Neuroscience and magnetic fields: David Dickman at TEDxRiceU 2014

Summary

This presentation explores the remarkable ability of various animals to navigate using the Earth's magnetic field, a sense humans lack. It delves into the brain's regions activated by magnetic fields, particularly in pigeons, and the potential mechanisms behind magnetoreception. The speaker suggests that while the brain evolved to control movement, it also adapts to navigate through technology, extending our natural capabilities.

Takeaways

• 🧠 The speaker is a neuroscientist discussing the fascinating abilities of certain animals to navigate using the Earth's magnetic field, a capability humans lack.
• 🌐 Animals such as migratory birds, sea turtles, and honeybees have evolved to detect the Earth's magnetic field for navigation, a sense referred to as 'magnetoreception'.
• 🕊️ Pigeons, known for their excellent navigation skills, were used in the study to understand how they might detect and process magnetic information.
• 🧲 The Earth acts as a large bar magnet with magnetic field lines exiting the South Pole and entering the North Pole, varying in inclination and intensity across latitudes.
• 🔬 The speaker's team built a specialized laboratory to study magnetoreception, including a magnetic field generator to simulate various magnetic conditions.
• 📊 They discovered that different regions of a pigeon's brain are activated by the magnetic field, suggesting a neural pathway for magnetic reception.
• 🔍 The study used molecular engineering to identify specific brain cells activated by magnetic fields, indicating regional specialization for this sense.
• 🌀 The brain cells respond to the magnetic field's direction and intensity, with some cells preferring specific inclination angles and intensity levels.
• 📈 The speaker describes a three-dimensional cosine function as the best mathematical model to fit the magnetic field responses of the recorded brain cells.
• 🤔 There are three theories on how animals might detect magnetic fields: photopigments in the eye, iron particles in beaks, and the presence of magnetite in the lagena of the inner ear.
• 📱 The speaker concludes by highlighting how human brains have evolved to use technology to overcome sensory limitations, such as detecting magnetic fields through smartphones.

Q & A

What is the main topic of the speaker's presentation?

The main topic of the presentation is the ability of some animals to detect and use the Earth's magnetic field for navigation, a phenomenon known as magnetoreception.

What is the term used to describe the animals' ability to detect the Earth's magnetic field?

The term used to describe this ability is 'magnetoreception'.

Why is the sense of magnetoreception considered mysterious?

It is considered mysterious because we do not fully understand how animals perceive and process the Earth's magnetic field, nor do we know the endpoint goal of their navigation mechanism.

Which animals are mentioned in the script as examples of magnetoreceptive species?

The animals mentioned include migratory birds in Northern Scandinavia, sea turtles, honey bees, and bats in North America.

What is the significance of the Earth's magnetic field for navigation in animals?

The Earth's magnetic field is significant for navigation as it allows animals to determine their special location, heading direction, and navigational goal endpoint.

What is the role of Bayesian inference in the context of this presentation?

Bayesian inference is used as a probabilistic statistics function that takes different cues such as magnetic reception, visual velocity, and the vestibular system to determine an animal's heading direction.

What is the Earth's magnetic field like, and how does it vary across the planet?

The Earth's magnetic field consists of lines that exit at the magnetic South Pole, circle the Earth, and enter at the North Pole. The field lines have different inclination angles and intensities that systematically vary, being highest at the poles and lowest at the equator.

What is the lab setup for studying the Earth's magnetic field in animals?

The lab setup includes a shielded room like an MRI facility, a motion platform, and a cube with field coils to generate a magnetic field in any direction and intensity. Pigeons were chosen as the animal model for these studies.

How do researchers determine which parts of the brain are activated by the magnetic field?

Researchers use molecular engineering with antibodies attached to fluorescent markers to identify cells activated by magnetic field stimulation. This reveals regions in the brain that are specifically activated by the magnetic field.

What are the three theories proposed for the magnetic transduction mechanism in animals?

The three theories are: 1) the presence of photopigments in the eye called cryptochromes, 2) the use of iron particles found in the beaks of pigeons, and 3) the presence of a third receptor type in the vestibular system, called the lagena, which contains iron particles.

What is the significance of the speaker's final point about the human brain and technology?

