Elevated motor threshold in drug-free, cocaine-dependent patients assessed with transcranial magnetic stimulation

Cortical paired associative stimulation shows impaired plasticity of inhibition networks as a function of chronic alcohol use

BACKGROUND

Response inhibition - or the ability to withhold a suboptimal response - relies on the efficacy of fronto-striatal networks, and is impaired in neuropsychiatric disorders including addiction. Cortical paired associative stimulation (cPAS) is a form of transcranial magnetic stimulation (TMS) which can strengthen neuronal connections via spike-timing-dependent plasticity mechanisms. Here, we used cPAS targeting the fronto-striatal inhibitory network to modulate performance on a response inhibition measure in chronic alcohol use.

METHODS

Fifty-five participants (20 patients with a formal alcohol use disorder (AUD) diagnosis (26-74 years, 6[30%] females) and 20 matched healthy controls (HCs) (27-73 years, 6[30%] females) within a larger sample of 35 HCs (23-84 years, 11[31.4%] females) underwent two randomized sessions of cPAS 1-week apart: right inferior frontal cortex stimulation preceding right presupplementary motor area stimulation by either 4 ms (excitation condition) or 100 ms (control condition), and were subsequently administered the Stop Signal Task (SST) in both sessions.

RESULTS

HCs showed decreased stop signal reaction time in the excitation condition (t(19) = -3.01, p = 0.007, [CIs]:-35.6 to -6.42); this facilitatory effect was not observed for AUD (F(1,31) = 9.57, p = 0.004, CIs: -68.64 to -14.11). Individually, rates of SST improvement were substantially higher for healthy (72%) relative to AUD (13.6%) groups (OR: 2.33, p = 0.006, CIs:-3.34 to -0.55).

CONCLUSION

In line with previous findings, cPAS improved response inhibition in healthy adults by strengthening the fronto-striatal network through putative long-term potentiation-like plasticity mechanisms. Furthermore, we identified a possible marker of impaired cortical excitability, and, thus, diminished capacity for cPAS-induced neuroplasticity in AUD with direct implications to a disorder-relevant cognitive process.

Managing substance use in patients receiving therapeutic repetitive transcranial magnetic stimulation: A scoping review

Repetitive Transcranial Magnetic Stimulation (rTMS) is an invaluable treatment option for neuropsychiatric disorders. Co-occurring recreational and nonmedical substance use can be common in those presenting for rTMS treatment, and it is unknown how it may affect the safety and efficacy of rTMS for the treatment of currently approved neuropsychiatric indications. This scoping review aimed to map the literature on humans receiving rTMS and had a history of any type of substance use. The search identified 274 articles providing information on inclusion/exclusion criteria, withdrawal criteria, safety protocols, type of rTMS and treatment parameters, adverse events and effect on primary outcomes that related to substance use. There are neurophysiological effects of substance use on cortical excitability, although the relevance to clinical rTMS practice is unknown. The current literature supports the safety and feasibility of delivering rTMS to those who have co-occurring neuropsychiatric disorder and substance use. However, specific details on how varying degrees of substance use alters the safety, efficacy, and mechanisms of rTMS remains poorly described.

Repetitive transcranial magnetic stimulation as a potential treatment approach for cannabis use disorder

The expanding legalization of cannabis across the United States is associated with increases in cannabis use, and accordingly, an increase in the number and severity of individuals with cannabis use disorder (CUD). The lack of FDA-approved pharmacotherapies and modest efficacy of psychotherapeutic interventions means that many of those who seek treatment for CUD relapse within the first few months. Consequently, there is a pressing need for innovative, evidence-based treatment development for CUD. Preliminary evidence suggests that repetitive transcranial magnetic stimulation (rTMS) may be a novel, non-invasive therapeutic neuromodulation tool for the treatment of a variety of substance use disorders (SUDs), including recently receiving FDA clearance (August 2020) for use as a smoking cessation aid in tobacco cigarette smokers. However, the potential of rTMS for CUD has not yet been reviewed. This paper provides a primer on therapeutic neuromodulation techniques for SUDs, with a particular focus on reviewing the current status of rTMS research in people who use cannabis. Lastly, future directions are proposed for rTMS treatment development in CUD, with suggestions for study design parameters and clinical endpoints based on current gold-standard practices for therapeutic neuromodulation research.

