Changes in Synaptic Connections Underlie Memory and Learning – Memory (PSY,BIO)

00:01 Okay. So now that we’re talking about memory, let’s talk about what’s actually happening at the synaptic level in your brain.

00:08 So what I’m referring to is, in our brain we have synaptic connections between neurons or cells and they happen everywhere in your brain.

00:16 But we’re going to focus on the ones that are specific to memory.

00:20 Now, there’s a process called “neural plasticity”.

00:23 And that refers to the malleability of the brains pathways and synapses.

00:26 So, what does that mean in English? That means that pathways are not static and that the communication between neurons is actually a dynamic process and it can actually change over time.

00:37 And it can change in relation to activation or stimulation.

00:41 So, the connection or synapses in the brain are constantly being modulated over time.

00:46 And that’s what you want.

00:47 You don’t want it so that all the connections are static and are set for life and you aren’t able to adopt.

00:53 You want the exact opposite.

00:55 You want to be able to adapt to new situations.

00:57 You want to be able to require and change based on, say, new memories.

01:02 Now, how does memories applied to synaptic connections? Well, the working model is that when a new memory is formed, activity between neurons will increase.

01:14 And so, it kind of makes sense.

01:16 If you are trying to remember something or if you’re trying to repeat a word or if there’s a certain concept that you’re repeating over and over and over and you want to acquire to memory, you’re going to want your neurons in your brain to encode that information.

01:30 So one way they can do that is to increase communication between themselves through this synaptic connection.

01:37 Now, when a brain injury occurs, neurons will reorganize in attempt to compensate and adjust.

01:43 Again, we’re back to that phenomena of us trying to understand the brain through injury or insult, right? So, what we’re saying here is, say, you have a stroke or a trauma, you know, a gunshot wound to the head or you’re Phineas Gage and a tamping iron has gone through.

01:58 The neurons that were damaged were connected and were communicating something.

02:03 It could have been a memory.

02:04 It could have been a task.

02:05 And so, thanks to this neuroplasticity neurons can reorganize, readjust and try and pick up some the slack.

02:13 So, we also have the formation of new neurons in the brain and this is called “neurogenesis”.

02:17 And it’s not everywhere.

02:19 We know for a fact in areas like the spinal cord and other parts of the central and peripheral nervous system, you don’t get regeneration.

02:26 But the brain was fortunate enough to actually have neurogenesis.

02:29 So, specifically in the areas like the hippocampus and cerebellum.

02:32 This has been illustrated.

02:34 So, getting, applying this information that we just figured out here, this neuroplasticity and neurogenesis, we’re going to talk about how this applies to memory and learning.

02:42 And I’ve already alluded to when you’re trying to kind of code a memory, you want these two neurons to communicate.

02:49 So there’s a saying that we say, “What fires together, wires together.” So the more that neurons fire together at the same time or communicate, the tighter the connection.

02:59 So there’s no actual physical connection but we use that analogy of wires.

03:04 So, as they fire together, they form associations.

03:09 So, same thing with the network that we were talking about, about the nodes and the network, that network of meanings or memories or content, the more that these nodes are communicating, the tighter the associations and more meaningful and deeper the connections.

03:29 So, it’s not a coincidence that this network idea and the idea that, you know, the synaptic network is really a network of neurons are so similar because they’re essentially were trying to illustrate the same thing.

03:40 And so, having a model that reflects actual, physical organization makes sense.

03:45 So, the associations or neural nets or patterns of activation may represent formation of memory.

03:50 So again, it’s not that neuron A is talking to neuron B and that equals the memory associated with your address.

03:58 That’s not what we’re saying here.

03:59 We’re saying that there’s actually the formation of a network or a neural net which is very similar analogist to the network that we were talking about prior to the nodes.

04:09 And so, when you’re trying to form a memory, you might be actually activating a neural net.

04:14 And so, you can exactly pinpoint a specific memory because it’s a diffused network.

04:20 And this is actually a good thing because it allows for it to be dissipated and kind of contain in various spots of the brain as opposed to just being targeted in one exact spot.

04:28 So, neurological evidence for the network model of memory in retrieval context and cue is proving this looking at things like neuroimaging, and you look at how you activate and what affect that has.

04:40 So, frequency of activation in neural nets and emotional input can determine the strength of associations.

04:45 The more you fire a neural net, the more that it validates itself and the stronger the association.

04:54 You can even layer in things like emotional input and that can even impact the strength of the associations.

05:02 So, we’re going to take a look at some actual sections here.

05:05 So, the images that you are seeing here are one on the left, one of the right.

05:07 One being a section of a stimulated brain and one of an unstimulated brain.

