Hello and welcome to the review of chapter 58 of Gaitanen Hall's medical physiology textbook. In this chapter we go over the basics of the cerebral cortex and its role in learning and memory. If you enjoy the chapter please don't forget to give it a like and subscribe to the channel and if you're in need of the textbook there is a link within the description. So to begin with as with anything we need to know our anatomy of the cerebral.
cortex and we've already covered part of this in previous chapters going over this column-like structure of the cerebral cortex where the outer side of the cerebral cortex is up the top here next to row one and then the deep layer is down here near row six. So within each column we have three primary types of neurons. We have the granular neurons, fusiform and pyramidal. Granular neurons, they have a greater role as interneurons, and they may be excitatory using the glutamate neurotransmitter or inhibitory using the GABA neurotransmitter. Whereas the pyramidal and fusiform cells, they more give rise to our output fibers.
And looking back at this figure here, we can also see on the right side that all of these neurons have quite wide horizontal and vertical links. So it's able to spread signals throughout each column. column quite easily. Now when it comes to the actual processing of information, inputs usually come in in row four like we've touched on in previous chapters.
It may go upwards to then connect to other columns through interneurons or it may go downwards to rows five or six to go and become an output signal. Layer five typically goes out to the brainstem and has output connections to the brainstem. Whereas row six is output connections out to the thalamus.
And talking about the thalamus, it's very important to recognize that whenever you're talking about the cerebral cortex, you need to kind of talk about both the thalamus and the cerebral cortex together. That gives us the thalamocortical system. And that's because there are so many interconnections that removing one part of the thalamus will remove effectively the corresponding part of the cerebral. cortex.
So now we get to the functions of specific areas and we've kind of already talked about these in some other chapters but we're going to do a brief overview of everything here. So we have our primary areas so such as the primary motor and primary somatic for senses areas and they have direct connections to specific muscles and movements and senses and then we have our secondary areas and the secondary areas are more trying to make sense of the inputs and outputs that are arriving to the brain. We have our primary visual and secondary visual area down here.
And then that leaves us with these association areas right down the bottom here. So we've got the parietal, occipital, temporal association area. We have the limbic association area down ventrally. And then we have the prefrontal association area. So if we're able to blow up this area a little bit more and dive deeper into these specific areas, you can see that the...
parietal-occipital-temporal association here, shown over here, actually has some sub-parts to it. So we've got the visual processing of words, so obviously we're able to visualize words and then turn that into an image, and there's quite a lot of connections into this Winnikki's area, which is responsible for comprehensing language, and really the intelligence around our language that we speak and think in. We have the spatial coordinates for body and surrounding. We also have this area down the bottom here which is mainly for naming of objects as well.
And these guys have quite good connections with the Winnikis area which we'll dive into very shortly later on in this chapter. We obviously have the limbic association area. The limbic system is really just involved with behavior, emotions and motivation. We're going to touch on that a lot more in the next chapter. We have the broker's area here which is more the motor action for actually creating language and creating words.
So there's obviously a connection from the Winnikis area to the Brokers area to actually create those words to now speak. And then we have the prefrontal association area, which mainly has its role in planning these complex movements and then also having this elaboration of thoughts. So that thought that you're having in your head right now, that's all happening in this prefrontal area. And that's within your working memory. As a concept, your working memory is just that short-term memory where you temporarily store certain bits of information, and that allows you to problem-solve in the short term.
So then you're able to continue with whatever function you're trying to do. And all of that planning and imagery occurs within the prefrontal association area. And then if we look at the bottom side of the actual brain, the medial aspect of the bottom of the brain is actually a whole facial recognition area. You can actually remove just That's that portion.
And all you'll lose is the ability to recognize faces, which is obviously a very important part of our society and social constructs, is to be able to recognize someone's face and interact with someone's face. And so in the caudal portion, we have connections with the visual system to be able to actually visualize various faces. And then in the temporal region, we have an association with our limbic system, and that allows us to associate emotions and brain activation and behavior associated with it. facial recognition.
So moving now into the Winnikis area you can see that the auditory areas, the visual areas and our somatic areas all connect into this one portion and this is really our highly intelligent portion of our brain which is able to process all of this information and convert it into thought. So for instance people that do not have this area they may be able to hear words perfectly fine coming from the auditory system However, they are unable to be processed and you can't actually arrange these words into a thought. So although the words are coming in, they're almost going straight out and you're unable to actually process that information. So it's highly complex thought and our general intelligence, which is involved in this area right here called the Winnikies area.
It also talks about the angular gyrus down the back here, which is involved with processing visual information and sending it to the Winnikies area. So then you add. then able to process visual experiences and for instance an issue in the angular gyrus gives you dyslexia or word blindness you can see words but you can't put any thought behind the words that you're actually seeing now it's important to also know that there is actually a dominant hemisphere noted since birth so 95 percent of people actually have the left side of their Winniky's area to actually be the dominant side and the dominant one and then that will actually be a positive feedback where Eventually you have greater complexity and have greater processing occur in the larger area, which means that it's going to continue to grow at a faster rate.
So because it starts off at birth being larger, it then propagates to become the dominant side. But if that gets damaged or removed in early childhood, then the other side will actually develop those dominant characteristics. And that's the same with the broker's area, the motor areas, whereas some... most people are right-handed because typically it's the left side of the brain that becomes dominant.
So now to move on to the prefrontal association area, that area at the front of the brain that's involved with your working memory. People who have had prefrontal lobectomies, meaning that essentially there's been an incision straight through and cutting that prefrontal association area away from the rest of the brain, which they thought would be able to relieve severe depression. But what they found in these people is that they actually lost the ability to solve complex problems because you don't have this working memory. You can't string together sequential tasks to achieve complex goals. Once again, you don't have that working memory.
You can't do several tasks at one time. You actually lose some aggression and lose your ambition as well. Thought to occur because of a disassociation from the limbic system.
Social responses are also inappropriate. which pertains to also how people could still talk and comprehend language but they'll just carry on long trains of thoughts and their moods will change rapidly just because they can't have that social interaction and that reworking memory and they typically just go throughout life without much of a purpose which is a quite a sad complication from a surgery for severe depression so there's this gray box here goes on about how communication has two aspects you've got a sensory input And then you also have a motor output. So for instance, you hear or you see words, which then gets processed by the Winnikis area, either through the hearing system or through the primary visual system.
And then that has to then get processed and then sent through to the broker's area to then get processed and planned for which type of motor movements you're going to do that then gets sent to the motor cortex. So then you're able to actually create the motor movement for speech and create an actual sentence. There's this brief paragraph here talking about the anterior commissure and the corpus callosum. Basically the corpus callosum is the connection between the two hemispheres, so connecting the left and the right hemisphere, and that allows memories or functions stored on one side to be actually be able to be handled and available for the other side of the brain.
Whereas the anterior commissure Allows a connection with other areas of the brain such as the amygdala. So then this gets to the good part of thoughts, consciousness and memory. And the problem with all of these types of concepts of thoughts. consciousness and memory so we actually know very little about the mechanism of them at all so we know that obviously that we think we know that we have consciousness and we know that we have the ability to restore memory from the past but we don't truly know the mechanism behind it with a deep understanding now just for some general definitions a thought results from a pattern of stimulation of many parts of the nervous system at one time so that allows you to actually process multiple signals from multiple areas of the brain. Whereas consciousness is our continuing stream of awareness of the surroundings and our thoughts themselves.
And then that gets us to memories. So memories are really stored in the brain by changing the sensitivity of synaptic transmission between neurons. And then the new pathway or facilitated pathway is called a memory trace.
And then that can be easily re-stimulated to reproduce that memory. So we have to get into some... pretty simple concepts here or definitions and the first of which is negative versus positive memory negative memory means that you do not remember that stimulus so for instance right now as you're listening to this there are a lot of inputs coming in to your brain you've got visual inputs of whatever you're looking at you've got the hearing input from my voice whatever else is going on around you And then you've got various sensations just from where your body is located in space and time and what actions you are doing.
The majority of that you will not remember. And so that is a negative memory because you are purposefully inhibiting yourself from actually memorizing all of those signals that are coming into you. This occurs for 99% of the signals that actually comes to your brain. And so positive memory is just the act of actually forming a memory trace. So forming a memory, a pathway that's easily accessible.
So that's the 1% of your sensations. The actual act of creating a positive memory is called memory sensitization, whereas the act of forming a negative memory, or the act of actually not remembering it, is called habituation. So we actually have three types of positive memories.
We've got short-term memory, which lasts for several seconds to minutes, intermediate long-term memories, which lasts for days to weeks, and then long-term memory, which can be restored. for years or a lifetime. And then we also have this other concept of a working memory, which is mainly a short-term memory but is terminated as soon as the problem you're trying to solve is solved.
