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products at Amazon and

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other book retailers today. This

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is a science podcast for March 15, 2024. I'm

1:22

Sarah Crespi. We have two

1:24

neuroscience stories this week. First up,

1:26

freelancer Sarah Reardon asks, why do

1:28

infants' memories fade? We

1:30

discuss ongoing experiments that are looking

1:33

to pin down the hows and

1:35

whys of infantile amnesia. Next

1:37

on the show, more brain stuff. Researcher

1:40

Hue Kwan Lee is here to talk

1:42

about how the brain encodes generalized fear.

1:45

This is a symptom of some anxiety

1:47

disorders like social anxiety and

1:49

PTSD. I

1:56

think my earliest memory is from when

1:58

I was just about two, two years

2:00

old. I'm sitting or maybe walking on

2:02

this like mustardy brown carpet. Turns

2:05

out though that this is probably not a

2:07

real memory but something that I picked up

2:09

from photos or descriptions of the place I

2:12

was living right when my younger sister was

2:14

born. You know and actually if

2:16

I really think about it I just don't remember

2:18

anything in school at six.

2:21

So maybe like one or two back

2:23

there. This Week in Science freelance science

2:26

journalist Sarah Reardon wrote about this puzzle

2:28

of infantile amnesia. Why we

2:30

don't remember our babyhood. A time

2:33

when we are learning so much about

2:35

the world but we still don't

2:37

remember learning it. Hi Sarah welcome

2:39

back to the Science Podcast. Hi thanks for having

2:41

me. So are you gonna tell us

2:43

your earliest memory that you believe is actually

2:45

a memory? Yeah I think I remember our

2:48

family dog who died when I was

2:51

three but it could just be from

2:53

photos. I definitely remember the Gulf War.

2:56

Oh wow. So that's actually dateable

2:58

but I wasn't very old then I guess I

3:01

was five. Yeah it's

3:03

funny how little I remember

3:05

and I think some of it's kind of gone

3:07

away as I've gotten older but there's definitely a

3:10

huge chunk that's always been missing. And

3:12

so I guess the big question the story and

3:14

it definitely makes me think you know when our

3:17

brains are so busy devouring everything we're

3:19

learning to eat to move to see

3:21

to talk all this stuff we need

3:23

to remember to get on with our life. We

3:26

don't remember learning these things. What

3:28

are some of the explanations out there? What are

3:30

some of the ideas about why we do forget

3:32

this this key point in our lives? One

3:35

thing I learned from reporting that I thought

3:37

was really fun was that the first person

3:39

to really coin the term infantile amnesia and

3:42

study it in any sort of depth was

3:44

Sigmund Freud. And he of course thought that

3:46

it was because we had

3:48

this horrible psychosexual experience of being born

3:50

we needed to wipe that from our memories

3:52

or else we would be traumatized forever. And

3:55

the talk about in the story he wasn't

3:57

entirely wrong it's that to forget being born.

4:00

But there is a growing amount of evidence that

4:02

these memories are suppressed for some reason rather than

4:04

just not being formed in the first place So

4:07

now the question is how and why

4:09

and why does it matter? So it

4:12

could be possible that some of our

4:14

earliest experiences are housed somewhere in the

4:16

brain just archives But it's just not

4:19

accessible. Yes, that's the thinking What are

4:21

some other reasons that people besides Freud think

4:23

that we don't remember this part of our

4:25

lives? For a long time people

4:27

have just kind of dismissed this as well.

