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BIOL 6397 Cell Neuroscience Mo Wed 1-2.30pm - CELLULAR NEURO Lecture 11 IMAGING I - NEURONAL ACTIVITY
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00:03 This is lecture 11 of cellular And just to remind everyone that we
00:09 about the cellular and physiological soft strays plasticity. We discussed that there's short
00:18 plasticity uh that there's long term that short term facilitation or short term
00:27 can happen within the shorter train of . Because when we talk about stimulation
00:33 inevitably think that stimulation of these fibers the shopper collaterals and the hippocampus,
00:41 we're talking about represents the natural physiological which would be an input to the
00:49 , whatever the natural input is. different frequencies on a short term and
00:59 can evoke different levels of calcium So levels of calcium can influence whether
01:08 gonna be a potentially ation of the or depression of the signal. So
01:15 what you're talking about is that these of action potential also we've learned about
01:21 in the course and we said look this different dialects that different neurons,
01:27 the inhibitory cells happened, that diversity the inhibitory interneuron sub classes and how
01:33 can fire these very diverse frequencies of potentials. These very interesting patterns.
01:40 you realize that those patterns actually end being post synaptic physiological response and some
01:48 them are short term and some of patterns if they repeated if the stimulation
01:53 repeated, they can now have a term effect. So we talked about
01:59 term plasticity and we talked about long potentially ation and long term depression.
02:07 also discussed the spike timing dependent plasticity then spike timing dependent plasticity, what
02:14 really important for us is we want make sure that whenever the pre synaptic
02:21 fires neuron a fires that that activity the release of the neurotransmitter from a
02:31 a strong enough response and be but be when there is a stimulus and
02:39 potential can actually also respond with an potential. And with response with an
02:45 potential it produces a back propagating So we said that this order is
02:53 of pre versus post or post versus . So if you have pre versus
03:02 and you have a short window between the pre synaptic neuron fired. Here
03:08 a time interval on the Y. the which accesses that on the
03:15 Axis. Not just kidding on the access. So you have interval time
03:23 . And you can see that the in time the pre synaptic neuron fires
03:27 the process synaptic neuron responds. There's greater chance that there's going to be
03:32 ation of that communication of that tablet the reverse is that if the post
03:40 neuron fires before the pre synaptic neuron supposed to activate them, it just
03:47 the opposite. It depresses that So when you look here on the
03:53 the Y. Axis where you have change in synaptic weight, you can
03:57 view it as change in synaptic strength in the synoptic response and amplitude of
04:05 synaptic response. You can see that will increase it but that increase will
04:12 most significant interactivity between the two They either time in a short time
04:20 the proper order for potentially a shin in the reverse order if you may
04:27 not saying it's not proper but reverse which means something different for the signaling
04:32 the communication of these cells. So can alter these curves of spike timing
04:40 plasticity curves, that's what they're called you can alter them. You can
04:46 their shape. In some instances this between pre and post might be longer
04:53 it will still allow with the synopsis potentially eight. In other instances this
04:59 is going to be shorter. So if you look at neural transmission and
05:04 think of gaba as a minus and as a plus. So you have
05:10 minus and plus and you have one when you have just a plus and
05:19 when you just have excitation versus inhibition then you have all of these seven
05:27 classes and systems in the brain and neuro modulators such as serotonin such as
05:36 . And when they get introduced they reshape the excitation and inhibition the rules
05:42 they can also alter these curves and alter the rules for both the rate
05:51 or the rates plasticity in the spike code. And so this is the
05:57 that illustrates that in fact there are situations where the post synaptic activation to
06:05 before pre synaptic activation of the South also cause potentially ation or LTP.
06:14 what's quite evident is you can push curves but they all fall within tens
06:21 milliseconds range for a meaningful change, or strength change of the level of
06:28 synopsis. Most of these rules of and reshaping the curves, making them
06:37 , steeper decline or or or They they are all within about 100
06:48 . So if there is that tells that neuronal networks and the circuits and
06:54 that communicate if they all of a start communicating and engaging with each other
06:59 than every 102nd milliseconds. During a task. For the most part,
07:07 are pretty quiet and if you're not stimulating them with a specific task for
07:12 input with specific stimulus, they're not be responding, they're gonna produce one
07:17 potential here a few seconds later another potential. So these are all important
07:25 to understand how all of these other and other conditions can change the spike
07:33 dependent plasticity occurs and in a way of these other neurotransmitter systems that we
07:39 in the brain they add the So if you think of Gaba is
07:46 and blue, tomatoes, white and spike timing dependent plasticity in Gaba or
07:54 and black whatever you know, black white, you have this potentially ation
07:59 depression and you introduce other molecules and of a sudden you have color.
