It's a sad fact that as we get older, a lot of cognitive impairment can come along for the ride. Alzheimer's Disease, senile dementia, and more. There are many issues that can strike in old age, but it's usually easier for writers to just make old people forgetful. It should be noted that not everything going on inside the brain is a disease or a syndrome; sometimes the machinery just wears out, and sometimes people are just absentminded.
You can usually expect this to be played for pathos, as Grandma or Grandpa rages against the loss of their faculties and their family has to watch the person they love die by inches (not for nothing is Alzheimer's called "The Long Goodbye").
However, sometimes it's given a more immediate urgency, as when the person has forgotten some piece of information vital to saving the world, or doesn't remember that he's an agèd, ass-kicking hero with at least one more good fight in him. In this case, you can probable expect a variant of Easy Amnesia, if only temporarily.
Sometimes though, this trope can be downplayed, as Granny's memory is just shown to be faded, but has no real bearing on the plot, and can usually be used for a cheap laugh. Sometimes seniors take advantage of others' expectations and feign this as a form of Obfuscating Stupidity. Compare Grandparental Obliviousness and The Fog of Ages.
Please limit real life examples to notable cases of age related memory loss, and keep it civil.
- It was implied that Aunt May was a little senile in the early days of Spider-Man. Characterization Marches On and this is no longer the case (now she's sometimes more aware than Peter himself).
- In Brightest Day, the newly-resurrected Martian Manhunter tracks down Melissa Erdel, the daughter of the scientist who brought him to Earth, in hopes of learning more about the late Dr. Erdel's research. Unfortunately for him, Melissa is now an old woman whose memory is failing her, but she does remember enough to recall that J'onn wasn't the only Martian that she and her father managed to summon.
- Mama Coco in Coco is a sympathetically portrayed example. She is very old and is struggling to tell her family members apart, and she is mired in the memories of her Disappeared Dad, who she thinks is coming back, despite him being long dead. This is actually a plot point, since she is the only one who actually still remembers Héctor, but her memories of him are slipping, meaning that it's only a matter of time before he suffers his Final Death from being forgotten. However, in the end, once Miguel plays Remember Me for her, she remembers everything about Héctor and is for a while more lucid than she has been in the entire film.
- Angelo Ledda in The Alzheimer's Case, who is trying to do One Last Job while his memory is starting to fade.
- The film Still Alice is about a middle aged woman who suffers the onset of Alzheimer's.
- Rise of the Planet of the Apes: The development of the virus that would lead to intelligent apes and the pandemic that would dethrone humanity was originally designed to treat Alzheimers's.
- Mars Attacks!. Richie's grandmother calls both of her grandsons (Richie and Billy Glen) "Thomas".
- Friends with Benefits, the movie is pretty lighthearted, if not a bit raunchy, up until Dylan's father is introduced, who is clearly suffering from memory loss. The Death Cab for Cutie song "Follow You Into the Dark" is played during this scene, which doesn't help matters. Another scene has his father panic while out at dinner, when he wonders why his ex-wife isn't coming to dinner with him. At the end of the film, one of his memory lapses prompts him to advise Dylan to patch things up with Jamie, as the former cites an example of a woman he himself let go of.
- Peter Jackson's The Two Towers portrays King Theoden this way, sort of. He may be possessed by Saruman rather than just corrupted by Wormtongue's influence, but everyone assumes its old age robbing him of vitality. Particularly apparent when Gandalf removes the corruption/possession and all of a sudden he looks twenty years younger.
- One of the elderly Lost Boys in Hook has "lost his marbles". Literally and figuratively.
- In Revenge Of The Fallen, Jetfire, a decayed ancient robot, is less forgetful and more completely batshit insane. He changes subject back-and-forth at a incomprehensible pace, forgets to mention crucial detail (such as when he teleports everyone to Egypt without a warning), and seems to be overall a bit clueless. His memory in specific, though, is very good: One of his main roles is explaining a lot of ancient history nobody else but him knows.
