In this class session Professor Sapolsky discusses key elements of the limbic system.
The limbic system is most centrally involved in emotions. Originally it was studied in rats and known as the rhinencephalon, or nose brain because activity was being coordinated and run through the rat's olfactory centers. Within a rat it's a given that it'll go through the olfactory system because all rat emotions will be tied into smell. But for species that also take in, or primarily take in, information through the auditory or visual systems. So the wiring of the emotional stimuli will also depend on the sources of sensory information.
In the 1950's neuroscientist Paul MacLean presented the triune brain model. The brain is divided up into three sections.
1. Hypothalamus, pituitary, pathways down the spinal cord. This is the reptilian part of the brain. Automatic regulatory things - temperature regulation, blood pressure, blood glucose.
He then mentions Ondine's Curse (Congenital Central Hypoventilization Syndrome) involves a disruption in this mid-brain area. Once the person stops actively controlling their breathing, they stop breathing. Ultimately you die of sleep deprivation due to constantly interrupted sleep.
2. Above that is the emotional center of the brain, the limbic system, which is primarily a mammalian invention and function.
3. Finally above that is the cortex, which handles the higher level processes. It is greatly intertwined with the limbic system. As such it is far from being a completely rational, abstract, independent center. The limbic system absolutely influences decisions made in the cortex. Likewise the cortex influences the limbic system. Antonio D'Amasio's Descartes Error is recommended for more information on this topic.
James Papez is credited as advancing the research into the interconnections in the circuitry within the limbic system.
The wiring is complicated but the main thing is that every center wants to be king and to be king it really wants to be the one telling the hypothalamus what to do. The hypothalamus is the central hub for all the neuro-endocrine stuff, thus it would influence emotion and behavior, plus the hypothalamus plays a role in the autonomic activity. Every center also wants to ensure that no other center is telling the hypothalamus what to do. As a result the circuitry contains a lot of excitatory and inhibitory wiring and stimuli.
To calculate who has the pole position, look at how far away the projecting center is from the hypothalamus. The fewer neurons and synapses in between, the better your odds of calling the shots. As far as our senses go, every sensory modality has to go through three or four synapses to get a message to the limbic system, except for smell. The olfactory system is one synapse away.
The major structures are as follows (thanks Wikipedia):
Pituitary Gland - secretes hormones that help regulate growth, blood pressure, aspects of maternity, lactation, sexual activity, thyroid gland function, metabolism, water balance, water levels (osmosis), temperature regulation. Works along with hypothalamus.
Hypothalamus - links the nervous system to the endocrine system. Connects with the pituitary gland. Involved in the same major processes.
Amygdala - involved with fear, anxiety, aggression and sexual motivation. It is centrally involved in the formation and recollection of emotional memories.
Hippocampus - majorly involved in spatial tasks and hugely involved in the conversion of short term to long terms memories. A central location of neurogenesis.
Septum - a dividing section within the limbic system.
Mammillary bodies - They, along with the anterior and dorsomedial nuclei in the thalamus, are involved with the processing of recognition memory. They are believed to add the element of smell to memories.
Thalamus - Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness.
Ventral Tegmental Area - this is important in the function of dopamine within the limbic system and is, thus, involved with the natural reward centers of the brain. It has a role in addiction, motivation, depression, intense emotions, several psychiatric disorders.
Nucleus Accumbens - this is thought to play an important role in reward, pleasure, laughter, addiction, fear, aggression and the placebo effect.
And the last piece the prefrontal cortex (or frontal cortex), including the anterior cingulate. It is arguably the cortical component of the limbic system. The prefrontal cortex is involved in emotional items like impulse control, long term planning, delayed gratification. It isn't fully myelinated until the mid 20's, thus accounting for the changes people go through from the teenage years to their early 20's and on to adulthood.
Research by Dr. Ian Dunbar demonstrated that the size of the prefrontal cortex in primate species is directly correlated to the size of their social groups. This suggests that it evolved into a tool for correct social behavior.
