Alright, let's move on now and we want to begin to dive into the relevant brain anatomy that is in a position to do this job of associative learning and as we get to this anatomy, we really want to take on three kinds of topics as we explore the neurobiology of emotions. Connection, we want to talk about these effector systems that very well may be critical for the ilicitation of the emtotional response. So I will very briefly remind you of our parallel inputs to our effector systems. that are positioned. to do the job of motivating somatic motor and visceral motor activities in the experience and expression of emotion. Well we then want to move on and spend a fair bit of time talking about the cognitive aspects of emotion, and this is where we begin to understand Where the content of our emotion, the significance of that emotion comes from. And then, finally at the end, I want to spend just a few minutes proposing an idea that would help us understand the more subjective aspects of emotion. In fact, The most difficult of all aspects of emotion to explain in neurobiological terms, and that is the feelings associated with an emotion. One might have for example the somatic and visceral motor aspects of emotion on display. One might even have a sense of the significance of These emotions and what they contribute to cognition. But why should they feel the way that they do? So, I think it's important to recognize that the feeling of the emotion is it's own neurobiological construct. Which might be separate from the somatic and visceral motor display associated with the emotion. Information, and might be different from the role of that emotion in cognition. Okay, well what kind of brain system might be involved with these various dimensions of emotional experience and expression? Well, over the course of the 20th century studies of the emotions have led us into the ventral and medial parts of the forebrain into what has been proposed to be called the limbic system. Now, I don't particularly favor this term limbic system, because once you use the word, system. You're implying some kind of unimodal operation. And I think what we now know is that the set of structures that form a lymbus, or a rim around the medial part of the hemisphere really is not a unimodal system at all. In fact, there are multiple divisions. of this classical limbic system that seem to be largely engaged in functions that can be associated so I will refer you to a separate tutorial where I explore some of these topics in a little bit more detail and I will actually show you some of the key centers in the brain anatomy lab, again to refresh your understanding of where these structures actually are in a human brain. but just to make this point, I do want to just go through some of the key anatomical centers. That are associated classically with this limbic forebrain and highlight some of the distinctive functions that are associated with each. Well, believe it or not the concept of the limbic system really began with Pierre-Paul Broca. The famous French physician and anatomist who initially proposed the idea of functional localization for the production of speech. So, that same Broca who gave us Broca's area is the individual who coined The term, limbic lobe, or le grand lobe limbique. Now, in Broca's day, what was noted was the strong connection between the olfactory bulb, and this grand limbic lobe. So indeed there is an olfactory division. Of this limbic forebrain that Broca recognized, and we know that this includes the olfactory bulb, and the olfactory cortex, and the olfactory cortex extends over much of the ventral and medial distribution of the forebrain, including structures that are associated with this limbic forebrain. And so, that olfactory cortex together with the olfactory bulb is involved in special sensory functions associated with olfaction of course. With the sense of smell. And together with, with gustation, olfaction and gustation contribute to a sense of flavor. So, there is indeed an olfactory division in the limbic forebrain. There's also what I like to call, a parahippocampal division of the limbic forebrain. Now, the circuitry of the hippocampus was really a hot topic of investigation in the mid-twentieth century, and one of the leading. anatomist and physiologist that advanced understanding of this part of the brain was James Papes, and some of you may be familiar with the concept of Papes Circuit as the integral to the structure and function of the limbic system. Well much of pape circuit actually pertains to what I like to think of as this parahippocampal division of the limbic forebrain. It involves the hippocampus related regions in the parahippocampal gyrus that we might call the hippocampal formation. there are connections that run through the anterior nucleus of the thalamus via the fornix and the secondary relay, that then impact the posterior portion of the singular gyrus. There are also important connections of course, that run through the posterior parts of the hypothalamus including the mammillary body. So, many of the elements of [INAUDIBLE] circuit actually pertain to this parahippocampal division. and the functions of this parahippocampal division seem to be those that pertain to what I've been calling explicit processing. So this would include episodic memory, acquisition and consolidation and it would include spacial mapping. Not visual mapping, but mapping of our, location within this broader environment. So