Theta Waves and the Hippocampus

[Planewalker]

Reading "Leaving the Body" by D. Scott Rogo, I found this passage:

Quote:Palmer made a surprising discovery: Subjects whose brain-wave pattern showed an abundance of theta waves, while they were preparing for the experiment invariably reported OBEs during the forthcoming test. Palmer explained that during the course of his work, he came across three subjects who showed over 30 percent theta in their resting parietal EEGs. All three subsequently had OBEs as a result of his induction procedures. [...] The uncommon theta waves, which come between alpha and delta waves at 4-7 cycles, seem to manifest when a person is involved in a deep alteration of consciousness. Intense creative exercises or yogic meditation seem to induce them, and they also occur when an individual attempts to create intense mental imagery or when deliberately inducing an altered state of consciousness.

So I looked up "theta waves" on Wikipedia:

Quote:Most of the available information on human hippocampal theta comes from a few small studies of epileptic patients with intracranially implanted electrodes used as part of a treatment plan. In the largest and most systematic of these studies, Cantero et al. (2003) found that oscillations in the 4–7 Hz frequency range could be recorded from both the hippocampus and neocortex. 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 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.

Note that "the authors were unable to find any correlation between hippocampal and cortical theta waves". Nevertheless, I looked up "hippocampus", because in rats (and some other mammals) this is the primary site of theta rhythm activity in a similar frequency range. There I found this:

Quote:Studies conducted on freely moving rats and mice have shown that many hippocampal neurons have "place fields", that is, they fire bursts of action potentials when a rat passes through a particular part of the environment. Evidence for place cells in primates is limited, perhaps in part because it is difficult to record brain activity from freely-moving monkeys. Place-related hippocampal neural activity has been reported in monkeys moving around inside a room while seated in a restraint chair;[19] on the other hand, Edmund Rolls and his colleagues instead described hippocampal cells that fire in relation to the place a monkey is looking at, rather than the place its body is located.[20] In humans, place cells have been reported in a study of patients with drug-resistant epilepsy who were undergoing an invasive procedure to localize the source of their seizures, with a view to surgical resection. The patients had diagnostic electrodes implanted in their hippocampus and then used a computer to move around in a virtual reality town.[21]

Place responses in rats and mice have been studied in hundreds of experiments over four decades, yielding a large quantity of information.[14] Place cell responses are shown by pyramidal cells in the hippocampus proper, and granule cells in the dentate gyrus. These constitute the great majority of neurons in the densely-packed hippocampal layers. Inhibitory interneurons, which make up most of the remaining cell population, frequently show significant place-related variations in firing rate, but much weaker than that shown by pyramidal or granule cells. There is little if any spatial topography in the representation: cells lying next to each other in the hippocampus generally have uncorrelated spatial firing patterns. Place cells are typically almost silent when a rat is moving around outside the place field, but reach sustained rates as high as 40 Hz when the rat is near the center. Neural activity sampled from 30–40 randomly chosen place cells carries enough information to allow a rat's location to be reconstructed with high confidence. The size of place fields varies in a gradient along the length of the hippocampus, with cells at the dorsal end showing the smallest fields, cells near the center showing larger fields, and cells at the ventral tip fields that cover the entire environment.[14] In some cases, the firing rate of rat hippocampal cells depends not only on place but also on the direction a rat is moving, the destination toward which it is traveling, or other task-related variables.[22]

The discovery of place cells in the 1970s led to a theory that the hippocampus might act as a cognitive map—a neural representation of the layout of the environment.[23] Several lines of evidence support the hypothesis. It is a frequent observation that without a fully functional hippocampus, humans may not remember where they have been and how to get where they are going: getting lost is one of the most common symptoms of amnesia.[24] Studies with animals have shown that an intact hippocampus is required for some spatial memory tasks, particularly ones that require finding the way to a hidden goal.[25] The "cognitive map hypothesis" has been further advanced by recent discoveries of head direction cells, grid cells, and border cells in several parts of the rodent brain that are strongly connected to the hippocampus.[14][26]

Brain imaging shows that people have more active hippocampi when correctly navigating, as tested in a computer-simulated "virtual" navigation task.[27] Also, there is evidence that the hippocampus plays a role in finding shortcuts and new routes between familiar places. For example, London's taxi drivers must learn a large number of places and the most direct routes between them (they have to pass a strict test, The Knowledge, before being licensed to drive the famous black cabs). A study at University College London by Maguire, et al. (2000)[28] showed that part of the hippocampus is larger in taxi drivers than in the general public, and that more experienced drivers have bigger hippocampi. Whether having a bigger hippocampus helps an individual to become a cab driver, or if finding shortcuts for a living makes an individual's hippocampus grow is yet to be elucidated. However, in that study Maguire, et al. examined the correlation between size of the grey matter and length of time that had been spent as a taxi driver, and found a positive correlation between the length of time an individual had spent as a taxi driver and the volume of the right hippocampus. It was found that the total volume of the hippocampus remained constant, from the control group vs. taxi drivers. That is to say that the posterior portion of a taxi driver's hippocampus is indeed increased, but at the expense of the anterior portion. There have been no known detrimental effects reported from this disparity in hippocampal proportions.[28]

In other words, it is assumed that a cognitive environmental map is generated in the hippocampus.

