LIMBIC SYSTEM

3/30/2007

“The limbic system comprises the amygdala, hippocampus, medial thalamus, nucleus accumbens, and basal forebrain, all of which connect to the anterior cingulate gyrus, which is the major gateway to the frontal cortex.  This system is the launching point of emotions and the emotional connector to the cognitive prefrontal cortex.  Yet all of it is wrapped around the system for movement.  (Ratey/ug/227)”

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“…thalamus divides information into two “streams” – one that provides cognitive assessment and the other that creates physiological arousal and physical reaction to a stimulus.  (Ratey/ug/225)”  cc fiels

this visceral brain is named the limbic system, “and it is still generally assumed to be the network in the brain that senses and generates emotions.  (Ratey/ug/225)”  cc files

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“Some authors are reluctant to use the term “reticular formation” or “reticular nuclei” because new knowledge about the component structures reveals there is no homogeneity in he anatomy or function of the region. 10 [ch 8]  This is precisely the same problem we face with umbrella terms such as “limbic system.”  On the other hand, during a transitional period, it is reasonable and helpful to refer to terms such (Damasio/FWH/245) as “limbic” and “reticular,” in a qualified manner, to establish the connection between old and new views.  (Damasio/FWH/246)”

The Feeling of What Happens:  Body and Emotion in the Making of Consciousness

Harcourt Brace & Company

1999

Antonio R. Damasio

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Chapter eight The Neurology of Consciousness

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“Both the right and the left frontal lobes are very important for the regulation of emotion, needed for making decisions in the social and personal realm.  It may be that this area connects the limbic system and the motor cortex, establishing the link between areas that plan and those that carry out the actions.  There may even be an “upper” path between the limbic system and the cortex through the cingulate gyrus that deals with pleasure and sociability and a “lower” path involving the amygdala and ventromedial prefrontal coretex that deals with issues of self-preservation.  (Ratey/ug/230)”

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“The neuroanatomy of the olfactory tract is unique among the senses.  Hearing, a small part of vision, touch, and taste all enter the brain through the brainstem and are passed up to the thalamus.  From this central way station, millions of neural networks transfer signals to regions of the cortex specialized for each sense.  The signals are bounded around, then sent on for further processing to the limbic system, which is central to emotions, memory, pleasure, and learning.  The limbic system often adds an emotional tag…. It calls up memories and may initiate a bodily response….  As an emotional response is evoked, a person may begin planning a proper course of action.  (Ratey/ug/63)”

“Given the complexity of visual and auditory information, and the corresponding potential for misinterpretation of ambiguous situations, the brain tries to make sense of fine details before making a judgment call.  In contrast, olfactory nerves project directly into the amygdala and olfactory cortex, parts of the limbic system, without any mediation through the thalamus.  The olfactory nerves have a hotline to the emotional brain, and only then is the information sent to the orbitofrontal cortex for more associating, inhibiting, and further processing.  The “smell” connection is much faster and more decisive than the systems for the other senses and not much filtering goes on before action is called for by emotional memory.  (Ratey/ug/63)”

“Indeed, the nostrils are positioned directly above the mouth because they serve as a last-resort alarm system.  If you are about to eat something that is disgusting and would make you sick, the olfactory system must be able to detect the (Ratey/ug/63) telltale odor, match it to a memory encoded in the limbic system, and alter your behavior, all in the fraction of a second that it takes for a morsel of food to pass beneath the nose to the lips.  (Ratey/ug/64)”  cc all of this to amygdala –

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“Smell was a major catalyst in the evolution of the primitive brain (nicknamed the “smell brain” since it basically consisted of olfactory tissue on top of a nerve cord) into the modern, more complex brain.  The entire limbic system is thought to have evolve solely from its original function of interpreting odors and emitting pheromones – chemical scents that send social or sexual messages to other members of the same species.  As other brain connections evolved, our abilities to process sensory information grew more refined.  The olfactory cortex has not shrunk, but the rest of the brain has expanded.  (Ratey/ug/64)”

Well, that is interesting!  Not unlike ants and bees, then, who communicate through pheromones to their complex working social structure!  Before we could communicate through gesture or sound we communicated through scent!

“…the primary olfactory cortex…lies at the heart of the limbic system.  (Ratey/ug/64)”

“Our olfactory system recognizes certain smells from birth, notably ones that signal danger, such as those of rotting foods…..  humans are capable of recognizing and differentiating as many as 10,000 odors….  (Ratey/ug/64)”

“Women have a better smell sense than men and are better at picking up odors during certain times in their menstrual cycle.  (Ratey/ug/68)”

“The limbic system contains the brain’s pleasure centers, many of which can be activated by the scents of food and sex.  Therefore, the olfactory system can establish a link between intended behaviors and rewards, causing a person to pursue a mate or a good dinner.  The reward center is central to learning and provides the motivation for doing something or the sense of feeling satisfied.  Because the olfactory apparatus is wired directly to this system that determines pleasure and disgust, it is a powerful trigger that can motivate us very quickly and directly, without the associations or abstract thinking necessary for us to respond to vision or hearing.  It is simple, direct, and powerful.  (Ratey/ug/65)”

