The combinatorial wisdom of the limbic system (LS) selects one out of several possible behavior options. Over a million neurons in the LS link to several behavior control organs of the brain. These organs occupy various steps in the evolving improvement of such controls for the brain. They have the capacity to initiate a variety of competing and conflicting behaviors. These range from primitive howls and growls to those that formulate the highest aspirations of mankind.
Code recognition of the feedback/feed forward messages between these regions trigger the final decision. Starting from numerous options, intuition narrows the final choice to the action proposed by a particular behavior control organ. The whole system follows its instructions. That choice may be to strike with merciless cruelty, or to surrender in noble self sacrifice.
Limbic System Decisions – Intuition and Combinatorial Coding Intuition is an algorithmic process, which enables a bundle of neurons to deliver a single focused output by contextually eliminating irrelevant choices. Combinatorial codes enable nerve cells to store and retrieve their knowledge. Intuition and combinatorial coding enable the LS to deliver clearly focused decisions.
Evolutionary development witnessed the formation of several regions, each one of which increased the pattern recognition capacity of animals. The brain developed regions to identify touch, odors, taste, vision and sounds. Association regions developed to recognize objects and events from these identified sensory inputs. Other regions acquired the ability to respond with fear, or anger to the potential for pain. The highest levels triggered socially desirable behavior options. Ultimately, it was decision making by the LS, which narrowed choices to behaviors, which led to both the worst depredations as well as the noblest achievements of mankind.
Limbic System Decisions – An Assembly of Control Systems Increasingly sophisticated organs joined in to empower the decision making processes by the LS. Nature added organs, which constantly improved decision competence. The earliest decisions were made based on a raw evaluation of sensory data. The organism responded to just touch. A capacity to sense and respond to danger was added later and subsequently, a capacity to empower social cohesion. All along, the LS chose a single priority from the behavior options offered by these organs.
The first of these organs, the prefrontal regions responded to sensory inputs. The amygdala arrived to provide speedy responses to danger. The insular cortex later managed social interactions. Each of these organs provides a behavior option. The choice made by the LS decides whether the system will respond rationally, strike out in fear, or act with mature concern for others. Supporting these decisions, the hypothalamus triggers controlled muscle movements and converts the selected decision into actions. The septal nuclei motivates the system to follow desirable decisions adding pleasure sensations. The hippocampus assists in the long term storage of crucial event memories related to emotional decisions.
Limbic System Decisions – The Prefontal Function The prefrontal region (PFC) was part of the first group of nuclei, which made global decisions for animals. The spinal cord and regions below followed those decisions. The nuclei, which perform these functions form clusters of cells in birds and reptiles, while they are constructed as layers in mammals. Because of such differences in structure and anatomical organization, many scientists debated whether birds and reptiles do have a counterpart of the PFC. But, genetic research has confirmed that this essential and focused decision making function exists in all animals.
Detlev Arendt identified a common set of genes specifying the essential PFC functions, that exist in the common ancestors of annelids, insects and vertebrates. These master regulatory genes specify the identity and positional information of the forebrain, midbrain, hindbrain and even the cerebral cortex. Such genes act as “transcription factors,” that control the expression of sets of proteins which define the mature characteristics of the region. Detlev Arendt identified the patterns and sequences of genes which were expressed in the cortex of mammals and the “pallium” of birds and reptiles. The same patterns were expressed in the “mushroom bodies,” which are the sensory-associative regions for annelid worms. Sensory association regions are unemotional. In the earliest limbic system, the prefrontal regions enabled purely rational evaluation of data.
Limbic System Decisions – The Hypothalamus The limbic system decides whether to behave rationally, emotionally, or to act to meet the needs of the body. The hypothalamus represents the body in this decision making processes. Being older than other organs in the limbic system, the organ acts reflexively seeking to meet biological needs. It acts in an almost on/off manner, seeking to maintain the experience of pleasure and escape or avoid unpleasant, noxious conditions.
Functionally, the organ receives inputs about the needs of the body. Caloric and glucose receptors indicate the need for food and nourishment. Osmoreceptors indicate a a need for water. The organ has thermosensitive neurons, enabling it to decide to respond to excessive external cold or heat. The organ is sensitive to olfactory inputs related to sexual status. Functionally, the organ is in a position to trigger behaviors, which respond to bodily needs.
The hypothalamus controls the reproductive, vegetative, endocrine, hormonal, visceral and autonomic functions of the body. One region of this organ activates the sympathetic system, which heightens emotional arousal, while another region energizes the parasympathetic system, which dampens down the metabolic and somatic correlates of emotional tension.
Limbic System Decisions – The Amygdala Nature developed nociceptive neurons, which fire in response to painful stimuli such as high temperature, low pH and tissue damage. Nociception has been documented in non-mammalian animals, including fish nematode worms, sea slugs, and fruit flies. At this early stage, the amygdala became a component of the LS, with its ability to remember and recognize any sensory input, which held the potential for pain. To enable a swift response, the sensory inputs to the amygdala from the eyes, ears, and other sense organs bypass the inputs to the cortex. When amygdala recognizes relevant sensory inputs, the organ triggers the fear, or anger emotion. Electrical stimulation of the lateral amygdala initiates quick and/or anxious glancing and searching movements of the eyes and head such that the organism appears aroused and highly alert as if in expectation of something that is going to happen. When these signals reach the hypothalamus, the organ responds with pain avoidance behavior.