Reward-Related Responses and Tonic Craving in Cocaine Addiction: An Imaging Study of the Monetary Incentive Delay Task

BACKGROUND

Cocaine addiction is associated with altered sensitivity to natural reinforcers and intense drug craving. However, previous findings on reward-related responses were mixed, and few studies have examined whether reward responses relate to tonic cocaine craving.

METHODS

We combined functional magnetic resonance imaging and a monetary incentive delay task to investigate these issues. Imaging data were processed with published routines, and the results were evaluated with a corrected threshold. We compared reward responses of 50 cocaine-dependent individuals (CDs) and 45 healthy controls (HCs) for the ventral striatum (VS) and the whole brain. We also examined the regional responses in association with tonic cocaine craving, as assessed by the Cocaine Craving Questionnaire (CCQ) in CDs. We performed mediation analyses to evaluate the relationship between regional responses, CCQ score, and recent cocaine use.

RESULTS

The VS showed higher activation to large as compared with small or no wins, but this reward-related activity did not differ between CDs and HCs. The precentral gyrus (PCG), anterior insula, and supplementary motor area showed higher activation during large vs no wins in positive correlation with the CCQ score in CDs. Mediation analyses suggested that days of cocaine use in the prior month contributed to higher CCQ scores and, in turn, PCG reward responses.

CONCLUSIONS

The results highlight a unique relationship between reward responses of the primary motor cortex, tonic cocaine craving, and recent cocaine use. The motor cortex may partake in the cognitive motor processes critical to drug-seeking behavior in addicted individuals.

Intermittent Theta Burst Stimulation of the Prefrontal Cortex in Cocaine Use Disorder: A Pilot Study

Transcranial Magnetic Stimulation (TMS) is earning a role in the therapeutic arsenal of cocaine use disorder (CUD). A widespread and still growing number of studies have reported beneficial use of repeated TMS (rTMS) in reduction of craving, intake and cue-induced craving in cocaine addicts. In spite of these encouraging findings, many issues are still unresolved such as brain area to be stimulated, laterality of the effects, coil geometry and stimulation protocols/parameters. Intermittent theta burst stimulation (iTBS) is a more tolerable protocol administered at lower intensities and shorter intervals than conventional rTMS protocols. Yet, its effects on cocaine craving and length of abstinence in comparison with standard high frequency (10–15 Hz) protocols have never been evaluated so far. In the present paper, we describe the effect of the bilateral iTBS of the prefrontal cortex (PFC) in a population (n = 25) of treatment-seeking cocaine addicts, in an outpatient setting, and compare them with 15 Hz stimulation of the same brain area (n = 22). The results indicate that iTBS produces effects on cocaine consumption and cocaine craving virtually superimposable to the 15 Hz rTMS group. Both treatments had low numbers of dropouts and similar side-effects, safety and tolerability profiles. While larger studies are warranted to confirm these observations, iTBS appears to be a valid approach to be considered in treatment-seeking cocaine addicts, especially in light of its brief duration (3 min) vs. 15 Hz stimulation (15 min). The use of iTBS would allow increasing the number of patients treated per day with current rTMS devices, thus reducing patient discomfort and hopefully reducing drop-out rates without compromising clinical effectiveness.