The speaker suggests that while humans do not naturally possess magnetoreception, through science and technology, we have developed the ability to detect the Earth's magnetic field and use it for navigation, showcasing the brain's capacity to evolve and adapt.

Outlines

00:00

🧠 The Mysterious Magneto-Reception in Animals

The speaker, a neuroscientist, introduces the concept of magneto-reception, the ability of certain animals to detect the Earth's magnetic field, a skill humans lack. The talk focuses on how these animals use this sense for navigation, despite the mystery surrounding the exact mechanisms of their perception and processing. Examples include migratory birds, sea turtles, honeybees, and bats, all of which have evolved this ability for specific purposes. The speaker also humorously references Albert Einstein, a brilliant mathematician but poor navigator, to contrast human limitations with animal capabilities.

05:00

🌐 Understanding Earth's Magnetic Field for Animal Navigation

This paragraph delves into the properties of the Earth's magnetic field, explaining its structure as a large bar magnet with field lines that exit the magnetic South Pole and enter the North Pole. The variation in inclination angles and intensity of the magnetic field across different latitudes is highlighted, with measurements given in gauss. The speaker discusses the laboratory setup to study magneto-reception in pigeons, a species renowned for their navigational prowess, and how they were tested in a controlled magnetic field environment.

10:02

🔬 Investigating Neural Activation by the Earth's Magnetic Field

The speaker describes the scientific approach to identifying which parts of the pigeon's brain respond to the magnetic field. Using molecular engineering and fluorescent markers, the team discovered regionally compartmentalized activation within the brain, specifically in areas related to motion, heading direction, spatial memory, and multisensory integration. This reveals a neural pathway for magnetic reception, with cells encoding different parameters of the Earth's magnetic field, such as inclination angle and intensity.

15:04

🐦 Electrophysiological Recordings and Theories on Magneto-Reception

The paragraph discusses the electrophysiological recordings from the pigeon's brain, demonstrating how single neurons respond to changes in the magnetic field's direction and intensity. The speaker explains the use of a mathematical model, a three-dimensional cosine function, to understand the cells' encoding of magnetic information. Additionally, the speaker presents three theories on the magnetic transduction mechanism in animals, including photopigments in the eye, iron particles in beaks, and the possibility of the lagena in the inner ear, with a focus on the latter and the presence of biogenic magnetite.

🚀 The Evolution of Human Brain and Technology for Survival

In the concluding paragraph, the speaker reflects on the human brain's evolution, suggesting that while it evolved primarily for movement control, it also adapted to survive in ways not initially intended by nature. The speaker points out that through science and technology, humans have developed the ability to detect the Earth's magnetic field, as seen in modern navigational systems. The talk ends with an optimistic view of the future possibilities for human advancement, thanks to the brain's adaptability and our technological prowess.

Keywords

💡Neuroscience

Neuroscience is the scientific study of the nervous system, which includes the brain, spinal cord, and all the nerves. It is central to understanding how animals perceive the world, make decisions, and navigate. In the video, the speaker is a neuroscientist who explores how certain animals have evolved to detect the Earth's magnetic field, a capability beyond human senses, and how this relates to their navigational abilities.

💡Magnetoreception

Magnetoreception refers to the ability of an organism to sense magnetic fields. It is a key concept in the video as it explains how various animals, such as migratory birds and sea turtles, use the Earth's magnetic field to navigate. The speaker discusses the mysterious nature of this ability and how it is integral to these animals' survival and orientation.

💡Bayesian Inference

Bayesian Inference is a probabilistic method of statistical inference that combines prior knowledge with new evidence to form a new belief or hypothesis. In the context of the video, it is used as a theoretical model to explain how animals might integrate different cues, including the magnetic field, to determine their navigational path. The speaker uses this concept to illustrate the sophisticated mathematical processes that animals may employ for navigation.

💡Magnetic Field

The Earth's magnetic field is a complex system of magnetic forces that surrounds the planet and is generated by its core. The video discusses the properties of this field, such as its intensity and inclination, and how animals can detect these parameters to aid in their navigation. The speaker also explains how the field varies across different regions of the Earth.