08:09 not just all black and white but could be darker color could be lighter
08:14 and different spectrum of colors. So way the brain learns the way these
08:19 learn the way these networks established themselves the development during that period of critical
08:26 , critical period of development that we've with you guys is by using some
08:31 these rules that require high levels of to depressed certain synopses and to drive
08:38 away and to prune them or just opposite, strengthen certain ones and the
08:44 that are inactive to to drive them . So there's different things that are
08:49 and of course the chemistry of the is pretty complex. So spike timing
08:56 plasticity will be altered as we discussed neurodegenerative disorders and also and addiction and
09:04 circuits. And then I reminded you we studied the static anatomy of cells
09:12 synapses and communications and then we talked different levels of study. There are
09:19 levels of understanding from this macroscopic level Mezza skah pick two circuit centric connectivity
09:30 engram level, heavy and like engram cellular level. You're looking at the
09:37 are you looking at the distal So you're looking at the selma to
09:41 sub cellular level. I'm looking at know, distilled done dr one specific
09:46 maybe even molecular level. There is fact molecular imaging because you can tag
09:53 receptors such as ample receptors and you tag those receptors and and and and
10:00 how they get traffic in from extra spaces into the synaptic spaces. So
10:05 a molecular level imaging to that would on the sub cellular of course.
10:13 uh these levels of course in the most of the time when you're talking
10:20 non invasive imaging of the brain and medical clinical setting, you're talking about
10:26 . M. R. I. positron emission tomography. Uh M.
10:30 . I. Stands for functional magnetic imaging when you're talking about understanding at
10:38 really much finer resolution and this is big so far obstacle to some of
10:44 techniques. Uh that in case of invasive brain imaging you're typically looking at
10:54 resolution of about one cubic millimeter. you're very very lucky. And if
11:02 very very lucky that means that you access to an Fmri case two very
11:09 magnets that are very expensive. And we talk about it tomorrow, maybe
11:15 get into that a little bit. you will see that we just build
11:18 facility for five t. or 70 something to do with the strength of
11:24 magnet, the Tesla uh that And so you have to have a
11:29 special environment for this for this for clinical studies and for diagnosing people.
11:39 there's some funny stories, people walking F. M. R.
11:42 Room and they have like a metal in their pocket from lunch and applies
11:47 attached to the magnet across the you know. So they're they're a
11:50 magnets. But experimentally in experimental neuroscience you can look at all of these
11:56 levels. And remember when we talked the frequencies of action potential firings now
12:04 one of these what looks like an potential is actually an optical trace.
12:10 when we're talking about optical imaging, talking about several things. First of
12:17 we're talking about what what is this ? Mm hmm. Let's see.
12:32 so we're talking about functional imaging blood flow metabolism flux is of ions
12:41 of calcium in neurons flexes of sodium neurons fluxus of calcium and glia because
12:50 mostly functioned by propagating these calcium waves . So there are some imaging dyes
12:59 are specific to ions such as And there are guys that are specific
13:04 a change in the membrane potential and voltage across neuron which as you
13:09 is a combination of several ionic species at the same time. Then you
13:15 the receptor movements. So this would a molecular which also would be considered
13:20 imaging because you're looking at the migration something that is happening. Uh Now
13:30 you look at the at this at at this slide here. I think
13:35 start talking about uh similar material here I think I started telling you about
13:53 visual cortex and so this is the A. That I'm switching into
14:00 And I want to tell you about system. That is a really beautiful
14:05 that is displayed here. And you'll why we're talking about this. So
14:12 is a so matter toppy. the map, Samata topic map and
14:20 somatosensory system. It's a matter of system is all of the body
14:28 Stopwatch, temperature, pain, Oh not only from the body but also
14:39 the head and the face. And process that information in the face at
14:46 level of the face. There's a sensory nerve that's a matter of sensory
14:52 is a cranial nerve, trigeminal Um we'll come back to that in
14:59 second. But what what rodents do what is really important for rodents,
15:07 is not very important for humans, to whisk around. So they have
15:14 whisker pad and not only rodents, have whiskers. Dogs have whiskers,
15:23 have different arrangements or patterns in these too, but it's really really important
15:31 rodents in particular. The whiskers because smell, they have very large olfactory
15:39 in the front of their brains So they spend a lot of their
15:43 , they have poor vision. So road and spend a lot of their
15:49 walking around sniffing around and whisking around in fact they moved their whiskers at
15:57 specific frequency. Because this goes back when we talked about brain rhythms.
