1 00:00:02,040 --> 00:00:09,760 Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, I'm 2 00:00:09,800 --> 00:00:12,920 Speaker 1: Christian Sager, and welcome to brain stuff. A lot of 3 00:00:12,960 --> 00:00:16,560 Speaker 1: things are easy to remember. My high school graduation, for instance, 4 00:00:16,680 --> 00:00:19,160 Speaker 1: or my first summer job, or that time I got 5 00:00:19,239 --> 00:00:21,720 Speaker 1: arrested for emptying a bunch of jello packets into Brian 6 00:00:21,840 --> 00:00:25,080 Speaker 1: Kranston's gas tank. It's it's a long story, but it 7 00:00:25,120 --> 00:00:28,360 Speaker 1: doesn't take a scientist to notice that adults don't generally 8 00:00:28,440 --> 00:00:32,240 Speaker 1: remember things that happened before the age of about three 9 00:00:32,479 --> 00:00:36,599 Speaker 1: or four. Why is that, well, why can't we remember 10 00:00:36,640 --> 00:00:41,040 Speaker 1: the earliest events in our lives up to an including birth. Okay, 11 00:00:41,080 --> 00:00:44,000 Speaker 1: here's an experiment. Try to remember what happened the last 12 00:00:44,000 --> 00:00:46,720 Speaker 1: time you ate a burrito? Where were you? Who was 13 00:00:46,760 --> 00:00:50,120 Speaker 1: with you? Was the burrito full of spiders? These kind 14 00:00:50,159 --> 00:00:53,280 Speaker 1: of memories, being able to recall details of a particular 15 00:00:53,320 --> 00:00:57,240 Speaker 1: event in the past, are called episodic memories. A person 16 00:00:57,280 --> 00:01:00,800 Speaker 1: at age sixty will usually have some episode memories from 17 00:01:00,840 --> 00:01:03,880 Speaker 1: age thirty. She might not get all the details right, 18 00:01:04,160 --> 00:01:06,440 Speaker 1: but she will be able to recall some events and 19 00:01:06,480 --> 00:01:09,520 Speaker 1: explain what happened. But if you take that same person 20 00:01:09,560 --> 00:01:12,120 Speaker 1: at age thirty and ask her to describe something that 21 00:01:12,200 --> 00:01:14,800 Speaker 1: happened to her during her first year of life. You'll 22 00:01:14,840 --> 00:01:18,440 Speaker 1: typically get nothing at all. Sigmund Freud referred to this 23 00:01:18,480 --> 00:01:23,560 Speaker 1: whole in our memory as childhood amnesia or infantile amnesia. 24 00:01:23,800 --> 00:01:26,840 Speaker 1: Freud being Freud explained it by saying we needed to 25 00:01:26,880 --> 00:01:30,839 Speaker 1: repress memories from infancy because of their inappropriate or traumatic 26 00:01:30,880 --> 00:01:34,720 Speaker 1: sexual content. But sometimes a blank is just a blank, 27 00:01:35,120 --> 00:01:38,000 Speaker 1: and contemporary scientists don't tend to throw in with Freud 28 00:01:38,040 --> 00:01:41,600 Speaker 1: on this one. Another hypothesis that used to be popular 29 00:01:41,880 --> 00:01:45,600 Speaker 1: says that babies can't form episodic memories until they develop 30 00:01:45,680 --> 00:01:50,320 Speaker 1: certain cognitive capacities, like language. But there's a major problem 31 00:01:50,360 --> 00:01:54,280 Speaker 1: with the language based hypothesis. Experiments have shown that animals 32 00:01:54,320 --> 00:01:59,840 Speaker 1: like mice also display both long term memory and infantile amnesia. 