The Neuroscience of  Dreaming
and Other Altered States

We are already familiar with Bressloff's attempt to demonstrate that entoptic images experienced in states of shamanic trance are generated by specific brain processes. Altered states, however, involve much more than entoptic imagery. There are emotional and cognitive experiences, not just sensory images, of a world that is quite different than the one we encounter in everyday waking experience,  but that nevertheless "hangs together" in bizarre ways. Each of us spends around two hours per day in an altered state of conscious awareness that is in some ways similar to that of shamanic trance. Dreaming suspends the laws of physics and the norms of ordinary social interaction. In dreams we are capable of flying, of traveling instantaneously to distant places, of communicating with relatives long dead. In dreams people often change miraculously into other people. Even more dramatically, our own perspective may change, sometimes being located within the dream, sometimes viewing the dream scene from a point of view outside of it. In dreams we can realize our wildest sexual desires without difficulty, but we can also be caught in intensely embarrassing or anixiety-provoking social situations, such as appearing naked in public, or taking an exam without having studied. Unlike shamanic trance experiences, however, our dreams come upon us without being induced by special techniques. They are often difficult or impossible to remember, and they lack the religious and communal significance of the trance states shamans cultivate. Many of us also experience strange phenomena on the boundary between waking and sleep, a kaleidoscope of rapidly shifting colors and forms, known as "hypnogogic" imagery when it occurs in the twilight state before sleep, and "hypnopompic"  imagery when it  immediately precedes full awakening. Some of us are also capable of so-called "lucid dreaming," in which we are aware of dreaming while still in the dream, some even possessing the ability to control the dream scene and events consciously. Finally all of us experience dream-like states of abstraction in ordinary waking consciousness, such as day-dreams, highway hypnosis, and intense sensory immersion or deprivation. In other words, altered states of consciousness are part of our everyday lives. They do not depend only upon drug experience, mental illness, or religious ecstasy. Over the past two decades, the neuroscientist, Alan Hobson, has developed a theory of the brain processes involved in dreaming and other altered states that he calls the Activation-Imput- (Neuro)Modulation Model, AIM for short. In order to understand the AIM model, however, it's necessary to understand some basic facts of neuroscience.

The basic unit of brain functioning is the nerve cell or neuron, of which there are around 100 billion in the human brain. Each neuron connects to multiple others in complex pathways. The enormous number of neurons and connections between them is what makes the extraordinary human capacity to think and emote possible. There human brain can adopt more neural configurations than there are subatomic particles in the entire universe.

Real Neurons

Neurotransmitter being transported in vesicles (purple spheres) to
the synaptic cleft.

Basic Functional Anatomy of Neurons

Neurons convey information to other neurons by means of the generation of "action potentials." When electro-chemical stimulation of a neuron exceeds a certain critical threshold, a sodium (NA+) - potassium (K+) chemical pump changes the polarity, the distribution of electrical charges, across the cell membrane of the neuron. The result is a pulse-like wave of electrical energy that travels through the cell body and down a long projection called the axon.

The action potential causes vesicles filled with a chemical neurotransmitter to migrate to the end of the axon, and then dump into the synaptic cleft (the gap between neurons). By binding to receptor sites on the far side of the cleft, the neurotransmitter, depending upon its chemical composition, contributes to either exciting or inhibiting an action potential in the next neuron down the line. That neuron will in turn "fire," in other words, generate its own action potential, if the sum of excitatory and inhibitory impulses from all of the neurons that synapse onto it reaches the critical threshold.

Simulated Neurons

Next