Why do we desire? Psychologists and neuroscientists have been debating the purpose of dreams for hundreds of years, but there is continue to no recognized response.

Now, David M. Eagleman​​ and Don A. Vaughn​ have proposed a new principle. Their preprint article, which has not yet been peer reviewed, is called The Defensive Activation principle: dreaming as a system to avoid takeover of the visual cortex

To my mind, it truly is a hugely primary and creative principle, but I am not persuaded by it.

Here is Eagleman​​ and Vaughn​’s principle in nutshell: the part of dreams is to guarantee that the brain’s visual cortex is stimulated all through sleep. In any other case, if the visual program ended up deprived of input all evening lengthy, the visual cortex’s purpose may well degrade.

We know that the visual cortex, in the brain’s occipital lobe, can start off to reply to non-visual signals if it is deprived of visual input. In blind persons, for instance, the occipital lobe strongly responds to touch. This rewiring or repurposing of below-used mind places is a sort of neuroplasticity.

Neuroplasticity is frequently considered a very good factor. But Eagleman​​ and Vaughn level out that for the visual program, neuroplasticity could really pose a threat, simply because eyesight – contrary to our other senses – is not active all the time.

If we are in a dark location, or it truly is evening, we get minor or no visual input. So – in principle – our visual cortex would be vulnerable to ‘takeover’ by other senses, every single one evening. Dreams, on this view, are our brain’s way of defending the integrity of our visual program by maintaining it active.


As I explained, I enjoy the ingenuity of this principle, but I do not seriously acquire it. We know that dreams are related with stimulation of the occipital cortex all through a sleep stage called REM sleep. So it truly is correct that dreams stimulate the visual program. But I am not persuaded that this is the most important objective of dreams.

For one particular factor, Eagleman​​ and Vaughn’s principle only would make perception if neuroplastic repurposing of the cortex transpires really rapidly. For the visual cortex to want defending, destructive neuroplasticity would want to happen in the room of a number of several hours. The authors do focus on evidence that fast neuroplasticity can happen, but they do not demonstrate any evidence that these fast alterations are strong sufficient to be destructive.

In actuality, Eagleman​​ and Vaughn do not seriously focus on any direct evidence for the dreams-as-defense.

They demonstrate a correlation between amount of REM sleep and the tempo of advancement amid primate species. Primates whose babies discover to stroll more rapidly and achieve maturity more rapidly, are inclined to have less REM. (Humans, the slowest maturing primates, have the most REM.)

Primate development and REM sleep

Primate advancement and REM sleep, from Eagleman and Vaughn (2020)

The plan is that more rapidly advancement means slower neuroplasticity, and slower neuroplasticity means less want to guard the visual cortex from encroachment. This is really a lot circumstantial. The authors do cite some other oblique evidence, but acknowledge that: “The existing hypothesis could be analyzed a lot more thoroughly with direct actions of cortical plasticity.”

I consider this hypothesis could be analyzed very quickly. You’d acquire a group of human volunteers and give them an fMRI scan, at baseline, to create the extent of their visual cortex and how visually selective it is (i.e. how very well it responds only to visual input, not touch or other senses.)

Then, for 24 several hours, fifty percent of the volunteers would use a blindfold to create visual deprivation. Half would have REM sleep disrupted that evening (selective REM disruption is doable). At the 24 hour level, they get a second fMRI scan.

Eagleman​​ and Vaughn’s principle would predict that the eyesight-deprived persons would have less visually selective visual cortex, and, crucially, that REM disruption would greatly enhance this influence. The authors recommend a related experiment.