(CNN) When he first sees me, Sandy Halperin always gives a surprised snort and then a cackle of delight. Before I know it, I'm enveloped in a bear hug, snuggled close and patted heartily on the back. If I'm lucky and Sandy remembers that he really likes me, I'll get a back scratch too, a true Halperin hug.

"What a treat," Sandy says to me with a huge smile each time I visit, throwing his arm across my shoulders and inviting me for a stroll. His ready answer to my question "How are you feeling?" is, unfortunately, heartbreakingly familiar as well.

"I feel my decline more rapidly right now," Sandy has said many times. "Just like a confusion as the day goes on or times when I don't even have thoughts -- I'm awake, but ... what was the question?"

Sandy Halperin was a teacher and practicing prosthodontist at Harvard University in 1979. In this photo he is working on his father, Leon's, teeth.

In 2010, at the tragically young age of 60, Alexander "Sandy" Halperin, a former dentist and Harvard assistant professor, father of two and grandfather of three, was diagnosed with early-onset Alzheimer's. For the past five years, at Sandy's request, my CNN crew and I have been documenting his mental journey into twilight. His goal: to erase the stigma and shame that come with a diagnosis of dementia and to educate the world on how to best care for the growing numbers of people living with cognitive decline.

"I'm not 'Sandy Dementia'; I'm Sandy the person I always was," he has said with passion, arms waving wide. "I'm not missing a limb, but I've got a defect. But it doesn't mean I can't live my life to its fullest with that defect. So, as I decline, please treat me for who I am."

What is happening to Sandy is being repeated around the globe in the lives of the more than 47 million people living with Alzheimer's and other forms of dementia; over 5.5 million of those are Americans, including about 200,000 under the age of 65. Worldwide, the total number of people living with dementia is expected to rise to 131.5 million by midcentury.

It's a frightening reality that Microsoft co-founder Bill Gates is determined to change. He's investing $50 million of his own money to support cutting-edge research at the Dementia Discovery Fund, in the hope that an innovative approach to curing dementia will strike gold.

It was Sandy who was on my mind when I sat down with Gates recently.

"Any type of treatment would be a huge advance ... from where we are today," Gates told me. "The long-term goal has got to be cure."

Will those currently living with dementia, like Sandy Halperin, benefit from that research? We can only hope. But while we wait for that big breakthrough, Sandy's story is a powerful tale of what we can do now to help those living with Alzheimer's and their caregivers.

Sandy Halperin tells Dr. Sanjay Gupta that dementia is a "whirling-like confusion" with a sensation of cotton stuffed into the front of his brain.

'There's cotton stuffed in there'

It's a typical tropical afternoon on one of my first visits in 2013 with Sandy and his wife, Gail, at their retirement home in Tallahassee, Florida. Sandy and I swat bugs as we walk and talk.

"Are you suffering?" I ask. "Yeah, I'm suffering a lot," Sandy answers, stopping and gesturing to his forehead. "I often feel in the front of my head that there's cotton stuffed in there, and this whirling-like confusion with that sensation in the brain."

As a neurosurgeon, I'm fascinated by his description. I ask him to balance on his toes and then his heels, which he does with ease. "Neurologically, your balance is good," I tell him. "Does it hurt?"

"No," says Sandy, "It's just like a pressure feeling."

Like many people with early-stage Alzheimer's, Sandy looks fine physically. He even acts fine, joking and laughing and carrying on a normal conversation until, suddenly, he doesn't.

"I just lost my train of thought there, but ... um, I lost my ... where I was."

But tell Sandy he seems the same, like so many people do, and you ignite a smoldering flame of indignation, and not just for himself.

"They're going to say he doesn't have Alzheimer's, that because he's talking to me, he has a brain," says Sandy, voice rising. "Well, that's not right! People who have a cognitive impairment, have Alzheimer's, they can still think! They can still have feelings! They can still express themselves!"

Pharmacist Leon Halperin, Sandy's father, died of Alzheimer's in 1998.

'They don't want people to know'

For Sandy, eliminating the stereotypical image of dementia as an elderly person shuffling around in robe and slippers, unbathed, with stringy hair, is critical to bringing attention -- and critically needed funding -- to dementia research and caregiving efforts. Dismissing Alzheimer's as an "old person's" disease, he says, is a huge reason why the American government is spending only $1.4 billion on Alzheimer's research this year, compared with $6 billion for cancer, $3 billion on HIV/AIDS and $2 billion for heart disease.