Limbic System Decisions – The Hippocampus The theme of this website is that all nerve cells store combinatorial memories. Memories are stored in many regions in the context of emotions. An emotion indicates a crisis point, where a decision was made during the day. The hippocampus stores memories in the context of the geographic location, where the emotional event occurred. Hippocampal arousal generates rhythmic slow activity (theta). The theta rhythms create the spatial maps maintained by "place" neurons attuned to specific environmental features and landmarks. Hippocampal damage prevents an animal from learning even the simple task of ceasing to move.
During REM episodes of sleep, the hippocampus activates those regions, which were active during the experience of an event, strengthening the combinatorial links of the emotional signal to the sensory event memory. Subsequent recall of the emotion recalls the event. The key location of the hippocampus within the LS enables it to store real time decision memories in the ring of neurons, which carry the pivotal control signals.
Limbic System Decisions – The Septal Nuclei Signals from the septal nucleus energize the system on a single focus, while inhibiting activity in unrelated regions. This group of neurons has copious links to the control centers in the amygdala, the hippocampus, the hypothalamus and the brain stem reticular formation. Activation of the septal nucleus stimulates neurotransmitter production, which motivates the organism. It also has an inhibitory-GABAnergic effect, which empowers intuition by inhibiting irrelevant neural activity. The septal nucleus influences the generation of rhythmic slow activity (theta) which indicates hippocampal arousal connected to learning and memory. Lesions in the septal nucleus abolish hyppocampal theta and impact on memory.
Limbic System Decisions – The Insular Cortex The insular cortex, is a portion of the cerebral cortex folded deep within it. Its front portion is considered to be a part of LS. The insular cortex has access to bodily responses including movements of the body; by pain, temperature, itch and changes in local oxygen status. These inputs enable the organ to perform the function of identifying the self as an independent entity. Mirror neurons within the organ recognize the implications of social interactions to trigger a range of social emotions, including shame, guilt and compassion.
Limbic System Decisions – Smooth Coordination Of Opposing Forces Decisions of the mind range between numerous conflicting options. Early in the course of evolution, nature developed a system to manage the opposing forces exerted by muscles. Muscles can only contract. When one muscle relaxes, an opposing one contracts. Each one of the 60,000 motor neurons in the spinal cord has up to 20,000 interneurons, which report back the movements of other muscles. Feedback links inform the muscle of actions already taken and feed forward links, of actions about to be taken. Combinatorial memories within a nerve cells cause the cell to recognize incoming patterns of impulses and fire to activate or inhibit muscles. Since muscle movements are not computed, but learned through habit and practice, combinatorial memories manage this process.
Limbic System Decisions – Evolutionary Adaptation The spinal cord coordinates complex and opposing neural interactions. The limbic system has a million fibers, which carry a massive range of control signals along with complex and conflicting emotion signals. Fear, sadness, disgust, contempt, curiosity, surprise, love, pleasure, embarrassment, guilt, and shame impact on behavior. Competing with each other, emotions are generally agreeable, or disagreeable. Feedback/feed forward links within the LS grant control to a single emotion, while inhibiting conflicting ones. Anger gives way to fear. In the LS, nature adapted the spinal cord motor control system to suit the new emotional controls. Francois Jacob noted this adaptive quality of evolution. “In contrast to the engineer, evolution does not produce innovations from scratch. It works on what already exists, either transforming a system to give it a new function or combining several systems to produce a more complex one.”
Limbic System Decisions – Codes Overrule Prefrontal Will It is common experience that the decisions of the system bypass consciously willed decisions, when they do not pass the Worthwhile, Appropriate, Safe, or Practical (WASP) criteria. The system will not implement a conscious decision, if it does not fit the WASP criteria. Conscious decisions are initiated by the prefrontal regions, while emotional decisions are initiated by the amygdala, or the insular cortex. It is obvious that only the vast inherited wisdom of combinatorial codes can enable the LS to make such finely differentiated choices between competitive demands.
Limbic System Decisions – Emotions Gradually Overrule Instincts Evolutionary process inhibited the more primitive instincts to enable more cultured decisions. The hypothalamus controls essential homeostasis by motivating the organism with pleasure and triggering avoidance behaviors. A man, with severe brain damage, which spared the hypothalamus, reacted with howling, growling, and baring of teeth in response to simple sound or touch stimuli, or even if approached. The organ senses variations in levels of light to adjust mood, and activity. It motivates a hungry person to look for food, to avoid excessive external cold or heat, or even to trigger sexual posturing in females and males.
Infant development witnesses the inhibition of instinctive responses by the wisdom of higher levels. During the first few months, elementary touch, hunger and body movement sensations trigger screaming, crying, or rudimentary smiles and gurgles of pleasure. With development, these responses are overruled by the rational decisions of the prefrontal regions, or to the emotional outbursts of the amygdala, or the insular cortex. Intuition and combinatorial codes enable the LS to focus of the mind instantly on a single objective.