4:29

It's an immature brain babies just been born

4:32

It's not important that we remember

4:34

things and so these neurons

4:36

just aren't able to form these memories in the first

4:38

place or they form them for a little while then

4:40

they just get deleted to make room for other things

4:42

and That could be

4:44

true. And then the other hypothesis is that

4:46

they are formed and they're there forever But

4:49

are somehow suppressed to make room for

4:51

new memories I was really

4:54

surprised to learn from your story that

4:56

other mammals have infantile amnesia I guess

4:58

I just never really thought about whether a

5:00

kitten with me would remember or not remember

5:02

its earliest days So what does

5:04

that suggest about what's happening with us

5:07

if we're seeing these other mammals go through the

5:09

same thing? Yeah, yeah, and I've been one of

5:11

the things that people I thought for a long

5:13

time was that it was linked to language development

5:16

But until we could describe our experiences and

5:19

words, we weren't really remembering them But

5:21

so finding that mice and rats and

5:23

other sorts of mammals have this as

5:25

well kind of negated that theory But

5:27

it's really interesting one researcher found that

5:29

a few what they call precocial mammals

5:31

Which are mammals that are born with

5:33

their eyes open able to fend for

5:35

themselves right away guinea pigs are like

5:37

that They're not dependent on their mothers.

5:39

Really they can just fend for themselves.

5:41

They don't seem to have infantile amnesia

5:43

So maybe everything may learn they

5:45

don't have parents around that They

5:48

can just offload their care and

5:50

the need to remember things. So it's much

5:52

more important that they remember, you know where they

5:54

live or What is

5:56

a scary thing? But this brings up

5:58

an important point we're talking about a specific

6:00

type of memory. You know, we remember

6:02

how to talk, but we don't remember

6:04

what we're calling episodic memory, which

6:07

is what events are happening. So what

6:09

defines that? Episodic memory

6:11

is, it's been described to me as sort of the

6:13

what, where, when. I went to Disney

6:15

world when I was three years old and I met

6:17

Mickey Mouse. That would be an

6:19

episode that occurred in your life. And

6:21

it's a little hard to study that in animals

6:24

because they can't tell you where

6:26

and when. So instead researchers have been

6:28

looking at what they're calling contextual memories,

6:30

which are like, when I'm in this

6:32

box with a patterned floor, I

6:34

might get a shock if I step over here.

6:36

And that's sort of a proxy for

6:38

episodic memories that's being studied in mice.

6:41

One of the researchers who talked to us, I think

6:43

they were based in Berlin. They were working

6:45

with us on this question with

6:47

a big group of toddlers. What

6:50

are some of the questions they are trying to find out from

6:52

working with? I think it's like 300 toddlers. What

6:55

are the experiments like and what are they trying to

6:57

learn from this group? They're trying to study this

6:59

contextual memory again, rather than having them

7:02

recall episodes, which there's been a lot

7:04

of work on that, having people recall

7:06

early episodes in their life. And like you were

7:08

talking about earlier, you might be picking this up

7:11

from photos. So it's really hard to, uh, to

7:13

trust some of that data. So this

7:16

is the first prospective study where they

7:18

are giving toddlers these experiences and then

7:20

seeing what they remember months later. And

7:22

so they're having these kids learn

7:25

when they're in a certain room that's

7:27

got spaceships on the walls, for instance,

7:29

one of the boxes has a toy. If they're

7:31

in another room, it's a different box that has

7:34

a toy. And so the kids can learn that,

7:36

but they're not going to remember it very long.

7:38

And so they're repeatedly doing these tasks over the

7:40

course of months to see when did the kids

7:42

start actually being able to remember those cues and

7:45

that information. And the neat thing about this

7:47

experiment is it can be replicated exactly in mice.

7:49

So they're having mice do the same thing

7:51

with bits of food, and they're going to

7:53

be trying to figure out whether some of

7:55

the brain activity, some of the patterns, the

7:58

characteristics that they're observing in the kids are observable. When

8:00

miles and then they can say to a

8:02

more invasive things with the mice to try

8:04

and understand what's happening at the brain level

8:06

the when he can't with humans are we

8:08

able to then pinpoint when these toddlers. Can

8:11

suddenly start remembering when they go

8:13

into the space room. Those. Toys.

8:15

Gonna be in the specific box. There's still

8:17

early in the experiments for the think. right?

8:19

around twenty months is land. Sort of

8:22

switcher cursed from being able to. Not

8:24

remember anything to being able to remember things.

8:26

So I should add that they call infantile

8:28

amnesia up to about eighty three where you

8:31

really can't remember much of anything at all.

