), with limited research that investigated the fatigue-related white-matter changes within TBI and/or PTSD cohorts. This exploratory cross-sectional study used diffusion tensor imaging (DTI) and neuropsychological data collected from 153 male Vietnam War veterans, as part of the Alzheimer's Disease Neuroimaging Initiative - Department of Defense, and were divided clinically into control veterans, PTSD, TBI, and with both TBI and PTSD (TBI + PTSD). The existence of fatigue was defined by the question "Do you often feel tired, fatigued, or sleepy during the daytime?". DTI data were compared between fatigue and non-fatigue subgroups in each clinical group using tract-based spatial statistics voxel-based differences. Fatigue was reported in controls (29.55%), slightly higher in TBI (52.17%, PBenf = 0.06), and significantly higher in both TBI + PTSD (66.67%, PBenf = 0.001) and PTSD groups (79.25%, PBenf < 0.001). Compared to non-fatigued subgroups, no white-matter differences were observed in the fatigued subgroups of control or TBI, while the fatigued PTSD subgroup only showed increased diffusivity measures (i.e., radial and axial), and the fatigued TBI + PTSD subgroup showed decreased fractional anisotropy and increased diffusivity measures (PFWE ≤ 0.05). The results act as preliminary findings suggesting fatigue to be significantly reported in TBI + PTSD and PTSD decades post-trauma with a possible link to white-matter microstructural differences in both PTSD and TBI + PTSD. Future studies with larger cohorts and detailed fatigue assessments would be required to identify the white-matter changes associated with fatigue in these cohorts.

Corticomuscular coherence is reduced in relation to dorsiflexion fatigability to the same extent in adults with cerebral palsy as in neurologically intact adults

PURPOSE

Fatigue is frequent in adults with cerebral palsy (CP) and it is unclear whether this is due to altered corticospinal drive. We aimed to compare changes in corticospinal drive following sustained muscle contractions in adults with CP and neurologically intact (NI) adults.

METHODS

Fourteen adults with CP [age 37.6 (10.1), seven females, GMFCS levels I-II] and ten NI adults [age 35.4 (10.3), 6 females] performed 1-min static dorsiflexion at 30% of maximal voluntary contraction (MVC) before and after a submaximal contraction at 60% MVC. Electroencephalography (EEG) and electromyography (EMG) from the anterior tibial muscle were analyzed to quantify the coupling, expressed by corticomuscular coherence (CMC).

RESULTS

Adults with CP had lower MVCs but similar time to exhaustion during the relative load of the fatigability trial. Both groups exhibited fatigability-related changes in EMG median frequency and EMG amplitude. The CP group showed lower beta band (16-35 Hz) CMC before fatigability, but both groups decreased beta band CMC following fatigability. There was a linear correlation between decrease of beta band CMC and fatigability-related increase in EMG.

CONCLUSION

Fatigability following static contraction until failure was related to decreased beta band CMC in both NI adults and adults with CP. Our findings indicate that compensatory mechanisms to fatigability are present in both groups, and that fatigability affects the corticospinal drive in the same way. We suggest that the perceived physical fatigue in CP is related to the high relative load of activities of daily living rather than any particular physiological mechanism.

Submaximal Exercise Provokes Increased Activation of the Anterior Default Mode Network During the Resting State as a Biomarker of Postexertional Malaise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is characterized by disabling fatigue and postexertional malaise. We developed a provocation paradigm with two submaximal bicycle exercise stress tests on consecutive days bracketed by magnetic resonance imaging, orthostatic intolerance, and symptom assessments before and after exercise in order to induce objective changes of exercise induced symptom exacerbation and cognitive dysfunction. Method: Blood oxygenation level dependent (BOLD) scans were performed while at rest on the preexercise and postexercise days in 34 ME/CFS and 24 control subjects. Seed regions from the FSL data library with significant BOLD signals were nodes that clustered into networks using independent component analysis. Differences in signal amplitudes between groups on pre- and post-exercise days were determined by general linear model and ANOVA. Results: The most striking exercise-induced effect in ME/CFS was the increased spontaneous activity in the medial prefrontal cortex that is the anterior node of the Default Mode Network (DMN). In contrast, this region had decreased activation for controls. Overall, controls had higher BOLD signals suggesting reduced global cerebral blood flow in ME/CFS. Conclusion: The dynamic increase in activation of the anterior DMN node after exercise may be a biomarker of postexertional malaise and symptom exacerbation in CFS. The specificity of this postexertional finding in ME/CFS can now be assessed by comparison to post-COVID fatigue, Gulf War Illness, fibromyalgia, chronic idiopathic fatigue, and fatigue in systemic medical and psychiatric diseases.

Mental Fatigue after Mild Traumatic Brain Injury in Relation to Cognitive Tests and Brain Imaging Methods

Most people recover within months after a mild traumatic brain injury (TBI) or concussion, but some will suffer from long-term fatigue with a reduced quality of life and the inability to maintain their employment status or education. For many people, mental fatigue is one of the most distressing and long-lasting symptoms following an mTBI. No efficient treatment options can be offered. The best method for measuring fatigue today is with fatigue self-assessment scales, there being no objective clinical tests available for mental fatigue. The aim here is to provide a narrative review and identify fatigue in relation to cognitive tests and brain imaging methods. Suggestions for future research are presented.

Managing fatigue after an acquired brain injury: a pilot randomised controlled trial and qualitative investigation

Background/Aims

Fatigue after brain injury is common and enduring, and rehabilitation improves patient understanding and strategy development. The aim of this study was to determine whether therapy supporting fatigue management can be provided economically in groups to inpatients undertaking rehabilitation.