16:06 it turns out that the theta rhythm in rodents is slightly lower than humans
16:13 rodents I believe it's about 4-7 That theater rhythm is really important for
16:20 rodents to whisk around and to encode new information that it is learning from
16:28 outside environment. So you know, as humans, we don't come and
16:34 things around and then we decide if like that we're not, you
16:37 that would feel like, you not not not without the consent at
16:44 , but typically that's not what we , you know, just turn around
16:49 you know, so but that's what do and because of that's what they
16:54 , that is really important for their . And because it is really important
16:59 the survival, a very large part their brain is dedicated to the semantics
17:06 sensory system, particularly to the whisker of these rodents. And when you
17:13 in the whisker pad of these You see that there is a certain
17:19 that there's 1, 2, 34 rows of these whiskers. And you
17:28 go to an extra evident mouse rat you will see the same number of
17:35 And then you've count that 12345678. a certain number of whiskers in Israel
17:53 . So this is really cool. then when you stain the brain.
18:00 you stay in the brain and some sensory cortex which is area.
18:06 one. No matter of sensor cortex be receiving the information from the animals
18:13 from the nerve. And if you in that vortex you will reveal these
18:21 like structures. So. And then you looked at the whisker pad and
18:30 counted the rows and the number of and you look at the barrels in
18:36 matter sensory cortex of the rodent, will find the same number of
18:42 the same number of these barrels. each barrel is actually representation Of processing
18:55 this amount of sensory information from one whisker and a whisker pack. Okay
19:04 you have this external anatomy. And you have the cortical anatomy at the
19:11 of the cortex where each barrel is at the level of the cortex where
19:17 barrel. And this is the trigeminal that will pick up that information from
19:24 whisker. So trigeminal nerve is cranial five. It's the largest cranial
19:32 Five, servicing all of the somatic from the face. And it had
19:41 that information will be at the level these fibers from individual nerve terminal that
19:52 surrounding an individual hair follicle. Around whisker. And that information from the
20:02 we'll travel and we'll get encoded on opposite or contra lateral side.
20:12 And you have a map on the lateral side to the right, whisker
20:18 have a barrel cortex map on the side. It's simple. It's
20:31 It's observable. You don't have to immuno history chemistry to see the structure
20:39 the barrel cortex. You can use this cell stain and you will see
20:44 very densely packed areas. You use staying together with golgi stain. You
20:50 see the Golgi stain will show that have a lot of interconnections within the
20:57 . That's why they're called barrels. course there's inter barrel connectivity but within
21:02 barrel it's like a separate engram for one. Whisker where cells like to
21:10 within the barrel more so you can the system easily. You can move
21:18 whisker, you can disrupt the If this pattern of whisking forward to
21:26 Hz 4-7 times a second is You can disrupt that pattern. You
21:31 disrupt that pattern pharmacologically. You can something at the level of the whisker
21:38 and make partial inhibition of excitation. can increase inhibition by boosting inhibition.
21:50 you can move the whisker different You can actually capture whisker and move
21:56 and look at the brain map functional map, you can cut the whisker
22:04 and see how the cortical brain map . And if it does because neurons
22:11 plastic and even in adulthood, although as much of a plasticity that you
22:16 see in in early development in adulthood still plasticity and rearrangement that is
22:26 So let's look more carefully now and walk through this figure and before we
22:34 what is exactly happening, how we're this. We'll talk about these imaging
22:40 . Let's talk about this figure which also uh walks us through about
22:52 same. So you're stimulating right Two whisker. What is C.