💡Navigation

Navigation is the process of determining one's position and planning a course to reach a destination. In the video, the speaker highlights how animals use the Earth's magnetic field as a tool for navigation. This is particularly important for migratory species that travel long distances and need to find their way back to their nesting grounds.

💡Vestibular System

The vestibular system is a sensory system that provides a sense of spatial orientation and balance. The speaker mentions this system in relation to the inner ear's role in detecting acceleration and head movements. It is hypothesized that a part of this system, called the lagena, might be involved in magnetoreception in birds.

💡Hippocampus

The hippocampus is a region of the brain that is crucial for learning and memory, particularly for spatial memory and navigation. In the video, the speaker discusses how the hippocampus is involved in spatial location and how it might be activated in response to magnetic field stimulation, suggesting a link between magnetic perception and spatial memory.

💡Electrophysiology

Electrophysiology is the study of the electrical properties of biological cells and tissues, particularly neurons. The speaker describes using electrophysiological techniques to record the responses of brain cells to magnetic fields, providing insight into how these cells encode information about the magnetic field.

💡Neural Pathway

A neural pathway refers to the route that neural signals take from one part of the nervous system to another. In the context of the video, the speaker identifies a neural pathway for magnetoreception in birds, involving various brain regions that process magnetic information to aid in navigation.

💡Transduction Mechanism

Transduction in biology is the process by which a stimulus is converted into a cellular response. In the video, the speaker is investigating the transduction mechanism for magnetoreception, exploring theories such as the presence of magnetite in the lagena of birds, which could be responsible for detecting the Earth's magnetic field.

💡Magnetite

Magnetite is a naturally occurring iron oxide mineral with magnetic properties. The speaker discusses the possibility that magnetite particles in certain regions of the brain, specifically in the lagena, could be involved in the detection of the Earth's magnetic field, serving as a biological compass.

Highlights

The speaker discusses the unique abilities of various animals to navigate using the Earth's magnetic field, a sense humans lack.

Animals such as migratory birds and sea turtles use magnetoreception for navigation, a process still mysterious to science.

The concept of 'sense of mystery' is introduced to describe the unknown mechanisms behind animals' magnetoreception.

A Bayesian inference model is proposed as a method animals might use to integrate different cues for navigation.

Albert Einstein, despite being a brilliant mathematician, was reportedly a poor navigator, contrasting with the innate abilities of certain animals.

The Earth's magnetic field is described as a large bar magnet with properties that vary systematically across the globe.

A laboratory setup is detailed for studying how animals detect and process magnetic information, including a magnetic field generator.

Pigeons are highlighted as a model for studying magnetoreception due to their exceptional navigational skills.

Molecular engineering techniques are used to identify brain regions activated by magnetic fields in pigeons.

The speaker describes the discovery of regionally compartmentalized brain cells responding to magnetic field stimulation.

Electrophysiological recordings from the vestibular nuclei reveal neurons responding to changes in the magnetic field direction.

A mathematical model using a three-dimensional cosine function is fit to the magnetic field responses of neurons.

Different cells encode different parameters of the Earth's magnetic field, suggesting a neural map of magnetic space in the brain.

The speaker explores theories of magnetoreception, including photopigments in the eye and iron particles in beaks.

A potential transduction mechanism involving the lagena, a part of the vestibular system, and biogenic magnetite is presented.

The speaker concludes with the idea that the human brain evolves to survive by developing technologies弥补 we lack innately, such as detecting the Earth's magnetic field.

A quote from Dan Wilbert emphasizes the brain's evolution for controlling movement, while the speaker posits its role in adapting to environmental challenges.