05:12 So what do you notice? So, the one on the left is highly innervated.

05:16 It’s a got a lot of networks, a lot of branching and we see a lot of those little processes.

05:20 That is a really diverse, well-connected neural net or network.

05:26 As opposed to the one on the right, we see there’s -- the connections are fairly sparse.

05:30 That’s not a very strong network or it’s a developing network, and it hasn’t been stimulated much, right? So you can see, the more you stimulate, the more you learn, the more you interact, the more memories are going to get encoded, the more connected and the greater degree of inner connectivity of those neurons or that network, that neural net.

05:50 Now, we’re going to get into a process of something called “LTP”, which stands for long-term potentiation, and this occurs after brief periods of stimulation, you see an increase in the synaptic strength between those two neurons.

06:02 So, this is kind of near and dear to my heart because I have done quite a bit of research at the bench with this model of LTP and have actually done it where you initiate LTP.

06:14 A lot of times in research, it’s done in areas that are associated with memory.

06:17 So, in the research that I’ve done and research that most do, it’s in the area of the hippocampus.

06:23 And the idea is we want to create a model of what we believe memory formation might look like.

06:29 And we then try and validate this with what we’re seeing in the actual brain.

06:33 So the idea is this.

06:34 If I hear your name for the first time, so you tell me your name and you’re like, your name is Rita.

06:40 Hi Rita, nice to meet you! Now, I need to encode that memory.

06:45 So how am I doing that? Well, it’s going to the steps of we’ve already discussed before.

06:49 So it’s going to go in.

06:50 It’s going to go through the buffer.

06:51 It’s going to go in to short-term memory, and eventually, it’s going to get to long-term memory at which point we’ve encoded into our brain.

06:56 Now, how are the neurons going to actually do this? Well, when they hear the name Rita, it will activate a group of neurons which have formed a neural net.

07:06 And that neural net will start to fire.

07:08 And this rapid stimulation of that network is encoding.

07:11 It’s the actual encoding process of the name Rita.

07:15 So, think of it of being shocked for a brief, brief period and that represents us, literally type, if you want to use an analogy of us typing in to our brain Rita, and that is the neurons firing.

07:25 Now, that happens once and it increases the connection between your neurons.

07:31 So, once that happens, we have a more robust electrochemical response to a given stimulus.

07:38 So the next time I hear the term Rita or I’m asked and prompted, “What’s her name,” or “Do you know her name?” Those neurons will fire and fire more robustly because they have a pretty good connection.

07:51 That is due to the brief period of stimulation of when we’re actually encoding the name Rita.

07:55 So, once LTP has occurred, the subsequence threshold for firing is lower, therefore it’s easier to fire.

08:00 Again, the more you repeat something, the easier it is to remember.

08:04 And the more often you recall something, the easier it is to keep it in long-term memory.

08:09 So LTP is a process or a model that we can say to explain how we are increasing the synaptic strength between two neurons or within a neural net and response to us encoding a memory.

08:24 So LTP is loosely thought to be a model to explain memory consolidation.

08:28 And it also can create new synaptic connections and increase dendritic branching at synapses.

08:32 So that previous diagram that it show with all the branching, that increase branching can be when areas are stimulated, i.e. learning new memories, i.e. consolidating memories to the process of long-term potentiation, LTP.

08:47 So, let’s look at this in terms of a diagram.

08:50 And as you can see here, we’re going to go through a couple of steps of what it looks like.

08:53 So the first diagram is showing a presynaptic neuron, a postsynaptic neuron.

08:57 We have the synaptic cleft.

08:58 And we have vesicles filled with transmitter.

09:00 So we’re just kind of reviewing a little bit of the biology that you’ve probably studied to death, but we’re just going to go pretty quickly here.

09:05 So the presynaptic neuron is going to get a signal coming down the axon.

09:09 So it’s action potential.

09:10 It’s going to trigger release of a transmitter across the cleft and it’s going to interact with the postsynaptic receptor.

09:16 So you can see the little dots and the cleft are representing the transmitter binding to the postsynaptic receptor.

09:22 Now, if you look at the next figure to the right, we’re going to see all of these interacting and you’re seeing the propagation of the response.

09:29 Now, in periods of LTP or rapid stimulation, this is going to get strengthened.

09:34 And you can see in the third box we have quite a bit of transmitter being released and that is us strengthening the connection.

09:43 Okay. Now, in the final response, you can see that we have stimulation coming and you have -- it’s much easier to get a release of transmitter because we’ve initiated LTP, and therefore, not a lot of stimulation is required to initiate a fairly dramatic response.

09:59 Okay? So that is over viewing the process of LTP.