8:33

That between ages three and ten, they have

8:35

what is called childhood amnesia for their memories

8:37

are pretty spotty. Yeah, they're not very good

8:39

at separating memories. Lot of things tend to

8:42

run together and that is gradually improves. Over

8:44

the course of those years a super interesting.

8:47

Let's. Talk a little bit about that mouse experiments,

8:49

you know, As you say, To go a bit

8:51

further, for example, you talk to some. Folks that

8:53

use opto genetic such as. This

8:55

Saudis. Have very finely. Control Act Certain

8:57

are certain regions of the brain. What are

9:00

we learning from those? Types of experiments. Yes,

9:02

A. With the epigenetic experiments, what they're

9:04

able to do is figure out exactly

9:06

which neurons in the hippocampus to start.

9:09

A brain that processes memories. Which.

9:11

Neurons exact airing coating that memory

9:13

serves like a constellation. Of neurons is

9:15

a set of them that will connect the other

9:17

and fire together, and that's what forms memory. And

9:19

they call that an engram. Is the

9:21

weather able to do is to figure out when

9:23

the baby mouses first learning the task? Let's say

9:26

that the food is in. The. Box over here.

9:28

Which. Sells are firing at that moment

9:30

and they can label those cells with

9:33

a protein that banks the later activated.

9:35

And. So that city mouse ago about his. Business. it'll

9:37

forget how to do that as an adult.

9:40

It doesn't remember that either. But if the

9:42

researchers shine a light in the brain. These.

9:44

Light sensitive engram cells will fire and

9:46

that causes a mouse to suddenly recall

9:48

the memory. And know where the food as again. For.

9:52

That suggests that there is a way to

9:54

access it via I memory that was lost.

9:56

From infants amnesia are approximation

9:58

of that. Exact. It out.

10:00

It's a very artificial method. I

10:02

don't know that everyone's entirely convinced this

10:05

is. Evidence that this is what happens

10:07

in nature and that we are do all have

10:09

of these hidden and grams bad as is going

10:11

to. Take. Further research to sort out.

10:14

So. He tackled at about the role of

10:16

neurogenesis. Growing. Our brains, growing neurons

10:18

and our brain that it might have in

10:20

forgetting. So you know how would that work

10:23

at how that being tested if that's one

10:25

of several hypotheses for what's happening. And yet

10:27

is that these engram? So they're being formed

10:29

so like they're talking about earlier. It's not

10:31

that the brain can't form these memories that

10:34

can do it just fine, We just can't

10:36

access them. And so the idea here is

10:38

that forgetting. Whether. That's for getting

10:40

your childhood memories Are forgetting where you

10:42

left your car keys could just be

10:45

a function of. It Engram being

10:47

written over with the new engram with

10:49

neurons that the brain decides are more

10:51

important first one still there is just

10:53

not the one that's preferred. At

10:56

that point. Where. That comes in with

10:58

and somehow amnesia is that. What you're

11:00

saying earlier, the brain is growing. Really fast

11:02

learning all kinds of things. Lots and lots

11:04

of neuron growth that happening as well. And.

11:06

So once that starts to slow

11:08

down, maybe the brain is better

11:10

at keeping things rather than constantly

11:13

fighting over them. So. What

11:15

happens if you interfere with neurogenesis that

11:17

affects early memories in this particular experiment?

11:19

Ah yes, if they block neurogenesis than

11:21

they also seem to block and fantail

11:24

amnesia has a tried any other ways

11:26

to block the loss of memories from

11:28

baby mice. There's a few ways that

11:30

can be done. In one paper that

11:32

without and science advances last year found

11:35

that if the infects the mother mouth

11:37

when she's pregnant with a protein that

11:39

sort of mimics like a viral infection

11:41

d baby mice the males only for

11:43

some reason or. Less likely to have

11:46

infantile amnesia they seem be able.