Sandy also believes that stigma is the reason so many people, young and old, hide their early symptoms and forfeit the medications and treatments that might help them slow the disease progression.

"A lot of individuals don't go see a health care provider out of the stigma of the disease. They don't go for years," he told me in the past. "I see it. They're in denial. Their spouse has covered for them. They whisper in their ear. They help them. They don't want people to know."

In 2013, Sandy visited Washington to lobby for increased funding for Alzheimer's research.

Since his diagnosis, Sandy has advocated across the country on behalf of what he calls Care and Cure for Alzheimer's. Among his many accomplishments: serving on the early-stage advisory group for the Alzheimer's Association, traveling to Washington to lobby Congress for funding and giving a call to action speech on caregiving at the National Alzheimer's Project Act Advisory Council.

"I cannot look into the eyes of any other person with dementia -- never one -- and tell them everything possible is being done to enhance their lives," he told the council members. "Now is the time to act."

In his home state of Florida, one of the hardest-hit by Alzheimer's, Sandy has co-founded two early-stage support groups; hosted a fundraiser starring Peter Yarrow of the folk music trio Peter, Paul and Mary; and helped the state of Florida establish a Dementia Care and Cure Initiative. One of its first actions was to designate Tallahassee, where Sandy lives, as the first Dementia Caring Community in Florida, pledging money and services to help those living with cognitive impairment and their caregivers.

"CNN world, you're listening to me right now. ... Help!" Sandy said to our camera one day. "What are you going to do if you're a legislator, physician, plumber, educator? ... It's not about me, Sandy Halperin, it's about the Alzheimer's effort."

His wife of 43 years, Gail, and his youngest daughter, Lauren Halperin Crawford, credit Sandy's joie de vivre to his zeal for advocacy and believe that anyone facing a diagnosis of dementia should fight back by finding their own passion.

"Advocacy got him up and going and with a purpose," Gail has said. "So yes, it's helping him. It's giving him a life."

"It's just so powerful to me, the fact that he has this attitude," said Lauren, wiping a tear from her eye. "He's like, 'You may be in me, but you are not going to take me down.' I am so grateful for that."

In honor of all his work on behalf of those living with dementia, in 2016, Sandy was given the prestigious Proxmire Award at the Great Minds Gala , joining the ranks of such greats as musician Glen Campbell and former Supreme Court Justice Sandra Day O'Connor. (The committee was kind enough to bestow the award on me and my CNN team as well.)

Sandy Halperin says that, at times, his memory loss causes emotional pain. "All we really are is our thoughts."

But as the years have progressed, so has the disease that is claiming Sandy's mind, and he is finding it harder and harder to do the advocacy he loves.

"I want to do all that I can do on the advocacy side, but I have to determine where at this point with my abilities -- what I can do, " Sandy told me. "It doesn't feel good when you don't know how to -- when you can't finish a sentence. Do I feel that I've helped make an impact? Yes. Is that enough? No. But I have to pass the baton. Right now, it's time for me to do it part-time."

It's not just his memory that is changing, he tells me. He's not as social as he was, not as patient. He gets agitated more easily. He will fixate on what he forgets and fret about it until he remembers or gives up in frustration. He fights back against those feelings by trying his best to live in the moment.

Sandy Halperin with daughters Karen, left, 4, and Lauren, 2, at their home in Needham, Massachusetts, in 1984.

A fresh feast of memories

One of the most enjoyable ways he can do that is spend time with his older daughter, Karen Halperin Cyphers, and his precious grandchildren, Madeline, 7, Rebecca, 8, and Emma, 22, who live close by.

"He keeps saying, 'Do you think my grandkids will remember me? Are they old enough where they're going to remember me?' " Karen shared on one of our early visits.

"Our brains are our being," explained Sandy. "And when you lose your memory, the pain is a different pain. The pain is the emotional pain. And maybe that's why I wrote the grandpa books early, when I could get my thoughts down on paper for my children and my grandchildren as to how I felt about things."

Grandpa or "G-Paw" books, as Sandy calls them, are, in my mind, one of his most brilliant accomplishments. Filled with old pictures, mementos (an excised tooth represents his time as a dentist), his unique recipes for peanut butter and jelly sandwiches (he actually adds ham, cheese or salami), his musings on life and his memories of the girls as babies, Sandy's G-Paw scrapbooks paint an undeniable portrait of a caring and quirky father.

"They talk about formative years. I can only hope that all the love that I have for them will maybe make an impact on their lives from their grandpa," said Sandy wistfully.

But the books feed more than a child's memories. As his disease progresses, turning each page gives Sandy a fresh feast of past experiences.