Methods

A mixed-methods study was undertaken, including a pilot randomised control trial and a parallel qualitative investigation. A total of 78 adult inpatients with moderate to severe acquired brain injury were recruited to the study; 40 were allocated to routine usual care and 38 were allocated to the intervention, which consisted of routine usual care plus four group therapy sessions that took place over 2 weeks, run by an experienced occupational therapist. Participants were aged between 18 and 65 years and were considered to be able to manage learning in a group setting. Outcome measures were collected at baseline and at the end of the therapy intervention (Barrow Neurological Institute Fatigue Scale, Quality of Life after Brain Injury questionnaire and a Fatigue Knowledge questionnaire assessing knowledge related to the aims of the education modules). A qualitative study was conducted after the quantitative investigation in the form of patient interviews. A total of 10 patients were interviewed to discuss their fatigue journey and impressions of receiving fatigue management therapy in a group.

Results

A repeated measures analysis of variance with time as a within-subject factor and group as a between-subjects factor showed no interaction effect of group × time for fatigue, quality of life or acquisition of knowledge; however, knowledge improved over time, irrespective of group allocation (P<0.01). Although most participants found the group work satisfactory in terms of overall knowledge development, a number would have preferred to address their specific fatigue issues in an individual session. Participants described a confusing journey understanding fatigue symptoms before therapy, but reported an improved understanding and acquiring management strategies after receiving the educational therapy sessions.

Conclusions

Education regarding fatigue following brain injury can be provided successfully to inpatients receiving rehabilitation in group settings. However, it may be important to build in an additional individual therapy session to address each patient's individual issues and queries.

Diminished corticomotor excitability in Gulf War Illness related chronic pain symptoms; evidence from TMS study

Chronic diffuse body pain is unequivocally highly prevalent in Veterans who served in the 1990-91 Persian Gulf War and diagnosed with Gulf War Illness (GWI). Diminished motor cortical excitability, as a measurement of increased resting motor threshold (RMT) with transcranial magnetic stimulation (TMS), is known to be associated with chronic pain conditions. This study compared RMT in Veterans with GWI related diffuse body pain including headache, muscle and joint pain with their military counterparts without GWI related diffuse body pain. Single pulse TMS was administered over the left motor cortex, using anatomical scans of each subject to guide the TMS coil, starting at 25% of maximum stimulator output (MSO) and increasing in steps of 2% until a motor response with a 50 µV peak to peak amplitude, defined as the RMT, was evoked at the contralateral flexor pollicis brevis muscle. RMT was then analyzed using Repeated Measures Analysis of Variance (RM-ANOVA). Veterans with GWI related chronic headaches and body pain (N = 20, all males) had a significantly (P < 0.001) higher average RMT (% ± SD) of 77.2% ± 16.7% compared to age and gender matched military controls (N = 20, all males), whose average was 55.6% ± 8.8%. Veterans with GWI related diffuse body pain demonstrated a state of diminished corticomotor excitability, suggesting a maladaptive supraspinal pain modulatory state. The impact of this observed supraspinal functional impairment on other GWI related symptoms and the potential use of TMS in rectifying this abnormality and providing relief for pain and co-morbid symptoms requires further investigation.Trial registration: This study was registered on January 25, 2017, on ClinicalTrials.gov with the identifier: NCT03030794. Retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT03030794 .

Beyond a rod through the skull: A systematic review of lesion studies of the human ventromedial frontal lobe

Neuropsychological studies from the past century have associated damage to the ventromedial frontal lobes (VMF) with impairments in a variety of domains, including memory, executive function, emotion, social cognition, and valuation. A central question in the literature is whether these seemingly distinct functions are subserved by different sub-regions within the VMF, or whether VMF supports a broader cognitive process that is crucial to these varied domains. In this comprehensive review of the neuropsychological literature from the last two decades, we present a qualitative synthesis of 184 papers that have examined the psychological impairments that result from VMF damage. We discuss these findings in the context of several theoretical frameworks and advocate for the view that VMF is critical for the formation and representation of schema and cognitive maps.

Behaviour outcomes in children with epilepsy 1 year after surgical resection of the ventromedial prefrontal cortex

Early damage to the ventromedial prefrontal cortex (VM) has been associated with impaired behavioural functioning in children without epilepsy, yet behaviour in children with epilepsy and VM lesions has not been investigated. The primary aim of this study was to examine behavioural outcomes in children with epilepsy emanating from the VM preoperatively and one year after epilepsy surgery compared to the general population and matched epilepsy controls. Behavioural outcomes were defined as comprising both problems and competencies (i.e. social, school and co-curricular performance). A secondary aim was to examine whether seizure outcome, number of antiepileptic drugs (AEDs), or age at surgery related to behavioural outcomes. Ratings on the Child Behavior Checklist were examined preoperatively and 1 year after surgery for 20 children with epilepsy who had undergone surgical resection of the VM (N = 10) or temporal lobe (TL, N = 10). VM and TL groups were comparable on Full Scale IQ (40-101), age of seizure onset (0.5-9.0 years), age at surgery (3.1-16.9 years), seizure laterality (5 left in each group), age at assessments, sex (3 female in VM group, 2 female in TL group) and seizure outcome (7 seizure free in VM group, 6 seizure free in TL group). The VM group had significantly elevated behaviour problems (i.e. withdrawn, thought, social and attention problems) and reduced competencies (i.e. social and school) compared to the general population before and after surgery. VM and TL cases did not differ on any behaviour problem scales pre or postoperatively and neither group showed significant change in functioning over time; however, VM patients had significantly lower total competence than TL patients postoperatively. A significant seizure outcome × time interaction was observed: children who were seizure free following surgery (collapsed across surgical site) showed an improvement in total behaviour problems and aggression at 1 year follow-up, whereas children with ongoing seizures showed a deterioration in these domains. In conclusion, VM lesions in children with epilepsy are associated with behavioural problems but their profile does not differ from that of children with temporal lobe epilepsy. These results are consistent with the concept that seizures arise from epileptogenic networks that may affect multiple cortical areas, even when onset is in a focal site.