these functions pertain to the explicit representation of the here and the now, understanding where we are in our environment. And having the capacity to then take that knowledge and build it up into memory. So these are functions associated with this parahippocampal division. Well Lastly, there's a major division of the limbic forebrain that we'll spend the rest of our time talking about. And it's centered on the amygdala and the orbital immedial parts of the pre frontal cortex. So, these two regions of the telecephelon are intimately connected. They also maintain connections involving the singular gyrus, the temporal pole cortex, and of course they have loops that run through the basal ganglia, through the the ventral stratum, the ventral pallidum, as well as through the medial dorsal nucleus of the thalamus which then projects back on into these cortical regions. The amygdala also has very extensive connections into the medial part of the hypothalamus, and that allows it to have access then to the central circuits that regulate our visceral motor system. the amygdila also has direct projections to the brain stem. Where it can modulate brain systems that are responsible for organizing visceral motor output at that level of the nervous system. And also brain systems that can have an impact on our states of vigilance and attention. So this amygdala and orbital medial prefrontal division is involved with implicit processing. So, it's coordinating visceral motor activity. It is going to be central for the experience and expression of emotion. It's responsible for producing appetitive drives. And it will have a major influence over the expression of social behaviors. So, what I want you to pick out here is really this key contrast between the idea of explicit processing which is associated with the parahippocampal division and implicit processing which is associated with the amygdala and the orbital prefrontal cortex. And it's really this implicit processing that is important for understanding the neurobiology of emotion. Now I want to next just briefly remind you of the parallel pathways that we have from the fore brain to our motor neuronal pools that are expressing somatic motor and visceral motor behavior. So of course, we remember that for the expression of volitional movement we have descending projections that are derived from the posterior part of the frontal [UNKNOWN] lobe, where we have our motor cortex. projections they are mainly in the lateral part of the spinal cord pertaining to the expression of skill with our distal extremities in order to set the stage for The expression of that skill, they are medial projections. Many of which run through the brainstem reticular formation. And these medial projections are just posture, set the gain of local reflexes that allow for the coordinated expression of skill behavior. Now just to remind you of the point that we made briefly in unit four when we talked about the organization of the motor system that there are, indeed, parallel projections that are derived from the limbic forebrain that are involved in the expression of specific emotional behaviors as well as in setting the stage for the expression of those behaviors. And these are projections that are outside the classical pyramidal and extrapyramidal pathways. They run through rather profuse projections that are still not well characterized or understood. But they can gain access to the same kinds of pools of autonomic preganglionic cells and even our somatic. Motor neuronal pools that are involved in coordinating the expression of somatic motor and visceral motor behavior. A great example of these parallel pathways concerns the organization of facial expressions [SOUND]. Remember, we talked some about how. [INAUDIBLE] we are as human beings in telling the difference between a genuine emotional smile, and what we might call a contrived or fake smile. recall the last time you sat in front of a photographer and tried to produce a smile on command. What you were doing, was activating your volitional motor systems, which pertains For control of the face to the lateral aspect of the pre-central gyrus where the command centers governing the movements of the lower part of the face are found so that Voluntary smile that is the product of your volitional motor system is activated via this posterior frontal cortex. That is providing input to the columns of motor neurons in the facial motor nucleus, that are driving the activities of the lower part of the face. So, again, those are coordinated out here in the inferior segment of the precentral gyrus. Now, when we are actually engaged in a genuine emotion, that smile is coming from more medial parts of the forebrain that are gaining access to the lower motor neurons that are governing The expression of the face. But this system, this medial system, which is actually organized in a cingulate motor region. Which is found in the banks of the cingulate sulcus, right about. here is where we would find our singular motor area that's involved in generating motor facial expressions. So there are very different pathways that are derived from different parts of the fore brain that converge in the facial motor nucleus and can sculpt the activity of facial muscles in a way that is conveying emotional content. And we're quite good as human observers in differentiating those patterns of facial muscle activity, that are contrived from those that genuinely express true emotional content.