33 00:02:00,000 --> 00:02:03,680 Speaker 1: Since childhood amnesia across his species lines, it is probably 34 00:02:03,720 --> 00:02:07,720 Speaker 1: something to do with brain biology rather than language. One 35 00:02:07,800 --> 00:02:11,160 Speaker 1: possible answer would be to say that baby brains simply 36 00:02:11,320 --> 00:02:14,760 Speaker 1: can't make memories. It's true that memory and coding isn't 37 00:02:14,800 --> 00:02:17,320 Speaker 1: as efficient in infant brains as it is in the 38 00:02:17,400 --> 00:02:21,960 Speaker 1: brains of older children or adults, possibly because the prefrontal 39 00:02:22,040 --> 00:02:26,240 Speaker 1: cortex of a baby's brain hasn't reached maturity yet, but 40 00:02:26,400 --> 00:02:29,480 Speaker 1: recent studies have shown that very young children can form 41 00:02:29,639 --> 00:02:32,680 Speaker 1: some memories, leading scientists to think it's not that we 42 00:02:32,760 --> 00:02:35,560 Speaker 1: don't make memories early in life, but that after a 43 00:02:35,600 --> 00:02:39,320 Speaker 1: certain point we can't access them. The memories are made, 44 00:02:39,360 --> 00:02:42,720 Speaker 1: but something happens to them they get erased or put 45 00:02:42,760 --> 00:02:47,160 Speaker 1: behind some kind of memory blockade. Patricia Bauer and Marina 46 00:02:47,240 --> 00:02:51,000 Speaker 1: Larkina of Emory University have led research on this hypothesis. 47 00:02:51,320 --> 00:02:55,320 Speaker 1: For example, in one study, researchers recorded children at age 48 00:02:55,440 --> 00:02:58,320 Speaker 1: three describing a recent event, like a trip to a 49 00:02:58,400 --> 00:03:01,880 Speaker 1: theme park. Years later, the researchers followed up with these 50 00:03:01,880 --> 00:03:04,600 Speaker 1: same children to see how much they remembered, and at 51 00:03:04,680 --> 00:03:08,320 Speaker 1: ages five, six, and seven, the children could recall more 52 00:03:08,320 --> 00:03:11,839 Speaker 1: than sixty of the earlier events, but by ages eight 53 00:03:11,880 --> 00:03:16,040 Speaker 1: and nine, their recall was less than More research of 54 00:03:16,080 --> 00:03:18,680 Speaker 1: this kind is needed, but this looks like watching the 55 00:03:18,720 --> 00:03:23,280 Speaker 1: onset of childhood amnesia as it happens. Another recent study 56 00:03:23,320 --> 00:03:27,280 Speaker 1: has considered the role of neurogenesis in the hippocampus. The 57 00:03:27,360 --> 00:03:29,960 Speaker 1: hippocampus is a part of the brain that's crucial for 58 00:03:30,080 --> 00:03:33,800 Speaker 1: creating and storing episodic memories. If you don't have either 59 00:03:33,880 --> 00:03:36,480 Speaker 1: of your hippocampy, you could end up like that guy 60 00:03:36,480 --> 00:03:42,160 Speaker 1: in Memento, unable to make new episodic memories. Neuroscientists Shina 61 00:03:42,280 --> 00:03:46,320 Speaker 1: Jocelyn and Paul Franklin have proposed a theory that childhood 62 00:03:46,360 --> 00:03:50,440 Speaker 1: amnesia happens because of rapid formation of new cells in 63 00:03:50,440 --> 00:03:53,800 Speaker 1: the hippocampus when children are young. This is known as 64 00:03:53,920 --> 00:03:59,320 Speaker 1: hippocampal neurogenesis. Basically, while your brain is manufacturing lots of 65 00:03:59,360 --> 00:04:01,560 Speaker 1: the cells you will use to make memories for the 66 00:04:01,560 --> 00:04:04,680 Speaker 1: rest of your life, it wipes away or obscures the 67 00:04:04,720 --> 00:04:12,920 Speaker 1: memories you already created as a young child. Check out 68 00:04:12,960 --> 00:04:15,120 Speaker 1: the brainstuff channel on YouTube, and for more on this 69 00:04:15,280 --> 00:04:31,920 Speaker 1: and thousands of other topics, visit how stuff works dot com.