Emotions are associated with physical changes, including facial expression, and more generalised changes mediated by the autonomic nervous system and endocrine system.
Extremes of emotion can affect people adversely: excessive sadness can result in depression, or persistent anger can result in uncontrolled aggression; excessive fearfulness can cause anxiety states or panic attacks, while pleasure-seeking can lead to addiction.
All of these situations indicate some imbalance between emotional activity and the consciousness, attention to the outside world. The limbic system consists of areas of cerebral cortex connected to areas of the brain associated with the physical expression of emotion. These areas include the cingulate gyrus, the hippocampus and hypothalamus, which mediate autonomic and hormonal changes; and the amygdala, which is involved in facial recognition, including emotions, and mood.
The limbic cortex consists of a C-shaped ring of cortex on the medial side of each hemisphere, consisting of the cingulate gyrus and the para-hippocampal and dentate gyri on the medial side of the temporal lobe. These areas of the cortex are concerned with the awareness of the context in which emotions are triggered, and are connected to the temporal lobe through a sub-cortical band of association fibres called the cingulum.
Parts of the temporal lobe (hippocampus and amygdala) that deal with memories and emotions and are connected to the hypothalamus using two bands of nerve fibres. The hippocampus and the mamillary bodies of the hypothalamus are connected by the fornix, and the stria terminalis is a smaller bundle of axons that connects the amygdala and the anterior hypothalamic nuclei.
Electrical stimulation of limbic system can induce emotional experiences and autonomic responses, changes in mood and recall of memories.
Key Words: Orbital and Cingulate Cortex, Cingulum, Hippocampus, Amygdala, Fornix, Mamillary Bodies, Striae Terminalis and Septal Area of the Hypothalamus; Emotional Behaviour; Memory, Mood.
Image source: msconnection.org
Extremes of Emotion show as changes in facial expression, as well as generalised changes in the body mediated by the autonomic and endcrine systems.
Emotions - anger, fear, pleasure, love, happiness, surprise, sadness, disgust - are associated with physical changes, including facial expression, and more generalised changes mediated by the autonomic nervous system and endocrine system. Survival was possibly the reason that the emotional brain developed during evolution. it handles emotions such as fear, that initiates attempts to escape from a dangerous situation; while happiness and love induce relaxation. Emotions are also commony used in making lifestyle decisions that reflect individual personalities.
Extremes of emotion can affect people adversely, leading to depression, anxiety, phobias, rage or addiction, and reflectsome imbalance between internal emotional activity and consciousness, i.e. attention to the outside world.
Image source: www.brocku.ca
The limbic system: Connections between the Cingulate Cortex, Hippocampus and the Hypothalamus.
The Limbic System
The Limbic System consists of a ring of cerebral cortex on the medial side of each hemisphere consisting of the cingulate gyrus and the hippocampus, linked by a subcortical band of axons called the cingulum.
The distal part of the hippocampus within the temporal lobe is closely related to the amygdala.
The hippocampus and the mamillary bodies of the hypothalamus are connected by the fornix; and the amygdala is connected to the hypothalamus by the striae terminalis.
Electrical stimulation of the human limbic system evokes memories and emotions, and the physical changes associated with these are expressed though the connections with the hypothalamus.
The hypothalamus is a central regions controlling the endocrine and autonomic systems.
The C-shaped structures connecting the midline and temporal lobes.
Image source: www.slideshare.net
This diagram shows the fornix, and its connections with the hippocampus of each temporal lobe.
Image source: BodyParts3D, Japan
The 3-D animation helps to show the arrangement of the fornix as it passes from the hippocampus in the temporal lobe to the mammilary bodieson either side of the midline of the hypothalamus.
The Structure of the Limbic System
The limbic system (limbus = border in Latin) is a C-shaped ring of cortex on the medial aspect of the cerebral hemisphere consisting of the cingulate gyrus, entorhinal (or parahippocampal) gyrus, and septal cortex (the region in front of the hypothalamus which receives input from the olfactory system).
The cingulum, a C-shaped band of subcortical association fibres, connects these structures with the orbital and medial prefrontal cortex (anteriorly), and the temporal lobe (laterally).
The limbic cortex is connectd to the hippocampus and amygdala within the temporal lobe by the axons in the cingulum. These structures are concerned with memory and mood, and physical expressions of emotional state are achieved by connections to the hypothalamus.
Two C-shaped bands of axons connect the temporal lobe and the hypothalamus :
the fornix connects th hippocampus and mamillary bodies, and the striae terminalis connect the amygdala and the anterior hypothalamus.
The pathway involving the hippocampus, fornix and mamillary bodies is concerned with autonomic functions that express the emotive aspects of behaviour,such as blushing, sweating, pupillary changes etc. This circuit connects areas of the cerebral cortex with the posterior hypothalamus and structures regulating autonomic and endocrine functions, such as those associated with stress.
The pathway connecting the amygdala, striae terminalis and the anterior hypothalamus is also concerned with emotional behaviour. The amygdala are almond shaped areas within the temporal lobe, which when stimulated electrically induce changes in mood and emotional behaviour including fear, anger and pleasure, depending on the site stimulated.
The physiological accompaniments of aggression (sham rage; 'fright, fight or flight response') can be reproduced by electrical stimulation within areas of the limbic system. This pathway consists of
the cingulate cortex
the ventral tegmental area of the midbrain.
The 'flight or fight response' consists of:
increased in heart rate and blood pressure
shift of blood flow from skin snd viscera to skeletal muscle
increased rate and depth of ventilation
increase in the size of the pupil, piloerection, sweating
The hypothalamus weighs only 4 grams, but regulates energy, fluid and electrolyte metabolism, body temperature, autonomic and endocrine functions in the body, and has strong associations with the limbic system, stress, and emotional life.
The structure of the hypothalamus is complex, but its regions are extremely important physiologically, and in recent years the main functions of the many hypothalamic nuclei has been elucidated.
Their functions include thermoregulation, appetite, sleep, cardiovascular and autonomic control, control of the endocrine and reproductive systems through the anterior pituitary, and electrolyte balance.
Functions of the Limbic System
Unlike the major sensory and motor systems, which are involved with precise information and control of movements, the limbic system is concerned with the emotional overlays related to the complex context in which events occur. The temporal lobe deals with memory (the hippocampus) and emotions (amygdala), and receives complex inputs from many areas of association cortex.
The pathways between the hippocampus and amygdala and the hypothalamus mediate changes in a variety of bodily functions including:
Autonomic Responses Associated with Fear or Pleasure (depending on which area is stimulated)
Secretion of hormones
The limbic system is concerned with emotion and mood, and the physical expression of the emotions using axons in the fornix and striae terminalis to communicate with the hypothalamus, which influences mood, sleep, appetite, thermoregulation, endocrine and sexual behaviour, fluid balance and autonomic control of heart, blood vessels, sweat glands and visceral functions.