So purely for problem solving, you know, you're memorizing several key components that's relating to whatever problem you're trying to solve and then once you've solved that problem your working memory is finished for that particular time period. So once they're actually stored, they've been classified as either declarative memory or skill memory. Declarative memory is basically thinking back to when you're five years old and your birthday and all the sensations at that time point whereas skill memory is thinking back to how you actually do a particular skill. So that is if you play tennis and you know a certain tennis skill then you go out on the tennis court you're not going to play like it's your first time playing you're going to have skill memory.
and your motor movements are going to be able to perform using those memory tracks. So when it comes to the actual physiology behind each of these three periods of memory, short-term memory appears to either be some form of circuit of reverberating neurons. So you have a sensation that comes in, that reverberates around a particular circuit, and then it's gone after a brief moment, seconds to minutes, and then your memory is no longer there. But you may also have it from presynaptic facilitation or inhibition, meaning that a particular neuron may be facilitated to stay open for a little bit longer than it normally would, and then eventually it's shut off and you no longer have a stimulation of that neuron and you've lost that memory. When it comes to intermediate long-term memory, there's no real good classification behind this and our more permanent long-term memory, but in terms of the physiology behind it, intermediate long-term memory...
we have a chemical or physical change in the synapse presynaptic terminal. That's shown down in this diagram here, where, for instance, a normal stimulus may just come across, result in a release of calcium ion. So then we get neurotransmitter coming across the synaptic cleft, and then this neuron being stimulated.
That may be a normal system, but as soon as we get an intermediate's memory, that may be formed due to a noxious stimuli, that actually results in a molecular change within the presynaptic terminal, eventually resulting in more CAMP, that then results in a reduced potassium conductance. So then the action potential on the presynaptic neuron does not repolarize. So we get more calcium ions coming into the presynaptic terminal, more neurotransmitters, and in this area, this entire synapse is now ready to fire continuously and is now facilitated and is able to actually draw back on a memory. Whereas when it comes to long-term memory, there is an actual structural change in our neurons. So we may have an increase in vesicle release sites.
We may have an increase in the number of vesicles. We may have an increase in presynaptic terminals or the actual structure of the dendritic spine. So we get the transmission of stronger signals.
So there's actually a structural change in all the neurons and the connection. So then the pathway is easier. And if you want to think back to a memory, then you're able to just easily locate that memory and bring it back. Now, the process of actually creating a memory is called consolidation.
So that's creating an intermediate memory from a short-term memory or a long-term memory from an intermediate memory. And in order to convert a short-term memory into a longer memory, typically you need a lot of repetition to strengthen those neuronal changes. And then that new memory will be what's called codified, which basically means that it's going to be assimilated in the brain or your memory storage bins next to similar types of memories.
So your brain's able to realize that this memory is a particular type of memory, let's say a skill memory that's similar to, that is a tennis skill, then you're going to assimilate that or codify that next to your other tennis skills. And then lastly here we talk about the hippocampus and its role in memory. Now the hippocampus is involved with the limbic system and is involved with the reward and punishment area, as you'll see in the following chapter.
And it basically processes... experiences decides whether or not it's worth storing and then stores that memory for a long term if it's worth storing and it will store preferentially memories that are either a reward or a punishment so if you want to try and remember something better it's better to reward yourself to actually memorize that particular type of memory at the time or if you want to be harsh on yourself you could also make to get a punishment because then you'll be able to memorize that punishment you We are wired so then we're able to know where we can find food which is a reward so we're able to go to that particular area and find that food and we're also wired to know which areas to avoid and which foods to avoid based on punishment. Things in the middle which do not reward or punish us we are much more likely to forget. Now damage to the hippocampus can cause antegrade amnesia meaning that you can no longer form new memories because the hippocampus is no longer telling which short-term memories that turn into long-term. And then you can get retrograde amnesia from also damage from your hippocampal areas, but also from your thalamic areas as well, meaning that you forget experiences that have already occurred.
You're unable to actually grab those memories out of your memory storage box. You're more likely to only be able to remember those ones, those distant memories that have been walked so many times that there is a strong connection to them. And then that's the end of the chapter.
If you want to be able to memorize these chapters better, I suggest you have a look at the link in the description where you can find downloadable audio files through the Patreon link. Otherwise, I hope you enjoyed it. Feel free to leave a comment and we'll see you in the next video.