Deficits in working memory (WM) performance are the most significant cognitive impairments in schizophrenia (SCZ). It has also been shown that WM performance is contingent on the cortex synchronization, a process that relies on brain inhibition. Repetitive Transcranial Magnetic Stimulation (rTMS) has been demonstrated as an effective treatment for patients with SCZ and has been shown to increase brain inhibition and improve cognitive performance. In this study the investigators intend to: * evaluate rTMS as a treatment for WM deficits in SCZ * evaluate rTMS as a method to increase WM performance in healthy individuals * determine if improvements in WM performance are related to enhanced synchronization of brain networks * determine whether genetic polymorphisms predict cortical function and treatment response * evaluate the influence of rTMS treatment on brain structure.
To directly investigate whether enhanced gamma synchrony mediates rTMS enhancement of WM in patients with SCZ, and in healthy individuals the investigators propose the following study. The relationship between the improvements in WM performance and increased gamma synchrony following rTMS over the DLPFC will be investigated. Moreover, using statistical models, the investigators will further examine whether increased gamma synchrony mediates WM improvement in these patients. Therefore, in this study the investigators hope to clarify the neurophysiological mechanisms through which rTMS exerts its therapeutic effects on WM performance and develop rTMS as a novel therapeutic tool to enhance the treatment options available for one of the core cognitive deficits in this disorder. There is considerable evidence to support the fact that WM deficits in schizophrenia are heritable and have a strong genetic component. This evidence emerges from genetic association studies, and studies demonstrating that unaffected relatives of schizophrenia patients also suffer WM deficits. Therefore, treatment response to rTMS may be at least partly contingent on genetic variation within each individual. In particular, GABAergic genes that code for GABAergic proteins which largely determine cortical inhibition may play a key role in treatment response to rTMS over the DLPFC. However, several other gene systems that interact with the GABAergic system may also play a role, and would also merit investigation. Similarly brain structure may also determine treatment response. For instance, volume or thickness of the DLPFC and DLPFC related circuitry has been shown to play a role in WM performance, and therefore, may be a biomarker of treatment response. Objective 1: To improve WM in patients with SCZ, and in healthy individuals using rTMS. Hypothesis 1:20 Hz rTMS over the DLPFC will be superior to sham stimulation in improving WM performance in patients with SCZ, and healthy individuals. Objective 2: To evaluate if high frequency rTMS results in enhanced gamma synchrony SCZ and healthy individuals. Hypothesis 2: 20 Hz rTMS over the DLPRC will be superior to sham stimulation at increasing gamma synchrony in patients with SCZ, and healthy individuals. Objective 3: To determine if the rTMS induced increase in gamma band synchrony mediates the therapeutic effects of rTMS on WM performance in patients with SCZ and healthy individuals. Hypothesis 3: Increased gamma band synchrony will be shown to mediate the therapeutic effects of rTMS on WM performance in SCZ and healthy individuals. Objective 4: To test whether key polymorphisms in the GABAergic system, and related gene systems determine γ oscillatory activity and WM improvement following rTMS. Hypothesis 4: GABAergic gene and related gene polymorphisms will determine variation in γ oscillatory activity and WM performance following rTMS treatment. Objective 5: To examine whether brain structure is a biomarker of treatment response to rTMS Hypothesis 5: Increase in cortical thickness at DLPFC and in microstructural integrity in cortico-cortical white matter tracts connecting to DLPFC will correlate with n-back task performance after rTMS treatment.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
DOUBLE
Enrollment
122
Magnetic pulses to specified brain regions.
Centre for Addiction and Mental Health
Toronto, Ontario, Canada
The primary outcome measure will be the performance on the N-back working memory task.
Specifically, we will evaluate if rTMS results in changes to the number of correct answers, omissions and errors as well as reaction times.
Time frame: 4 weeks
Increase in gamma band synchrony
To ascertain whether high frequency rTMS is superior to sham stimulation in increasing gamma band synchrony our analysis will examine stimulus-locked changes in spectral power, phase, and coherence between electrodes.
Time frame: 4 weeks
Brain Imaging Changes
For brain imaging we will test for group differences using: (1) cortical thickness (2) volumetric measures, (3)diffusion based measures. Statistical tests measuring these differences will be conducted at baseline and at the conclusion of the study. We will control for possible effects of neuroleptic medication on MRI measures by regressing mean dosage levels multiplied by number of years on medication, for each of five classes of medication (typical neuroleptics, atypical neuroleptics, antiparkinsonian anticholinergics, lithium, benzodiazepines)
Time frame: 4 weeks
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