Natasha Radhu

A meta-analysis of cortical inhibition and excitability using transcranial magnetic stimulation in psychiatric disorders

OBJECTIVE To evaluate transcranial magnetic stimulation (TMS) measures of inhibition and excitation in obsessive-compulsive disorder (OCD), major depressive disorder (MDD) and schizophrenia (SCZ). METHODS Paradigms included: short-interval cortical inhibition (SICI), cortical silent period (CSP), resting motor threshold, intracortical facilitation, and motor evoked potential amplitude. A literature search was performed using PubMed, Ovid Medline, Embase Psychiatry and PsycINFO 1990 through April 2012. RESULTS A significant Hedges g was found for decreased SICI (g=0.572, 95% confidence interval [0.179, 0.966], p=0.004), enhanced intracortical facilitation (g=0.446, 95% confidence interval [0.042, 0.849], p=0.030) and decreased CSP (g=-0.466, 95% confidence interval [-0.881, -0.052], p=0.027) within the OCD population. For MDD, significant effect sizes were demonstrated for decreased SICI (g=0.641, 95% confidence interval [0.384, 0.898], p=0.000) and shortened CSP (g=-1.232, 95% confidence interval [-1.530, -0.933], p=0.000). In SCZ, a significant Hedges g was shown for decreased SICI (g=0.476, 95% confidence interval [0.331, 0.620], p=0.000). CONCLUSION Inhibitory deficits are a ubiquitous finding across OCD, MDD, SCZ and enhancement of intracortical facilitation is specific to OCD. SIGNIFICANCE Provides a clear platform from which diagnostic procedures can be developed.

Combined transcranial magnetic stimulation and electroencephalography: Its past, present and future

Transcranial magnetic stimulation (TMS) is used to index several neurophysiological processes including excitability, inhibition and plasticity. However, these measures are conventionally limited to the motor cortex and recorded from peripheral muscles. This represents a significant limitation when non-motor neurophysiological processes are of primary interest. In the last several years, TMS has been combined with electroencephalography (EEG) to derive such measures directly from the cortex. Initial studies demonstrated that meaningful recordings could be derived without being substantially affected by TMS stimulus artifact due to advancements in EEG amplifier technology. Subsequently, TMS measures of cortical excitability were reliably recorded and found to be related with more conventional TMS electromyography recordings of excitability in the cortex. More recently, other key neurophysiological indices including cortical inhibition and interhemispheric connectivity have also been reported. In this article, such findings will be reviewed and their importance discussed vis à vis healthy and disease states. We will conclude by highlighting the limitations of this work and discuss their potential future applications as a biomarker of disease states.

Evaluating a Web-Based Cognitive-Behavioral Therapy for Maladaptive Perfectionism in University Students

Abstract Objective: This study assessed a Web-based cognitive-behavioral therapy (CBT) for maladaptive perfectionism, investigating perfectionism, anxiety, depression, negative automatic thoughts, and perceived stress. Participants: Participants were undergraduate students defined as maladaptive perfectionists through a screening questionnaire at an urban university. The data were collected from July 2009 to August 2010. Methods: Forty-seven maladaptive perfectionists were randomly assigned to a 12-week CBT or a wait-list control group and assessed via questionnaires at pre- and postintervention. Statistical procedures included t tests, Pearson correlations, and analysis of covariance. Results: At the postintervention measure, the CBT group demonstrated significant decreases in anxiety sensitivity and negative automatic thoughts compared to the control group. Within the CBT group, changes in perfectionism scores were significantly correlated with positive changes in depression, anxiety, stress, and automatic thoughts. Conclusions: The treatment group improved on psychological outcomes, demonstrating the effectiveness of a Web-based CBT for perfectionism in a university setting.

