Gamma waves (30–100 Hz) — what they are and what the research actually shows
What the band is
Gamma covers roughly 30 to 100 Hz, the fastest of the conventional bands. It is low in amplitude and hard to record cleanly from the scalp, because muscle activity from the jaw and eyes produces signal in the same range — a long-standing problem in the literature and a reason to read gamma findings carefully.
What research associates with it
Gamma synchrony has been proposed as a mechanism for binding separate features into a single percept — the temporal correlation hypothesis, reviewed by Singer and Gray (1995, Annual Review of Neuroscience). It is an influential hypothesis rather than a settled account.
In mouse models, 40 Hz sensory stimulation has been shown to drive gamma activity and to reduce amyloid load (Iaccarino and colleagues, 2016, Nature). That work uses combined light and sound in a laboratory, in mice; human trials are ongoing and it says nothing about an audio track in headphones.
For attention specifically, the picture is mixed. Colzato, Barone, Sellaro and Hommel (2017, Psychological Research) reported effects on attentional focusing, while Reedijk, Bolders and Hommel (2013, Frontiers in Human Neuroscience) found the response depended on the listener's baseline state. The evidence for focus is weaker than the evidence for anxiety.
What it is not
Gamma is not a cognitive enhancer you can switch on, and a 40 Hz audio session is not the MIT work. That research combines light and sound in a clinical context and is about disease pathology in animal models; this is an eleven-minute tone for a person trying to start a task.
It is also not a treatment for Alzheimer's disease, and nothing on this site should be read as suggesting otherwise.
What listeners report
Individual response varies, and some people notice nothing. Most commonly reported: