College of Medicine, Babylon University Behavioral and Motivational Mechanisms of the Brain-The Limbic System and the Hypothalamus Dr.Farah Nabil Abbas MBChB, MSc, PhD College of Medicine, Babylon University

Limbic System "limbic" means "border or ring.“ Limbic system = neuronal circuit that controls emotional behavior and motivational drives. Hypothalamus with its related structures represent major part of limbic system.

Limbic System Limbic Functions: Olfaction Feeding behavior & control of body weight Sexual behavior (with hypothalamus) Emotions of rage & fear Motivation Role in memory Autonomic effects (changes in blood pressure & respiration)

Anatomical Structures of Limbic System Hypothalamus Septal nuclei Cingulate gyrus Paraolfactory area Anterior nucleus of thalamus Portions of basal ganglia Hippocampus Amygdala.

Papez Circuit Closed circuit of information flow between limbic system and thalamus and hypothalamus. Fiber tract “fornix” connects hippocampus to mammillary bodies of hypothalamus. In turn project to anterior nuclei of thalamus. In turn send fibers to cingulate gyrus. Sending fibers to hippocampus  completes circuit.

Limbic System Sexual behavior: Mating is a basic but complex phenomenon in which many parts of the nervous system are involved. Copulation itself is made up of a series of reflexes integrated in spinal and lower brain stem centers, but the behavioral components that accompany it, the urge to copulate, and the coordinated sequence of events in the male and female that lead to pregnancy are regulated to a large degree in the limbic system and hypothalamus. Learning plays a part in the development of mating behavior, particularly in primates, but in non primate mammals, courtship and successful mating can occur with no previous sexual experience. The basic responses are therefore innate and are undoubtedly present in all mammals. However, in humans, the sexual functions have become extensively encephalized and conditioned by social and psychic factors. The basic physiologic mechanisms of sexual behavior in experimental animals are therefore considered first and then compared with the responses in humans.

Limbic System Maternal behavior: is depressed by lesions of the cingulate and retrosplenial portions of the limbic cortex in animals. Hormones do not appear to be necessary for its occurrence, but prolactin, which is secreted in large amounts during pregnancy and lactation, facilitates it. In addition, there is evidence that prolactin facilitates paternal behavior.

Limbic System OTHEREMOTIONS Fear The fear reaction can be produced in conscious animals by stimulation of the hypothalamus and the amygdaloid nuclei. Conversely, after destruction of the amygdalas, the fear reaction and its autonomic and endocrine manifestations are absent in situations in which they would normally be evoked. A dramatic example is the reaction of monkeys to snakes. Monkeys are normally terrified by snakes. After bilateral temporal lobectomy, monkeys approach snakes without fear, pick them up, and even eatthem. Anxiety Anxiety is a normal emotion in appropriate situations, but excessive anxiety and anxiety in inappropriate situations can be disabling. Anxiety is associated with a bilateral increase in blood flow in a discrete portion of the anterior end of each temporal lobe.

Limbic System Rage and Placidity: Rage responses to minor stimuli are observed after removal of the neocortex and after destruction of the ventromedial hypothalamic nuclei and septal nuclei in animals with intact cerebral cortices. These were once thought to be only the physical motor manifestations of rage without the emotion and came to be called "sham rage." However, this appears to be incorrect. The rage reactions appear to be unpleasant to animals because the animals become conditioned against the place where the experiment was conducted. These also occur in humans who have sustained damage to the hypothalamus. On the other hand, bilateral destruction of the amygdaloid nuclei in monkeys causes a state of abnormal placidity. The placidity produced by amygdaloid lesions in animals is converted into rage by subsequent destruction of the ventromedial nuclei of the hypothalamus. Rage can also be produced by stimulation of an area extending back through the lateral hypothalamus to the central gray area of the midbrain. Gonadal hormones appear to affect aggressive behavior. In male animals, aggression is decreased by castration and increased by androgens. It is also conditioned by social factors; it is more prominent in males that live with females and increases when a stranger is introduced into an animal's territory. Rage may be related to violence. There has been considerable interest in the search for brain abnormalities in murderers and others who commit violent acts. Studies of this sort are difficult to conduct because of the multiple differences between the groups studied. For instance, people who have committed violent acts are usually confined whereas the normal controls are free. In addition, the studies are subject to inappropriate or premature use in current cases. However, it does appear that violent criminals generally have lower activity in the prefrontal cortex than normals.

