femme Neuroscience Notes

Some Topics

Limbic System

The idea of the limbic system originated with attempts to explain how emotions are generated. The limbic system involves old brain modules that keep us alive and involved in worldly interactions. These innate programs link us to the world with appetites and drives. You can begin with four interconnected modules: the hypothalamus, the anterior thalamic nucleus, the cingulate gyrus and the hippocampus. Paul McLean added the orbitofrontal and medialfrontal cortices (prefrontal area), the parahippocampal gyrus and subcortical modules such as the amygdala, the medial thalamic nucleus, the septal area, basal nuclei and a few brainstem formations. The limbic system contributes the for-me-ness of experiences and generates cathexes. McLean stated: The primitive limbic system has the capacity to generate the strong feelings of conviction that we attached to our beliefs, regardless of whether they are true or false...

The limbic system generates the 4 F’s, feeding, fighting, fleeing and sex, generates our feelings, emotions and participates in the regulation of body functions. Appetites are states of need, giving rise to drives which energize our behavior and send us searching for gratification out there in the competitive, not-always-forgiving world. Hunger for food, food searches, and eating gratification are priorities for living creatures. After you are fed you can attend to the other 3 F's. There is an obvious reciprocity among the 4 F's, since you may need one or more of the behaviors to obtain the food you need.

The distinction between inside and outside is useful only when you understand the continuous interaction between events outside and body responses which act on the outside and adjust internal states at the same time. A correct understanding would assume a close correspondence between visible behaviors using skeletal muscles as the motors and visceral changes which are achieved by smooth muscle activity and the secretion of signaling molecules.

Visceral regulation is always a component of emotional processing and is affected by social experience. Dysfunction in visceral regulation systems can be both causes and effects of emotions. Anger for example, involves increased breathing, heart rate and blood pressure. The vagus nerve is the tenth cranial nerve, integrated with the activities of other cranial nerves involved in social engagement: hearing, facial expression via facial musculature and eye movements; the coordination of breathing with sound production via laryngeal, pharyngeal and head-moving muscles.

Old programs nested in the limbic system include the most essential routines of animals: establishment and fighting in defense of territory, foraging, hunting, homing, hoarding, formation of social groups, greeting, grooming, courtship, mating, flocking, and establishment of social hierarchy by ritualistic display. Nested in these old modules are programs inherited from reptiles that continue to dominate the human experience.

The anterior cingulate cortex (ACC) is the cortical part of the limbic system. The cingulate gyrus lies above the corpus callosum and is reciprocally connected with the anterior nuclear group of the thalamus through the thalamic radiations and with the hypothalamus by way of the mammillothalamic tract. The cingulate cortex is also connected with the parahippocampal gyrus and septal area by way of the cingulum.This central position gives the ACC control over cognitive and emotional processing. The ACC is part of a system that monitors performance to regulate behavior. For example the left anterior cingulate cortex (ACC) is coupled with left inferior frontal gyrus during letter-recognition decisions. The right ACC is coupled with right parietal areas during visuospatial decisions. The ACC can detect errors in action but also predicts the probability of error based on past experience. The ACC provides a competitive advantage by anticipating and avoiding errors. Conflict monitoring by the ACC can determine the need for greater cognitive control and cause greater prefrontal cortex activity and appropriate adjustments in behavior.

Decision making involves prediction of the outcome of a given action. Obviously, the expectation of a pleasant outcome makes a behavior more likely. When outcomes are not pleasurable, regret is attached to the decision to act. Cricelli et al found that regret involved the orbitofrontal, and anterior cingulate cortex. They stated: ‘We measured brain activity using functional magnetic resonance imaging (fMRI) while subjects selected between two gambles; regret followed information about the favorable outcome of choices not made. Subjects became increasingly regret-aversive, a cumulative effect reflected in enhanced activity within the medial orbitofrontal cortex and amygdala. This pattern of activity reoccurred just before making a choice, suggesting that the same neural circuitry mediates direct experience of regret and its anticipation.

The posterior cingulate cortex assesses the risk involved in obtaining rewards. Lee suggested: “Choosing to accept enough risk, but not too much, is an important survival skill, and depending on the circumstances, animals may either seek or avoid risk. Given the choice between a sure bet and a larger but uncertain reward, Macaques consistently take the riskier option, and posterior cingulate cortex neurons represent the risk of those choices.”

Drives to maintain brain concentrations of food (and drug) substances are organized in the old brain or limbic structures which do not ask consciousness for permission to operate. The old brain is characterized by a low-level consciousness and a high level of automaticity.

Insightful people will describe a split in their personalities as though automatic behaviors take over and consciousness simply monitors the events which follow. The idea of "will-power" is difficult to substantiate since there does not seem to be a brain procedure with which we reach from higher-level cognition down to machine level programming where automatic behaviors are produced. The characteristic of addictive behavior is the recurrent search for a food, beverage, or drug which supplies specific molecules. Drugs can be ingested, inhaled or injected. This substance search mode may be concealed by layers of social behavior that are more or less acceptable. The drinker, smoker and drug user develop repertoires of social behaviors and mannerisms which conceal and support their habit.