How the Brain Stores Memories | The Science Behind Memory Explained
IFLScience
0:00 The question of how memories are stored in the human brain is an age old puzzle.
0:04 With diseases that affect memory posing a huge threat to public health,
0:09 there is arguably a greater need than ever before to unlock
0:12 the secrets of how our brains hold on to information.
0:21 In the 1890s, Santiago Ramón y Cajal was the first
0:26 to suggest that synapses might be the key to memory function.
0:29 Cajal used a technique developed by Italian scientist,
0:33 Camillo Golgi to produce unbelievably detailed images of brain tissue.
0:37 Other experiments, including
0:39 those of Canadian-American neurosurgeon Wilder Penfield,
0:42 helped the next generation of scientists figure out
0:45 where in the brain to look for memory storage.
0:47 Penfield pioneered a new way of treating epilepsy,
0:50 where he would open up a patient's skull to expose their brains,
0:54 and while they were still awake, probe the brain with an electrode
0:58 to determine which tissues were causing the seizures.
1:01 Penfield noted that stimulating certain parts
1:03 of the brain triggered memories in his patients.
1:06 Eventually, there was one brain region that would come
1:09 to be thought of as the most linked to memory.
1:12 And to understand that, you have to know the story of patient H.M.
1:17 As a child, H.M.
1:18 was involved in an accident that caused him to experience seizures,
1:22 which became debilitating by his late 20s.
1:25 As a last resort, H.M.
1:26 underwent drastic surgery to remove part of his brain.
1:30 Whilst this procedure did manage to control his seizures,
1:33 there was one very notable side effect, amnesia.
1:36 Evocatively, H.M.
1:37 described his condition as like waking from a dream,
1:41 every day is alone in itself.
1:43 It turned out that the part of HM.’s
1:45 brain that had been removed included the hippocampus.
1:48 Buried deep inside the brain, this structure has since been considered
1:51 the cornerstones of learning and recollection.
1:54 And this discovery is all thanks to the legacy of patients like H.M.
1:58 We now know, however,
1:59 that no one part of the brain is responsible for everything to do with memory.
2:03 For example, a recent study revealed that the cerebellum
2:06 helps us store memories associated with strong emotions.
2:09 However, what all this still doesn't address is
2:11 how the memories are formed in the first place.
2:14 Synapses are the connections between neurons.
2:17 Information crosses the synapse through three main steps.
2:20 First, chemical neurotransmitters are released into a signed synaptic cleft.
2:24 These bind to receptors on the neuron at the opposite side of the cleft.
2:28 This binding triggers the opening of ion channels,
2:31 which are what allows electrical current to flow.
2:33 One theory of memory holds that persistent changes in the strength
2:37 of these connections over time allow the brain to store information.
2:40 When this effect happens in a long lasting way,
2:43 it is called long term potentiation, also known as LTP.
2:47 LTP can be achieved either when
2:49 there are more neurotransmitter molecules released,
2:51 or when there are more receptors available for them to bind to.
2:55 Either way, more electrical current is going to get
2:58 through the ion channels making the synaptic connections stronger.
3:01 Over the years, however,
3:03 many scientists have suggested that whilst LTP is involved in memory formation,
3:08 memory engrams are necessary for long term storage.
3:11 Memory engrams were thought to have been a collection of cells
3:15 that have undergone lasting chemical or physical changes and which,
3:19 when reactivated, allow for the recall of a specific memory.
3:23 A series of studies provided compelling evidence
3:26 for the existence of so-called silent engrams.
3:29 The researchers were able to artificially retrieve memories of events
3:33 that were stored in the brains of mice with retrograde amnesia.
3:36 One of the main conclusions of the study was that a specific
3:39 memory is stored in a specific
3:41 pattern of connectivity between engram cell assembles,
3:44 that lie along an anatomical pathway.
3:47 And in 2021, a brand new theory arose
3:50 in which the human brain was likened to a computer.