Effort Displayed During Appetitive Phase of Feeding Behavior Requires Infralimbic Cortex Activity and Histamine H1 Receptor Signaling

The chances to succeed in goal-directed behaviors, such as food or water-seeking, improve when the subject is in an increased arousal state. The appetitive phase of these motivated behaviors is characterized by high levels of behavioral and vegetative excitation. The key decision of engaging in those particular behaviors depends primarily on prefrontal cortical areas, such as the ventromedial prefrontal cortex. We propose that the infralimbic cortex (ILC) located in the medial prefrontal cortex induces an increase in arousal during the appetitive phase of motivated behavior, and that this increase in arousal is, in turn, mediated by the activation of the brain histaminergic system, resulting in higher motivation for getting food rewards. To test this hypothesis, we conduct a progressive ratio operant conditioning to test the degree of motivation for food, while simultaneously manipulating the histaminergic system through pharmacologic interventions. We found that the behavioral responses to obtain food in hungry rats were disrupted when the ILC was inhibited through muscimol infusion, blocking brain H1 histamine receptors by intracerebroventricular infusion of pyrilamine or by satiety. In contrast, the consummatory behavior was not affected by ILC inhibition. The extracellular histamine levels in the ILC were increased in direct correlation with the degree of motivation measured in the progressive ratio test. ILC inhibition also prevented this increase in histamine levels. The rise in extracellular histamine levels during the progressive ratio test was similar (ca. 200%) during the active or the resting period of the day. However, different basal levels are observed for these two periods. Our findings suggest that increased histamine levels during this behavior are not simply explained by the awaked state, but instead, there is a motivation-related release of histamine, suggestive of a specific form of brain activation. Serotonin (another critical component of the ascending arousal system) was also tested. Interestingly, changes in levels of this neuromodulator were not detected during the progressive ratio test. In conclusion, our results suggest that ILC activation and subsequent increase in brain histamine release are both necessary for the normal performance of a motivated behavior such as feeding.

Trait Self-Control Outperforms Trait Fatigue in Predicting MS Patients' Cortical and Perceptual Responses to an Exhaustive Task

Patients with multiple sclerosis (PwMS) frequently suffer from fatigue, but this debilitating symptom is not yet fully understood. We propose that self-control can be conceptually and mechanistically linked to the fatigue concept and might help explain some of the diversity on how PwMS who suffer from fatigue deal with this symptom. To test this claim, we first assessed how cortical oxygenation and measures of motor and cognitive state fatigue change during a strenuous physical task, and then we tested the predictive validity of trait fatigue and trait self-control in explaining the observed changes. A sample of N = 51 PwMS first completed a test battery to collect trait measures of fatigue and self-control. PwMS then performed an isometric hand contraction task at 10% of their maximum voluntary contraction until exhaustion while we repeatedly assessed ratings of perceived cognitive and motor exertion. In addition, we continuously measured oxygenation of the prefrontal cortex (PFC) using functional near-infrared spectroscopy. Linear mixed-effect models revealed significant increases in perceived motor and cognitive exertion, as well as increases in PFC oxygenation. Hierarchical stepwise regression analyses showed that higher trait self-control predicted a less steep increase in PFC oxygenation and perceived cognitive exertion, while trait fatigue did not predict change in any dependent variable. These results provide preliminary evidence for the suggested link between self-control and fatigue. As self-control can be enhanced with training, this finding possibly has important implications for devising nonpharmacological interventions to help patients deal with symptoms of fatigue.

Structural brain correlates of fatigue in older adults with and without Parkinson's disease

Fatigue is one of the most common and disabling nonmotor symptoms seen in Parkinson's disease (PD) and is also commonly seen in healthy older adults. Our understanding of the etiology of fatigue in older adults with or without PD is limited and it remains unclear whether fatigue in PD is specifically related to PD pathology. The objective of this study was thus to determine whether fatigue in PD was associated with structural changes in gray or white matter and explore whether these changes were similar in older adults without PD. Magnetic resonance imaging (T₁ weighted) and diffusion tensor imaging were performed in 60 patients with PD (17 females; age = 67.58 ± 5.51; disease duration = 5.67 ± 5.83 years) and 41 age- and sex- matched healthy controls. FSL image processing was used to measure gray matter volume, fractional anisotropy, and leukoariosis differences. Voxel-based morphometry confirmed gray matter loss across the dorsal striatum and insula in the PD patient cohort. PD patients with fatigue had reduced gray matter volume in dorsal striatum relative to PD patients without fatigue (P < 0.05 False Discovery Rate corrected). No significant fatigue-related structural atrophy was found in controls. There were no areas of significant fractional anisotropy differences between high and low fatigue subjects in either the PD or non-PD groups. Control participants with high fatigue, but not PD, showed significantly greater total leukoariosis volumes (p = 0.03). Fatigue in PD is associated with unique structural changes in the caudate and putamen suggesting fatigue in PD is primarily related to PD pathology, particularly in the dorsal striatum, and not simply a consequence of aging.

•

Fatigue is a disabling symptom in Parkinson's disease (PD) and healthy older adults.

•

We studied structural correlates of fatigue using MRI morphometry.

•

PD patients with high fatigue had caudate atrophy.

•

Healthy older adults with fatigue had increased burden of leukoariosis.

•

Patterns of structural brain changes were distinct between PD and healthy group.

