We think of memory as a reliable recording of our lives. But we also have false memories, often pieced together from communal experience. Those false memories shape our identity the same as the real ones do. I was 11 years old when the 9/11 attacks occurred. I have vividly remember walking home from school in the UK with my grandmother that day. We passed a shop with a bank of TVs facing into the street through a big window. We stood there for a while with a large group of strangers, watching the attacks unfold live on the news. Where others were shocked or crying, I felt calm.

But I know this memory to be false. There were no TV shops in our village, and my grandmother never walked me home from school — she lived too far away. Having false memories is normal. We are all built from real and false memories, said Gerald Echterhoff, a social psychologist specializing in memory at the University of Münster, Germany. "Memories are dynamically constructed. They are susceptible to social influences or from inadvertently altering [y]our own memories," Echterhoff said.

I likely picked up this memory of standing in front of a TV shop from disaster films or other people's stories of watching the news unfold. We tell ourselves that we are our memories. We hold onto memories to understand our past selves and build a narrative of our lives, cross-comparing them with other people's memories and asking, “What I was I like back then?”

And if I could recall more vivid memories, I could create a fuller narrative of my life, and so I could know myself more. The reverse seems true as well: If you lose memories, you become less of the person you feel you were. Dementia or age muddles memories: You forget yourself. But if so many of our memories are false or forgotten, how do we know who we really are — our true identity? The answer starts with how our memories are stored in the brain.

How is a memory stored in the brain?

Scientific research shows us that a memory is hard-wired into the structure of the brain. The brain physically stores memories as connections between neurons, particularly in the hippocampus or amygdala brain regions. New memories are formed when neurons create new synapses with other neurons, building a mesh of neuronal connections. Memories need to be actively maintained to last. Recalling a memory strengthens the connections between the neurons, forming it through remembrance.

Then there's the act of forgetting. Forgetting is an act of "pruning" the connections between neurons. Neglect or befuddlement withers a memory away. We tend to fill in the blanks with what other people have told us. The problem is that those false memories — memories of things we didn't experience the way we remember them — are stored in the brain in exactly the same way as our real memories are stored. The same is true of biased information.

Researchers and psychologists have tried to differentiate reality from falsehoods, but have yet to design a perfectly reliable "recipe" for distinguishing accurate from inaccurate memories, Echterhoff said. The Paul Ingram case: When false memories get scary. In 1988, Paul Ingram was arrested by Washington State police in the US. His two daughters had accused him of sexual abuse and sacrificial acts.

Ingram said he had no memory of any of the alleged events, so initially denied the charges. Police also found no physical evidence of the alleged abuse or any ritual sacrifices. But he started to doubt his pristine memory, saying, “My girls know me. They wouldn't lie about something like this.” Ingram, a deeply religious man, prayed for guidance and began imagining what it would be like to abuse his daughters. During Ingram's interrogation, a psychologist told Ingram it was common for sexual offenders to repress their memory of crimes. The psychologist effectively helped guide Ingram's imagination and "memory" of abusing his children. God, Ingram believed, was revealing the truth to him.

Eventually, Ingram pleaded guilty to the charges, even elaborating on them during the trial, leading to Ingram having "memories" of performing satanic, ritualistic sacrifices of animals and babies. Ingram received a 20-year prison sentence. But a second psychologist doubted Ingram's memories were real. After extensive interviews with Ingram, the second psychologist concluded that Ingram's memories had been planted in his brain through established methods of suggestion during the interrogation process. This report was not available for use in the trial.

Ingram's case (State of Washington v. Ingram) is a textbook example of how strong, false memories can be implanted by social interactions, said Echterhoff. Horror scenes from fictional films are also known to serve as inspiration for false memories in witnesses' descriptions of horrendous events. In a review of memory in judicial processes published in 2015, Mark Howe and Lauren Knott write that therapists can sometimes transform fictional scenes into powerful false memories, especially when the therapist suspects repressed abuse.

But, then again, memories of horrendous abuse that emerge years after an event may well be real memories, repressed or otherwise. The #MeToo and Black Lives Matter movements showed this.

How #MeToo made memory political

The assumption that memories can be easily falsified came under heavy criticism during sociopolitical movements like #MeToo and Black Lives Matter (BLM). #MeToo showed how victims of sexual and physical abuse are often discredited through rhetoric that their memories were false or distorted. Lawyers used the "false memory" defence to smear abuse victims during the Harvey Weinstein rape trial. But it didn't work — Weinstein's victims came together to present a common memory of their abuse. Weinstein's defence failed and he was found guilty of rape and sexual misconduct.

Campaigns like #MeToo and BLM helped change our ideas of how memory shapes our identity, said Echterhoff. Memory can be in the service of shared, cultural experience, not just an individual recollection. This notion echoes older ideas from research, he said. The boundaries of the "self" based on personal memories are now seen as porous: Our memories and other people's memories bleed into each other based on shared experiences.

"Now there is a stronger idea of communities based on a shared memory of the past, often based on suffering. This is very powerful in bringing people together and building cultural identities," said Echterhoff. But unearthing a nation's cultural memories can also sow division, as Germany is finding while it debates its history of colonialism. I'm sure my false memory of seeing the 9/11 attacks on TV have helped build my sense of cultural identity, sharing a defining moment of the 21st century with a group of strangers.

I still hang on to the false memory, almost preferring it the more accurate memory of my hearing about the attacks the next day at school, after I'd missed the event in real time. In the false memory, I'd witnessed a shared history.

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