23:00 ? It's rosie A. B. . Okay, so you're stimulating Row
23:05 two. Whisker right here, it's C. Two whisker. This is
23:10 C. Two whisker and this is C two barrel in the somatosensory
23:17 And this is stimulation of the right . And you can see that this
23:26 produces a rather small response. And , what you're measuring is the
23:34 the color yellow and red color means more activity. There's more fluorescent sits
23:40 F over fo which is steady state before activity before stimulation. And you're
23:48 basically that you have a small barrel gets activated with C tune that the
23:56 of activity. It is confined to barrel now spreads into the adjacent areas
24:03 the barrel cortex. And also you activation of other areas such as the
24:10 cortex year and larger adjacent areas of brain in general. And this is
24:16 timeline, this is the scale of and the timeline of about 60
24:24 This is fast. But you can that initially it's quite confined to just
24:30 one barrel that would be responding or is assigned to Whisker C two anatomical
24:39 . Mhm. So now you do experiment where you stimulate whisker C2 in
24:46 control condition and in this bottom images whisker et tube. And of course
24:56 shouldn't produce the same initial map because . Zero C. E. is
25:02 row over from C. And it enough produces a slightly different area That
25:13 an E. two whisker E two cortex. And you can see the
25:18 to activity spreads over time again. is now 26 milliseconds total And the
25:25 two has its own map of So first of all you have the
25:33 barrels. Second of all you have function. And if you are stimulating
25:40 single whisker you get very specific very specific functional response from a single
25:47 in the cortex. Mhm. So happens here now you have created a
25:58 of activity. So these brain maps are based on the structure, If
26:05 recall structure is interconnected, meaning these are connected to other neurons from primary
26:16 cortex, secondary somatosensory cortex to motor because they may need to move to
26:23 that are called association areas that will several sense information to gather vision and
26:32 whisking. So these are brain waves brain maps. This is how you
26:41 image how the activity spreads across areas the brain. Is this a single
26:49 imaging? What level are we looking here? This is macroscopic level because
26:58 we're we haven't gotten into and to I would say this is nestle's coptic
27:05 because we have gotten down to a barrel. We haven't gotten to a
27:10 level though. So if you now you had an image of 26 milliseconds
27:18 you would say this is a macroscopic because it's no longer that specific.
27:22 so the same technique I can give a visual of meso and and the
27:30 but it's rare that it gives you visual of macro meso the circuit and
27:37 more single cell sub cellular. Even so combination of these is difficult.
27:45 what can you do now? Well what you're going to do is you're
27:50 to see how if I alter activity one of these whiskers and you've identified
27:57 C. Two. If I inactivate C two, what happens to that
28:04 map? And the way that this was done and see is there is
28:09 injection of C. N. Qu recall. We talked about glutamate receptors
28:16 we talked about an M. A receptor and it had a specific
28:20 called a PV or a P And we also talked about ample teenager
28:27 and ample receptors will have their own block or antagonists CN Q.
28:35 So we have injection of CN X. And a PV in this
28:42 . Two barrel column to locally inhibit a tropical glutamate receptors And what it
28:53 block the entire sensory motor response devoted sea to whisker stimulation but had little
29:00 on E two driven sensor response. this is what can be done.
29:10 can actually inject blockers of activity around whisker and if you block ample in
29:20 M. D. A. There no excitatory signaling And if you block
29:26 signaling around Whisker C2 and it's localized injection that you have done is very
29:33 . It should not affect surrounding whiskers surrounding rose. And so when you
29:40 this experiment and you now stimulate inactivated C two at the level of the
29:47 you get almost no response and it's faint response and it's a different spatial
29:54 pattern. So this is an important to know. When we talk about
29:58 imaging. Were quite often looking at spatial temporal patterns of activity in space
30:07 entire and when you stimulate whispery And you compare it to the control
30:13 , the map of whiskey to especially initial map over the 1st 18 milliseconds
30:21 really changed that much. So you this structural specificity, you have functional
30:31 , you have different levels of study and imaging and manipulations that can be
30:38 pharmacological manipulations. You could cut off whisker or injure the whisker it happens
30:45 see what happens to the maps if return or if the surrounding whisker maps
30:51 larger. So how would you measure across these different levels? And what
31:04 would you use to measure? Mez opic versus circuit centric versus cellular.
31:14 cellular. And a very good technique Mesozoic opic activity imaging which means in
31:21 opic imaging, you don't get a cell resolution. You're not looking,
31:28 sorry, you may get down to single cell resolution but you may know
31:33 numbers of cells that you're looking at network but you will not know the
31:37 and the connectivity. You're not looking that. You're not visualizing that.
