December 22, 2006

Inducing a dreamy state

braineletrodes.jpgBrain stimulation provides an interesting tool to study the functions of a given area of the brain. In a study by Vignal et al. published in Brain, artificial stimulation or seizures in specific mesial temporal lobe structures were assessed both in terms of location and phenomenology.

Among the findings, the researchers found that “Forty-five per cent of dreamy states were evoked by stimulation of the amygdala, 37.5% by the hippocampus and 17.5% by the para-hippocampal gyrus.”

Furthermore, they found that their study “demonstrates the existence of large neural networks that produce recall of memories via activation of the hippocampus, amygdala and rhinal cortex.”
The dreamy state: hallucinations of autobiographic memory evoked by temporal lobe stimulations and seizures.

Vignal JP, Maillard L, McGonigal A, Chauvel P Brain. 2007 Jan ; 130(Pt 1): 88-99Using results from cortical stimulations, as well as the symptoms of spontaneous epileptic seizures recorded by stereoelectroencephalography we re-studied the phenomenon of the dreamy state, as described by Jackson (Jackson JH. Selected writings of John Hughlins Jackson. Vol 1. On epilepsy and epileptiform convulsions. Taylor J, editor. London: Hodder and Stoughton; 1931).

A total of 15 sensations of déjà vécu, 35 visual hallucinations consisting of the image of a scene and 5 ‘feelings of strangeness’ occurred. These were recorded during 40 stimulations in 16 subjects, and 15 seizures in 5 subjects.

Forty-five per cent of dreamy states were evoked by stimulation of the amygdala, 37.5% by the hippocampus and 17.5% by the para-hippocampal gyrus. During both spontaneous and provoked dreamy state, the electrical discharge was localized within mesial temporal lobe structures, without involvement of the temporal neocortex. Early spread of the discharge to the temporal neocortex appeared to prevent the occurrence of the dreamy state.

Semiological analysis showed a clinical continuity between déjà vécu and visual hallucinations, the latter often consisting of a personal memory that was ‘relived’ by the subject; such memories could be recent, distant or from childhood. With one exception, the particular memory evoked differed from one seizure to another, but were always drawn from the same period of the subject’s life.

Given the role of the amygdala and hippocampus in autobiographic memory, their pathological activation during seizures may trigger memory recall. This study of the dreamy state is in keeping with other evidence demonstrating the constant and central role of the amygdala and hippocampus (right as much as left) in the recall of recent and distant memories. It demonstrates the existence of large neural networks that produce recall of memories via activation of the hippocampus, amygdala and rhinal cortex.

HubMed

2 Comments »

  1. How do “the large neural networks that produce recall of [autobiographic] memories” actually work? A proposed system of neuronal mechanisms that can do the job of episodic learning and temporal routing of memory is detailed in *The Cognitive Brain*, MIT Press 1991. See in particular pp. 93-97, and pp. 183-187.

    Comment by trehub — December 22, 2006 @ 10:53 pm

  2. On the subject of dreamy states, why is there so little material available on the subject of hypnagogic imagery ?

    I only came across the subject in literature a few years back when I related to my sister a bizarre experience of lying in bed fully conscious ( though in some sense not fully awake ) and before my eyes ( which were open ) multiple rapidly moving , pastel coloured geometric shapes moved around in a sort of kaleidoscope effect. Like something out of a shaman vision.

    I was amazed to hear my sister relate that she had experienced that exact same phenomenon. It is not the same as the ordinary blobs of light and stuff that you see if you simply close your eyes. The imagery is somehow ‘alive’, often moving very rapidly, and has a curious 3 dimensional aspect ( or as my sister put it ‘ it seems to occupy its own space ‘ ). I have experienced this about a dozen times in my life, almost always accompanied by sleep paralysis…..though one is at the time fully conscious and able to actually study the phenomenon.

    There appear to be very few scientific studies of this phenomenon.

    Comment by Peter — January 21, 2007 @ 11:06 am

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