11:48

To. For memory as much earlier, it's

11:50

not entirely clear why that is to

11:52

be that some immune cells in the

11:54

brain seem to be implicated. They might

11:57

be affecting how the brain is developing

11:59

Overall, Or how certain connection to be

12:01

informed tweener on. But. Lie that's

12:03

very early days still. The. Data suggests

12:05

that maybe there are some people that had

12:08

adverse effects on who were hurt real with

12:10

little or where they are in utero that

12:12

might actually have the super early memories. Yeah,

12:14

yet there is some sort parallel evidence that

12:17

as well that. In animals if you

12:19

separate them for their mothers friends since. Their

12:21

brains seem to mature earlier. And. Whether

12:23

or not that's a good thing, For the rest of

12:25

their lives we don't really know. Those animals seem

12:27

to have higher levels of anxiety and

12:30

we know in humans and so many

12:32

ways, those first. Years of life for

12:34

so crucial for forming your personality,

12:36

forming your. Mental abilities so kind

12:38

of makes sense that if that maturation

12:40

process is sped up or interfered with

12:43

in some ways that could be some

12:45

really lasting effects that are. Difficult.

12:47

If not impossible to reverse, Looking.

12:50

Across all these different experiments that you report

12:52

on, do you feel like they're getting closer

12:54

to the answer to the Why question? You

12:57

know, why might we not remember this stuff?

12:59

Here there's several varying ideas. The I think

13:01

the lot of them come down to. What

13:04

The brain Science important? It's

13:06

more important. At that stage in your life. And

13:08

unless you're a guinea. Pig on because you can

13:10

depend on your parents is more important at

13:12

that stage and your life to be learning

13:14

about the world in general. To be learning

13:16

what a cat is versus. Remembering I

13:19

live next door to this particular orange cat,

13:21

so you can forget about the orange cat.

13:23

but you remember the word for cat. You

13:25

remember what of things associated with it and

13:27

you could kind of. Focus. More

13:29

on finding patterns than having individual memory

13:31

is. I. Really like this idea that

13:34

you talk about here. sorry where. There.

13:36

Is it's kind of suits capacity in the

13:38

infant brain that we can't even conceive of

13:40

as adults exists as big differences in it.

13:42

And that might be one of the reasons

13:44

that we're not. We're not able to access

13:46

those memories. Infant. Brains go through a

13:48

number of what are called critical period. Example

13:51

I always think about is a learning a language

13:53

friends as we know the kids can learn a

13:55

language so much more easily than adults do as

13:57

because their brain is just very plastic can pick

13:59

up. all sorts of things and

14:01

that critical period, they say it closes

14:04

at a certain age and after that point

14:06

you really can't reopen it and

14:08

your brain will never be that plastic

14:10

and malleable again and memory formation seems

14:12

to be a similar thing where your

14:14

brain is going along picking up all sorts

14:17

of things, forming these memories in

14:19

a very different way than it will later

14:21

on in life and so there's a

14:23

lot of research into that as well

14:25

like what's happening during these critical periods

14:28

that's changing how the brain matures

14:30

and you were talking about like the experiences

14:32

too, there's some research finding

14:35

that depending on the experiences you have

14:37

during that critical period the brain

14:39

will mature faster or in different ways

14:41

than if you had a different set

14:44

of experiences so it really all comes

14:46

down to just how crucial those first

14:48

few years are. Infantile amnesia is an

14:50

interesting puzzle, definitely something that I could just

14:52

keep talking about for hours but can

14:55

we talk a little bit about how learning

14:57

the why of it, the how of it,

15:00

you know what can we do with that information to either

15:02

look at how adults forget or remember or

15:04

you know other things that we also care

15:06

about? There could be some

15:09

implications for early childhood learning

15:11

like preschool, daycare even, what's it worth

15:13

teaching children at this age? Should we

15:15

be teaching them music? Do you have

15:17

to be fighting to get them into

15:19

the best preschool? One researcher I talked to

15:21

said that she'd written a column for the

15:23

New York Times where for grandparents, so grandparents

15:25

were concerned that their grandchildren might not remember

15:27

them if they died too young so how

15:29

could they, how could you get your kids

15:31

to be able to remember their grandparents? But

15:34

there's this broader question too which is

15:36

very controversial over whether infantile amnesia this

15:39

kind of forgetting is similar to the

15:41

forgetting we do as adults and we talked

15:43

about the neurogenesis for instance and that whole

15:45

idea is very controversial but if it

15:47

is the same kind of forgetting we

15:49

might be able to understand that a

15:51

little bit better by studying this sort

15:53

of as a model. There's some evidence

15:55

for instance that during Alzheimer's of course

15:57

your brain gets all of these plaques.