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“Olfactory projections are also found in the hypothalamus, the brain’s hormonal center, which is responsible for the fight-or-flight response.  Consequently, odors can alter heartbeat and blood pressure (Ratey/ug/66) directly, with very little mediation.  Olfactory fibers also project into the pleasure areas of the limbic system, including the amygdala and the septal area, where dysfunctions are seen in schizophrenia, addictions, ADHD, and the ability simply to feel satisfied.  (Ratey/ug/67)”

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:Epilepsy that starts in the limbic area is notorious for overwhelming the sufferer with strange or overtly foul odors and tastes during a seizure.  (Ratey/ug/68)”

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“…taste signals enter the brain at the medulla in the brainstem from three cranial nerves.  From the nucleus solitarius, the arrival area in the medulla, signals are sent to the thalamus and then on to the taste centers in the cortex, which sends them on parallel pathways to the hypothalamus and amygdala, and then on to other parts of the limbic system, where emotions and memory are stored and retrieved in regard to qualities of the taste.  This can cause us to avoid food that tastes a certain way or seek food that can satisfy the nutritional needs of the body, such as salt. The signals traveling back and forth along these pathways also affect consumption reflexes such as salivating and swallowing.  (Ratey/ug/71)”

“The hypothalamus plays a key role in feeding mechanisms…..problems in the lateral hypothalamus area cause the animals to stop eating and drinking, while lesions in the ventromedial nucleus of the thalamus cause overeating.  (Ratey/ug/71)”

“Areas in the thalamus and hypothalamus are involved in feedback patterns that maintain the body’s energy balance and body weight.  Decisions about whether to eat or drink, what to eat or drink, whether to continue eating or drinking, and when to stop eating or drinking – the balance between eating and satiety – result from the interchange between these areas.  Since the hypothalamus is also a key play in the motor system, emotions, and memory, it is believed to control our hunger by triggering the release of dopamine, which is greeted as a (Ratey/ug/71) reward by our reward system.  When these areas determine that satiety has been reached, the dopamine is stopped, and our desire to eat wanes.  (Ratey/ug/72)”

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“…autism, a developmental disability that affects several areas of the brain, including the cerebellum, hippocampus, and limbic system, beginning at a very young age.  (Ratey/ug/78)”

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the limbic system accomplishes both novelty detection and reward

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“Arousal is controlled by the reticular activating system, which connects the frontal lobes, limbic system, brainstem, and sense organs.  Incoming information from the sense, or thoughts, can arouse us, and depending on the startle value it alerts the rest of the arousal circuit.  The hippocampus – a key player in long-term memory – also communicates with the reticular activating system.  With its store of knowledge, the hippocampus is the way station to our memories, able to compare the present with the past and thus monitor events as either novel or ordinary.  That way, if the reticular activating system startles over something harmless, the hippocampus works as a protective filter to conserve the brain’s energy by inhibiting the system.  (Ratey/ug/115)”

cc to reticular activating system, frontal lobes, limbic system, brainstem, hippocampus,

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MOTOR ORIENTATION:

3 steps disengage-move-engage

“First the posterior parietal cortex helps us disengage from a stimulus….  Now your brain can prepare your motor pathways to do something new.  Next, the basal ganglia and the frontal parietal attention circuits shifts the focus of attention to the new stimulus….  Finally, a group of neurons in the thalamus engages attention by focusing the brain on the new stimulus and inhibiting other noise and therefore distraction….  (Ratey/ug/116)”

mesolimbic pathway

“Once we are aroused and oriented, the reward and novelty system kicks in, governed by the mesolimbic pathway (a group of dopamine-containing neurons), which is a key driver of the limbic system. This system is integral not only to attention but to many other brain functions, notably the emotional and social brain.  (Ratey/ug/116)”

“Detecting novelty and seeking reward are the two primary forces that direct the selection of where to focus our attention.  The novelty system takes note of new stimuli.  The reward system produces sensations of pleasure, assigning an emotional value to a stimulus, which (Ratey/ug/116) also marks it for memory.  If, later, the same stimulus reappears, the memory of these visceral emotions provides a response, from joy to disgust, which then directs the individual to seek out a plan of action.  The mesolimbic system also functions as the novelty detection system, which is sensitive to unexpected scene changes.  (Ratey/ug/117)”

“The nucleus accumbens is a central player in the reward system.  This small cluster of cells is located in the forebrain and is well connected to the amygdala and other parts of the limbic system.  It has long been identified as the principal pleasure center of the brain.  It contains one of the highest stores of dopamine in the entire brain, and is sensitive to other pleasure neurotransmitters such as serotonin and endorphins.  These chemicals are key factors in feeling satisfied and rewarded, and therefore in providing motivation.  (Ratey/ug/117)”

rest is with nucleus accumbens file

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“Motor activity is affected by many factors, including some we may not immediately think of, such as motivation.  The anterior cingulate gyrus, also on the second floor, appears to play a crucial role in initiation, motivation, and goal-directed behaviors.  It is well interconnected with the amygdala and other structures of the limbic system that regulate our emotions, the fight-or-flight mechanism, and conditioned emotional learning.  In short, it assesses just how important something is, determines an appropriate response, and decides how quickly the response will be executed.  (Ratey/ug/165)”

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