The painting where we could see the painter was insane?

[darom03]

A while back some professor claimed that by looking at this one picture depicting a hill with horses and sleighs, you could see exactly what his illness was.

Many an hour did I spent reading about it, analyzing the painting and perusing psychology pages on the Internet. But little did I learn. And then I forgot about it.

But now I am wondering if we ever learned what the illness was. I have tried to google it but to no avail. But perhaps someone in here, who might even read russian as it was a russian professor, knows more about what happened?