A Neurosensory Account of Anxiety and Stress (Study 1)

Inclusion Criteria: * Right-handed * With normal or corrected-to-normal vision and normal olfaction * Between the ages of 18 and 50 years * Meeting the tACS screening criteria (see List I below; e.g., lack of a serious head injury or loss of consciousness) * Patients: Diagnosis of PTSD * Patients: If taking psychotropic medications, medication stability in the past 2 months * If having mild substance use disorder (for patients) or occasional substance use, abstention from use 48 hours before the experiment. Exclusion Criteria: * A history of diagnosis for a major medical illness (e.g., cancer, metabolic syndrome, cardiovascular disease, inflammatory disorders) or a neurological disorder (e.g., seizure, stroke, Parkinson's disease). * Patients: Concurrent Axis I diagnosis (depression, anxiety, and mild substance use disorder are allowed given their high comorbidity with PTSD). * Healthy controls: A history of diagnosis for a DSM-5 Axis I disorder or current use of psychoactive medications. * Severe psychiatric instability or severe situational life crises, including evidence of being actively suicidal or homicidal, or any behavior that poses an immediate danger to self or others. * History of head trauma with unconsciousness (\> 5 minutes) * Report that they regularly drink 3 or more alcoholic beverages a day. * Report that they are unable to abstain from substance use (including alcohol, nicotine, cannabis, amphetamines, narcotics, solvents, cocaine, hallucinogens, tranquilizers, barbiturates, etc.) or sleep medication for 48 hours before being scanned. * Are on calcium channel blockers (e.g., verapamil, nifedipine) or alpha-blockers (e.g., prazosin, terazosin) and are unable to stop these medications for a 48-hour period prior to scanning (to exclude the impact of these medications on the interpretation of fMRI/EEG). * Failed Urine Drug Screening Test: A rapid urine screening test that utilizes monoclonal antibodies to detect elevated levels of specific drugs (including alcohol, amphetamines, benzodiazepines, barbiturates, cocaine, marijuana, opiates, etc.) in urine (iCup) * Pregnancy based on urine test. The safety of MR systems has not been established for fetuses * Having electrically, magnetically, or mechanically activated implants (e.g., cardiac pacemakers), because the electromagnetic fields produced by the MR system may interfere with the operation of these devices.