Modulating Neural Circuits with Transcranial Magnetic Stimulation: Implications for Addiction Treatment Development

Although the last 50 years of clinical and preclinical research have demonstrated that addiction is a brain disease, we still have no neural circuit-based treatments for substance dependence or cue reactivity at large. Now, for the first time, it appears that a noninvasive brain stimulation technique known as transcranial magnetic stimulation (TMS), which is Food and Drug Administration approved to treat depression, may be the first tool available to fill this critical void in addiction treatment development. The goals of this review are to 1) introduce TMS as a tool to induce causal change in behavior, cortical excitability, and frontal-striatal activity; 2) describe repetitive TMS (rTMS) as an interventional tool; 3) provide an overview of the studies that have evaluated rTMS as a therapeutic tool for alcohol and drug use disorders; and 4) outline a conceptual framework for target selection when designing future rTMS clinical trials in substance use disorders. The manuscript concludes with some suggestions for methodological innovation, specifically with regard to combining rTMS with pharmacotherapy as well as cognitive behavioral training paradigms. We have attempted to create a comprehensive manuscript that provides the reader with a basic set of knowledge and an introduction to the primary experimental questions that will likely drive the field of TMS treatment development forward for the next several years.

Transcranial Magnetic Stimulation of Medial Prefrontal and Cingulate Cortices Reduces Cocaine Self-Administration: A Pilot Study

BACKGROUND

Previous studies have shown that repetitive transcranial magnetic stimulation (rTMS) to the dorsolateral prefrontal cortex may serve as a potential treatment for cocaine use disorder (CUD), which remains a public health problem that is refractory to treatment. The goal of this pilot study was to investigate the effect of rTMS on cocaine self-administration in the laboratory. In the self-administration sessions, CUD participants chose between cocaine and an alternative reinforcer (money) in order to directly measure cocaine-seeking behavior. The rTMS was delivered with the H7 coil, which provides stimulation to the medial prefrontal cortex (mPFC) and anterior cingulate cortex (ACC). These brain regions were targeted based on previous imaging studies demonstrating alterations in their activation and connectivity in CUD.

METHODS

Volunteers with CUD were admitted to an inpatient unit for the entire study and assigned to one of three rTMS groups: high frequency (10 Hz), low frequency (1 Hz), and sham. Six participants were included in each group and the rTMS was delivered on weekdays for 3 weeks. The cocaine self-administration sessions were performed at three time points: at baseline (pre-TMS, session 1), after 4 days of rTMS (session 2), and after 13 days of rTMS (session 3). During each self-administration session, the outcome measure was the number of choices for cocaine.

RESULTS

The results showed a significant group by time effect (p = 0.02), where the choices for cocaine decreased between sessions 2 and 3 in the high frequency group. There was no effect of rTMS on cocaine self-administration in the low frequency or sham groups.

CONCLUSION

Taken in the context of the existing literature, these results contribute to the data showing that high frequency rTMS to the prefrontal cortex may serve as a potential treatment for CUD.

Cortical excitability in tramadol dependent patients: A transcranial magnetic stimulation study

BACKGROUND

Addiction to tramadol, a widely used analgesic, is becoming increasingly common. Tramadol can also induce seizures even after a single clinical dose. We tested whether the epileptogenicity of tramadol was associated with any changes in cortical excitability and inhibitory transmission using transcranial magnetic stimulation (TMS).

METHODS

The study included 16 tramadol dependent patients and 15 age and sex matched healthy volunteers. Clinical evaluation was conducted using an addiction severity index. TMS assessment of excitability was conducted on the motor cortex since the response to each TMS pulse at that site is easily measured in terms of the amplitude of the twitches it evokes in contralateral muscles. Measures included resting and active motor threshold (RMT and AMT respectively), motor evoked potential (MEP) amplitude, cortical silent period (CSP) duration, transcallosal inhibition (TCI), and short interval intracortical inhibition and facilitation (SICI and ICF respectively). Urinary level of tramadol was measured immediately before assessing cortical excitability in each patient.

RESULTS

RMT and AMT were significantly lower, the duration of the CSP was shorter and SICI was reduced in patients compared with the control group. These findings are suggestive of increased neural excitability and reduced GABAergic inhibition following exposure to tramadol. Also there were negative correlations between the severity of tramadol dependence and a number of cortical excitability parameters (AMT, RMT, and CSP with P=0.002, 0.005, and 0.04 respectively).

CONCLUSIONS

The results provide evidence for hyperexcitability of the motor cortex coupled with inhibitory deficits in tramadol dependent patients.