Evidence for inhibitory deficits in the prefrontal cortex in schizophrenia

Abnormal gamma-aminobutyric acid inhibitory neurotransmission is a key pathophysiological mechanism underlying schizophrenia. Transcranial magnetic stimulation can be combined with electroencephalography to index long-interval cortical inhibition, a measure of GABAergic receptor-mediated inhibitory neurotransmission from the frontal and motor cortex. In previous studies we have reported that schizophrenia is associated with inhibitory deficits in the dorsolateral prefrontal cortex compared to healthy subjects and patients with bipolar disorder. The main objective of the current study was to replicate and extend these initial findings by evaluating long-interval cortical inhibition from the dorsolateral prefrontal cortex in patients with schizophrenia compared to patients with obsessive-compulsive disorder. A total of 111 participants were assessed: 38 patients with schizophrenia (average age: 35.71 years, 25 males, 13 females), 27 patients with obsessive-compulsive disorder (average age: 36.15 years, 11 males, 16 females) and 46 healthy subjects (average age: 33.63 years, 23 females, 23 males). Long-interval cortical inhibition was measured from the dorsolateral prefrontal cortex and motor cortex through combined transcranial magnetic stimulation and electroencephalography. In the dorsolateral prefrontal cortex, long-interval cortical inhibition was significantly reduced in patients with schizophrenia compared to healthy subjects (P = 0.004) and not significantly different between patients with obsessive-compulsive disorder and healthy subjects (P = 0.5445). Long-interval cortical inhibition deficits in the dorsolateral prefrontal cortex were also significantly greater in patients with schizophrenia compared to patients with obsessive-compulsive disorder (P = 0.0465). There were no significant differences in long-interval cortical inhibition across all three groups in the motor cortex. These results demonstrate that long-interval cortical inhibition deficits in the dorsolateral prefrontal cortex are specific to patients with schizophrenia and are not a generalized deficit that is shared by disorders of severe psychopathology.

Impact of participant incentives and direct and snowball sampling on survey response rate in an ethnically diverse community: results from a pilot study of physical activity and the built environment.

Community-wide efforts to encourage healthy behaviours must respond to the needs of existing neighbourhoods, especially those where low physical activity (PA) is associated with social, economic, and cultural challenges. This study reports on the effect of direct and snowball sampling strategies and financial incentive levels on the response rates of a built environment and PA survey in a predominately urban, low-SES new-immigrant community. Women residing in the Jane-Finch neighbourhood of Toronto, Ontario were selected to participate by quasi-random sampling, yielding a response rate of 41.5%. The survey completion rate per contact attempt increased 2-fold when incentives were increased from

Meditation-Related Increases in GABAB Modulated Cortical Inhibition

10 to

A meta-analysis of the effects of aging on motor cortex neurophysiology assessed by transcranial magnetic stimulation.

20 and a further threefold following the increase from

Cognitive behavioral therapy-related increases in cortical inhibition in problematic perfectionists

20 to

Characterization of Glutamatergic and GABA A -Mediated Neurotransmission in Motor and Dorsolateral Prefrontal Cortex Using Paired-Pulse TMS–EEG

30. Snowball sampled respondents were older, less likely to have full-time employment, and had lower educational attainment than directly sampled participants. With appropriate incentives, face-to-face contact, and snowball sampling, survey-based research is feasible within a low-SES, high minority population.

Characterizing Long Interval Cortical Inhibition over the Time-Frequency Domain

BACKGROUND Recent reports suggest meditation practice improves attentional performance and emotional regulation. The process of meditation apparently increases activation in the prefrontal cortex (PFC) and stimulates the reticular nucleus of the thalamus, implicating the production and delivery of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). GABAergic inhibitory interneurons have a central role in cortical inhibition (CI), modulating cortical excitability and neural plasticity. OBJECTIVE/HYPOTHESIS Changes in CI, after completion of a single meditation session, were investigated and compared to a non-meditating control activity. METHODS Transcranial magnetic stimulation (TMS), a non-invasive method of examining CI, was used to evaluate changes before and after a 60 min meditation session. Seventy right-handed healthy subjects (n = 35 meditators, n = 35 non-meditators) were assessed using TMS related measures of cortical silent period (CSP) and short intra cortical inhibition (SICI), with stimulation of the motor cortex coordinated with EMG recording of peripheral hand muscles. RESULTS For the meditators, CSP and SICI were measured before and after meditation sessions while age-sex matched healthy control subjects were identically assessed after a non-meditating activity (television watching). The meditators showed a statistically significant increase in CSP after meditation compared to non-meditators after an equivalent period of television watching (P = 0.02) while no significant between-group differences were observed in the SICI. CONCLUSION These findings indicate meditation processes are linked to GABAergic cortical inhibition, a mechanism previously implicated in improved cognitive performance and enhanced emotional regulation.