Effort and Fatigue-Related Functional Connectivity in Mild Traumatic Brain Injury

Mental fatigue in healthy individuals is typically observed under conditions of high cognitive demand, particularly when effort is required to perform a task for a long period of time-thus the concepts of fatigue and effort are closely related. In brain injured individuals, mental fatigue can be a persistent and debilitating symptom. Presence of fatigue after brain injury is prognostic for return to work/school and engagement in activities of daily life. As such, it should be a high priority for treatment in this population, but because there is little understanding of its behavioral and neural underpinnings, the target for such treatment is unknown. Here, the neural underpinnings of fatigue and effort are investigated in active duty military service members with mild traumatic brain injury (mTBI) and demographically-matched orthopedic controls. Participants performed a Constant Effort task for which they were to hold a pre-defined effort level constant for long durations during fMRI scanning. The task allowed for investigation of the neural systems underlying fatigue and their relationship with sense of effort. While brain activation associated with effort and fatigue did not differentiate the mTBI and controls, functional connectivity amongst active brain regions did. The mTBI group demonstrated immediate hyper-connectivity that increased with effort level but diminished quickly when there was a need to maintain effort. Controls, in contrast, demonstrated a similar pattern of hyper-connectivity, but only when maintaining effort over time. Connectivity, particularly between the left anterior insula, rostral anterior cingulate cortex, and right-sided inferior frontal regions, correlated with effort-level and state fatigue in mTBI participants. These connections also correlated with effort level in the Control group, but only the connection between the left insula and superior medial frontal gyrus correlated with fatigue, suggesting a differing pattern of connectivity. These findings align, in part, with the dopamine imbalance, and neural efficiency hypotheses that pose key roles for medial frontal connections with insular or striatal regions in motivating or optimizing performance. Sense of effort and fatigue are closely related. As people fatigue, sense of effort increases systematically. The data propose a complex link between sense of effort, fatigue, and mTBI that is centered in what may be an inefficient neural system due to brain trauma that warrants further investigation.

Sleep and fatigue after TBI

BACKGROUND

Whilst post traumatic brain injury fatigue (PTBIF) and sleep disturbance are common sequelae following brain injury, underlying mechanisms, and the potential for targeted interventions remain unclear.

OBJECTIVE

To present a review of recent studies exploring the epidemiology of PTBIF and sleep disturbance, the relationship and neuropsychological correlates of these issues, potential approaches to intervention, and implications for neurorehabilitation.

METHODS

A review of relevant literature was undertaken, with a focus on PTBIF relating to sleep disturbance, the neuropsychological correlates of these issues and implications for neurorehabilitation. This paper does not set out to provide a systematic review.

RESULTS

Multidimensional approaches to assessment and treatment of sleep disturbance and PTBIF are required.

CONCLUSIONS

There is a need for more robust findings in determining the complex nature of relationships between PTBIF, sleep disturbance, and correlates. Longitudinal prospective data is required to increase our understanding of the nature and course of PTBIF and sleep disturbance post TBI. Large scale clinical trials are required in evaluating the potential benefits of interventions.

Fatigue in Gulf War Illness is associated with tonically high activation in the executive control network

Gulf War Illness (GWI) is a chronic, multi-symptom illness that affects approximately 25% of Gulf veterans, with cognitive fatigue as one of its primary symptoms. Here, we investigated the neural networks associated with cognitive fatigue in GWI by asking 35 veterans with GWI and 25 healthy control subjects to perform a series of fatiguing tasks while in the MRI scanner. Two types of cognitive fatigue were assessed: state fatigue, which is the fatigue that developed as the tasks were completed, and trait fatigue, or one's propensity to experience fatigue when assessed over several weeks. Our results showed that the neural networks associated with state and trait fatigue differed. Irrespective of group, the network underlying trait fatigue included areas associated with memory whereas the neural network associated with state fatigue included key areas of a fronto-striatal-thalamic circuit that has been implicated in fatigue in other populations. As in other investigations of fatigue, the caudate of the basal ganglia was implicated in fatigue. Furthermore, individuals with GWI showed greater activation than the HC group in frontal and parietal areas for the less difficult task. This suggests that an inability to modulate brain activation as task demands change may underlie fatigue in GWI.

•

Fatigue-related brain activation can be induced and measured in veterans with GWI.

•

A network of brain areas was associated with cognitive fatigue during a working memory task.

•

The fatigue network included the basal ganglia, prefrontal and parietal areas.

•

Persistent activation in frontal and parietal areas in the GWI group suggests dysregulation of the cognitive control network.

Affective, neurocognitive and psychosocial disorders associated with traumatic brain injury and post-traumatic epilepsy

Survivors of traumatic brain injury (TBI) often develop chronic neurological, neurocognitive, psychological, and psychosocial deficits that can have a profound impact on an individual's wellbeing and quality of life. TBI is also a common cause of acquired epilepsy, which is itself associated with significant behavioral morbidity. This review considers the clinical and preclinical evidence that post-traumatic epilepsy (PTE) acts as a 'second-hit' insult to worsen chronic behavioral outcomes for brain-injured patients, across the domains of emotional, cognitive, and psychosocial functioning. Surprisingly, few well-designed studies have specifically examined the relationship between seizures and behavioral outcomes after TBI. The complex mechanisms underlying these comorbidities remain incompletely understood, although many of the biological processes that precipitate seizure occurrence and epileptogenesis may also contribute to the development of chronic behavioral deficits. Further, the relationship between PTE and behavioral dysfunction is increasingly recognized to be a bidirectional one, whereby premorbid conditions are a risk factor for PTE. Clinical studies in this arena are often challenged by the confounding effects of anti-seizure medications, while preclinical studies have rarely examined an adequately extended time course to fully capture the time course of epilepsy development after a TBI. To drive the field forward towards improved treatment strategies, it is imperative that both seizures and neurobehavioral outcomes are assessed in parallel after TBI, both in patient populations and preclinical models.

