 Good day everybody. Welcome to our next episode of the dissection of the human brain Today we shall talk about the little bit about the limbic system and its most important connection the so-called papay circuit Before that, my name is Dr. Sanjay Sanyal professor and co-director of neuroscience and the camera person is Mr. Mark Lesser our IT administrator way back in 1937 James Pappais Published a book about emotions and he've postulated what is known as the papay circuit because James was very passionately in favor of the role of emotions and how the limbic system played a role in emotions Subsequently in 1952 McLean modified that papay circuit and expanded it to include two other structures namely the amygdala and the septal area and That came to be known as the McLean circuit, which is actually a more comprehensive and it deals not only with Emotions, but it also deals with memory, behavior, olfaction and many other functions however The national board still believes and the national board of medical education still believes papay circuit is important and the papay circuit Nowadays is believed not only to play a role in emotions, but it also plays a role in memory Therefore I decided that I'm going to give you a demonstration of the components of the papay circuit And show it to you on a dissection of the human brain. So let's start off The papay circuit starts from the hippocampus the so-called hippocampo mammillary tract Now if you look very closely inside here, you will see this structure Which is running on the inner surface of the on the inner surface of the temporal lobe This is known as the fimbriae. What is the fimbriae? The fimbriae is actually The medially converging axons the white matter from the hippocampus which is located here And if you look further closely, you'll see a sedative structure here on the inner surface of the temporal lobe This is the dentate gyrus. So this white portion medial to that is the fimbriae Which is the axon of the hippocampus now these fibers of the hippocampus they converge and Posterior to the thalamus under the spleenium of corpus callosum they form what is known as the Crust of phonics and this is the crust of phonics which you can see here This crust of phonics then continues around the pulmonary of the thalamus which you can see here And it becomes merges with the opposite side to form what is known as the body of phonics and this is the body of Phonics unfortunately in this it is ruptured, but this is the body of phonics This body of phonics then curves around and Anteriorly it splits again into two anterior columns of phonics in this we can see only one anterior column of phonics This anterior column of phonics goes in front of this opening here Which is the interventricular foramen of Monroe and you can see my probe is going right this from here into the ventricle so the anterior column of phonics winds around in front of the interventricular foramen of Monroe and Ends in this structure here, which is called the mammary body So therefore this entire structure which we traced from the medial surface of the temporal lobe all the way around and Came to the mammary body. This is known as the hippocampo mammary tract This is the first component of the papay circuit now. Let's take the next component of the papay circuit from the mammary body Clamping fibers ascend up inside and end in the anterior nucleus of the thalamus So this is known as the mammilothalamic tract This is the second component of the papay circuit From the mammary from the anti nucleus of thalamus again. We have fibers which are ascending From the thalamus through the anterior limb of the internal capsule, which I'm going to show you a little later Go through the anterior limb of the internal capsule and they end in this structure here This is known as the cingulate gyrus. So these are the thalamocortical fibers Which go through the anterior limb of the cingulate of the cortex and internal capsule and the end in the cingulate gyrus This is the cingulate gyrus, which is located just above the corpus callosum here Now what happens from the cingulate gyrus? There are a bunch of curved fibers which are located inside the cingulate gyrus They are known as cingulum and I will show you the cingulum just now. Let me just reflect the cingulate gyrus Once I reflect the cingulate gyrus, we can see under the cingulate gyrus. There are white matter here This is the cingulum. This cingulum it connects the cingulate gyrus goes all the way around and connects it to the This structure here on the medial surface of the temporal lobe which is known as the parahepocampal gyrus So the cingulum connects the cingulate gyrus to the a portion of the parahepocampal gyrus Which is known as the entorhinal area of the parahepocampal gyrus This is the next component of the papis circuit and from the entorhinal area of the parahepocampal gyrus, we have fibers which enter into the Hepocampal formation, which is located again where we started from and this is the hippocampal formation on our inner surface This hippocampal formation fibers which come from the entorhinal area to the hippocampus They are by means of two pathways. One of them is known as the alveolar pathway and other is known as the perforant pathway The details of which are not relevant to this discussion. So this completes the papis circuit now Let me tell you a few other extra points here If you were to look at the medial and the inferior surface of the temporal lobe We notice this portion is the occipital lobe. We shall not bother about it Just under the calcarine sulcus. We have another sulcus here This sulcus is known as the collateral sulcus This collateral sulcus is the one which demarcates a portion medially which we call just now as the parahepocampal gyrus. If we trace this collateral sulcus further anteriorly it changes its name now It is known as the rhino sulcus. Why is it called the rhino sulcus? Because it is in relation to two important old factory areas One of them we mentioned just now which I showed you here We call it as the entorhinal area. This is actually the secondary old factory area broadman area number 28 And just anterior to that we have another old factory area, which is the primary old factory area Which is broadman area 33 therefore this sulcus, which is an actually the continuation of the collateral sulcus in this region It is called the rhino sulcus So therefore we can see that the limbic system has got close connections with the old factory system And that is why Maclean included the old faction also into the components of the papis circuit So therefore to summarize What we saw just now was the first step of the papis circuit namely the hippocampo mammillary tract This is the hippocampo mammary tract. I'm tracing it further. I'm tracing it all around This is the phonics Hippocampo mammary tract running in the phonics This is the body of the phonics splitting into the anterior column of phonics ending in the mammillary body here From the mammary body. We have the mammalothalamic tract from the thalamus anterior nucleus of thalamus. We have the Through the anterior limb of the internal capsule. We have the thalamocortical tract going to the singulate gyrus From the singulate gyrus. We have the singulum fibers Which connect the singulate gyrus with the entorhinal area of the hippocampal formation and Intorhinal area of the hippocampal formation is also known as the input source From here the fibers go by means of the alveolar pathway and Perferent pathway and they end in the place where we started from namely the hippocampus here So this is in a nutshell the papis circuit So what is the current theory about the role of papis circuit? The current theory about the role of papis circuit is that it is concerned not so much with emotion It is an important component of memory consolidation the process by which the hippocampus By repeated rehearsal converts or what is known as consolidates short-term memory into long-term memory So this is the role which the papis circuit is supposed to play and as I mentioned earlier McLean has expanded this to include the amygdala and the septal area and therefore the McLean circuit Includes not only emotion and memory, but it also includes other functions like behavior and olfaction So this is in a nutshell what is the role of papis circuit and the structures which are visible on the medial surface If you have any questions or comments, please note them in the comments below. Thank you for watching. Have a nice day