31:43 in this Mezza SKOp IQ level which not really allow you to visualize activity
31:49 single individual cells or at least it not allow you to discern that activity
31:54 it does not have enough of the resolution. So when we're talking about
32:04 waves and the Sturm spatial temporal you to have enough of spatial resolution and
32:15 of temporal resolution spatial resolution is how pick megapixels you have in your camera
32:26 means that that image is going to How many megapixels, 3000 pixel representation
32:34 7000 pixel representation. So the more , the more mega size you can
32:41 in these cameras, the more of spatial resolution you have that typically comes
32:47 an expense of a temporal resolution and cameras that are capable of performing both
32:57 very, very high resolution visually and very, very fast. Those are
33:02 things you see like on tv the where they can explode things and see
33:08 how particles fly apart and see the spatial resolution. So those are very
33:15 tools and of course we have them the labs but not everywhere. Um
33:21 this imaging technique is called Baltic sensitive imaging, optical imaging of cortical dynamics
33:29 viva and this is vault IX sensitive es de imaging that we will
33:37 Go ahead, temporal temporal is in . How fast can you sample?
33:48 some cameras are 30 frames per second believe. That's like a typical iPhone
33:55 started to maybe 60 frames per That means you're gonna take 60 samples
34:02 whatever that imaging ongoing image. You're take 30 30 samples in one second
34:09 that motion. So if you're moving hand in one second 1001 you're gonna
34:14 30 representations in time of that So that's the temporal resolution, you
34:19 have 2000. That means that when moves that hand that's 1001 you're gonna
34:24 2000 and presentations which is much higher resolution than when you think about spatial
34:31 resolution, what can you resolve when looking at neuronal activity? Uh And
34:39 that I mean how fast are action ? 1 - two milliseconds. How
34:50 what's the frequency then if it's 1122 let's say two millisecond duration. What's
34:56 frequency? One second is 1000 500 500 Hz. So you need
35:11 minimum of 500 hertz to get one in time of that action potential.
35:21 guess what if you're a fraction of off, you will not get a
35:26 representation of that. So then you need at least double of that
35:32 Which is one kHz, 1900 maybe ? Maybe two kilohertz, 10 kilohertz
35:40 physiologically when you measure activity, electro you can get down to kilohertz
35:47 There are amplifiers 10 kHz. It's problem but amplifiers that will sample and
35:54 that information. But when you go an optical imaging level it is this
36:01 very fast imaging. It's very important you want to record E.
36:07 S. P. S, how is an ep sp? Well it's
36:11 least 5 to 10 milliseconds. So you need an extremely fast camera to
36:17 up PPS pdf that even know how glial waves are actually on the order
36:21 seconds. So would you then if studying Glee on calcium dynamics and you're
36:27 the lab and you have you starting as a new professor with a
36:32 of $500,000. And you're looking at camera that costs $100,000. Which one
36:41 you gonna take? You're gonna take really fast one or you're gonna pick
36:45 really slow one but it's gonna have resolution that maybe you can see
36:50 it's everywhere. There is kind of trade off and all of these
36:55 you know. Um So you would to for optical imaging and for optical
37:01 and fluctuations. So by the ways got 5, 10 millisecond DPS
37:06 Now you have 500 Hz, that's beautiful livers. You have a lot
37:10 you know, samples, you can a long so because wherever you don't
37:17 , that's when the computers just filled in. Right? Uh so in
37:23 sensitive dyes their molecules that can be and these molecules are chemicals, they
37:33 these little warm like molecules that embed in the plasma membrane and they sit
37:39 the plasma membrane. So, to voltage sensitive dye experiment in this
37:45 this window is made in the And you're looking at the surface of
37:52 cortex, you have a microscope because not going down to the level of
37:58 single cell rather than you're looking at macro and mesozoic opic levels of
38:05 And now you have an electrode in too. Because you want to
38:12 And one of the things that you're with both of sensitive dies is that
38:16 imaging voltage. So if you're imaging , you already know a great way
38:20 track voltages, electro physiological micro electric and that's been accepted. It's been
38:27 for many years and we understand it well and there's different frequencies of different
38:32 that we've used for these experiments. so now you have to apply the
38:37 and the dye is going to embed in the plasma membrane. And this
38:44 an experiment where a monkey is presented visual stimulus. It's alternating bands that
38:55 crossing across its field of view and are recording activity in the primary visual
39:04 . And that is also important that wanted to do studies of visual
39:11 You would go to the higher order that have that visual cortex better
39:17 If you wanted to study the olfactory it's a matter of sensory you would
39:24 to go into rodents but in monkeys humans and other higher order species,
39:32 is very well developed. And you access on the back of the brand
39:36 the occipital lobe And the primary visual area called v. one. And