A comprehensive study of sensorimotor cortex excitability in chronic cocaine users: Integrating TMS and functional MRI data

BACKGROUND

Disruptions in motor control are often overlooked features of chronic cocaine users. During a simple sensorimotor integration task, for example, cocaine users activate a larger area of cortex than controls but have lower functional connectivity between the cortex and dorsal striatum, which is further correlated with poor performance. The purpose of this study was to determine whether abnormal cortical excitability in cocaine users was related to disrupted inhibitory or excitatory mechanisms, as measured by transcranial magnetic stimulation (TMS).

METHODS

A battery of TMS measures were acquired from 87 individuals (50 cocaine dependent, 37 controls). Functional MRI data were acquired from a subset of 28 individuals who performed a block-design finger tapping task.

RESULTS

TMS measures revealed that cocaine users had significantly higher resting motor thresholds and higher intracortical cortical facilitation (ICF) than controls. There was no between-group difference in either measure of cortical inhibition. Task-evoked BOLD signal in the motor cortex was significantly correlated with ICF in the cocaine users. There was no significant difference in brain-skull distance between groups.

CONCLUSION

These data demonstrated that cocaine users have disrupted cortical facilitation (as measured with TMS), which is related to elevated BOLD signal. Cortical inhibition, however, is largely intact. Given the relationship between ICF and glutamatergic agents, this may be a potentially fruitful and treatable target in addiction. Finally, among controls the distance from the scalp to the cortex was correlated with the motor threshold which may be a useful parameter to integrate into therapeutic TMS protocols in the future.

Noninvasive brain stimulation for addiction medicine: From monitoring to modulation

Addiction is a chronic relapsing brain disease with significant economical and medical burden on the societies but with limited effectiveness in the available treatment options. Better understanding of the chemical, neuronal, regional, and network alterations of the brain due to drug abuse can ultimately lead to tailoring individualized and more effective interventions. To this end, employing new assessment and intervention procedures seems crucial. Noninvasive brain stimulation (NIBS) techniques including transcranial electrical and magnetic stimulations (tES and TMS) have provided promising opportunities for the addiction medicine in two main domains: (1) providing new insights into neurochemical and neural circuit changes in the human brain cortex and (2) understanding the role of different brain regions by using NIBS and modulating cognitive functions, such as drug craving, risky decision making, inhibitory control and executive functions to obtain specific treatment outcomes. In spite of preliminary positive results, there are several open questions, which need to be addressed before routine clinical utilization of NIBS techniques in addiction to medicine, such as how to account for interindividual differences, define optimal cognitive and neural targets, optimize stimulation protocols, and integrate NIBS with other therapeutic methods. Therefore, in this chapter we revise the available literature on the use of NIBS (TMS and tES) in the diagnostic, prognostic, and therapeutic aspects of the addiction medicine.

Relationships of behavioral measures of frontal lobe dysfunction with underlying electrophysiology in cocaine-dependent patients

BACKGROUND AND OBJECTIVES

Despite evidence that frontal lobe functioning is impaired in cocaine-dependent individuals, relationships between behavioral measures of frontal dysfunction and electrophysiological measures of inhibition in cocaine use have not been explored.

METHODS

Using the Frontal Systems Behavior Scale (FrSBe), frontal dysfunction was assessed in a group of abstinent cocaine-dependent subjects (N = 49) and healthy controls (N = 32). Using transcranial magnetic stimulation (TMS) and evoked potential (EP)-based electrophysiological measures of inhibition, we assessed associations between these measures and FrSBe estimates of frontal dysfunction.

RESULTS

Patients had significantly higher FrSBe scores for executive dysfunction, disinhibition, and apathy than controls. Lower TMS-based resting motor thresholds (ie, hyperexcitability) were significantly associated with higher executive dysfunction scores in the patients.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Relationships between FrSBe scores and TMS-based measures highlight neurophysiological aberrations underlying frontal lobe dysfunction in cocaine abusers. TMS and EP measures may be useful probes of the intermediary steps between frontal lobe dysfunction and addictive behavior.