Transcripts

well thank you all for coming as a VJ

thank you for that great introduction as

well it's a real pleasure to be with you

this afternoon and as GJ said I'm a

neuroscience and what I'd like to share

with you today is a vision of how some

animals are able to do imaginary and

fantastic things with their brains that

you and I

cannot all of these animals that are

pictured in this slide have evolved an

ability to detect parameters about the

Earth that you and I cannot do and they

do it very effectively for specific

purposes they use it in order to

determine their special location their

heading Direction and their navigational

goal

endpoint I call it the sense of mystery

why is it mysterious because we have no

clue how they actually do this we don't

know how they perceive it we don't know

how they process it and we don't know

the endpoint goal of the navigation

mechanism but I can promise you they are

very good at it and without this sense

of ability they would be clueless and

loss what is the sense I'm talking about

it's the detection of the Earth's

magnetic field we call it Magneto

reception and all of these animals have

capability of doing exactly that from

birds in Northern Scandinavia that

migrate across the Mediterranean into

Africa to sea turtles that live for two

years before they come back to their

nesting grounds to honey be that

basically fly from their mess across a

magnetic line forage for the day turn

around and fly back to bat live in North

fat in the United States that use the

magnetic field for their foraging at

night how do they do

this well as I mentioned humans don't

have this ability we cannot detect the

Earth's magnetic field in any way or

form that we know about but I'll come to

that point later in the

talk here's a famous human who's

extremely gifted in science and physics

and math Albert Einstein shares a

passion with me likes to sail and this

is a picture of Albert Einstein in the

late 30s up in the fingerlakes of New

York although Albert was quite brilliant

at mathematics he's actually a very poor

Navigator as most humans are and in fact

reports are that he would quite often

get lost in a sailboat run ground and

have people try to come out and get him

not a great Navigator a brilliant

mathematician however the little black

cap as pictured on the side is both a

great Navigator because they go from

Scandinavia across the Mediterranean

into Africa and they perform some very

sophisticated mathematics the

mathematics that we pictured here is

actually a formula that the brain uses a

lot to solve many complicated problems

in perception it's called basian

inference Theory and it's really a

probabilistic statistics function that

takes cues and weights them according to

their

reliability how reliable are the cues in

order to get pathfind to my end goal in

this case I've used the equation the

basian inference to take three different

cues that an animal could use for

navigation purpose the first is a

magnetic reception the other is visual

velocity as they're flying through space

and the third is the distributor system

which actually detects motion and

acceleration relative to gravity and

then passes that information on into

brain you combine these three

reliability cues and you come up with

the animal's heading direction is this

how the brain actually does it we're not

sure but we're performing recordings in

different brain regions to try to answer

that very

question so the birds are really good at

two different things they're great

Navigators and they're great

mathematicians so the next time someone

calls you bird brain take it as a

compliment now what is it about the

Earth's magnetic field that could

actually be used for purposes of

navigation and positioning well let's

take a look at what the magnetic field

actually consists of the earth is

actually just a very large bar magnet

and how it's generated is still debated

among geophysic today but what we can

see is that there are magnetic field

lines if you look at the left side of

the earth that exit the Earth at the

magnetic South Pole circle the Earth and

enter the Earth at the north magnetic

pole and there's a polarity to them

they're positive in the Southern

Hemisphere and they're negative in the

positive uh sorry sorry the Northern

Hemisphere so in a sense you can divide

the earth into two hemispheres a

positive region and a negative region

you can also notice that the field lines

exit the South magnetic pole almost

perpendicular to the Earth's surface

they come out in an inclination angle of

around

90° however the field lines that come

out close to the equator actually have a

parallel course to the surface of the

Earth so they have a0 degree inclination

angle and that difference between 0° and

90° systematically varies as you travel

across latitude across the

planet now to give you a point of

reference Houston Texas we have an

inclination angle of around

42° there's a second property that's

important over on the right of the globe

you can see that the field lines have a

magnitude associated with them it's

called an intensity this intensity also

systematically vary it's highest at the

poles and it's lowest at the equator and

to give you an idea of what the

magnitude is metrically we measure

magnetic fields in a term called gaus so

at the lowest level near the equator the

magnetic field is around 0.2 G whereas

at the poles it's around 0.7 G and we'll

come back to this point a little bit

later talk again for reference the gaus

level at Houston Texas is about

0.5 now knowing these properties of the

Earth's magnetic field if one was to go