16:00

that just completely tear up its integrity

16:02

and make it impossible to remember

16:04

anything. But even before those start

16:06

forming, people start forgetting things and

16:09

we're not entirely sure what's happening at that

16:11

point. If we do understand this better, we

16:13

might be able to start getting some clues

16:15

into whether those memories are still there and

16:17

just not accessible before the brain starts accumulating

16:19

all of this damage. Do you want

16:21

to say that there's a lot of different

16:23

hypotheses floating around and they're not

16:26

necessarily mutually exclusive. There could be

16:28

some neurogenesis going on at certain points. There could

16:30

be these critical periods opening and closing

16:32

in ways that we don't fully understand

16:35

just yet. But the fact

16:37

that we have these optogenetic techniques, we're

16:39

getting better at human brain imaging as

16:41

well with younger and younger children. We

16:43

might really start to be learning a lot more

16:46

about this and answering some of these questions over

16:48

the next few years. This really reminds me of

16:50

sleep research. You know, it's something that is omnipresent

16:52

in our lives and we just never think about

16:55

how like technical it is and what it's

16:57

doing and you know how important it is. We

17:00

just don't know. You know, there's just so much

17:02

there's so much to learn about. That's such

17:04

a basic piece of human biology. It's really interesting.

17:06

One of the researchers I barely quoted in here

17:08

is doing stuff on naps and whether kids who

17:11

give up naps at certain ages might have more

17:13

or less mature brains and might like it might

17:15

be more useful to teach them friendship if they

17:17

stop napping on their own. But only those kids

17:20

who've already stopped napping. That's so interesting. Yeah, it's

17:22

all very new but I thought it was really

17:24

interesting. Wow, that's really cool. I just remember being

17:26

forced to take naps and just reading under my

17:29

covers. That's my earliest memory. All

17:34

right, thank you so much Sarah for coming

17:36

on the show. Yeah, thanks for having me.

17:38

Sarah Reardon is a freelance science journalist. You

17:40

can find a link to the story we

17:42

discuss at science.org/podcast. Stay

17:45

tuned for a chat with researcher Hui

17:47

Kuan Li about how fear after acute

17:49

stress lingers in the brain. Researchers

17:59

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19:46

Generalized fear is a symptom in

19:48

some anxiety disorders, in panic disorder

19:51

or social anxiety or PTSD. Generalized

19:54

fear is basically reacting in a

19:56

fearful way to events or environments

19:58

that don't relate specifically. to

20:00

the original stressors from the past.

20:03

There are plenty of cues around suggesting that

20:05

there's no danger, but you still

20:07

feel afraid. This generalized fear can

20:10

cause stress and reduce quality of life. And

20:12

we don't know much about how to turn

20:14

it off, but we are learning

20:16

about how it might get turned on. This

20:19

week in science, Hui Quan Li and

20:21

colleagues wrote about changes in the brain

20:23

linked with the onset of generalized fear.

20:26

Hi, Hui Quan, welcome to the Science

20:28

Podcast. Hi, Sarah, thanks for having me

20:30

here. Sure, let's talk a little bit

20:33

about the work you did here. It

20:35

was in mice and also in some

20:37

post-mortem brains. So let's start with what's

20:40

happening with the mice. Going

20:42

into this work, you had an idea of

20:44

where in the brain the switch might

20:47

be happening, where generalized fear might

20:49

be starting, but not the specifics

20:51

of how this change occurs. In

20:54

order to get at those details, you looked

20:56

at mouse brains across a variety of conditions.

20:58

What were the different setups for the mice?

21:00

How were they set up to

21:02

experience generalized fear? We

21:05

used a mouse model and use

21:07

a foot shock as the stressor

21:09

to trigger fear in mice.

