Why do people hallucinate geometric tunnels?

Whenever you imagine any kind of altered reality — from dreams, to drug trips, to warp speed — the main image is always a tunnel, ringed by regular geometric patterns. And most of us see those odd, tunneling patterns at some point in our lives. What exactly is it about our brains that creates them?

There's a certain area in the brain that is the first stop for visual information. This visual cortex, called V1, is awash with nerves that interact with each other near-instantaneously. There are neurons that encourage activity among others, and neurons that inhibit activity among others. The combination of the both of them firing - say, during a drug trip - creates some interesting, and regular, patterns.

Why do people hallucinate geometric tunnels?

These patterns, though, don't create the tunnel effect. The tunnel springs from the fact that the visual system needs to perceive more than just a picture of contrasting values of light and dark. It also needs to perceive contour. The neurons in V1 are linked up in structures called hypercolumns. Each neuron in a hypercolumn perceives a different edge value. One neuron in a hypercolumn would perceive the vertical edge that two walls make when they come together. Another would detect the horizontal edge that a wall makes when it meets the floor. Although the neurons in each hypercolumn can interact with each other, they can't interact with all the neurons in the next hypercolumn. They can only interact with some, and the selective links between the columns are what scientists believe gives us the ability to perceive smooth, continuous curves.

It also means that, when we are hallucinating a pattern, we don't see the just the pattern. We create a symmetric pattern that comes together at certain angles. The interaction of the nerves in each hypercolumn causes an otherwise flat honeycomb or grid to curve around a central point in our vision. We see a tunnel, because our brain connects up that way.

Top Image: Garish

Second Image: Ksd5

Via Plus Magazine.