The relationship between outcome prediction and cognitive fatigue: A convergence of paradigms

Cognitive fatigue is common after strenuous cognitive effort. A large body of literature has implicated a network of brain areas in fatigue, including the basal ganglia and cortical areas including ventro-medal prefrontal cortex and anterior cingulate cortex (ACC). Furthermore, the ACC has been shown to be involved in processes such as error and conflict monitoring, outcome prediction, and effort processing. Thus, the ACC appears to be one common denominator between clinical work on fatigue and research on outcome prediction and effort. In the present study, we examined whether the same region of the ACC is activated during the processing of errors and fatigue. Cognitive fatigue was induced by having subjects perform a difficult working memory task, during which they rated on-task fatigue. Activation associated with error processing was determined by using error trials on the working memory task. After localizing the region engaged in error processing, we evaluated whether there was a relationship between BOLD activation of that region and on-task fatigue scores. The results showed that as subjects became more fatigued, they responded with longer latencies and increased accuracy for the more difficult task. Moreover, the ACC areas that were activated by error processing were also associated with fatigue. These results suggest that cognitive fatigue may be related to changes in effort and reward. We speculate that as the brain detects these changes, cognitive fatigue is generated as a way for the brain to signal itself that the effort required for the task no longer merits the rewards received for performing it.

Impaired Valuation Leads to Increased Apathy Following Ventromedial Prefrontal Cortex Damage

Apathy is defined by reduced goal-directed behavior, and is common in patients with damage to the ventromedial prefrontal cortex (vmPFC). Separately, in neuroeconomics research, the vmPFC has been shown to play a role in reward processing-namely, in "stimulus valuation," or the computation of the subjective reward value of a stimulus. Here, we used a sample of patients with focal brain lesions (N = 93) and matched healthy controls (N = 21) to determine whether the association between vmPFC damage and increased apathy is driven by impaired valuation. An auction task was used to measure valuation, and apathy was assessed via caregiver ratings of patients' day-to-day behavior. Lesion-symptom mapping identified the locus of impaired valuation in the vmPFC, and patients with damage to this region demonstrated increased apathy relative to patients with damage to dorsomedial prefrontal cortex (dmPFC), patients with damage to other brain regions, and healthy controls. Critically, the association between vmPFC damage and apathy was mediated by impaired valuation, with no effect as a function of dmPFC damage. Our results implicate a valuation-based mechanism underlying the relationship between vmPFC integrity and apathy, bridging findings from both the clinical literature and neuroeconomics research.

Glial Activation and Expression of the Serotonin Transporter in Chronic Fatigue Syndrome

Fatigue is commonly reported in a variety of illnesses and has major impact on quality of life. Chronic fatigue syndrome (CFS) is a debilitating syndrome of unknown etiology. The clinical symptoms include problems in neuroendocrine, autonomic, and immune systems. It is becoming clear that the brain is the central regulator of CFS. For example, neuroinflammation, especially induced by activation of microglia and astrocytes, may play a prominent role in the development of CFS, though little is known about molecular mechanisms. Many possible causes of CFS have been proposed. However, in this mini-review, we summarize evidence for a role for microglia and astrocytes in the onset and the maintenance of immunologically induced CFS. In a model using virus mimicking synthetic double-stranded RNA, infection causes sequential signaling such as increased blood brain barrier (BBB) permeability, microglia/macrophage activation through Toll-like receptor 3 (TLR3) signaling, secretion of IL-1β, upregulation of the serotonin transporter (5-HTT) in astrocytes, reducing extracellular serotonin (5-HT) levels and hence reduced activation of 5-HT_1A receptor subtype. Hopefully, drug discovery targeting these pathways may be effective for CFS therapy.

Cognitive fatigue in individuals with traumatic brain injury is associated with caudate activation

We investigated differences in brain activation associated with cognitive fatigue between persons with traumatic brain injury (TBI) and healthy controls (HCs). Twenty-two participants with moderate-severe TBI and 20 HCs performed four blocks of a difficult working memory task and four blocks of a control task during fMRI imaging. Cognitive fatigue, assessed before and after each block, was used as a covariate to assess fatigue-related brain activation. The TBI group reported more fatigue than the HCs, though their performance was comparable. Regarding brain activation, the TBI group showed a Task X Fatigue interaction in the caudate tail resulting from a positive correlation between fatigue and brain activation for the difficult task and a negative relationship for the control task. The HC group showed the same Task X Fatigue interaction in the caudate head. Because we had prior hypotheses about the caudate, we performed a confirmatory analysis of a separate dataset in which the same subjects performed a processing speed task. A relationship between Fatigue and brain activation was evident in the caudate for this task as well. These results underscore the importance of the caudate nucleus in relation to cognitive fatigue.

Post-stroke Mood and Emotional Disturbances: Pharmacological Therapy Based on Mechanisms

Post-stroke mood and emotional disturbances are frequent and diverse in their manifestations. Out of the many post-stroke disturbances, post-stroke depression, post-stroke anxiety, post-stroke emotional incontinence, post-stroke anger proneness, and post-stroke fatigue are frequent and important symptoms. These symptoms are distressing for both the patients and their caregivers, and negatively influence the patient's quality of life. Unfortunately, these emotional disturbances are not apparent and are therefore often unnoticed by busy clinicians. Their phenomenology, predicting factors, and pathophysiology have been under-studied, and are under-recognized. In addition, well-designed clinical trials regarding these symptoms are rare. Fortunately, these mood and emotional disturbances may be treated or prevented by various methods, including pharmacological therapy. To administer the appropriate therapy, we have to understand the phenomenology and the similarities and differences in the pathophysiological mechanisms associated with these emotional symptoms. This narrative review will describe some of the most common or relevant post-stroke mood and emotional disturbances. The phenomenology, factors or predictors, and relevant lesion locations will be described, and pharmacological treatment of these emotional disturbances will be discussed based on presumable pathophysiological mechanisms.

Brain lesion correlates of fatigue in individuals with traumatic brain injury

The purpose of this study was to investigate the neurological correlates of both subjective fatigue as well as objective fatigability in individuals with traumatic brain injury (TBI). The study has a cross-sectional design. Participants (N = 53) with TBI (77% male, mean age at injury 38 years, mean time since injury 1.8 years) underwent a structural magnetic resonance imaging (MRI) scan and completed the Fatigue Severity Scale (FSS), while a subsample (N = 36) was also tested with a vigilance task. While subjective fatigue (FSS) was not related to measures of brain lesions, multilevel analyses showed that a change in the participants' decision time was significantly predicted by grey matter (GM) lesions in the right frontal lobe. The time-dependent development of the participants' error rate was predicted by total brain white matter (WM) lesion volumes, as well as right temporal GM and WM lesion volumes. These findings could be explained by decreased functional connectivity of attentional networks, which results in accelerated exhaustion during cognitive task performance. The disparate nature of objectively measurable fatigability on the one hand and the subjective experience of fatigue on the other needs further investigation.