21:12

And we observed conditioned

21:15

fear and generalized fear

21:17

were produced after this foot

21:20

shock. In some cases, the

21:22

mouse would go into a space and get shocked,

21:25

and then it would never want to go back to that

21:27

specific spot. It would freeze. It would be afraid of going

21:29

back there. That's kind of the basic fear response, right? But

21:32

then generalized fear is something a little bit different in

21:34

a mouse? Exactly. In

21:37

the same environment, this type of

21:39

fear is called conditioned fear. But

21:41

generalized fear is that the mice

21:44

were put into a novel environment.

21:47

We have never been experiencing any

21:49

stress in those environment. But

21:51

these still show fearful response. As

21:54

you said, that is generalized fear. So

21:57

in the setup, you have one

21:59

condition. that gives you fear

22:01

specific to a specific environment. And then

22:04

you have another set up where

22:06

you get generalized fear, and that

22:08

means that the mice are afraid

22:10

in different environments, novel places. So

22:13

when you looked at the neurons in

22:15

this region that you knew was important to

22:18

generalized fear, how

22:20

is it different after generalized fear

22:22

had been induced in these mice? Tell

22:25

us about the brain region and the changes

22:27

that you saw there. We observed

22:30

neurotransmitter changes in

22:32

a brain region called dalsoraphate

22:34

that is in the midbrain.

22:37

And we observed that the

22:40

cell-to-nurgeous neurons in this region

22:43

changed their co-transmitter

22:46

from glutamate into GABA. Let's break

22:48

that down real quick. There

22:50

are basically co-transmitters, so there's two

22:52

kinds of neurotransmitters being released by

22:54

these neurons. Exactly. So

22:57

they have serotonin as their

22:59

major transmitter, and they

23:01

could release glutamate. And

23:04

when they were in the generalized fear condition, you saw

23:06

a switch for that co-transmitter from

23:08

glutamate to GABA, is that right? Yes. And

23:11

when we blocked the switch from

23:14

glutamate to GABA, we observed that

23:16

the generalized fear was blocked.

23:19

Yeah. So this was all in

23:21

mice. You were able to show this relationship

23:23

between the neurotransmitter expression

23:26

and generalized fear. What did you

23:28

see in the human postmortem tissue

23:31

that you were able to look

23:33

at? We observed a

23:35

similar increase in the

23:37

cell-to-numergeous neurons co-expressing GABA

23:39

synthesis in the

23:41

individuals of PTSD compared

23:45

to the control subjects,

23:48

similarly as what we have

23:50

found in mice. The

23:52

correlation and causality between

23:55

the neurotransmitter switch and

23:57

the generalized fear production.

24:00

was demonstrated in the mouse model.

24:02

In human, we have found this

24:04

correlation. The causality is hard to

24:06

be investigated. Yeah, because you have

24:09

to go deep into the midbrain,

24:11

find this very specific region of

24:13

neurons and say, oh, did

24:15

you change what neurotransmitter you're dealing with?

24:17

That's not easy to do in people

24:20

at all. Exactly.

24:22

Yeah. One of the things that you administer

24:25

to the mice to see if you could

24:27

block this progression to the different neurotransmitters, the

24:29

switch in this region of the brain

24:31

was Prozac. So that worked on the

24:33

mice, but there was somewhat of

24:35

a limitation on the timing. True. When

24:38

we provide Prozac immediately

24:41

after the foot shock, two

24:43

weeks later, the generalized fear

24:46

was gone, was not observed

24:48

for these mice. But

24:50

when we provided Prozac two

24:52

weeks after the foot shock,

24:54

when the fear response is

24:57

already produced, there was

24:59

no effect. So it's not reversing

25:01

the switch. It might prevent it from

25:03

happening. So you showed that there

25:05

is a switch in the neurotransmitters in this region of the

25:07

brain. What happens next? So what

25:10

are the downstream effects of these

25:12

neurotransmitters being different? You know,

25:14

how do we know that that might

25:16

translate into generalized fear? What are some

25:18

suspected mechanisms there? We have

25:20

identified two oral regions

25:23

downstream of atosorafate.