Transcranial magnetic stimulation in the treatment of substance addiction

Transcranial magnetic stimulation (TMS) is a noninvasive method of brain stimulation used to treat a variety of neuropsychiatric disorders, but is still in the early stages of study as addiction treatment. We identified 19 human studies using repetitive TMS (rTMS) to manipulate drug craving or use, which exposed a total of 316 adults to active rTMS. Nine studies involved tobacco, six alcohol, three cocaine, and one methamphetamine. The majority of studies targeted high-frequency (5-20 Hz; expected to stimulate neuronal activity) rTMS pulses to the dorsolateral prefrontal cortex. Only five studies were controlled clinical trials: two of four nicotine trials found decreased cigarette smoking; the cocaine trial found decreased cocaine use. Many aspects of optimal treatment remain unknown, including rTMS parameters, duration of treatment, relationship to cue-induced craving, and concomitant treatment. The mechanisms of rTMS potential therapeutic action in treating addictions are poorly understood, but may involve increased dopamine and glutamate function in corticomesolimbic brain circuits and modulation of neural activity in brain circuits that mediate cognitive processes relevant to addiction, such as response inhibition, selective attention, and reactivity to drug-associated cues. rTMS treatment of addiction must be considered experimental at this time, but appears to have a promising future.

rTMS in the treatment of drug addiction: an update about human studies

Drug addiction can be a devastating and chronic relapsing disorder with social, psychological, and physical consequences, and more effective treatment options are needed. Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that has been assessed in a growing number of studies for its therapeutic potential in treating addiction. This review paper offers an overview on the current state of clinical research in treating drug addiction with rTMS. Because of the limited research in this area, all studies (including case reports) that evaluated the therapeutic use of rTMS in nicotine, alcohol, or illicit drug addiction were included in this review. Papers published prior to December 2012 were found through an NCBI PubMed search. A total of eleven studies were identified that met review criteria. There is nascent evidence that rTMS could be effective in reducing cocaine craving and nicotine and alcohol craving and consumption and might represent a potential therapeutic tool for treating addiction. Further studies are needed to identify the optimal parameters of stimulation for the most effective treatment of drug addiction, to improve our comprehension of the treatment neurophysiological effects, and to conduct rigorous, controlled efficacy studies with adequate power.

Motor cortical excitability assessed by transcranial magnetic stimulation in psychiatric disorders: a systematic review

BACKGROUND

Transcranial magnetic stimulation (TMS) is a popular neurostimulation technique suitable for the investigation of inhibitory and facilitatory networks in the human motor system. In the last 20 years, several studies have used TMS to investigate cortical excitability in various psychiatric disorders, leading to a consequent improvement in pathophysiological understanding. However, little is known about the overlap and specificity of these findings across these conditions.

OBJECTIVE

To provide a systematic review of TMS studies (1985-2013) focusing on motor cortical excitability in dementia, schizophrenia, affective disorders (major depression and bipolar), attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), Tourette Syndrome (TS), substance abuse (alcohol, cocaine, cannabis, nicotine) and other disorders (borderline personality disorder, posttraumatic stress disorder (PTSD)).

METHODS

Systematic literature-based review.

RESULTS

Across disorders, patients displayed a general pattern of cortical disinhibition, while the most consistent results of reduced short-interval intracortical inhibition could be found in schizophrenia, OCD and Tourette Syndrome. In dementia, the most frequently reported finding was reduced short-latency afferent inhibition as a marker of cholinergic dysfunction.

CONCLUSIONS

The results of this systematic review indicate a general alteration in motor cortical inhibition in mental illness, rather than disease-specific changes. Changes in motor cortical excitability provide insight that can advance understanding of the pathophysiology underlying various psychiatric disorders. Further investigations are needed to improve the diagnostic application of these parameters.

