The Theta Brain-Wave Frequency Machine is a technology developed by the Centipede Project. It induces Theta brain-wave frequencies to uncover memories buried in the subconscious.
Captive of Centipede
In an attempt to discover the secret of S.H.I.E.L.D. agent Phil Coulson's continued survival after the Battle of New York, information buried within Coulson's subconscious, Centipede Project agents Edison Po and Raina exposed the abducted Coulson to the effects of the Theta Brain-Wave Frequency Machine. The machine was successful in unlocking Coulson's memory, but Coulson was rescued by his team before he could divulge that information to his captors. Before undergoing the treatment, Raina assured Coulson that she knew it would work because it had previously been used and worked on her.
When Agent John Garrett accidentally revealed to Agent Coulson that he knew both Coulson and Raina were subjected to the treatment (a fact Coulson told no one), Coulson realized that Garrett was the Clairvoyant. 
Remembering the Past
The machine was taken to the Playground. For over six weeks, Leo Fitz and Jemma Simmons worked on understanding the machine and how a person responded mentally and physically under its power. Coulson wanted to remember all he could about Project T.A.H.I.T.I. after the death of Janice Robbins, so he used the machine to find out the number, names and status of the test subjects. Skye was stationed to monitor him and talk him through the procedure as his anchor to the real world; Simmons was stationed to observe his mental and physical health; Alphonso Mackenzie and Fitz were to use their strength to hold Coulson if he acted wildly or psychotic during or after the memory recall.
While remembering the past, Coulson gave the names of four of the six S.H.I.E.L.D. agents that were given GH.325: Robbins, Lewis Seaver, Sebastian Derik and Hank Thompson. As Coulson gave the names, Skye researched their past to find their locations, learning that Seaver died in the fire at Santa Maria de las Flores and Thompson lived nearby. When Coulson's brainwave and heart activity became too erratic, Simmons told them to stop using the machine.
Gideon Malick's Location
- "Just kill me. Just kill me! Just kill me!"
- ―Werner von Strucker
Needing information about Gideon Malick's location, Phil Coulson attempted to extract it from Werner von Strucker. As von Strucker was in a vegetative state, Coulson, supervised by Leo Fitz and Lincoln Campbell, used the machine to stimulate his brain. However, while von Strucker was brought to consciousness by the machine, he ended up reliving his torture at the hands of Kebo, and began repeating the words "just kill me", nearly going brain-dead. Campbell was forced to shock von Strucker in order to stimulate the remainder of his brain.
Use as a Trap
The machine was dismantled by Alphonso Mackenzie and Elena Rodriguez to produce a trap for Hive, with Lincoln Campbell acting as a power source, forcing the dark Inhuman to recall a plethora of at least three of his hosts' most painful memories simultaneously. Hive was freed of the torture when the three S.H.I.E.L.D. agents fled, but was incapacitated. When Giyera and Hellfire came to help him, the dark Inhuman had lost control of his memories and was reduced to incoherently babbling past quotes from Nathaniel Malick, Will Daniels, and current host Grant Ward, leaving the two Inhumans utterly baffled. After realizing what was going on, Giyera attempted to get his enthraller to focus, despite Hellfire's doubts. Fixating on Ward's memories, Hive managed to get his mind under some sort of control and ordered Giyera and Hellfire to disconnect the warhead before S.H.I.E.L.D. could claim it for themselves, but still struggled to focus and was unable to recover before he was captured by S.H.I.E.L.D. moments later.
In chronological order:
- Agents of S.H.I.E.L.D.