Is just four hours of porn a week enough to reduce the size of a man’s brain? According to a recent study, less than an hour a day might be enough to see gray matter decay.

For the investigation, scientists at the Max Planck Institute for Human Development in Berlin recruited 64 healthy males between the ages of 21-45. By studying their porn-watching habits, they hoped to determine if there was a connection between viewing pornographic viewing and gray matter volume in a particular region of the brain, which is associated with cognition and processing.

From the get go, the men were simply told that they were participating in "a scientific study including magnetic resonance imaging (MRI) measurements."

Later, during telephone interviews, they were told that questions about pornography would be a component of the research.

The men were then asked to fill out surveys regarding their porn viewing habits. The average participant clocked in just over four hours a week.

Researchers then showed the men both sexually explicit and non-sexual images while scanning brain activity with MRI.

"Our findings indicated that gray matter volume of the right caudate of the striatum is smaller with higher pornography use," the author’s of the study say.

The forebrain part striatum, incidentally, helps coordinate motivation with body movement. It facilitates and balances motivation with both higher-level and lower-level functions, such as inhibiting one's behavior in a complex social interaction as well as fine motor skills involved with delicate, voluntary movements.

Not only was an inverse correlation seen between gray matter volume and porn viewing, but real time drops in the striatium were observed when the subjects were shown sexually explicit images.

While the scientists believe it is the first evidence of the kind connecting pornographic viewing with reductions in brain size, so far they have only shown correlation, and not causation.

To put it in a nutshell, the researchers still don’t know if watching porn reduces gray-matter volume in porn-watchers, or more frequent viewers of porn have less gray matter to begin with.

"Individuals with lower striatum volume may need more external stimulation to experience pleasure and might therefore experience pornography consumption as more rewarding, which may in turn lead to more porn watching,” write the authors, who said further investigation would be required.

The report does, however, gel with previous studies, which have shown a connection between frequent porn consumption and negative social behavior. The reasoning goes that if porn can affect social behavior, it can likely affect cognitive behavior as well.