Addiction

Drug and alcohol addiction is a debilitating disorder characterized by persistent drug-seeking behaviors despite negative physiological, medical, or social consequences. Neurobiological models of addiction propose that the reinforcing effects of addictive drugs are associated with altered neurotransmission within the reward 'mesocorticolimbic' circuitry in the brain. Immense efforts are therefore designed to target the mesocorticolimbic circuitry in attenuating drug dependence and addiction-related behaviors. Yet, to date, most addiction treatments have demonstrated only limited success in reducing addiction-related behaviors. Accumulating and compelling evidence suggests that novel nonsurgical brain stimulation techniques, such as transcranial magnetic stimulation and transcranial direct current stimulation, could serve as promising tools for indexing altered neurotransmission associated with repetitive drug use, and moreover, may hold therapeutic potential for the treatment of drug dependence and addiction-related behaviors. This chapter reviews and discusses the current and potential applications of such techniques in the study and treatment of addiction; we focus on a number of common drugs of abuse, including nicotine, alcohol, cocaine, cannabis, and ecstasy.

Motor cortex and corticospinal excitability in humans with a history of illicit stimulant use

Illicit use of stimulant drugs such as methamphetamine, ecstasy, and cocaine is a current and growing problem throughout the world. The aim of the current study was to investigate the long-term effect of illicit stimulant use on human motor cortical and corticospinal circuitry. We hypothesized that individuals with a history of primarily methamphetamine and ecstasy use would exhibit altered corticospinal excitability and intracortical inhibition within motor cortex. The study involved 52 healthy adults (aged 26 ± 7 yr) comprising 26 abstinent stimulant users, 9 cannabis users, and 17 nondrug users. The experiment involved a routine urine drug screen, drug history questionnaire, neuropsychological assessment, and single- and paired-pulse transcranial magnetic stimulation (TMS) over motor cortex. EMG responses to stimulation [motor evoked potentials (MEPs)] were recorded from the contralateral first dorsal interosseus. At a given stimulus intensity, MEP area was significantly larger in abstinent stimulant users than in nondrug users during both relaxation (P = 0.045) and muscle contraction (P < 0.001). MEP latency was also significantly longer in abstinent stimulant users (P < 0.009), and they exhibited significantly greater muscle activity during performance of a given task (P = 0.004). However, resting motor threshold and the response to paired-pulse TMS were unaffected. The results suggest that abstinent stimulant users exhibit long-term changes in the excitability of motor cortical and corticospinal circuitry and muscle activity during movement. These changes may partly underlie anecdotal and objective reports of movement dysfunction in chronic stimulant users.

Dysbalance of cortical inhibition and excitation in abstinent cocaine-dependent patients

The effects of chronic cocaine dependence on cortical inhibitory/excitatory processes are not well characterized. Employing transcranial magnetic stimulation measures of motor cortical excitability, we have previously reported an elevation of motor threshold (MT) suggesting reduced excitability and an increased long-interval intracortical facilitation (LICF) suggesting increased excitability. In the current study, we used an expanded battery of TMS cortical excitability measures to further examine motor cortex excitability in a larger sample of well-characterized and closely monitored for drug use, abstinent cocaine-dependent subjects (N = 52) and healthy controls (N = 42). Furthermore, coil-to-cortex distance was assessed in a subsample of both groups. We verified that long-interval intracortical facilitation (LICF), possibly representing glutamatergic cortical neurotransmission, was significantly increased in cocaine-dependent patients. Significantly longer cortical silent periods (CSP) and elevated MT were also observed while there was no significant abnormality in long-interval intracortical inhibition (LICI). Increased LICF and CSP duration suggest increased cortical excitability and increased inhibition, respectively, of different neurotransmitter systems in cocaine-dependent patients. Increased MT might reflect an adaptation to those effects of cocaine abuse that enhance cortical excitability. Overall, the data point to the complex nature of chronic cocaine dependence on the balance of cortical inhibitory/excitatory mechanisms.

