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Theta wave

Historical Background of Theta Waves: – First described in hippocampal EEG by Jung and Kornmüller in 1938. – Green and Arduini’s study in 1954 outlined […]

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Historical Background of Theta Waves:
– First described in hippocampal EEG by Jung and Kornmüller in 1938.
– Green and Arduini’s study in 1954 outlined basic properties of theta oscillations.
– Charles Stumpf’s 1965 review cited numerous publications on drug effects on hippocampal electrical activity.
– Vienna researchers, including Stumpf and Petsche, highlighted the role of the medial septum in controlling hippocampal activity.

Characteristics and Types of Theta Waves:
– Theta rhythm generates neural oscillations underlying cognition and behavior.
– Hippocampal theta observed during active motor behavior and REM sleep in mammals.
– Cortical theta rhythms are low-frequency components of human scalp EEG.
– Two types of theta proposed in rats: Type 1 during locomotion and REM sleep, Type 2 during immobility and anesthesia.

Functional Significance of Theta Waves:
– Linked to memory formation and navigation in humans and animals.
– Associated with REM sleep, meditation, and memory processes.
– Theories suggest theta waves may facilitate the transition between encoding and recall in memory.

Mechanisms and Generators of Theta Waves:
– Medial septal area plays a central role in generating hippocampal theta.
– Theta waves are generated by synchronized synaptic input to densely packed neurons.
– Different brain regions, including the hippocampus, are modulated by the medial septal area.
– CA1 layer in the hippocampus generates the strongest theta waves.

Research Studies and Clinical Applications of Theta Waves:
– Various research studies explore the role of theta waves in memory, navigation, and psychiatric illnesses.
– Clinical applications include understanding drug effects on hippocampal activity and the use of theta rhythm as a marker for memory processes.
– Theta waves have implications in brain oscillations, hypnosis, and sensorimotor integration.

Theta wave (Wikipedia)

Theta waves generate the theta rhythm, a neural oscillation in the brain that underlies various aspects of cognition and behavior, including learning, memory, and spatial navigation in many animals. It can be recorded using various electrophysiological methods, such as electroencephalogram (EEG), recorded either from inside the brain or from electrodes attached to the scalp.

An EEG theta wave

At least two types of theta rhythm have been described. The hippocampal theta rhythm is a strong oscillation that can be observed in the hippocampus and other brain structures in numerous species of mammals including rodents, rabbits, dogs, cats, and marsupials. "Cortical theta rhythms" are low-frequency components of scalp EEG, usually recorded from humans. Theta rhythms can be quantified using quantitative electroencephalography (qEEG) using freely available toolboxes, such as, EEGLAB or the Neurophysiological Biomarker Toolbox (NBT).

In rats, theta wave rhythmicity is easily observed in the hippocampus, but can also be detected in numerous other cortical and subcortical brain structures. Hippocampal theta waves, with a frequency range of 6–10 Hz, appear when a rat is engaged in active motor behavior such as walking or exploratory sniffing, and also during REM sleep. Theta waves with a lower frequency range, usually around 6–7 Hz, are sometimes observed when a rat is motionless but alert. When a rat is eating, grooming, or sleeping, the hippocampal EEG usually shows a non-rhythmic pattern known as large irregular activity or LIA. The hippocampal theta rhythm depends critically on projections from the medial septal area, which in turn receives input from the hypothalamus and several brainstem areas. Hippocampal theta rhythms in other species differ in some respects from those in rats. In cats and rabbits, the frequency range is lower (around 4–6 Hz), and theta is less strongly associated with movement than in rats. In bats, theta appears in short bursts associated with echolocation.

In humans, hippocampal theta rhythm has been observed and linked to memory formation and navigation. As with rats, humans exhibit hippocampal theta wave activity during REM sleep. Humans also exhibit predominantly cortical theta wave activity during REM sleep. Increased sleepiness is associated with decreased alpha wave power and increased theta wave power. Meditation has been shown to increase theta power.

The function of the hippocampal theta rhythm is not clearly understood. Green and Arduini, in the first major study of this phenomenon, noted that hippocampal theta usually occurs together with desynchronized EEG in the neocortex, and proposed that it is related to arousal. Vanderwolf and his colleagues, noting the strong relationship between theta and motor behavior, have argued that it is related to sensorimotor processing. Another school, led by John O'Keefe, have suggested that theta is part of the mechanism animals use to keep track of their location within the environment. Another theory links the theta rhythm to mechanisms of learning and memory (Hasselmo, 2005). This theory states that theta waves may act as a switch between encoding and recall mechanisms, and experimental data on rodents and humans support this idea. Another study on humans has showed that theta oscillations determine memory function (encoding or recall) when interacting with high frequency gamma activity in the hippocampus. These findings support the idea that theta oscillations support memory formation and retrieval in interaction with other oscillatory rhythms. These different theories have since been combined, as it has been shown that the firing patterns can support both navigation and memory.

In human EEG studies, the term theta refers to frequency components in the 4–7 Hz range, regardless of their source. Cortical theta is observed frequently in young children. In older children and adults, it tends to appear during meditative, drowsy, hypnotic or sleeping states, but not during the deepest stages of sleep. Theta from the midfrontal cortex is specifically related to cognitive control and alterations in these theta signals are found in multiple psychiatric and neurodevelopmental disorders.

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