in and look in the animals now to see

how they might actually detect and

process magnetic information one has to

go to the

laboratory

and in building a laboratory to study

the Earth's magnetic field we had to

start from scratch so first we built a

room that was shielded like an MRI

facility that would cancel out the Stray

magnetic lines that would be coming into

the room then we built a motion platform

which I won't be talking about today but

on top of it we made a cube and this

Cube had field coils buried inside so

that we could generate a magnetic field

in any direction intensity that we

wished and we then chose an animal model

pigeons we chose pigeons because they're

extremely smart and they're fantastic

Navigators pigeons have been used for

thousands of years even by the Egyptian

and Roman soldiers to track their way

back home and carry news of the battles

back to the Kings they're very good home

you can take a pigeon today to an

unknown location they've never seen

before and within hours or days they can

fly back home

so we placed pigeons inside our magnetic

field generator and we had to keep them

in the dark and we paded their bodies

and made them so they couldn't move

around well because we wanted the only

stimulus that was being presented to

them the magnetic field we can't see

magnetic fields as humans so we had to

take a magnetometer chip and put it

below the animal's head in order to

measure the field and then use a very

sophisticated computer algorithm that we

made to cancel the natural field that

was existing in the box and then

generate our own field in any direction

and intensity that we wished on the

right you go ahead and play the

video is my uh postto cell phone that

was placed in the magnetic field and if

you watch as we turn the magnetic field

on you'll see that the direction of the

magnetic field changes first in a

clockwise direction or excuse mechanic

clockwise and then in a clockwise

Direction and we can do this in any

plane that we wish relative to the

end

now our first line of inquiry was well

you all cells in the brain respond to

the Earth's magnetic field are there

just pieces are there just regions

within the brain that have specialized s

Sensations for the magnetic field

detection and we used a little bit of

molecular engineering to answer that

question today there is a protein that's

released from the cell nucleus they're

called immediate early release genes at

the time that brain cells are activated

for tens of minutes then they get into

the cytoplasm and we've developed

antibodies to find those particular

proteins and attached fluorescent martic

or uh markers that can be looked at

under the microscope so we took pigeons

and we placed them in our magnetic field

generator and stimulated with a direct

magnetic field for about an hour then we

took them out kept the brains and slice

the brains and look for the magnetic

neural activation marker and what you

can see by the section that's located on

the bottom right there are regions that

are specifically activated each of the

blue dots was a cell that was activated

by magnetic field stimulation and

they're not homogeneous throughout their

brain in fact they're regionally

compartmentalized if you look on the

section on the bottom right this is an

area called the vular nuclei which

receives information about motion

through space and it lies next to the

spinal cord so it's in the back part

bottom of the brain whereas on the top

left is a region of the brain that's

associated with the front of the brain

close to the

beat other than the vular nuclei again

in that bottom right section if you look

in the bottom left section there is a

region in the middle brain called the

anterior Thalamus where we know from

animal studies mostly in mice that many

of these cells respond to heading

direction of the animal as he moves

through the environment so it's

interesting that we found magnetic

sensitivity in that same place just

above it labeled HP is an area you've

probably heard about it's called the

hippocampus

and we know in human studies and well as

many animal studies that hippocampus is

highly involved in spatial memory and

spatial location and then finally the

top two sections on the left show a

region of Cortex that receives

multisensory information from the visual

system the vestibular system and the

trigeminal system and we know from other

animal studies that these cells are

involved in in perception of motion

through space so what we have is a

neural pathway for magnetic reception in

the brain of the bird and now we can

selectively go in and look at each of

these processing stations to see how the

cells encode different parameters of the

earth magnetic

field oh can we play this video so what

we did is we took fine wire electrodes

and we started the vestibular nuclei

which is a very uh familiar place for us

to record and in the top what you see

are the electrical discharges that come

from a single brain cell as it's talking

in a language of firing pattern we say

action potentials that are being

generated and passed on to the next

neuron and when you play that through a

loudspeaker you hear these popping

noises these popping noises are actually

the electrical discharge that are being

passed on as information sequences to

the next brain region it's the language

of communication that the brain uses to

talk you'll also notice on the bottom

that this is the magnetic field as it's

spinning around the animal and the red

arrow indicates the direction as we're

in different planes can we play one more

time now listen and you'll hear the