Abnormal adaptation over time of motor network recruitment in multiple sclerosis patients with fatigue

OBJECTIVES

Using functional magnetic resonance imaging (fMRI) during a motor task, we investigated the functional correlates of central fatigue in multiple sclerosis (MS), and adaptation of motor network recruitment during a prolonged effort.

METHODS

Motor fMRI was obtained from 79 MS patients (50 fatigued (F), 29 non-fatigued (nF)) and 26 matched healthy controls (HC). Cognitive and physical fatigue were rated using the Modified Fatigue Impact Scale (MFIS).

RESULTS

Compared to HC and nF patients, F-MS patients experienced reduced activations of the left middle temporal gyrus, left supplementary motor area (SMA), bilateral superior frontal gyrus, left postcentral gyrus and basal ganglia regions. They also showed increased activation of the right middle frontal gyrus (MFG). Time-modulation analysis showed a reduced activity of the SMA and right precentral gyrus, and increased activity of the basal ganglia in HC. Such a trend was impaired in F-MS patients. In MS patients, increased MFG activity was related to MFIS scores. Physical MFIS score was related to a reduced recruitment of the right thalamus and SMA.

CONCLUSIONS

Abnormalities and impaired timing of activation between different areas of the motor and executive networks occur in F-MS patients. The dysfunction of critical cortical areas contributes to the occurrence of central fatigue.

Neuropsychology of Neuroendocrine Dysregulation after Traumatic Brain Injury

Endocrine dysfunction is a common effect of traumatic brain injury (TBI). In addition to affecting the regulation of important body functions, the disruption of endocrine physiology can significantly impair mental functions, such as attention, memory, executive function, and mood. This mini-review focuses on alterations in mental functioning that are associated with neuroendocrine disturbances in adults who suffered TBI. It summarizes the contribution of hormones to the regulation of mental functions, the consequences of TBI on mental health and neuroendocrine homeostasis, and the effects of hormone substitution on mental dysfunction caused by TBI. The available empirical evidence suggests that comprehensive assessment of mental functions should be standard in TBI subjects presenting with hormone deficiency and that hormone replacement therapy should be accompanied by pre- and post-assessments.

The dopamine imbalance hypothesis of fatigue in multiple sclerosis and other neurological disorders

Fatigue is one of the most pervasive symptoms of multiple sclerosis (MS), and has engendered hundreds of investigations on the topic. While there is a growing literature using various methods to study fatigue, a unified theory of fatigue in MS is yet to emerge. In the current review, we synthesize findings from neuroimaging, pharmacological, neuropsychological, and immunological studies of fatigue in MS, which point to a specific hypothesis of fatigue in MS: the dopamine imbalance hypothesis. The communication between the striatum and prefrontal cortex is reliant on dopamine, a modulatory neurotransmitter. Neuroimaging findings suggest that fatigue results from the disruption of communication between these regions. Supporting the dopamine imbalance hypothesis, structural and functional neuroimaging studies show abnormalities in the frontal and striatal regions that are heavily innervated by dopamine neurons. Further, dopaminergic psychostimulant medication has been shown to alleviate fatigue in individuals with traumatic brain injury, chronic fatigue syndrome, and in cancer patients, also indicating that dopamine might play an important role in fatigue perception. This paper reviews the structural and functional neuroimaging evidence as well as pharmacological studies that suggest that dopamine plays a critical role in the phenomenon of fatigue. We conclude with how specific aspects of the dopamine imbalance hypothesis can be tested in future research.

The effects of age on resting state functional connectivity of the basal ganglia from young to middle adulthood

The basal ganglia nuclei are critical for a variety of cognitive and motor functions. Much work has shown age-related structural changes of the basal ganglia. Yet less is known about how the functional interactions of these regions with the cerebral cortex and the cerebellum change throughout the lifespan. Here, we took advantage of a convenient sample and examined resting state functional magnetic resonance imaging data from 250 adults 18 to 49 years of age, focusing specifically on the caudate nucleus, pallidum, putamen, and ventral tegmental area/substantia nigra (VTA/SN). There are a few main findings to report. First, with age, caudate head connectivity increased with a large region of ventromedial prefrontal/medial orbitofrontal cortex. Second, across all subjects, pallidum and putamen showed negative connectivity with default mode network (DMN) regions such as the ventromedial prefrontal cortex and posterior cingulate cortex, in support of anti-correlation of the "task-positive" network (TPN) and DMN. This negative connectivity was reduced with age. Furthermore, pallidum, posterior putamen and VTA/SN connectivity to other TPN regions, such as somatomotor cortex, decreased with age. These results highlight a distinct effect of age on cerebral functional connectivity of the dorsal striatum and VTA/SN from young to middle adulthood and may help research investigating the etiologies or monitoring outcomes of neuropsychiatric conditions that implicate dopaminergic dysfunction.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

Cingulum bundle alterations underlie subjective fatigue in multiple sclerosis

OBJECTIVE

To evaluate the neural basis of subjective fatigue in subjects with multiple sclerosis (MS) using a connectionist framework.

METHODS

Seventy seven subjects with relapsing-remitting MS were recruited in the study and underwent subjective fatigue evaluations and a diffusion MRI scan. Firstly, local white matter Fractional Anisotropy values were correlated with subjective fatigue scores using a voxel-wise approach. The long-range loss of connectivity due to structural damage in the white matter voxels thus associated with subjective fatigue was then assessed using the Network Modification (NeMo) package.