The dopamine hypothesis of drug addiction and its potential therapeutic value

Dopamine (DA) transmission is deeply affected by drugs of abuse, and alterations in DA function are involved in the various phases of drug addiction and potentially exploitable therapeutically. In particular, basic studies have documented a reduction in the electrophysiological activity of DA neurons in alcohol, opiate, cannabinoid, and other drug-dependent rats. Further, DA release in the Nucleus accumbens (Nacc) is decreased in virtually all drug-dependent rodents. In parallel, these studies are supported by increments in intracranial self stimulation (ICSS) thresholds during withdrawal from alcohol, nicotine, opiates, and other drugs of abuse, thereby suggesting a hypofunction of the neural substrate of ICSS. Accordingly, morphological evaluations fed into realistic computational analysis of the medium spiny neuron of the Nacc, post-synaptic counterpart of DA terminals, show profound changes in structure and function of the entire mesolimbic system. In line with these findings, human imaging studies have shown a reduction of dopamine receptors accompanied by a lesser release of endogenous DA in the ventral striatum of cocaine, heroin, and alcohol-dependent subjects, thereby offering visual proof of the "dopamine-impoverished" addicted human brain. The lasting reduction in physiological activity of the DA system leads to the idea that an increment in its activity, to restore pre-drug levels, may yield significant clinical improvements (reduction of craving, relapse, and drug-seeking/taking). In theory, it may be achieved pharmacologically and/or with novel interventions such as transcranial magnetic stimulation (TMS). Its anatomo-physiological rationale as a possible therapeutic aid in alcoholics and other addicts will be described and proposed as a theoretical framework to be subjected to experimental testing in human addicts.

The motor evoked potential in aids and HAM/TSP State of the evidence

OBJECTIVE: We aimed to better understand the involvement of the corticospinal tract, assessed by non-invasive transcranial stimulation, in order to determine the actual involvement of the motor system in patients with HAM/TSP and AIDS. METHOD: An exhaustive MEDLINE search for the period of 1985 to 2008 for all articles cross-referenced for "HTLV-I, HTLV-II, HTLV-III and HIV, HIV1, HIV2, evoked potential, motor evoked potential, high voltage electrical stimulation, transcranial magnetic stimulation, magnetic stimulation, corticomotor physiology, motor pathways, acquired immunodeficiency syndrome, AIDS, SIDA, tropical spastic paraparesis, HTLV-I-associated myelopathy, HAM, TSP, and HAM/TSP" were selected and analysed. RESULTS: Eighteen papers published in English, Spanish, Portuguese, French and Japanese were identified. Only the central motor conduction time has been analyzed in seropositive patients to human retroviruses. The investigations done on HAM/TSP support the involvement of the pyramidal tract mainly at lower levels, following a centripetal pattern; in AIDS, such an involvement seems to be more prominent at brain levels following a centrifugal pattern. CONCLUSION: The central motor conduction time abnormalities and involvement differences of the corticospinal tract of patients with AIDS and HAM/TSP dissected here would allow to re-orient early neurorehabilitation measures in these retroviruses-associated neurodegenerative disorders. Besides this, more sophisticated and sensitive non-invasive corticospinal stimulation measures that detect early changes in thalamocortical-basal ganglia circuitry will be needed in both clinically established as well as asymptomatic patients at times when the fastest corticospinal fibers remain uninvolved.

Brain stimulation in the study and treatment of addiction

Addiction is a devastating and chronically relapsing disorder. Repeated drug administration induces neuroadaptations associated with abnormal dopaminergic activity in the mesocorticolimbic circuitry, resulting in altered cortical neurotransmission and excitability. Electrical stimulation of specific brain regions can be used in animal models and humans to induce local activation or disruption of specific circuitries or alter neuronal excitability and cause neuroadaptations. Non-surgical stimulation of specific brain regions in human addicts can be achieved by transcranial magnetic stimulation (TMS). TMS is used for transient stimulation or disruption of neural activity in specific cortical regions, which can be used to assess cortical excitability, and to induce changes in cortical excitability. Moreover, it is suggested that repeated stimulation can cause long-lasting neuroadaptations. Therefore, TMS paradigms were used in some studies to assess the presence of altered cortical excitability associated with chronic drug consumption, while other studies have begun to assess the therapeutic potential of repetitive TMS. Similarly, transcranial direct current stimulation (tDCS) is used to modulate neuronal resting membrane potential in humans and alter cortical excitability. The current review describes how these brain stimulation techniques have recently been used for the study and treatment of addiction in animal models and humans.