All the limbic parts are connected to each other. Key connections include -
Amygdala to hippocampus. The amygdala is involved in fear, aggression and anxiety. The hippocampus handles the formation of new memories. Thus this pathway is largely about the brain forming new memories in emotionally laden territory.
Hippocampus to septum. Septum then sending a huge projection to the hypothalamus and mammillary bodies. This is known as the medial forebrain bundle.
Imaging studies (CAT, PET, fMRI) enables researchers to track activity and see things like metabolic increases in areas depending on context. For example, in patients with PTSD the amygdala is enlarged and more metabolically reactive than normal. People with long term major depression will sometimes have a smaller hippocampus due to atrophy.
In general the areas that are fed grow larger and those that are starved grow smaller. The more active, the more dendritic connections that are formed and the stronger those connections become.
However, he notes issues with pathways vs. nuclei and the overall complexity which make it overly simplistic to boil something down to a simple rule along the lines of this is the center that does fear for you. There are simply too many connections running back and forth everywhere to define the brain that way. Additionally one has to be an ethologist to place the behavior in context (aggression versus predatory behavior). Social structures also impact the expression of behaviors. A dominant animal will show a threat gesture while a subordinate will inhibit the behavior. The takeaway is that even though that's the part of the brain that "does" a certain behavior, it will not be expressed. This points to the importance of knowing the individual as well as the species and also demonstrated the complexity of the brain.
The amygdala is centrally involved in fear, anxiety, and aggression. This tells us that we cannot understand the neurobiology of being violent without also understanding the neurobiology of being afraid. It also plays a role in male sexual behavior.
The septum inhibits aggression. These two will try to inhibit the other in order to help their message to win out.
The hippocampus is a central figure in memory and learning. It also measures the levels of glucocorticoids in the bloodstream. Thus memory and stress are intertwined, which makes sense. For example, if you encounter a stressful, scary situation, it's important to remember how you survived it if you do.
Mammillary bodies - aspects relative to maternal behavior.
Prefrontal cortex - maturation, correct sexual behavior, correct context for aggressive behavior.
Anterior cingulate - it's tied in with empathy and concern for others (the pain of others). It lights up when people are in compassionate states. But it is also implicated in depression, an overactivation in which the pains of the world make it a bleak, hopeless place to be.
VTM and nucleaus accumbens - this is the part of the brain that has all the neurons involved with the release of dopamine (a neurotransmitter deeply involved in pleasure). It's the part of the brain that cocaine works on, that all drugs work on indirectly (including key elements of addiction). This part of the brain activates when you are anticipating getting the reward. More so, it's about powering the behavior you need to do in order to get the reward.
For example, when a rat has to pull a lever to get a food reward, dopamine is the agent that will make him look forward to doing this and get him motivated to take action. Dopamine is like a homuncular version of Tony Robbins running around in your head urging you to take action. If you block the rise in dopamine, the behavior won't happen, the rat or monkey will just sit there. Thus it is about stimulating the pursuit of pleasure rather than simply rewarding pleasure itself.
He next covers several different areas of the hypothalamus before moving on to the James Lange Theory of emotions which in essence posits that your body reacts and then you figure out (label) that reaction as an emotion. While many have tried to knock this theory down, recent research shows that yes, in fact your emotions can come from your brain trying to figure out what your body is doing.
He mentions a famous epinephrine study in which subjects were given long acting epinephrine and then exposed to either an angry fellow participant or a happy, excited one. People responded to their increased epinephrine based on the environment. The takeaway is that the stimulus prompts you to decide what it means and when you do so, you'll create the meaning for you.
He then mentions a classic example of state dependent learning in which a couple argues, their bodies get stressed and after they resolve issue number one, one of them remembers another wrong from the past that induced a similar feeling and off you go. The feelings themselves are tied in with the emotional state.
