No idea about audio frequencies close to hearing, but I'm pretty sure it's common to manipulate the brain with ultrasonic frequencies these days.
Yeah, I'm sure that technology has existed for decades. Common folks just not allowed to know about it. It's "for our own good!" sarcastically speaking :(
- US20030171688A1: Mind controller - Induces alpha/theta brainwaves via audio messages. - US20070084473A1: Brain wave entrainment in sound - Modulates music for desired brain states. - US11309858: Inducing brainwaves by sound - Adjusts volume gains for specific frequencies. - US5036858A: Changing brain wave frequency - Generates binaural beats to alter waves. - US3951134: Remotely altering brain waves - Monitors and modifies via RF/EM waves. - US5306228A: Brain wave synchronizer - Uses light/sound for entrainment. - US6587729: RF hearing effect - Transmits speech via microwaves to brain. - US6488617: Desired brain state - Electromagnetic pulses for mind states. - US4858612: Microwave hearing simulation - Induces sounds in auditory cortex. - US6930235B2: EM to sound waves - Relates waves for brain influence. - EP0747080A1: Brain wave inducing - Sine waves via speaker for alpha waves. - US5954629A: Brain wave system - Feedback light stimulation. - US5954630A: FM theta sound - Superposes low frequencies for theta induction. - US5159703A: Silent subliminal - Ultrasonic carriers for brain inducement. - US6017302A: Acoustic manipulation - Subaudio pulses for nervous system control.