Theta is a frequency of 4-8Hz that emanates from the thalamus to the cortex and back again, it is a thalamo-cortical frequency and arrives in states of trance, deep meditation, drowsiness, under hypnosis and at the top of sleep cycle for healthy adults (REM sleep) during dream state. Theta also arrives in non rapid eye movement sleep (NREM 2 and NREM 3) at the midline and is part of what is called a “K-complex.”<br><br>Otherwise, healthy theta is seen in children under 9 years of age and is linked up to the visual gestalt in infants. Theta is similar to delta in that it is indicative of neurogenesis in the infant and child. From an empirical perspective, theta is one of the main rhythms of the hippocampus, where it is linked to memory encoding, spatial memory, and cognitive processes (Gorochowski, 2009; Stam, 2006). This has been found in many studies using rats. However, from intracranially implanted electrodes in seizure patients, Cantero et al. (2003) found that oscillations in the 4–7 Hz frequency range could be recorded from both the hippocampus and neocortex in humans, whereas previously it was not known if humans created hippocampal theta, as rats do. The hippocampal oscillations were associated with REM sleep and the transition from sleep to waking, and came in brief bursts, usually less than a second long. Cortical theta oscillations, arising from the thalamus and other subcortical structures, were observed during the transition from sleep and during quiet wakefulness; however, the authors were unable to find any correlation between hippocampal and cortical theta waves, and concluded that the two processes are probably controlled by independent mechanisms, however they are likely related. Cortical theta is generated from the thalamus and the nucleus accumbens in the forebrain. Frontal midline theta, as seen in brief bursts on memory retrieval tasks as the nucleus accumbens provides acetylcholine to the temporal lobe's limbic structures via the diagonal band of Broca, which is connected to the amygdala/hippocampus complex, allowing rhythmicity (Gunkelman, 2014).&nbsp; Memory uses theta as a carrier wave, upon which other, faster frequencies can ride; the nesting of faster, gamma waves upon theta waves promotes short term memory (DeRidder, 2014; Klimesh, Sauseng, &amp; Hanslmeyer, 2007). According to Gorochowski (2009), theta modulates gamma, which allows for the construction (and reconstruction) of a low-frequency-modulating-phase.<br><br><br>