Limbic System Motivation: Brain system – Reward or approach system (medial band from frontal cortex to hypothalamus to midbrain tegmentum) Punishment or avoidance system (lateral portion of posterior hypothalamus to dorsal midbrain to entorhinal cortex). Bar-pressing experiment: In human, each bar press delivers stimulus to electrode implanted chronically in brain (usually schizophrenic, epileptic & few with visceral neoplasms or intractable pain) like animals human press the bar repeatedly, then report “relief of pain”, “quiet”, or “relaxed feeling”. When electrodes are in the areas where stimulation is avoided, patients report sensation from vague fear to terror. It has been reported that in rats repeated pressing is obtained from 35% of the brain, avoidance from 5% & indifferent responses from 60%. A variety of habit forming substances that produce addictive behavior may act by increasing dopaminergic activity in the reward system of the brain e.g. cocaine, amphetamine, nicotine, alcohol … etc These studies indicates that behavior is motivated not only by reducing or preventing of an unpleasant effect but also by primary rewards such as those produced by stimulation of the approach system of the brain.

Diencephalon Switching and relay center Integration of conscious and unconscious motor and sensory pathways Consists of three paired structures – Thalamus Hypothalamus Epithalamus Encloses the third ventricle

Thalamus Paired, egg-shaped masses form supero-lateral walls of third ventricle Contains four groups of gray matter nuclei anterior, ventral, dorsal, and posterior Nuclei connected with tracts of white matter & project to and receive fibers from cerebral cortex Afferent impulses from all senses and all parts of body converge on the thalamus.

Thalamic Function “gateway to the cerebral cortex” Major relay station for most sensory impulses that arrive to primary sensory areas in CC: taste, smell, hearing, equilibrium, vision, touch, pain, pressure, temperature Contributes to motor functions by transmitting information from cerebellum and basal ganglia to 1ry motor area in CC. Connects areas of cerebrum

Hypothalamus Location: below thalamus and forms inferolateral walls of third ventricle Infundibulum: stalk of hypothalamus; connects to pituitary gland Mammillary bodies Small, paired nuclei bulging interiorly from the hypothalamus Relay station for olfactory pathways.

Vegetative and Endocrine Functions Cardiovascular regulation Regulation of body temperature Regulation of body water Regulation of uterine contractility and of milk ejection from breasts Gastrointestinal and feeding regulation Control of endocrine hormone secretion by anterior pituitary gland.

Functional Grouping of Hypothalamic Nuclei 1. The Anterior Hypothalamus: It includes the supraoptic and paraventricular nuclei, which are concerned with fluid balance via the antidiuretic hormone (ADH) secretion. It also controls the thirst mechanisms. Damage to those nuclei causes Diabetes Inspidus. Damage to the supraoptic or suprachiasmatic nuclei alters the circadian rhythms. This part of the hypothalamus is likely to be damaged by pituitary tumors, craniopharyngioma, head injuries and intracranial surgery directed at tumors at this region. 2. The Central Nuclei: These are concerned with body temperature regulation by controlling the skin blood vessels and sweating mechanisms. Damage to this area or nuclei causes hyperpyrexia. .

3. The Posterior Hypothalamus: This contains the following nuclei: A 3. The Posterior Hypothalamus: This contains the following nuclei: A. Dorsal nuclei B. Posterior Hyopthalamic nucles C. Supramammillary and Mamillary nuclei These nuclei are concerned with appetite, satiety, feeding reflexes, peristalsis, and control of secretions associated with eating and digestion. Lesions in this region or nuclei may be associated with loss of appetite leading to gross emaciation or gross overeating leading to obesity or altered personality leading to bad temper and aggression. 4. Lateral Hypothalamic Nuclei: Lesions in this area or nuclei causes somnolence, shivering, pilo-erection, small pupils, hypothermia, and low blood pressure

Epithalamus Most dorsal portion of diencephalon; forms roof of the third ventricle Contain: Pineal gland – extends from posterior border and secretes melatonin Melatonin – a hormone involved with sleep regulation, sleep-wake cycles, and mood Choroid plexus – a structure that secretes cerebral spinal fluid (CSF).