39:42 you have a window into this primary cortical area. We know that that
39:48 processes the visual information. So we the dye and we put an electrode
39:56 the primary visual cortex and we present animal with a stimulus that goes and
40:02 the primary visual cortex. One of traces in red is an electrical
40:09 extra cellular signal that's coming and you actually do inter cellular signals to and
40:17 other color. I can't remember. let's see it's been a while since
40:25 similarity between the two traces above the intracellular. Okay, so it's
40:32 So somebody dropped a sharp electrode inside cortex. Remember that sharp electric recordings
40:38 easy to give up intracellular recording and is uh in blue and voltage sensitive
40:47 , population activity, population of So we're again looking at this Mezza
40:54 IQ level, not individual cellular level resolution. Uh in these cameras,
41:01 pixel could potentially contain few cells. can get maybe down to resolution about
41:08 cells. So wherever you're seeing some red and blue And that signal red
41:14 blue, that one pixel. So you had this matrix of pixels
41:35 this is what cameras look like. little those little squares I called photo
41:43 and they capture the information. So can have this number of these squares
41:53 you can have double number of these . And if you have a double
42:00 of these squares, you have a better spatial resolution. But if you
42:14 down, do these vault of sensitive imaging techniques at the level of one
42:23 these small linda's here. What you're . What you're measuring here is the
42:30 , you're measuring one signal which is say in red. But that one
42:39 is a representation of activity of several . And some of them may be
42:54 but they may be interconnected chemically. . With chemical synopsis. So they
43:01 be interconnected electrically with gap junctions electrical . So each pixel but we'll show
43:10 which means that pixel is active. if you look what does that mean
43:15 the spatial resolution, on the spatial , we're talking about potentially 50
43:26 A single sal salma. It's about microcomputers. So what is this in
43:39 one pixel in the camera? With picking up your picking up selectivity average
43:48 from all of the south underneath that . That that that that you're looking
43:53 both of sensitive dyes will really let look at the surface activity. Those
44:00 will not allow you to penetrate very deep into the tissue. So you're
44:05 much looking at the surface activity with sensitive guys. So really cool how
44:18 know how the voltage changes. To polarize the cell voltage changes. How
44:24 the signaling the camera change with these ? The signal and the camera changes
44:34 neurons traverse through these ion channels. charge on the inside and the outside
44:42 the number of changes. And as charge across the membrane changes. These
44:51 are sensitive to voltage. So these change their confirmation and by changing their
45:02 . Now the beam of light that shining to pick up this fluorescent signal
45:08 transmit or reflect a different wavelengths of . So instead of picking up red
45:16 pick up yellow or you'll pick up . Okay so this is how this
45:22 when there is changes in membrane We recorded electrically Changes imaging. Using
45:31 of sensitive dyes we recorded optically. it's essentially 1-1 representation of even single
45:40 . So electrode is recording activity from cells. But the pixel, an
45:47 pixel is a representation of an average underneath that window that the camera is
45:55 at. That's right. One pixel can think it's a circuit but you
46:06 know how it's connected. So you have the connectivity in it. It's
46:11 an average over space and time but uh maybe the sequence of connectivity or
46:25 . So how would you be able see the connectivity between each pair if
46:30 saying it does this conflict listens up isn't. This isn't enough.
46:35 but it's really fast. And it's electrical activity. That's near real
46:44 You can see that there's no lag the electrical trace and blue and
46:50 Remember young ah one is electrical one optical changes. So there is no
46:57 . It's almost immediate. It's almost time. It's recording electrical activity recording
47:02 optical activity, which is really Mhm. Because when we talk about
47:08 imaging techniques, there's a delay from stimulus to when the magnets turn on
47:17 process of information that can be accounted calculated for. But it is not
47:25 it as it is happening. You , It is post processing after requires
47:31 . This is sampling it as it happening. It's a real advantage is
47:37 fast. So it's fast voltage sensitive imaging uh can also be genetically encoded
47:47 dies. So you can, certain would encode these dies only. And
47:54 really cool. Because if you just to look at the activity of
47:57 types of cells and you would just the genetic encoding encoding of these dives
48:01 you would know that I'm just recording basket cells in the hippocampus. How
48:06 . Because those are the only ones will be expressing the dye molecules.
48:15 question. So, in terms of of like a cell. So first
48:23 not not like a barrel like the between one barrel to another for talking
48:28 circuit or something out between cells. ? Not like barrels or like
48:37 I think it's like there's different types circuits. There's circuits between cells and
48:43 circuits between variables. So there's different of connectivity that we're talking about.