A transcranial magnetic stimulation study of the effects of cannabis use on motor cortical inhibition and excitability

Active compounds in cannabis such as tetrahydrocannabinol (THC) interact with the inhibitory neurotransmitter delta-aminobutyric acid (GABA) but little is known about the functional effects of cannabis on human cortical brain processes. Therefore, the aim of the study was to investigate whether patients with chronic cannabis use demonstrate abnormalities in cortical inhibition or excitability. In all, 42 chronic cannabis using subjects (divided into heavy and light using subjects) and 19 controls were included in the study. Single and paired pulse transcranial magnetic stimulation were used to assess a number of parameters of cortical inhibition and cortical excitability. In addition, psychomotor function and THC plasma levels were measured. Both cannabis using groups (heavy and light use) demonstrated a reduction in short interval cortical inhibition compared with healthy controls, but there was no difference in other measures of cortical inhibition or cortical excitability. There was also no difference between the two groups on measures of psychomotor performance. Chronic cannabis use is associated with a reduction in cortical inhibition potentially related to activity at the GABA(A) receptors. Further research is required to explore whether this results from chronic cannabis use or reflects an underlying predisposition to developing chronic substance use problems.

Cortical excitability in cocaine-dependent patients: a replication and extension of TMS findings

Cortical excitability can be assessed by transcranial magnetic stimulation (TMS). Previously we observed that TMS motor threshold (MT) was elevated in abstinent cocaine-dependent subjects. In the current study we aimed at replicating our initial finding, exploring other TMS-based measures of excitability, and examining association with personality characteristics. Nineteen cocaine-dependent and 12 healthy control subjects were examined. Resting and activated motor thresholds (RMT and AMT) and duration of the cortical silent period (CSP) were examined. The Cocaine Experience Questionnaire (CEQ) was administered to assess cocaine-induced psychotic symptoms. The relationship between Minnesota Multiphasic Personality Inventory (MMPI) scales and cortical excitability measures was also examined. AMT was significantly elevated in cocaine-dependent subjects on both hemispheres. RMT was also significantly elevated on the right hemisphere. No CSP changes were noted. Patients with cocaine-induced paranoia had longer CSPs on the right hemisphere compared to subjects reporting no paranoid experiences. The patients displayed significantly elevated scores on several MMPI scales, though the scale scores did not correlate with cortical excitability measures. These data support our initial finding of decreased cortical excitability in abstinent cocaine-dependent subjects. We interpret this finding as a compensatory mechanism against the stimulating and epileptogenic effects of cocaine.

Transcranial magnetic stimulation: studying motor neurophysiology of psychiatric disorders

RATIONALE

Transcranial magnetic stimulation (TMS) is a noninvasive tool that directly stimulates cortical neurons by inducing magnetic and secondary electric fields. Traditionally TMS has been used to study the motor neurophysiology of healthy subjects and those with neurological disorders.

OBJECTIVE

Given the known motor dysfunctions in many psychiatric disorders supplemental usage of TMS to study the underlying pathophysiology of certain psychiatric disorders and to assess treatment outcomes is underway. Such studies include examination of motor neuronal membrane, corticospinal and intracortical excitability. Our objective is to overview the past findings.

METHODS

We review the past literature that used TMS as an assessment tool in psychiatric disorders such as schizophrenia, mood disorders, Tourette's syndrome, obsessive-compulsive disorder, attention-deficit hyperactivity disorder, and substance abuse.

RESULTS

While the findings are still preliminary due to small sample-size, inconsistent patient population (diagnosis, medication), differences in methodology between research groups, studies restricted to the motor region and possible lack of sensitivity and specificity, the studies are yielding interesting results which could potentially lead to trait- and state-markers of psychiatric disorders.

CONCLUSIONS

Future studies using TMS alone or in combination with other neuroimaging techniques promise to further expand the application of TMS from studies of motor excitability to higher cognitive functions.