- The present day story in The Notebook has an elderly Noah reading the titular book to his wife, Allie, whose memory has faded. She has a few moments of lucidity, but they come and go in waves. Her last moment of lucidity results in her and Noah peacefully dying in their sleep.
- Max's mother in The Cobbler, obviously suffers from senile dementia. In one scene Max finds her purse in the microwave.
- Sir Graham in Mortdecai, who seems to be having a bad case of dementia and forgets things every ten seconds or so.
- Professor Xavier in Logan suffers from a degenerative brain disease that's affected his memory, as he doesn't seem to recognize Logan when he's first introduced and rambled about random things, and has also affected his control over his telepathy as when he has a seizure, he can freeze hundreds of people if they're in range to the point harming them and possibly killing them, as it's implied this is how the X-Men died.
- The Dresser: Played very tragically with Sir, the leading man of a troupe of Shakespearean actors. He is unable to remember lines or even remember what play they're doing. He also has wild emotional outbursts in public, as well as occasionally slipping into near-catatonia.
- A Brother's Price: The Porters had some mothers who were rather scatterbrained, and described as "ancient". They died in an explosion, caused by a bomb the Porter family had planted there. The younger ones wanted to get rid of the scatterbrained seniors who they feared would spill their murderous secrets.
- The Knight Camaris, in Tad Williams' Memory, Sorrow and Thorn trilogy needs to be awakened from a long senescence.
- El Patron in House of the Scorpion suffers from this towards the end of his life. He harvests brain implants from fetal clones of himself to regain his lucidity however.
- The elderly and absent-minded Professor Regius Chronotis ('Reg') from Dirk Gently's Holistic Detective Agency describes his memory as being "like the Queen Alexandria butterfly, in that it is colorful, flits prettily here and there, and is now, sadly, almost completely extinct."
- A Song of Ice and Fire:
- Archmaester Valgrave, the ravenology teacher at the Citadel of Oldtown, is known for being particularly senile, and a younger aspirant usually takes his place on the Conclave of Archmaesters. Another maester, Aemon, was, on the contrary, unusually lucid for his (very) advanced age, but shortly before his death he started succumbing to scatterbrainedness. And this was Played for Drama (unlike with Valgrave above) and led to a particular Tear Jerker.
- This was also the case with Aemon's great-great-great-great-great (-great, depending on how you trace the line of descent) grandfather Jaehaerys I. For both of them, it was probably due to their impending deaths wracking their minds as well as their bodies; as senility doesn't usually manifest itself so quickly and the 69 year-old Jaehaerys was a little young to be going senile.
- One of Mr. Wednesday's cons in American Gods was pretending to be a helpless old man completely befuddled by modern gadgetry.
Shadow: By my count, that young lady just paid you twice for the privilege of having you at her gas station.
- Warrior Cats:
- Graypool has something like dementia: she gets confused frequently, getting the past and present mixed up. She tragically meets her death this way: she wanders off alone, thinking she's going to a Gathering, confuses Tigerstar for the long-dead father of her adopted kits, Oakheart, and reveals the secret that the kits are from ThunderClan. Tigerstar gets impatient with her, and, flustered, she steps backward, loses her balance, and falls down a slope, hitting her head.
- Played for Drama with Bluestar. During her last life she turned into this mainly due to Sanity Slippage caused by her deputy Tigerclaw betraying her. Bluestar couldn't focus and would get the past mixed up with the present, amongst other issues. Word of God is that she suffered from dementia. Bluestar wasn't even that old when she started becoming scatterbrained; she wasn't even seven years old.
- Holden's unseen grandmother in The Catcher in the Rye is senile. She sends him birthday money multiple times a year.