25:25

One of them is central

25:27

amygdala. The other one

25:29

is lateral hypothalamus.

25:31

So these two regions that

25:33

you found downstream, you did see changes

25:36

in their neurotransmitter setup, if you will.

25:39

What do we know about the central

25:41

amygdala and the lateral hypothalamus? You know,

25:43

are these regions associated with fear in

25:45

other settings? Yes, they

25:47

have been studied by other

25:49

researchers that they have a

25:51

role in fear,

25:53

regulation or anxiety

25:56

related behavior. So let's go

25:58

to the other end before we get to

26:00

the switch in neurotransmitters in the

26:02

dorsal reef, in the midbrain. What

26:04

do we know about the causes for that? How do we

26:06

go from fear, a foot shock, to

26:09

a change in neurotransmitters? We

26:12

have identified that stress hormones

26:14

play a role in

26:16

producing generalized fear, particularly

26:19

when we have blocked

26:22

the synthesis of cortical steroid,

26:24

that is a stress hormone,

26:27

when we blocked its

26:29

production, we were able

26:31

to block the transmitter switch, as

26:34

well as generalized fear. So

26:36

how do you see this

26:38

research going forward be integrated

26:41

into therapies or interventions for

26:43

generalized fear? I think

26:45

our study have pointed

26:47

two directions. One

26:49

is with existing

26:51

therapies. Our

26:54

study has suggested that

26:57

earlier intervention is

26:59

likely to produce better effect.

27:02

And for chronic

27:04

PTSD or similar fear-related disorders,

27:09

it may be hard when the

27:12

patients have already a long history

27:15

of the disease. Then our

27:18

study suggest new therapeutic

27:20

target to treat this disease.

27:24

Were you surprised that neurons would

27:26

switch which neurotransmitters they used? I

27:29

don't know, when I took neurophysiology for

27:31

some reason, we

27:34

didn't really talk about neurons switching

27:36

up which neurotransmitters it would use.

27:38

We kind of were like, okay, this

27:40

is the one that you use, this

27:42

is your destiny. Were you surprised that

27:44

these neurons were able to change which

27:46

co-neurotransmitters they were releasing? Yes,

27:49

so for a very

27:52

long history, like in

27:54

classical neurobiology, people

27:56

believe neurons have only

27:59

a single. neurotransmitters throughout their

28:01

life and their neurotransmitter

28:03

is fixed. But

28:05

recently in the last few decades,

28:08

more and more evidence supports

28:10

that neurons do not express

28:12

only one neurotransmitter and surprisingly,

28:15

they can switch their transmitter.

28:18

The Spitzer Lab and

28:20

at UCSD as well as

28:22

other labs who work on

28:24

neurotransmitter switching have not accumulated

28:27

vast evidence in different

28:29

origins in response

28:31

to different stimuli that neurons

28:34

have the ability to switch

28:36

their neurotransmitters. And what

28:38

is more important is that this

28:40

switch contributes to

28:43

behavior changes. So this

28:45

plasticity has an effect all the way at

28:47

what we do or what we think or how

28:49

we feel? Right. Very cool. Thank

28:52

you so much, Hui Quan. Thank you, Sarah.

28:54

Hui Quan Li works as a senior

28:57

scientist at NeuroCrin Biosciences in San Diego.

29:00

When she was doing the work for this paper, she was an

29:02

assistant project scientist in the School of

29:04

Biological Sciences and Center for Neural Circuits

29:06

and Behavior at the University of California,

29:09

San Diego. And

29:12

that concludes this edition of the Science Podcast. If you

29:14

have any comments or suggestions, any of you who are

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interested in learning more about the science podcast,

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please visit us at sciencepodcast.aaaas.org. To

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listen on our website, science.org.podcast. This

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wall was edited by me, Sarah Krusty,

29:30

and Kevin McClain with production help from

29:32

Megan Todges. On

29:36

behalf of Science and its publisher, AAAS,

29:39

thanks for joining us.