London: How do actors learn all those lines? How can dancers reproduce all those steps?

These can seem like hackneyed questions so it’s refreshing to realise that actors and dancers are fascinated by them too.

I can barely get a question in when I meet Tanya Moodie and Sarah Lamb as they’re busy quizzing each other about the friable business of memory and performance.

Lamb is a principal dancer with the Royal Ballet and has performed this season in works by Twyla Tharp and Kenneth MacMillan, as well as resuming her part as the Sugar Plum Fairy in The Nutcracker.

Moodie’s successes include playing Gertrude in the RSC’s Hamlet; she recently reprised her role as the defiant actor Wiletta in Alice Childress’s Trouble in Mind.

Learning new material and retaining it in live performance is the foundation for the way they both work but striking differences leap out.

The brain and the body absorb information at different rates; muscle memory arrives quicker and lasts longer than language.

Moodie likes to learn her lines in cafés. Her secret weapon is her “rainbow of highlighters”. Like someone with synaesthesia, she will often see a speech in a particular colour. She argues that you can learn a Shakespeare role in advance, “because the intentions are on the line. There’s no subtext.”

For a contemporary play, however, “I start with my character’s objective, and then I break it down. But I have to know what I want first.”

Meaning makes memory, so that the lines feel inevitable. If lines elude her, she tries a variety of techniques: punching her leg to link a speech to a physical sensation; adding an action; linking lines to objects in her flat, like a bowl or potted plant. “I’ll throw lots of stuff at it, so something has to stick.”

‘Like neutrinos scattering’

Screen work is very different from developing a character on stage, to be replayed night after night.

Moodie, playing Benedict Cumberbatch’s therapist in the BBC’s Sherlock, had no rehearsal period.

“I get the script a month or so beforehand, learn it, go in, do it. It is so easy to retain. Like a tennis match.”

More extreme is her friend’s tale of a film director who would announce: “’Here’s a speech we’re going to shoot in 10 minutes.’ The actors were just bricking it.”

There is a particular technical vocabulary to classical ballet and Moodie asks whether Lamb consciously recites the names of the steps. “Sometimes,” she replies, “if it’s something that I find not very organic. Then in your head you have to say: pas de chat, glissade — to drill it. Other times you don’t have to do that at all, it’s like a flow.” Illogical structures are especially challenging: Lamb cites the central act of Wayne McGregor’s Woolf Works, in which dancers scurry from one side of the stage to the other for rapid, overlapping sequences with different counts.

“That is so hard,” she cries. “It’s like neutrinos scattering, it doesn’t seem to have any real logic.”

Whenever I watch dancers in daily class, I’m awed by their ability to absorb and immediately reproduce a sequence. Lamb is less impressed by these feats of working memory

. “It would be like a musician doing scales. We do it every day from six, seven, eight years old.” Can she retrieve this morning’s class? A moment’s thought. “It’s probably gone.”

My own acts of memory are academic — drumming information into a recalcitrant skull during exam season.

It’s an approach Lamb uses only in extremity, when learning a role at short notice.

“Most of the time I don’t need to do that. We are so habituated to the vocabulary of classical dance.”

Her advice is to head for bed.

“Sleeping is actually the best way to process a lot of things, rather than staying up for an all-nighter. I’ve had a choreographer say, ‘Oh you seem to really have it now — did you work on it a lot?’ And I’m thinking, no, I just went to bed!”

Dancers rely on music to trigger memory.

“I’m never going to hear the music for act four and think, ‘Oh is this act one?’” Lamb argues. “It’s very obvious.”

This means she can learn out of sequence — a visiting choreographer to the Royal Ballet may create a work at intervals across the year before a premiere.

“They’re trying things out on their dancers, and you might learn sections way in advance.”

How is it different for musicians? Unlike these stage performers, Petur Jonasson, an Icelandic classical guitarist specialising in new music, largely works alone.

A few months ago he took part in a London premiere; with only two ensemble rehearsals beforehand, advance learning was imperative. No wonder most musicians retain a score in performance.

“Contemporary pieces are often extremely complicated,” Jonasson says.

Learning trap

Researching memory for a PhD at the Royal College of Music’s centre for performance science, he was surprised that a project involving fellow musicians revealed fiendish new music as easier to learn than classical repertoire.

“When the tonal material and rhythms are much more complicated, you have to learn them slowly — you can’t just sight read,” he tells me. “In dire circumstances” — challenging score, little time — “I often begin at the end, and then go backwards.

It works really well, especially if you are under time pressure, so that you’re heading towards something you know better and better.” (Moodie used this technique on her solo show Joanne, after a friend advised that “if you learn it in order, the last couple of monologues are always going to be the weakest.”)

There’s a trap when learning material in chunks, argues Nicky Clayton, professor of comparative cognition at Cambridge and also scientist-in-residence with the dance company Rambert.

“When you make a mistake, it’s always at the same place, between the chunks.”

The brain seems to stutter in these transitions — Clayton notes that even an experienced broadcaster like David Attenborough faltered between segments when they worked together. Memorising something as an experience, rather than as pure information, seems to help — “wordless thoughts” as Clayton calls them.

“A big myth is that memory is about the past,” she says. “I think our memories were designed for thinking about the future.”

For performers, memory is a blueprint for a future performance.

— Guardian News & Media Ltd