"Seeing him remember is, like, the best," said Lauren with a chuckle. "When he goes 'ah' and he gets it, it's like, YES! Tiny little victories of remembering."

Sandy walks daughter Lauren down the aisle in September 2015. "I feel so happy that we get to do this ... major thing on his bucket list," she said.

The ultimate bucket list moment

Lauren was only 28 when Sandy was diagnosed with Alzheimer's and not yet engaged to her now-husband, Jacob. But she knew how important it was to her father to be able to attend -- and remember -- her special moment, that bucket list moment.

"You don't know how fast things are going to progress. You don't know how healthy he will be," Lauren said when she told me of their wedding plans for September 2015. "I feel so happy that this major thing on his bucket list is going to be a reality. It's like just the most enormous relief."

At elder daughter Karen's wedding in 2008, Sandy gave an extemporaneous toast. For Lauren's wedding, Sandy spent weeks writing and rewriting his speech and brought his notes with him to the reception. It's a perfect Sandy delivery, full of wit, wisdom and laughter, when he noticed something was wrong.

"What? Did I miss something? Oh, I missed an entire page," he said and turned to the packed room with a sheepish grin as everyone burst into laughter.

Sandy and Lauren dance at her reception to one of their favorite songs: "It's a Wonderful World" by Louis Armstrong. "Honestly, I have known since I was 5 what song I'm going to have with my first dance with my dad to," said Lauren.

"The thing I'm most grateful for," Lauren said, "is that even though he struggles with his memory, he gets confused, he can't follow stories or direction, he is still so deeply who he is. His personality, his instinct, his humor, his wit -- all of that is so wonderful, and it's remained."

The story continues ...

It's just over two years since Lauren and Jacob were married, and Sandy has moved to a new stage in his disease. He's had to give up all his advocacy; the tiny victories of remembering are fewer now.

Today, instead of describing the congested feeling in the front of his brain as "cotton," he says it just feels empty.

"I feel ... It just happened right now. I just feel, um ... I totally lost what I was saying," he says. "It's just like a blank."

Daughter Karen and family have moved less than a mile away, and she sees Sandy almost daily.

"We've been dealing with a more negative Dad that we are used to seeing, for sure," Karen says. "The ruminating has gotten worse, and he obsesses over thoughts. It's like his brain can't now choose to filter out the negative thinking the way it used to."

Part of his decline may well be due to chronic pain. Longstanding back and leg pain was partially addressed by a hip-replacement surgery in early 2016, but more surgery is not an option, and wife Gail worries about the future.

"The hip surgery helped a lot, but he is still constantly rubbing his left leg," says Gail. "I think he's getting worse again. He limps a little, shuffles a lot. He has all his other health problems, and he constantly says he's too weak to do anything and in too much pain."

"Even when he's in pain, in the past, my dad normally wouldn't talk about it," agrees Lauren. "So the fact that he's so vocal speaks to the level of pain he is in. And I feel that when his pain is really intense, it affects not only his memory but his ability to cope with stuff."

Lauren's right. Even without Alzheimer's, physical pain can affect your mind and make it increasingly difficult to form thoughts. For Sandy, it's clear his pain is slowly but steadily accelerating the rate of his decline.

Sandy snuggles with granddaughter Maggie during a birthday party in 2013.

Still, when he's distracted, the old Sandy comes back. For that, he can thank his precious granddaughters.

"He's lost a lot of motivation to get out of the house or talk to people, but when the girls come around, it gives him a spark of life," says Lauren. "Nothing else that I can think of does that for him right now.

"He just gets so silly, mindlessly silly with them, and they love it. He has this little lamp outside that he will dress up like a person, with goggles and a hat," Lauren says with a chuckle. "Every time the kids come over, he'll add something else, and they have to figure out what's new about the 'lamp guy.' It's almost like his subconscious creativity is still there, pouring out."

Sandy teases older daughter Karen in 2013. "His personality, his instinct, his humor, his wit -- all of that is so wonderful, and it's remained," said younger daughter Lauren.

Dementia, and chronic pain, may be slowing Sandy down, but they have not taken him away from us -- yet.

"The diagnosis doesn't mean tomorrow you are no longer who you are," Lauren has told me. "There is still so much life to live, and there is so much happiness and joy he still experiences."

"We're all terminal," Sandy puts it. "I may pass faster, but I have to live my life for now. So I want people to know there's still a good life for anyone with a diagnosis with dementia. That's what they have to know: There's a quality of life they can still have."