48:48 circuits and there it is just between . Right? Yeah, it's like
48:55 surfaces between circuits between populations to you have your favorite friends on the
49:07 , favorite contacts. And then you the contacts And those contacts. Talk
49:12 other contacts. So, all so let's talk about this uh,
49:23 and calcium imaging. These are two very interesting techniques. Most of what
49:29 know about the response properties of neurons visual system and every other system.
49:34 the brain has been learned from intracellular salary recordings. Micro lectures until really
49:40 21st century, I would say These give precise information about the activity of
49:46 or a few cells. However, one and serves thousands of the
49:53 it's not possible to observe patterns of across large populations of neurons. So
49:58 has its own limitations. Now. know that you can actually have more
50:03 electoral race inserted on the surface of brain. You can have these crazy
50:09 Baylor Putting like an array of 300 electrodes, monkey brains. I think
50:20 and Mosque. How many electrons can but through the neural link, you
50:26 , we don't we don't know. so is the limitation too though.
50:31 if you're putting an electrode, that it's it's your penetrating the tissue.
50:39 an electrode doesn't hang above like a . Even with the camera when you're
50:46 the surface, you already have two the skull to expose the brain
50:54 But you're imaging in some techniques like intrinsic optical signal imaging, there's no
51:02 . So you're not even putting anything the brain like a chemical with,
51:06 an electrode, there's an actual physical with the brain tissue with the
51:15 And just like with anything else. know, you can put a lot
51:20 needles on their hand, maybe it's or maybe there will be an infection
51:24 maybe there will be damage to So, so these recordings of lava
51:32 populations of cells. So in these intracellular recording electrodes, I think I
51:39 maybe the record is like eight intracellular at the same time In the in
51:46 in the slice. So that's But that's not. We don't want
51:51 know about eight cells of 12 or 20. We want to know about
51:55 cells in the whole network too. this is a view of neuronal coding
52:01 a scale much larger than individual neurons provided by optical imaging. Brain
52:07 There's one version of optical recording involved sensitive dye is applied to the surface
52:12 the brain, the molecules and the to cell membranes. And there are
52:17 detectives. Video camera records changes in optical properties that are proportional to variations
52:23 the membrane potential. The second way to optically study cortical activities to image
52:29 signals. So this is a vasculature of the primary visual cortex.
52:37 when neurons are active, blood volume oxygenation changes to degree that will be
52:47 with neural activity. Blood flow and influenced the reflection of light from brain
52:54 and reflecting changes. Can be used indirectly assess mental activity, assess light
53:01 projected onto the brain and the video records the reflected light. That's when
53:07 signals are used to study brain Membrane potentials for action potentials are not
53:13 measured. Okay, so what are talking about? We talked about vaulted
53:19 to die and we said that actually exactly the number of agricultural. But
53:26 we were talking about intrinsic optical signal , we're talking about oxygen. We're
53:35 about self swelling. Because active neurons be absorbing a lot of energy.
53:41 a lot of energy breathing a lot oxygen. Very high oxygen demand for
53:48 . And as they do that they're us are going to swell and as
53:54 almost swell, it's, you like a balloon that swells and you're
54:00 a light on that balloon. So it's not so swollen, it will
54:05 darker if it's a darker color and you stretch that balloon, you're shining
54:09 light and all of a sudden the is gonna look lighter. It's the
54:14 properties that are changing. So the way these active neurons will start drawing
54:21 will start drawing oxygen to themselves. as they are generating a lot of
54:27 potentials that will start swelling and in case you're shining a light on the
54:34 of the brain and you're seeing the in reflective properties. This is before
54:41 , on the on the left and is after the stimulation of the
54:46 So figure it is a photograph. b shows ocular dominance columns. So
54:53 the visual cortex we have these ocular columns and we have them in the
54:59 human on human. These ocular dominance . We have cats actually, these
55:07 dominance calls, where you see this line that means that that is activity
55:13 the south of process activity from one . It's dominated. They're ocular dominated
55:22 one eye. Ocular is um I because in the cortex they form a
55:29 of structure. Will look at the anatomy and I believe in a few
55:33 or so. So you have these or stripes that are running across the
55:42 visual cortex and you can use intrinsic signal that you can stimulate with a
55:49 one eye and have this macroscopic view the visual cortex and see these really
55:56 striatum a pair doing or following immediately stimulation and there's no die here.
