MBSR Mechanisms in GAD

Inclusion Criteria: * Male or pre-menopausal female outpatients aged 18 to 50 years of age * A primary mental health complaint (designated by the patient as the most important source of current distress and confirmed on structured clinical interview for DSM-5 diagnoses by a certified clinical evaluator) of Generalized Anxiety Disorder (GAD), as defined by DSM-5 criteria. * Overall clinical anxiety severity of at least mild as defined by a CGI-S of at least 3. * Willingness and ability to participate in the informed consent process and comply with the requirements of the study protocol. Exclusion Criteria: * A lifetime history of bipolar disorder, schizophrenia, psychosis, or delusional disorders; obsessive-compulsive disorder or an eating disorder in the past 12 months; neurocognitive disorders, intellectual disabilities, communication disorders or other cognitive dysfunction that could interfere with capacity to engage in therapy or complete study procedures; substance or alcohol use disorder (other than nicotine) in the last 6 months or otherwise unable to commit to refraining from alcohol use during the acute period of study participation. * Patients with significant suicidal ideation (assessed by CSSR-S SI score greater than 2) or who have enacted suicidal behaviors within 6 months prior to intake will be excluded from study participation and referred for appropriate clinical intervention. * Patients must be free of concurrent benzodiazepine, antipsychotic, and stimulant medication for at least 4 weeks prior to initiation of randomized treatment. Other psychiatric medications such as antidepressants that have been stable for at least 4 weeks prior to randomization will be permitted. * Inability to understand study procedures or informed consent process, or significant personality dysfunction likely to interfere with study participation (assessed during the clinical interview) or inability to comply with study procedures (such as planned extended travel) assessed on clinical interview * Serious current unstable medical illness, or a condition for which hospitalization may be likely within the next year as assessed by medical history and physical exam. If any questions about medical safety emerge, consent will be formally obtained to contact patient's PCP in order to determine whether any medical concerns making participation unsafe or not feasible (such as need for extended inpatient care) are present; MBSR and SE, however, do not require intensive exercise capacity or mobility. * Pregnant women (to be ruled out by urine ß-HCG) and women of childbearing potential who are not using medically accepted forms of contraception (such as IUD, oral contraceptives, barrier devices, condoms and foam, or implanted progesterone rods stabilized for at least 3 months). * Any concurrent psychotherapy initiated within 3 months of baseline, or ongoing psychotherapy of any duration directed specifically toward treatment of GAD or with any mindfulness and/or meditation component is excluded. Prohibited psychotherapy includes CBT, DBT, ACT, mindfulness based approaches, or psychodynamic therapy focusing on exploring specific, dynamic causes of the GAD symptomatology and providing management skills. General supportive therapy initiated greater than 3 months prior is acceptable. * Individuals who have completed a course of MBSR or an equivalent meditation training or who have an ongoing regular meditation practice in the past 2 years. * Patients with a history of head trauma causing loss of consciousness, seizure or ongoing cognitive impairment. * Contraindications for MRI including metal implants, surgical clips, probability of metal fragments, or braces that are prohibited due to severe risk of injury. * Left handed