Image caption Poet Luke Wright has to be in a relaxed, stress-free frame of mind to begin writing

Byron was "mad, bad and dangerous to know" according to one lover, Keats was driven to distraction by obsessive love and Sylvia Plath ended her own life.

Depression, madness and insanity are themes which have run throughout the history of poetry.

The incidence of mood disorders, suicide and institutionalisation was 20 times higher among major British and Irish poets between 1600 and 1800 according to a study by psychologist Kay Redfield Jamison.

In other words, poets are 20 times more likely to end up in an asylum than the general population.

Science has puzzled to explain it. One recent study found similar brain patterns in artists at work to those of schizophrenics. Another study found that creative graduates share more personality traits with bipolar patients than less creative ones.

As far back as the mid 1800s, Emily Dickinson stated that "much madness is Divinest sense" and Edgar Allan Poe questioned "whether madness is or is not the loftiest intelligence".

Men have called me mad but the question is not yet settled, whether madness is or is not the loftiest intelligence Edgar Allan Poe

So what is it about poetry that seems to attract those more likely to suffer a mental disorder?

"If you're a creative person, then poetry is a great format because it's short," says poet Luke Wright.

"You can do almost anything with it and it's not like a novel - it's not going to take you years and you have no idea if it's going to be any good."

Poetry allows for the nuance of language and the different way someone sees the world.

"I think you've always got to be interested in a slightly different aspect of the universe to even want to pick up a pen and analyse the world through poetry," says spoken word artist Laura Dockrill.

"I think our brains are big scribbles and always active. Because you can write about anything, you're always on the go - trying to put something to your Velcro head hoping it will stick on.

"Part of poetry is making words do more work that they usually should do and so you're looking for every angle of what a word might mean and so your brain starts working like as well - over-analysing everything and zooming in to minute detail."

'Creative conflict'

Many psychologists have tried to define what makes someone creative or not, and how that can be calculated.

Experiments measuring how many uses a participant could think of for a brick have been carried out but JP Guildford's model of creativity, published in 1950, is still often used. The ideas of fluency, flexibility and originality of ideas, along with the ability to elaborate on them were the four points of his theory.

Image caption Painters and musicians as well as poets have been associated with mental illness

"Creativity is certainly about not being constrained by rules or accepting the restrictions that society places on us," chartered psychologist Gary Fitzgibbon told the BBC earlier this year.

"Of course the more people break the rules, the more likely they are to be perceived as 'mentally ill'."

So is it mental illness that drives people to art or art that drives people to mental illness?

"A lot of creativity comes from a conflict somewhere in your mind," says Wright.

"I don't think you have to be 'mad' to be a poet but if your mind is alive, then it can produce both positive and negative responses. It can mean wonderful things but it can mean that fitting into 'normal' life is difficult."

'Happy chap'

With the increase of mental disorder diagnosis, the idea of what "normal" is has become more difficult. Around 1% of the US population have schizophrenia, attention deficit hyperactivity disorder (ADHD) affects an estimated 4% of adults and bipolar disorder affects 2.5% of people, according to the US Census Bureau.

Some see expressing emotions and experiencing the highs and lows of life as positive things.

"I've got poems about all sorts of dark subjects but in general I'm a pretty happy chap," says spoken word artist and musician Scroobius Pip.

"In my life, I don't sit around discussing murder, suicide and spousal abuse with my mates. I talk about football and normal stuff. It's important to feel an array of emotions and it's great for the mind and soul.

"Though poetry, I'm sure, has a lot of people with mental illness, because if these people are having these feelings anyway, expressing them and writing them down and sharing them can help."

Indeed, the Art Therapy Credentials Board says that art can "reduce anxiety, and increase self-esteem".

Out of the Vortex - poems inspired by depressive illnesses is on BBC Radio 4, Monday 7 February, 2300 GMT and then afterwards on iPlayer.