56:05 it's also not direct correlation to Toronto and potential. These are all great
56:12 actions by the way. You know ? It's correlated to the number of
56:15 but it's not. So uh We have to think about your quiz because
56:21 week and then a spring break. I don't know if you guys would
56:24 to have your quiz before spring break after spring break. What's better uh
56:31 you from a learning perspective because I want you to study and then kind
56:38 forget about it. And then so think about it. And then we'll
56:44 guys can let me know on mm . Okay. We can we can
56:58 can take a vote. Let's see do it video about that will kill
57:07 . Well something to think about. get back to that, do
57:16 What? Yeah. Yeah. The day it should be on casa
57:23 be all listed. Yeah. Uh this is the description of optical
57:33 And then we are this is So it's called intrinsic Because you're not
57:41 anything. You're not adding any That you're not tagging any molecule.
57:49 just looking at the changes in the properties of the tissue. This comparison
57:57 cortical maps of aquila dramas the blood picture of the cortical surface. You
58:04 see you have an incredible micro vasculature the Bryant And the micro vessels are
58:12 close as 50 microns from each So there's no micro vessels that are
58:18 within about a few. So Mazz from uh from the micro vessel,
58:25 neurons that are few cinemas away from vessels. This is N.
58:30 A picture of the ocular dominance columns intrinsic optical signal. This is the
58:37 of local blood volume change. And can see that the blood volume
58:43 If you just studied the blood volume , you wouldn't get as much of
58:47 optical specificity is if you were looking the intrinsic optical signal here And then
58:56 have detained at 600. To facilitate the scaling of the pseudo color maps
59:01 normalized to wave lines here. And now kind of trying to overlap and
59:09 that map that you're seeing with here see of the blood flow and try
59:16 refine the map and see if you correlate the map of the blood to
59:22 map of the activity that you're measuring the reflective reflective properties of the
59:31 And you can see that it's getting little bit more specific in this
59:35 And maybe you can even see some the larger players here reflected in in
59:41 this blood map now, not just activity but the blood supply of
59:47 So, okay, let me see . Uh mm hmm. If you
59:56 resting state brain activity, if you to a quiet room, lie down
60:00 close your eyes but stay awake. do you suppose your brain is
60:05 If your answer is not much, probably in good company in our discussions
60:14 various brain systems, We have described neurons become active in response to incoming
60:19 information, our generation of movement. modern brain imaging techniques are consistent with
60:28 view that in response to behavioral neurons become more active in cortical areas
60:33 process ongoing perceptual of modern information, is reasonable to infer that the brain
60:39 quiet and the absence of active However, when the entire brain is
60:44 with the pad or F. R. I. Has founded its
60:48 state activity includes some regions that really fairly quiet and others that are surprisingly
60:57 . An important question is if anything the resting activity signify. So there's
61:06 there there there is you think that you close your eyes there's activity.
61:10 just different activity when you sleep, brain circuits and those brain waves become
61:17 . Um It talks about brains default . Mm hmm mm hmm. And
61:28 default network mode which is sentinel and meditation. Then we're gonna cover that
61:40 dominance columns, individual cortex and then going to cover the pet and
61:48 M. R. I. And look at some of the class supporting
61:54 documents that you have such as neuromodulation spike timing dependent plasticity. You
62:05 I think I showed you you can this figures here and the descriptions of
62:14 . Uh Let's see. Mhm. are for later this is the from
62:31 cells to networks. We talked about back propagation. So some very interesting
62:41 here. Some of the experiments that discussed like in the barrel cortex.
62:46 you want to read more details, clicked on some of the better images
62:53 . Um What else is in I think it would be good if
63:00 added maybe uh a broader review on imaging techniques that we talked about voltage
63:12 dye in terms of coptic called calcium . So I'm gonna look for
63:17 I'm gonna add it down and you use that as your class supporting electoral
63:24 . And then once we decide when doing a quiz. I will point
63:29 one of those articles as the one you guys should focus on for the
63:35 . And there might be a couple questions that are quite detailed that would
63:41 required you to, uh, read at least speed through the speed,
63:50 through the article for specific section of article that I will point you
63:56 So okay. I think it's a point to take a break today,
64:01 , and uh, we'll just finish up, finish up on imaging and
64:05 on with the rest of the lecture today is Wednesday. So we'll see
64:11 guys on monday. All right, hmm. Of
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