On the positive side, you can induce positive emotions by doing the things you would do if you were happy. As an example he mentions that smiling can help create more positive emotions, even in someone that is depressed. (The difficulty is our old pal dopamine who is often lacking in a depressed person and who is needed to get someone to take the actions needed to produce pleasure).
The ultimate takeaway is that physiology can be used to influence emotions.
In the 1950's neuroscientist Paul MacLean presented the triune brain model. The brain is divided up into three sections.
1. Hypothalamus, pituitary, pathways down the spinal cord. This is the reptilian part of the brain. Automatic regulatory things - temperature regulation, blood pressure, blood glucose.
He then mentions Ondine's Curse (Congenital Central Hypoventilization Syndrome) involves a disruption in this mid-brain area. Once the person stops actively controlling their breathing, they stop breathing. Ultimately you die of sleep deprivation due to constantly interrupted sleep.
2. Above that is the emotional center of the brain, the limbic system, which is primarily a mammalian invention and function.
3. Finally above that is the cortex, which handles the higher level processes. It is greatly intertwined with the limbic system. As such it is far from being a completely rational, abstract, independent center. The limbic system absolutely influences decisions made in the cortex. Likewise the cortex influences the limbic system. Antonio D'Amasio's Descartes Error is recommended for more information on this topic.
James Papez is credited as advancing the research into the interconnections in the circuitry within the limbic system.
The wiring is complicated but the main thing is that every center wants to be king and to be king it really wants to be the one telling the hypothalamus what to do. The hypothalamus is the central hub for all the neuro-endocrine stuff, thus it would influence emotion and behavior, plus the hypothalamus plays a role in the autonomic activity. Every center also wants to ensure that no other center is telling the hypothalamus what to do. As a result the circuitry contains a lot of excitatory and inhibitory wiring and stimuli.
To calculate who has the pole position, look at how far away the projecting center is from the hypothalamus. The fewer neurons and synapses in between, the better your odds of calling the shots. As far as our senses go, every sensory modality has to go through three or four synapses to get a message to the limbic system, except for smell. The olfactory system is one synapse away.
The major structures are as follows (thanks Wikipedia):
Pituitary Gland - secretes hormones that help regulate growth, blood pressure, aspects of maternity, lactation, sexual activity, thyroid gland function, metabolism, water balance, water levels (osmosis), temperature regulation. Works along with hypothalamus.
Hypothalamus - links the nervous system to the endocrine system. Connects with the pituitary gland. Involved in the same major processes.
Amygdala - involved with fear, anxiety, aggression and sexual motivation. It is centrally involved in the formation and recollection of emotional memories.
Hippocampus - majorly involved in spatial tasks and hugely involved in the conversion of short term to long terms memories. A central location of neurogenesis.
Septum - a dividing section within the limbic system.
Mammillary bodies - They, along with the anterior and dorsomedial nuclei in the thalamus, are involved with the processing of recognition memory. They are believed to add the element of smell to memories.
Thalamus - Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness.
Ventral Tegmental Area - this is important in the function of dopamine within the limbic system and is, thus, involved with the natural reward centers of the brain. It has a role in addiction, motivation, depression, intense emotions, several psychiatric disorders.
Nucleus Accumbens - this is thought to play an important role in reward, pleasure, laughter, addiction, fear, aggression and the placebo effect.
And the last piece the prefrontal cortex (or frontal cortex), including the anterior cingulate. It is arguably the cortical component of the limbic system. The prefrontal cortex is involved in emotional items like impulse control, long term planning, delayed gratification. It isn't fully myelinated until the mid 20's, thus accounting for the changes people go through from the teenage years to their early 20's and on to adulthood.
Research by Dr. Ian Dunbar demonstrated that the size of the prefrontal cortex in primate species is directly correlated to the size of their social groups. This suggests that it evolved into a tool for correct social behavior.
All the limbic parts are connected to each other. Key connections include -
Amygdala to hippocampus. The amygdala is involved in fear, aggression and anxiety. The hippocampus handles the formation of new memories. Thus this pathway is largely about the brain forming new memories in emotionally laden territory.
