Eigengrau: the hallucinatory color we see when we close our eyes.

This grayish, changing image is actually a type of non-pathological hallucination.

Close your eyes, what do you see? Probably the first thing we answer is nothing, or darkness. A darkness that we usually associate with blackness.

But let's close our eyes again and take a closer look, is it really blackness what we see? The truth is that what we see is rather a grayish color, the eigengrauof which we are going to speak in this article.

What is eigengrau and why is it a false color?

We call eigengrau the color that we perceive when we maintain the eyes closed or we are in the most complete darkness, being this color less dark than the color of the eye.This color is less dark than the one that corresponds to black.

It is a dark gray color, close to black but curiously and despite being perceived in the absence of light is lighter than an object of the latter color in full light. The intensity of the perceived gray may be slightly different depending on the person. In fact the term in question means intrinsic gray or proper gray in German. This term is considered to have been researched and popularized by Gustav Theodor Fechner, known for his important role in the genesis of psychophysics and the measurement of human perception.

Its perception is considered to be a phenomenon generated by the retina or its nerve connections with the brain, or a product of the brain's action. However, it has been observed that perceived color is not totally stable. As time passes and we keep our eyes closed, the gray gradually appears to become lighter or even color perceptions may appear.

Explanation of its perception when closing the eyes

The perception of the color eigengrau may seem strange if we take into account that we should not really be able to detect anything with our eyes closed or in complete darkness, and there are several explanations that have been tried to be offered at a scientific level.

1. General interpretation

Already since the first investigations of Fechner it was suspected and considered that this perception arose as a kind of residue or background noise of neuronal activity. Even with the eyes closed, the various nerves remain active and discharge, generating neuronal activity in the absence of light that the brain is not able to separate from a single neuronal activity. is not able to separate it from a true perception of luminosity.. It would therefore be the product of nervous activity, something that is in fact true to a greater or lesser extent.

2. Isomerization of rhodopsin

Another theory that seeks to delve deeper into the cause of eigengrau perception links this perception to isomerization of rhodopsin, the type of pigment linked not to color perception but to the perception of movement and luminosityallowing vision in the dark and in the half-light.

3. Neuromelanin

Finally, another of the main explanations links the perception of this grayish tone especially to the formation of neuromelanin. the formation of neuromelanin.. This is a photosensitive pigment produced by the oxidation of dopamine and noradrenaline.

This production is carried out in different areas of the brain, especially in the substantia nigraespecially in the substantia nigra, the locus coeruleus, the pons or the cranial vagus nerve.

Link with hallucinatory phenomena

The eigengrau and its perception have been linked with the existence of hallucinations, being considered in fact a hallucinatory phenomenon of a biological, physiological and non-pathological nature.. The reason for this consideration is the fact that in the background one would be perceiving something that does not really correspond to an external reality.

Some authors also link the perception of this color with a different hallucinatory phenomenon: the appearance of hypnagogic and hypnopompic hallucinations. hypnagogic and hypnopompic hallucinations..

In both cases we would be dealing with objectless perceptions of variable complexity that usually occur in moments of transition between different states of consciousness, namely the transition from wakefulness to sleep (hypnagogic hallucinations) or vice versa (hypnopompic hallucinations), and which they do not consider pathological but rather the product of imbalances between the activation and deactivation of different processes and networks in the process of falling asleep and waking up (being also called physiological hallucinations).

Bibliographical references:

• Bynum, E. B.; Brown, A. C.; King, R. D., & Moore, T. O. (2005). Why Darkness Matters: The Power of Melanin in the Brain. African American Images: Chicago, Ill.
• Bynum, E. B. (2014). Dark light consciousness: the Pathway Through Our Neural Substrate. Psychdiscourse, 48 (2).
• Fechner, G.T. (1860). Elemente der Psychophysik. Leipzig: Breitkopf und Härtel.
• Nieto, A.; Torrero, C. y Salas, M. (1997). Estudio comparativo de la densidad de la neuromelanina en el locus ceruleus y la sustancia negra en algunos mamíferos, incluyendo al hombre. Revista de Psicopatología, 17 (4): 162-167. CSIC.