neuron increase and decrease its

activity proportional to where the red

arrow is pointing in this case down and

to the

left

okay now that kind of discharge rate is

the first thing that when you send a

graduate student into electrophysiology

lab and they hear the language of the

brain their eyes just light up and

that's how we hook them into becoming

Neuroscience so this is the first thing

that I do on day one of

grad now from those responses we can

take them all from the different planes

that you saw rotating we can take all

those magnetic responses and we can put

them in a large Matrix and then fit it

with a mathematical function and the

function that it turns fits best this

magnetic parameters response is a

three-dimensional cosine function and

that has specific properties associated

with it about telling us what the

information is if you look across all

the cells we recorded what you find is

that each cell has a different direction

in magnetic space that it likes they

actually encode that inclination angle

that I was telling you there's some

cells that respond best to the angle at

Houston there's some cells that respond

best the angle at the equator and

they're cells that respond best to all

places in between up to the pole it's a

map of inclination magnetic space and

it's in your brain the other thing we

did was look about intensity we varied

the intensity at shown on the left to

0.2 which is the lowest mag intensity

that you can find on Earth to about

three times Earth rink which is the last

dots on the right and I'm just showing

you three cells and their

responses at 0.2 the neurons don't

respond with very high firing ratees at

0.5 as the cell is in Houston it's

accelerated in its firing rate but

double that or trip that triple that

there was a saturation phenomenon

meaning that the cell didn't respond

anymore all right and why is this

important is because that's exactly the

range that animals would have to evolve

in in order to be Pro biologically

active within the Earth's magnetic field

if they only responded to high strength

magnetic fields it would be useless to

them they have to respond in the earth

strength and they

do

okay back to the

mystery where is the magnetic

transduction mechanism how is this

actually done well there are three

theories the first is that there are

photop pigments in the eye and these

photopigments the eyes are called

cryptochromes and in a blue wavelength

of light the cryptochromes have

molecules with spin rates that can be

aligned just much very similar to the

way an MRI works on water molecules and

those alignments could be transduced

into neural signals and transferred to

the brain but this is all Theory no one

has physiologically identified that yet

there were some studies a while back in

the 70s that found iron particles in the

beaks of pigeons and in other birds as

well and it was proposed that these iron

particles could serve as a magnetic

Source but as of today no one has been

able to physiologically show

that the third theory is the one we're

pursuing that in the vestibular system

in your inner ear there are receptors

that detect acceleration and head

movements relative to gravity but

amphibians reptiles fish and birds have

three of these receptor types whereas

all mammals that we know about have two

the third one is called the

leina and since there's a special organ

in the ear and we record it from

vestibular neurons in the brain stem

that detect yours magnetic field we

thought is it possible that the leina is

the receptor so we looked we took leinas

out of birds we went to the Argon

National facility south of Chicago which

is a high energy Photon Source meaning

large X-rays and you can put your

tissues in the beam line we did that

with the lagina and then you can look

for Isotopes or any element in the

periodic table selective so we chose

magnesium copper iron other particles

like that zinc could have magnetic

properties and what I'm showing you here

by the Red Arrows is a cross-section of

that lagina receptor where iron is

indicated in red and the lack of iron is

indicated in blue and what you see is

there's a concentration of iron

particles specifically in certain

regions of the epithelium and not only

that the analysis that we performed

showed us that these iron particles are

actually

fe304 a form of biogenic magnetite with

permanent magnetic characteristics

so there's these clusters of magnetic

crystals that exist in this receptor

epithelium could it be that this is the

transduction mechanism we don't know yet

but we're isolating these cells to try

to figure that

out so I'd like to leave you today with

first a quote and then a posit Dan

wilpert another very famous

neuroscientist who studies movement has

said in a series of papers that the

brain evolved to do one thing and one

thing only and that is control movement

all of your behavior goes down to

movement love sex everything it's all

about movement but I give you this posit

there's another thing that the human

brain does it evolves to survive in ways

that nature didn't give us control over

and here's why I say it you don't have

the ability to detect the Earth's

magnetic field in your brain but through

Science and Technology of applied we

develop the ability to detect the

Earth's magnetic field combine it with

acceleration and satellite information

to create a navigational system that all

of us carry in our smartphones in our

pocket so through the evolution using

our brain we provide capacities that we

don't have otherwise and I can only hope

what the future will bring in that

regard thank

you