RESULTS

A voxel-wise regression analysis with fatigue scores revealed a significant association between structural damage and fatigue levels in two discrete white matter clusters, both included in the left cingulate bundle. The connectivity analysis revealed that damage in these clusters was associated with loss of structural connectivity in the anterior and medial cingulate cortices, dorsolateral prefrontal areas and in the left caudate.

DISCUSSION

Our data point to the cingulum bundle and its projections as the key network involved in subjective fatigue perception in MS. More generally, these results suggest the potential of the connectionist framework to generate coherent models of the neural basis of complex symptomatology in MS.

Induction of interleukin-1β by activated microglia is a prerequisite for immunologically induced fatigue

We previously reported that an intraperitoneal (i.p.) injection of synthetic double-stranded RNA, polyriboinosinic:polyribocytidylic acid (poly-I:C), produced prolonged fatigue in rats, which might serve as a model for chronic fatigue syndrome. The poly-I:C-induced fatigue was associated with serotonin transporter (5-HTT) overexpression in the prefrontal cortex (PFC), a brain region that has been suggested to be critical for fatigue sensation. In the present study, we demonstrated that microglial activation in the PFC was important for poly-I:C-induced fatigue in rats, as pretreatment with minocycline, an inhibitor of microglial activation, prevented the decrease in running wheel activity. Poly-I:C injection increased the microglial interleukin (IL)-1β expression in the PFC. An intracerebroventricular (i.c.v.) injection of IL-1β neutralising antibody limited the poly-I:C-induced decrease in activity, whereas IL-1β (i.c.v.) reduced the activity in a dose-dependent manner. 5-HTT expression was enhanced by IL-1β in primary cultured astrocytes but not in microglia. Poly-I:C injection (i.p.) caused an increase in 5-HTT expression in astrocytes in the PFC of the rat, which was inhibited by pretreatment with minocycline (i.p.) and rat recombinant IL-1 receptor antagonist (i.c.v.). Poly-I:C injection (i.p.) led to a breakdown of the blood-brain barrier and enhanced Toll-like receptor 3 signaling in the brain. Furthermore, direct application of poly-I:C enhanced IL-1β expression in primary microglia. We therefore propose that poly-I:C-induced microglial activation, which may be at least partly caused by a direct action of poly-I:C, enhances IL-1β expression. Then, IL-1β induces 5-HTT expression in astrocytes, resulting in the immunologically induced fatigue.

Agomelatine but not melatonin improves fatigue perception: a longitudinal proof-of-concept study

Chronic Fatigue Syndrome (CFS) represents a disabling condition characterized by persistent mental and physical fatigue, bodily discomfort and cognitive difficulties. To date the neural bases of CFS are poorly understood; however, mono-aminergic abnormalities, sleep-wake cycle changes and prefrontal dysfunctions are all thought to play a role in the development and maintenance of this condition. Here we explored in a group of 62 CFS subjects the impact on fatigue levels of agomelatine, an antidepressant with agonist activity at melatonin receptors (MT1 and MT2) and antagonist activity at serotoninergic 2C receptors (5HT2C). To tease out the relative effects of MT-agonism and 5HT2C antagonism on fatigue, we compared agomelatine 50mg u.i.d. with sustained release melatonin 10mg u.i.d. in the first 12-week-long phase of the study, and then switched all melatonin-treated subjects to agomelatine in the second 12-week-long phase of the study. Agomelatine treatment, but not melatonin, was associated with a significant reduction of perceived fatigue and an increase in perceived quality of life. Moreover the switch from melatonin to agomelatine was associated with a reduction of fatigue levels. Agomelatine was well tolerated by all enrolled subjects. Our data, albeit preliminary, suggest that agomelatine treatment could represent a novel useful approach to the clinical care of subjects with CFS.

Neural correlates of cognitive fatigue: cortico-striatal circuitry and effort-reward imbalance

Recently, there has been renewed interest in the study of cognitive fatigue. It is known that fatigue is one of the most disabling symptoms in numerous neurological populations, including stroke, multiple sclerosis, Parkinson’s disease, and traumatic brain injury. Behavioral studies of cognitive fatigue are hampered by lack of correlation of self-report measures with objective performance. Neuroimaging studies provide new insight about cognitive fatigue and its neural correlates.Impairment within the cortico-striatal network, involved in effort–reward calculation, has been suggested to be critically related to fatigue. The current review surveys the recent neuroimaging literature, and suggests promising avenues for future research.

Increased brain white matter axial diffusivity associated with fatigue, pain and hyperalgesia in Gulf War illness

BACKGROUND

Gulf War exposures in 1990 and 1991 have caused 25% to 30% of deployed personnel to develop a syndrome of chronic fatigue, pain, hyperalgesia, cognitive and affective dysfunction.

METHODS

Gulf War veterans (n = 31) and sedentary veteran and civilian controls (n = 20) completed fMRI scans for diffusion tensor imaging. A combination of dolorimetry, subjective reports of pain and fatigue were correlated to white matter diffusivity properties to identify tracts associated with symptom constructs.

RESULTS

Gulf War Illness subjects had significantly correlated fatigue, pain, hyperalgesia, and increased axial diffusivity in the right inferior fronto-occipital fasciculus. ROC generated thresholds and subsequent binary regression analysis predicted CMI classification based upon axial diffusivity in the right inferior fronto-occipital fasciculus. These correlates were absent for controls in dichotomous regression analysis.

CONCLUSION

The right inferior fronto-occipital fasciculus may be a potential biomarker for Gulf War Illness. This tract links cortical regions involved in fatigue, pain, emotional and reward processing, and the right ventral attention network in cognition. The axonal neuropathological mechanism(s) explaining increased axial diffusivity may account for the most prominent symptoms of Gulf War Illness.