- Madam Secretary: After Air Force One goes missing with the President and Speaker of the House on board, and the Vice President is out sick, an elderly Senator is called in to swear in as president. However, a comment he makes reveals that he believes Ronald Reagan is still president, forcing Elizabeth to become president.
- An episode of The Dumping Ground has Gina, one of the care workers, bring her elderly mother, Hattie, to Elm Tree House after Hattie's carer is taken ill. As the episode progresses, it becomes evident that Hattie requires care because she has Alzheimer's. For instance, she mistakes Faith (one of the young people) for Gina, fails to recognise Tee (another of the young people), who ends up having to keep re-introducing herself, and forgets repeatedly that she has been brought to Elm Tree House.
- House of Cards (US):
- Donald Blythe's wife suffers from Alzheimer's disease. Frank uses this to his advantage to aid getting him to support a budget bill.
- In Season 3, a Supreme Court Justice comes to the President and quietly admits to being diagnosed with Alzheimer's, requesting retirement. He's encouraged to remain on the bench because it would be politically inconvenient. He has an episode of losing his train of thought during a public legal proceeding, and forgets the name of a long-time colleague. Later, because the wind has shifted, the Pres. needs him off the court but he refuses to quit, confounding the Commander in Chief's schemes.
- Jimmy Cavanaugh in Orange Is the New Black. She ends up breaking her arm when she mistakes the chapel altar for a diving board, and is later given compassionate release. Considering the state of the social net in the modern day United States plus the fact she is a convict, it's pretty much a death sentence for her.
- In Law & Order, Det. Ed Green's dad is mentioned as having Alzheimer's.
- Star Trek: The Original Series episode "The Deadly Years". As a result of exposure to radiation from a comet Captain Kirk and several other Enterprise officers undergo Rapid Aging. Captain Kirk is shown forgetting things several times, including several orders he had given, that he had signed a fuel consumption report and that the Romulans had broken Code 2.
- In the premiere of NCIS: New Orleans a former NCIS agent is murdered causing Pride and Gibbs to reinvestigate a case all of them worked on together decades ago. Only one other member of that team is still alive so they go to visit him to see if he can give them any insight into what really happened back then. However, the guy suffers from Alzheimer's and while he remembers Pride and Gibbs, he quickly forgets why they are visiting and cannot provide them with any useful information.
- In Unforgettable Carrie has a Photographic Memory. The Ironic Twist is that her mother is in a nursing home and due to Alzheimer's doesn't remember Carrie.
- Nash Bridges has a rare instance of this afflicting a regular character: Nash's father Nick (James Gammon).
- Cougar Town plays this distinctly not for laughs. Late in season four, Jules takes her father to the doctor for what she thinks is an overdue physical only to discover he'd already gone the previous month and forgot about it. It turns out he's stricken with Alzheimer's.
- Geriatric issues show up several times on Scrubs, naturally. There's Johnny, the tackling Alzheimer's patient, Pickles (an old man who only says "Pickles!"), and more.
- An Emmy Bait episode of The West Wing sent C.J. Cregg home to visit with her father, whose struggling with Alzheimer's. Notable in that it depicts and describes the condition accurately. Also, it's heartbreaking.
- One season saw a running sub-plot of a Justice on the Supreme Court writing opinions in verse. Eventually it becomes clear that he's having episodes where his faculties are failing, but "On my good days, I'm better than anyone you could hope to get on the bench", and refuses to step down.
- Shows up on two different occasions on Lost Girl
- A second-season episode is built around the purchase of a weapon of mass destruction, however the weapon is a geriatric grandma... her trigger is taking away her portable TV, then telling her your enemies are responsible.
- A third-season episode sends Bo back to her childhood home for some Epiphany Therapy with her sex-hating mother, only for her to find a sweet old widow who barely remembers that Bo even left, let alone why.
- An episode of Psych has Shawn investigating two related crimes committed some thirty years apart, motivated to help his father's former partner, now rather lost to Alzheimer's.
