Netflix, Lightbox, TVNZ OnDemand: everyone's doing it now. But instead of having to wait for next week's exciting episode — living our less dramatic lives in between — we can engorge episode after episode in our hunger to know what happens next.

And the scenes in online television productions continue to stretch out to new, unwatched frontiers so that we need more to feel fully satisfied. In a world of so much incredible stimuli, these dramas need to do things differently to keep viewers engaged.

Did I really just watch a pregnant woman being raped by a husband and a wife in The Handmaid's Tale, or a fictitious British Prime Minister screw a pig in front of an international audience in Black Mirror? Did that quietly spoken nerd just bludgeon his wife with a hammer in Fargo, leaving brain gunk clinging to the walls of their suburban basement?

Added to the extreme nature of these mainstream scenes is the fact that we consume them in intense sessions. One isn't enough. The dishes are done, the kids are in bed, I can squeeze in just one more episode tonight.

How many successive, violent, extraordinary scenes can this poor brain take? Prehistoric that it is, can this ancient organ cope with all that I am giving it?

"We don't know," says Nathan Wallis, neuroscientist from XFactor Education Ltd.

"There's been some research on violent gaming and the impact on the brain, which leads to a measurable increase in violent behaviour for about two hours after the game has ended. The effects seem to be short-term. But brain science hasn't yet told us what the effects of binge-watching are."

Wallis says that dopamine, that pleasure-giving, desire-satiating neurotransmitter, plays a central role. "It's like any other addiction — heroin, alcohol, sex — we're used to getting hits of dopamine from certain activities, and if watching several episodes of our favourite TV series is pleasurable, our brains will want to keep doing it."

A new way of watching

And doing it we are. In December, Netflix, the most popular platform for binge-worthy material, issued its statistics from 2017 — titled "A Year in Bingeing" — revealing its 118 million streamers around the world "watched more than 140 million hours per day (that's a little more than one billion hours per week in case you were wondering). The most popular of which fell on Sunday, January 1 — one day in and we already needed a comfort binge.

And a 2015 survey of subscribers to a popular digital video recorder (DVR) service reported that nine out of 10 American viewers had regularly watched three episodes or more in a single day.

Will Smith, a 20-year-old student at Ara Institute of Canterbury, consumes up to five episodes in a single sitting most weekends, especially on days when he and his flatmates aren't working.

"Generally, it's my day off," he says, "and in between organising things in the flat, we're content to just keep watching. It's interesting to dive into a different world and to get away from it all."

Researchers call the pleasure derived from feelings of fun and fantasy "hedonic consumption", with some arguing that it has important restorative value for the brain. It can also be associated with a guilty, voyeuristic pleasure involved with spending an entire day or night staring at a flat screen instead of getting on with more productive activities.

Although binge-watching surely has a role in helping us get away from it all, a University of Oregon study says it is viewer engagement — not escapism — that is the key motivation for binge-watching. Participants reported an active involvement in the viewing, rather than a more passive approach for appointment-based and single-sitting viewing. It was the quality of the programmes, binge-watchers reported, that kept them on the couch.

Just so good

Television dramas with multiple episodes have the time to develop complex plots and multi-layered narratives which intensify viewers' need to watch more. Main characters are seldom straightforward; their creators have endeared them with Shakespearean-like flaws so that their apparent strength and cleverness can potentially be overcome by their destructive traits and inner demons.

This makes them more human and relatable — who among us doesn't see a little part of ourselves in Marty Bryde in Ozark, a family guy who gets caught up in a money-laundering ring and finds himself in way over his head? Or empathise with Sarah Linden in The Killing as her captivating detective work comes at the expense of every single relationship in her damaged personal life.

And what about the charming but conniving US President and First Lady in House of Cards? Didn't you sort of want them to succeed in their ferocious ascent to the Oval Office, despite their entirely narcissistic motivations?

Combined with several connecting and provocative storylines, these characters draw us in to become completely immersed in their onscreen lives. We not only want to know what is going to happen to them, but we care about what does.

Geoff Evans, a small-business owner, agrees it's the quality of the story that draws him in. "Online streaming is competing with such a load of rubbish on television. All television seems to offer is reality stuff.

"My gateway drug into binge-watching was the docu-drama Narcos. The story seems so far-fetched but the bulk of it was based on a true story. I just couldn't stop watching it — reality was even more bizarre than fiction."

Comfortably numb

Since the 1970s, research evidence has accumulated that demonstrate how exposure to media violence increases aggression and de-sensitises viewers to real-life violence.

In a 2007 paper published in the Journal of Experimental Social Psychology, researchers concluded violent gamers, "had lower heart rate and galvanic skin response while viewing filmed real violence, demonstrating a physiological desensitisation to violence".

Increases in aggressive thoughts, anger and physiological arousal following violent gaming sessions are also well-established in research.

But as neuroscientist Wallis points out, these studies involve violent video gaming, rather than the relatively new phenomenon of marathon online viewing of violent images. And while decades of research illustrate the negative effects of chronic electronic media on a formative child's brain — and more recently, even its physical structure — few studies tackle the implications for the adaptive, more mature adult brain. Especially one that has been at work all day.

There's more. A 2012 research paper from Christopher Ferguson — Stetson University department chair of psychology — and Dominic Dyck argued that "the human brain learns to distinguish between reality and fiction at an early age … To claim that this powerful ability plays no role in the evaluation of information … is absurd".

Soldiers returning from war and individuals witnessing a murder, for example, may have substantive neurological damage that addicted gamers or chronic horror film watchers do not.

Intuitively, it seems hard to argue that persistent viewing of extremely violent or aggressive images wouldn't, at the very least, normalise violence and improve our ability to digest it.

For student Will Smith, some of the onscreen images he sees make him feel "really uncomfortable but they want it to be that way. I may think 'oh my god, this is horrible and a terrible injustice' but at the same time I can tell the difference between that show and something that I see on, say, the news."

Smith remembers watching a motorbike race on TV with his dad when he was around 14 years old. One of the motorbikes crashed and he watched the driver get run over by another motorbike at a very high speed on live TV.

Later he found out that the man died. "It was much worse for me than seeing the same thing in fiction. Knowing that genuinely happened is much worse. That image stuck in my mind and I couldn't let it go. It was very powerful for me and still is."

Evans reckons every form of media is getting more violent and that they "keep having to up the ante. I do notice if something is outside the norm, but I'm not that offended by it. I think everybody's doing it and if I don't like it, I'll just stop watching."

Bendy brain

In the absence of any conclusive data that can illustrate the effect of prolonged online streaming on the adult brain, Wallis argues we need to turn to common sense.

When his mother was young, he recalls, watching Elvis Presley gyrating his hips on stage was thought to be at best, corruptive of youth and at worst, a sure path to hell and damnation.

"I tend to have a naïve faith in the self-adapting model of the brain. Its neuroplasticity means it's trying to look after itself, so if we give it a chance to recover from intense or violent images, it will."

Researchers Matthew Pittman and Kim Sheehan concluded in 2015 that the restorative power of having a good viewing session on the couch should not be underestimated, and that there are psychological benefits which may enhance overall wellbeing, such as the reduction of stress and social time with others (on that couch). These benefits, as well as "the opportunity to engage in thoughts and activities distinct from the every day", might mitigate the negative effects that any prolonged viewing might have, allowing us to recharge through those captivating storylines and relatable characters.

Wallis sniggles: "Binge-watching is probably as bad for us as watching Elvis' pelvis was to my mother."

Okay cat, move over. Narcos here I come.