Neural correlates of apathy revealed by lesion mapping in participants with traumatic brain injuries

Apathy, common in neurological disorders, is defined as disinterest and loss of motivation, with a reduction in self-initiated activity. Research in diseased populations has shown that apathy is associated with variations in the volume of brain regions such as the anterior cingulate and the frontal lobes. The goal of this study was to determine the neural signatures of apathy in people with penetrating traumatic brain injuries (pTBIs), as to our knowledge, these have not been studied in this sample. We studied 176 male Vietnam War veterans with pTBIs using voxel-based lesion-symptom mapping (VLSM) and apathy scores from the UCLA Neuropsychiatric Inventory (NPI), a structured inventory of symptoms completed by a caregiver. Our results revealed that increased apathy symptoms were associated with brain damage in limbic and cortical areas of the left hemisphere including the anterior cingulate, inferior, middle, and superior frontal regions, insula, and supplementary motor area. Our results are consistent with the literature, and extend them to people with focal pTBI. Apathy is a significant symptom since it can reduce participation of the patient in family and other social interactions, and diminish affective decision-making.

Poststroke fatigue: an emerging, critical issue in stroke medicine

Poststroke fatigue is a common and disabling condition. However, few studies on or therapeutic trials addressing poststroke fatigue have appeared in the literature. We aimed to review the prevalence, natural course, potential predisposing factors (physiological, psychocognitive, and organic), and pharmacological and nonpharmacological treatments of poststroke fatigue. Using PubMed CINAHL and PsycINFO, we reviewed all the available literature on poststroke fatigue and related issues. The prevalence of poststroke fatigue ranges from 23% to 75%, depending on the definition of fatigue and the characteristics of the patients included. Poststroke fatigue seems to be of complex etiology. Predisposing factors were physiological ones including functional disability, prestroke fatigue, medical comorbidities, medication, sleep disturbances, and nutritional problems; psychocognitive ones including depression and cognitive dysfunction; and organic ones including damage to particular brain areas with consequent neurochemical alterations, perfusion deficit, and neuroinflammation. Poststroke fatigue is a persistent and debilitating symptom in some patients, and can have adverse affects on patient's neurological recovery, quality of life, and mortality. Few therapeutic trials have been reported, and the therapy was rarely successful, possibly because of the complex nature of poststroke fatigue. Poststroke fatigue is a common and frequently disabling problem of complex etiology. Further studies are urgently needed to improve our understanding of the pathophysiology of poststroke fatigue and to develop better treatments for this condition.

"Studying injured minds" - the Vietnam head injury study and 40 years of brain injury research

The study of those who have sustained traumatic brain injuries (TBI) during military conflicts has greatly facilitated research in the fields of neuropsychology, neurosurgery, psychiatry, neurology, and neuroimaging. The Vietnam Head Injury Study (VHIS) is a prospective, long-term follow-up study of a cohort of 1,221 Vietnam veterans with mostly penetrating brain injuries, which has stretched over more than 40 years. The scope of this study, both in terms of the types of injury and fields of examination, has been extremely broad. It has been instrumental in extending the field of TBI research and in exposing pressing medical and social issues that affect those who suffer such injuries. This review summarizes the history of conflict-related TBI research and the VHIS to date, as well as the vast range of important findings the VHIS has established.

Amisulpride vs. fluoxetine treatment of chronic fatigue syndrome: a pilot study

Different pharmacologic agents have been evaluated in the treatment of Chronic Fatigue Syndrome (CFS), albeit with moderate efficacy. Among the compounds thought to present with potential to be efficacious in CFS patients stands out low-dose amisulpride, a substituted benzamide that has been shown to be an useful treatment for conditions which exhibit some overlap with CFS such as dysthymia and somatoform disorders. We thus recruited forty non-depressed CFS patients that were randomized to receive either amisulpride 25mg bid, or fluoxetine 20mg uid; all subjects were un-blinded to the treatment regimen. At the time of enrollment in the study and after twelve weeks of treatment, enrolled subjects completed the Krupp Fatigue Severity Scale, the Hospital Anxiety and Depression Scale and a visual analog scale focused on pain and bodily discomfort. Moreover, all subjects were evaluated by a clinician, blinded to the treatment regimen, using the Clinical Global Impression Severity Scale. Our data revealed a significant improvement both in self-report, and observer-based measures for the amisulpride-treated, but not for the fluoxetine-treated patients. Amisulpride-treated subjects also presented with a significant reduction of somatic complaints, while the amisulpride effect on anxiety and mood levels was not significant. Both drugs were equally well tolerated. Summing up, we showed a positive symptomatic effect of amisulpride, compared to SSRI treatment, in a group of non-depressed CSF patients on self-report and on observer-based measures of fatigue and somatic complaints. If confirmed by larger, blinded studies, amisulpride thus could represent an effective approach to this difficult-to-treat condition.

Biological markers of the effects of intravenous methylphenidate on improving inhibitory control in cocaine-dependent patients

Prior research points to the importance of psychostimulants in improving self-control. However, the neural substrates underlying such improvement remain unclear. Here, in a pharmacological functional MRI study of the stop signal task, we show that methylphenidate (as compared with placebo) robustly decreased stop signal reaction time (SSRT), an index of improved control, in cocaine-dependent patients (a population in which inhibitory control is impaired). Methylphenidate-induced decreases in SSRT were positively correlated with inhibition-related activation of left middle frontal cortex (MFC) and negatively with activation of the ventromedial prefrontal cortex (vmPFC) in whole brain linear regressions. Inhibition-related MFC but not vmPFC activation distinguished individuals with short and long SSRT in 36 demographically matched healthy individuals, whereas vmPFC but not MFC activation, along with improvement in SSRT, was correlated with a previously implicated biomarker of methylphenidate response (systolic blood pressure). These results implicate a specific neural (i.e., vmPFC) mechanism whereby stimulants improve inhibitory control. Altered ventromedial prefrontal activation and increased blood pressure may represent useful CNS and peripheral biomarkers in individualized treatment with methylphenidate for patients with cocaine dependence.