- An early episode of Eureka involves a long-forgotten relic of the Cold War, and Carter has to hunt down the guy who invented it. Then he has to find a way to get the guy's noodle back in order.
- Played very darkly (naturally), in the Torchwood episode "Out of Time". A biplane containing passengers from the 1950s gets displaced in time and ends up in the present. One passenger wants to track down his son, who would now be an elderly man. Turns out he's in a nursing home with Alzheimer's and while he can remember random bits of his past, he isn't nearly lucid enough to know what any of his memories mean and doesn't recognize his own father. Seeing his son in that state is what convinces him there's nothing left for him, and he is Driven to Suicide.
- One episode of Community had Pierce join a gang of seniors who kept being jerks to people, relying on their age to get away with it. One of their gags was pretending to be lost and senile so that random cops would take pity on them. This was subverted when one of them actually did have a serious lapse... while driving a car. Ultimately not played for laughs.
- Played for laughs with Pierce himself, who can't seem to remember anything past a week. At one point the group exploits his memory problems to convince him they didn't forgot his birthday. The last one didn't work out as well as they thought, though.
- In the later seasons of Stargate SG-1, it's discovered that the Goa'uld System Lord Yu is beginning to go senile, though his First Prime is doing his best to hide this fact and run the empire in his place. This is troubling to the heroes, because while Yu is just as evil and megalomaniacal as any other System Lord, he was at least rational and pragmatic compared to the outright psychosis of his fellows, and thus could be counted on for an Enemy Mine situation when it was necessary.
- Absolutely, positively not Played for Laughs in Black Mirror "Playtest". The protagonist of the episode, Cooper, lost his father to Alzheimers and succumbing to it himself (or even worse, losing his mother to it) is one of his deepest, most personal fears. The brain-altering horror game he was playtesting uses this against him and it completely shatters his mind, Room 101 style.
- Deus Salve O Rei: Queen Crisélia is going senile by the start of the story and beings suffering very random memory losses (such as forgetting that her daughter died a long time ago) and begins talking to herself. This is why in one of her lucid moments, she tells her grandson Afonso to succeed her when he returns from his expedition.
- Harper thinks this of Woods in Call of Duty: Black Ops II during the introductory scene. However, he is proven wrong seconds later, as the latter is still very with it.
- Rosine of Granblue Fantasy is often featured in events and is interacting with other younger characters. Sadly she has some mild dementia due to her age and often forgets Lyria and Vyrn's names. She mistakes Vaseraga for her husband in a Fate Episode due to some very thin similarities (i.e. a large man carrying a large scythe) even though the latter always wears a helmet.
- Old Reece from Grand Theft Auto: San Andreas is implied to be this, as Ryder mentions the former having 'popped his membrane years ago'. Indeed, he will talk to CJ in a manner that suggests he is mentally in the past.
- Michelle Walthers in Deus Ex: Human Revolution is this. Her mind is probably years ago in the past, as she insists to an adult Adam that he is only in his childhood (while thinking that the adult Adam is a food delivery driver). After completing her side-quest, if the player tries to press her for information about Adam's real parents after she discusses the White Helix labs, she will continue to forget the conversation, leaving the player no choice but to leave.
- Anju's grandmother appears to have this in The Legend of Zelda: Majora's Mask, as she thinks Link is her deceased son (or the mayor as a child if he's wearing Kafei's mask). However, reading her diary shows that she is quite lucid, and she only fakes it to avoid having to eat Anju's terrible cooking.
- The premise of Ether One is that you are using cutting-edge technology to embark on a Journey to the Center of the Mind of such a person. Through it, you learn some information about the patient's experiences with their failing mental facilities including that the patient could not remember why he was attending a funeral (for what turns out to be the patient's spouse, that the patient once struggled to make a music box work only to be told that it was actually a cushion, that the patient has suffered extremely unpleasant outbursts due to misplacing things and, finally, that the technology does not exist, and that you are the dementia-afflicted patient and that your experience is an internal struggle to sort out your own memories.