There is even a special paragraph about Theta activity in the hippocampus:

Quote:Because of its densely packed neural layers, the hippocampus generates some of the largest EEG signals of any brain structure. In some situations the EEG is dominated by regular waves at 3–10 Hz, often continuing for many seconds. These reflect subthreshold membrane potentials and strongly modulate the spiking of hippocampal neurons and synchronise across the hippocampus in a travelling wave pattern.[37] This EEG pattern is known as a theta rhythm.[38] Theta rhythmicity is very obvious in rabbits and rodents, and also clearly present in cats and dogs. Whether theta can be seen in primates is a vexing question.[39] In rats (the animals that have been the most extensively studied), theta is seen mainly in two conditions: first, when an animal is walking or in some other way actively interacting with its surroundings; second, during REM sleep.[40] The function of theta has not yet been convincingly explained, although numerous theories have been proposed.[41] The most popular hypothesis has been to relate it to learning and memory. For example, the phase with which theta at the time of stimulation of a neuron shapes the effect of that stimulation upon its synapses and therefore may affect learning and memory dependent upon synaptic plasticity.[42] It is well-established that lesions of the medial septum—the central node of the theta system—cause severe disruptions of memory. However, the medium septum is more than just the controller of theta, it is also the main source of cholinergic projections to the hippocampus.[29] It has not been established that septal lesions exert their effects specifically by eliminating the theta rhythm.

I leave any conclusions of that data regarding OBEs up to you. I don't say this is an explanation, I just found the correlation interesting. Of course only a small ratio of OBEs actually resemble the "physical world" more or less closely.

I am well aware of the irrelevance of such speculations though. You can't meaningfully describe a system using the system itself. Nevertheless I felt I should write down my little train of thought.

[moxley]

Havent read though all of that, but certainly some interesting reading for everyone who wants to know more about the inner workings of the brain.

So basically you are saying that the brain is building a map of every environment a rat/mammal/human is moving through and when we are going out of body our brain uses that information to credibly create similar environments for us to move through? Is that about right?

Wouldnt that mean that most of this information would have to be stored and/or connected to the visual centers of the brain? Then what about the other senses, are they not involved in that process? This all seems so visual and location based.

(Btw, I wonder if you could willingly give up your sense of sight in OBEs or LDs and still keep up a stable state where you can use all your other senses, more fully even, and are able to think and act, without that state breaking down instantly.)

Honestly, I am not an expert in the workings or structure of the brain, but it's certainly something I would like to catch up with. I can hardly understand how the brain is able to oscillate and sort of 'pump' at different frequencies according to how it's used at a given time. (this actually has nothing to do with blood pressure,right?)

It's a crazy and wonderful thing, this brain.

[Planewalker]

moxley Wrote:So basically you are saying that the brain is building a map of every environment a rat/mammal/human is moving through and when we are going out of body our brain uses that information to credibly create similar environments for us to move through? Is that about right?

It's not what I say, but it can be interpreted as a possible explanation for some parts of the experience.

moxley Wrote:(Btw, I wonder if you could willingly give up your sense of sight in OBEs or LDs and still keep up a stable state where you can use all your other senses, more fully even, and are able to think and act, without that state breaking down instantly.)

I never tried to do so willingly, but such a state is possible. You can even navigate by memory without visual perception.

[eyeoneblack]

Kriya yoga focuses a great deal on the pituitary and the pineal. It is interesting that the hippocampus lies just behing the pituitary and ahead of the pineal. Anyway, my point is, bio-feedback wise, concentrating on an 'organ' of the brain tends to activate the function of that organ and that's why I've spent a good amount of time studying the brain.

FYI, I have a great book that is an overview of the brain that a doctor friend, neuorologist, gave me; The Mysteries of the Brain by Richard Restak and before I say much more about Planewalker's info I need to review some stuff.

Hippocampus, Theta waves... there's also something to be said about the amygdala and working with it. I ran across an excersize a few years ago referred to as 'amygdala clicking' which was interesting. Anyway, I love this line of study, more later.

---

Whoops, Mysteries of the MIND by R Restak

Sorry

[debraJane]

Wow! (to this whole thread) gonna print it out and Aristotle it (i mean study it) when I get to Netzone Internet Cafe.

(06-14-2010 05:46 PM)eyeoneblack Wrote:  Kriya yoga focuses a great deal on the pituitary and the pineal. It is interesting that the hippocampus lies just behing the pituitary and ahead of the pineal. Anyway, my point is, bio-feedback wise, concentrating on an 'organ' of the brain tends to activate the function of that organ and that's why I've spent a good amount of time studying the brain.

FYI, I have a great book that is an overview of the brain that a doctor friend, neuorologist, gave me; The Mysteries of the Brain by Richard Restak and before I say much more about Planewalker's info I need to review some stuff.

Hippocampus, Theta waves... there's also something to be said about the amygdala and working with it. I ran across an excersize a few years ago referred to as 'amygdala clicking' which was interesting. Anyway, I love this line of study, more later.

---

Whoops, Mysteries of the MIND by R Restak

Sorry