3:53 It's called meshCODE,
3:54 and this computer like machinery works like biological code,
3:57 where an array of biological switches alter
4:00 the structural states of protein called talin.
4:02 In this biological code,
4:04 the talin is equivalent to the ones and zeros of digital code.
4:08 When we spoke to scientist Ben Goult about this theory he said,
4:20 The one state is approximately ten times longer than the zero state.
4:23 Since one talin molecule has 13 switches along its length.
4:27 This means that the protein could theoretically
4:29 be stretched out to nearly one micron.
4:31 This idea has led to further work on the potential role of talin,
4:35 plus other proteins that form the eponymous
4:38 meshwork of proteins at each synapse.
4:40 The work has led to some intriguing
4:42 theories about memory loss in diseases like Alzheimer's,
4:45 and back in 2018, scientists achieved
4:49 something that still sounds unbelievable today.
4:52 They transplanted memories from one snail into another.
4:56 By injecting snails with RNA from other snails that had
4:59 been sensitized was enough to make them exhibit the same behavior.
5:03 The study also proposed that long term
5:05 memory may not be held in synaptic connections,
5:07 but was rather encoded in a series of modifications to an animal's DNA,
5:12 known as epigenetic alterations.
5:14 The results of the snail experiment certainly seem to support this view.
5:18 The author was quoted saying, “If memories were stored at synapses,
5:21 there is no way our experiment would have worked”.
5:23 But as well as trying to understand exactly how memories work,
5:27 many also ask the question as to whether there
5:30 is a finite number of memories one can hold.
5:32 Another thing brains and computers have in common is memory storage.
5:36 In fact, there are theories about how our brains store
5:39 memories that look more like a computer than modern computers do.
5:42 One widely cited estimate for memory storage was published in 2015.
5:47 Using synaptic strength as a proxy for information storage,
5:50 scientists calculated that the brain can store
5:52 4.7 bits of information at each synapse,
5:55 whilst another study put the total capacity
5:58 at somewhere between 4.1 and 4.59 bits.
6:02 However, the approximately 86 billion neurons in the brain
6:05 are not enough to fully explain its memory capacity,
6:08 so therefore there must be some other cells doing some of the work.
6:12 And whilst the brain's capacity is technically finite,
6:14 its size is so great that it's functionally infinite.
6:17 Our memory is meant to be adaptable and fluid.
6:20 We are evolutionarily adapted to make
6:22 distinctions of what's important and what's unimportant,
6:24 and we lose track of what's important and unimportant,
6:27 that's the decline of memory.
6:29 Our memories evolved to optimize us for an early Homo sapien,
6:33 hunter gatherer lifestyle.
6:35 In that ancient environment,
6:36 it was vital to our survival to recognize recurring patterns,
6:40 to correctly separate friends from foes within the natural world.
6:44 But in modern life, we’re exposed to so much more information on a minute
6:48 by minute basis than our ancestors would have ever had to cope with.
6:52 And it may be becoming more than our memories can handle.
6:55 Clinical associate professor of life Science
6:57 at New York University, Nikolay Kukushkin,
7:00 believes it's not a lack of absolute capacity that's the problem.
7:03 Rather, it's the rate at which our modern information ecosystem
7:07 requires us to overwrite our old memories with new ones,
7:11 That means things like our 24 hour rolling news
7:14 cycle and constant doomscrolling through short form social media content.
7:18 Kukushkin would like to see more of a focus on what he terms mental hygiene,
7:23 Where people would be is mindful about what they're exposing
7:26 their brains to as the food they're putting into their bodies.
7:29 Overall though, this is an exciting time in the field of memory research.
7:33 Modern technological advances mean that theories and ideas
7:36 that have been postulated since the earliest
7:39 days of neuroscience can now be tested
7:41 experimentally in ways have not been possible before.
7:44 Much of the functioning of the human brain remains elusive, however,
7:48 as long as there are new theories being proposed and older ones remembered,
7:52 we will continue to edge towards a greater
7:55 understanding of our minds and of ourselves.
7:58 Thank you for watching IFLScience.
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