- In Persona 4, Hisano's husband was clearly suffering from some sort of dementia, probably Alzheimer's, before his death (even if the game never uses the word) to the point of forgetting who she was. She considered his passing a mercy and is still incredibly broken up by it when you meet her.
- Davan Macintire's father, Fred, is diagnosed with Alzheimer's several years into Something*Positive. He's still entirely lucid, but he does have the occasional foggy moment. For the most part, Fred just uses it as an excuse to play pranks on his kids.
- In The Tourettes Guy, Danny's ex-wife Shirlena has a grandpa with Alzheimer's who began taking his clothes off in a K-Mart one day. Danny found this story more hillarious than heartbreaking.
- In It Makes A Sound, the Other Voice in Deirdre's house, whose outbursts and activities consistently interrupt the broadcast of her amateur radio show, is heavily implied to have some form of dementia, especially judging by her attempt to speak into Deirdre's mic while she's away.
The Other Voice: "Who's there? I'm in the hole. Yes, I'm n-the sixteenth hole. If you can find, wined and dime it...*clapping noises* I am the hole-holy smokes..."
- The Proud Family: Suga Mama dates another senior citizen named Clarence. While her family assumes he is trying to take advantage of her, it is later revealed at the end of the episode that his memory is addled, and had been missing from home for awhile. The wedding they planned to have is called off, leaving Suga Mama heartbroken.
- Goldie Delicious from My Little Pony: Friendship Is Magic is a distant relative of the Apples; she is portrayed as an elderly woman that lives with dozens of cats in a dusty house filled with junk. It's never stated but she seems to fit perfectly within the symptoms of Diogenes syndrome.
- Granny Smith was at least a little senile in the early seasons, but she's mostly lucid nowadays due to Characterization Marches On.
- Hey Arnold! Arnold's Grandma is pretty much insane. This trope is played for laughs though, as her shenanigans are used for comedic effect. The only time she is shown to be normal is in flashbacks and in an episode with a rough heat wave droves everyone else crazy while driving her sane.
- One interpretation of Granddad's tall tales in The Boondocks is that he is suffering from the early stages of dementia.
- Played for Laughs in SpongeBob SquarePants with Mermaid Man, whose memory leaves much to be desired.
- Grandpa Dave is implied to have an early stage of this in the Arthur episode, "Grandpa Dave's Memory Album".
- The South Park episode "Cash for Gold" implies that grandpa Marvin Marsh has Alzheimer's.
- The Simpsons:
- Abraham "Grandpa" Simpson has a pretty heavily eroded mind. This can range from simple forgetfulness to being completely divorced from reality. He once kept two policemen occupied by claiming to be the Lindbergh baby and wanting his "fly-fly dada". When the police ask if he's trying to stall them, or if he's just senile, he admits it's "a little from Column A, a little from Column B". This is consistently played for laughs.
- Mr. Burns, Homer's elderly employer, dips his toe in and out of this trope. Sometimes he's quite clever and shrewd, but other times he seems unaware that it's not still the 19th Century, and he's never able to remember who Homer is, even after being reminded that "all the recent events of your life have revolved around him in some way." This is also played for laughs.
- Danger Mouse's superior Colonel K became this as this series went on. He can never remember how to end a transmission or gets transmission sign-offs confused.
Colonel K: Over and out? No, 127 to 5, last thing I heard.
- In season 4 of BoJack Horseman, BoJack's mother Beatrice has succumbed to dementia, which BoJack very reluctantly deals with since she wasn't the best mother to him. She confuses him for a maid named Henrietta and tends to get the past and present day mixed up. The episode "Time's Arrow" is a Whole Episode Flashback to her youth as shown through the lens of her now senile mind, with disturbing details like background characters' faces being completely blank and the letters on signs glitching and getting mixed up.