Ask most people about February 5, 1980 and they draw a blank. Jill Price can relive it. Known in the research literature as AJ, she contacted scientists in the early 2000s pleading for help, and her 2006 case introduced hyperthymesia, or highly superior autobiographical memory (HSAM), a condition with fewer than 100 documented cases. She recalls every day of her life since she was 14 with no effort at all. Yet her memory is no video camera: after hours with interviewers she could not describe their clothing, and she performed poorly on standard memorization tests and in school.

Price describes living with a split screen, the past playing constantly beside the present, and Joey DeGrandis explains how memories of breakups and loss never lose their emotional sting. Her brain scans showed an enlarged temporal lobe and caudate nucleus, prompting an obsessive compulsive theory that researcher James McGaugh rejected on the math of rehearsal time. At Vanderbilt, H.K. Derryberry, born at 27 weeks and blind, showed a right amygdala 20 percent larger than typical with strong links to the hippocampus. The research also overturned Wilder Penfield’s 1961 tape recorder model of memory.

• How HSAM differs from mnemonists like Solomon Shereshevsky, who used memory palaces and synesthesia
• The difference between egocentric memory and allocentric facts in the classroom
• Painter Nima Veiseh and Australian Rebecca Sharrock, who says her memories reach back to her 12th day
• Why even people with HSAM can absorb false memories during reconsolidation
• Microglia and synaptic pruning, the brain’s built-in system for forgetting