Hippocampus to septum. Septum then sending a huge projection to the hypothalamus and mammillary bodies. This is known as the medial forebrain bundle.
Imaging studies (CAT, PET, fMRI) enables researchers to track activity and see things like metabolic increases in areas depending on context. For example, in patients with PTSD the amygdala is enlarged and more metabolically reactive than normal. People with long term major depression will sometimes have a smaller hippocampus due to atrophy.
In general the areas that are fed grow larger and those that are starved grow smaller. The more active, the more dendritic connections that are formed and the stronger those connections become.
However, he notes issues with pathways vs. nuclei and the overall complexity which make it overly simplistic to boil something down to a simple rule along the lines of this is the center that does fear for you. There are simply too many connections running back and forth everywhere to define the brain that way. Additionally one has to be an ethologist to place the behavior in context (aggression versus predatory behavior). Social structures also impact the expression of behaviors. A dominant animal will show a threat gesture while a subordinate will inhibit the behavior. The takeaway is that even though that's the part of the brain that "does" a certain behavior, it will not be expressed. This points to the importance of knowing the individual as well as the species and also demonstrated the complexity of the brain.
The amygdala is centrally involved in fear, anxiety, and aggression. This tells us that we cannot understand the neurobiology of being violent without also understanding the neurobiology of being afraid. It also plays a role in male sexual behavior.
The septum inhibits aggression. These two will try to inhibit the other in order to help their message to win out.
The hippocampus is a central figure in memory and learning. It also measures the levels of glucocorticoids in the bloodstream. Thus memory and stress are intertwined, which makes sense. For example, if you encounter a stressful, scary situation, it's important to remember how you survived it if you do.
Mammillary bodies - aspects relative to maternal behavior.
Prefrontal cortex - maturation, correct sexual behavior, correct context for aggressive behavior.
Anterior cingulate - it's tied in with empathy and concern for others (the pain of others). It lights up when people are in compassionate states. But it is also implicated in depression, an overactivation in which the pains of the world make it a bleak, hopeless place to be.
VTM and nucleaus accumbens - this is the part of the brain that has all the neurons involved with the release of dopamine (a neurotransmitter deeply involved in pleasure). It's the part of the brain that cocaine works on, that all drugs work on indirectly (including key elements of addiction). This part of the brain activates when you are anticipating getting the reward. More so, it's about powering the behavior you need to do in order to get the reward.
For example, when a rat has to pull a lever to get a food reward, dopamine is the agent that will make him look forward to doing this and get him motivated to take action. Dopamine is like a homuncular version of Tony Robbins running around in your head urging you to take action. If you block the rise in dopamine, the behavior won't happen, the rat or monkey will just sit there. Thus it is about stimulating the pursuit of pleasure rather than simply rewarding pleasure itself.
He next covers several different areas of the hypothalamus before moving on to the James Lange Theory of emotions which in essence posits that your body reacts and then you figure out (label) that reaction as an emotion. While many have tried to knock this theory down, recent research shows that yes, in fact your emotions can come from your brain trying to figure out what your body is doing.
He mentions a famous epinephrine study in which subjects were given long acting epinephrine and then exposed to either an angry fellow participant or a happy, excited one. People responded to their increased epinephrine based on the environment. The takeaway is that the stimulus prompts you to decide what it means and when you do so, you'll create the meaning for you.
He then mentions a classic example of state dependent learning in which a couple argues, their bodies get stressed and after they resolve issue number one, one of them remembers another wrong from the past that induced a similar feeling and off you go. The feelings themselves are tied in with the emotional state.
On the positive side, you can induce positive emotions by doing the things you would do if you were happy. As an example he mentions that smiling can help create more positive emotions, even in someone that is depressed. (The difficulty is our old pal dopamine who is often lacking in a depressed person and who is needed to get someone to take the actions needed to produce pleasure).
The ultimate takeaway is that physiology can be used to influence emotions.
