Behavioral and Motivational Mechanisms of the Brain

1. Behavioral and Motivational Mechanisms of the Brain

2. Functional Brain Systems • Networks of neurons working together and spanning wide areas of the brain • The two systems are: • Limbic system • Reticular formation

3. Diencephalon • Central core of the forebrain • Thalamus, hypothalamus and epithalamus • Encloses the third ventricle

4. Reticular Formation • Composed of three broad columns along the length of the brain stem • Raphe nuclei • Medial (large cell) group • Lateral (small cell) group • Has axonal connections with hypothalamus, thalamus, cerebellum, and spinal cord

5. Reticular Formation

6. Functions of the Reticular Formation 1. Excitatory stimulus to the brain & Consciousness 2. Regulation of muscle relfexes 3. Co-ordination of the autonomic reflexes (Respiratory and Cardiovascular reflexes) 4. Regulation of pain sensation (Reticulospinal pathways modulate impuls transmission in the dorsal horn of the spinal cord) • Brain stem monoaminergic systems play important roles in the control of these functions

7. Activating-Driving Systems of the Brain • Continuoustransmission of nervesignalsfromthelowerbraintothecerebrum • Blockagebytumors (e.g. Pinealtumor) • 1) Directstimulationof background level of neuronalactivity in wideareas of thebrain • 2) Activation of neurohormonalsystemsthatspecificfacilitatoryorinhibitoryneurotransmitterstoselectedareas of thebrain

8. Continuous Excitatory Signals from the Brain Stem • Reticular excitatpry area of the brain • Located in the reticular substance of the pons and mesencephalon • Also called “bulboreticular facilitatory area” • This system also maintain tone in the antigravity muscles and controls the levels of spinal reflexes

9. Continuous Excitatory Signals from the Brain Stem

10. Continuous Excitatory Signals from the Brain Stem • Two types of excitatory signals passing through the thalamus: • Rapid stimulus (ACh) and Small neurons of the brain stem (Monoamines)

11. Excitation of the excitatory area by peripheral sensory signals • Level of activity of the excitatory area in the brain stem is determined by the peripheral sensory signals • Stimulation by pain signals • Entrance of 5th cranial nerve to the pons • Transection of the brain stem below or above the 5th cranial nerve

12. Excitation by the feedback signals from the cerebral cortex

13. A reticular inhibitory area located in the lower brain stem • This inhibitory area is located in the medulla • This area can inhibit reticular facilitatory area and thus decrease activity in the brain • Inhibitory signals from serotonergic neurons

14. Neurohormonal Control of Brain Activity

15. Neurohormonal Control of Brain Activity • Norepineprine system and locus coeruleus: located at the juncture between the pons and mesencephalon • Dopaminergic system and Substantia nigra: It lies anteriorly in the superior mesencephalon • Serotonergic system and the raphe nuclei: Located in the midline of pons and medulla, several thin nuclei called raphe nuclei • ACh system: Gigantocellular neurons of the reticular formation (pons and mesencephalon) : tracts go both to the brain and spinal cord

16. Neurohormonal Control of Brain Activity

17. Central Noradrenergic System

18. Central Serotonergic System

19. Central Dopaminergic System

20. Acetylcholinergic System LDT: Latero Dorsal Tegmental Nucleus PPT: Pedunculopontine Tegmental Nucleus

21. Other Neurotransmitters and Neurohormonal Substances • Enkephalins • Glutamate • Vasopressin • Epinephrine • Histamine • Endorphins • In most places in the brain ACh functions as an excitatory neurotransmitter

22. Limbic System(TheEmotional & MotivationalBrain) EmotionsIf only it were as simple as the diagrams below…

23. Limbic System • Limbic system • Rhinencephalon = smell brain • Hypothalamus, hippocampus, anterior nucleus of thalamus, septal nuclei, amygdala, paraolfactory area, portions of basal ganglia

24. Limbic System • Medial forebrain bundle connects the limbic system to the brain stem

25. Hypothalamus • Thalamus and the third ventricle • Mammillary bodies Relay station for olfactory pathways • Infundibulum – the pituitary gland

26. Hypothalamus • Output signals from the hypothalamus: • 1) Brain stem • 2) Diencephalon and Cerebrum • 3) Infundibulum – the pituitary gland • Hypothalamus represents less than 1 % of the brain mass

27. Papez Circuit (circa 1930)

28. Hypothalamic Function • Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of breathing, and many other visceral activities • Perception of pleasure, fear, and rage • Regulation of body temperature • Regulates feelings of hunger and satiety • Regulates sleep and the sleep cycle • Endocrine functions of the hypothalamus

29. Vegetative and Endocrine Functions of the Hypothalamus

30. Vegetative and Endocrine Functions of the Hypothalamus • Cardiovascular regulation: Stimulation of posterior and lateral hypothalamus increases arterial pressure and HR; preoptic area produces opposite effects • Regulation of body temperature (preoptic area) • Regulation of body water: ADH (vasopressin) • Uterine contractility and milk ejection: Oxytocin • Control of anterior pituitary hormone secretion

31. Behavioral Functions of the Hypothalamus and Associated Limbic Structures • Stimulation of lateral hypothalamus • Ventromedial nucleus and surrounding areas • Periventricular nuclei – 3rd ventricle • Sexual drive – anterior and posterior hypothalamus • Effects of hypothalamic lesions

32. Reward and Punishment Function of the Limbic System • Reward centers: Medial forebrain bundle, VMN, LHA • Less potent reward centers reside in the septum and some basal ganglial areas • Punishment centers: Central gray surrounding the aqueduct of Sylvius in the mesencephalon, Periventricular area • Less potent punishment areas are found in the amygdala and hippocampus

33. Reward and Punishment Function of the Limbic System

34. Reward and Punishment Function of the Limbic System • Rage and its association with the punishment centers • Effects of tranquilizers on the reward or punishment centers • Importance of reward or punishment in learning and memory

35. Associative Learning (Fear Response) Before Training – a transient orienting response is induced to the sound Training – sound is paired with the shock After Training – placement in the box induces freezing when the sound is present.

36. Memory &Hippocampus • Memory is the storage and retrieval of information • The three principles of memory are: • Storage – occurs in stages and is continually changing • Processing – accomplished by the hippocampus and surrounding structures • Memory traces – chemical or structural changes that encode memory

37. Hippocampus • Hippocampus and adjacent temporal and parietal structures are called “hippocampal formation” • This formation has connections with the cerebral cortex, hypothalamus, septum, amygdala, limbic cortex and mamillary bodies • Hippocampus is hyperexcitable • Epileptic sezures • Less layers in the hippocampal cortex

38. Functions of Amygdala • The amygdala is a complex multiple small nuclei located immediately beneath the cerebral cortex of medial anterior pole of each temporal lobe • It has abundant directional connections with the hypothalamus and other parts of the limbic system

39. Functions of Amygdala • Effects initiated from the amygdala and sent through the hypothalamus – mostly autonomic functions • Direct stimulation of amygdala results in several types of involuntary movements • Bilateral ablation of amygdala (Klüwer-Bucy Syndrome) • Not afraid of anything • Extreme curiosity about everything • Forgets rapidly • Tendency to place everything in mouth & eating objects • Strong sexual drive

40. Functions of Limbic Cortex • Cerebral association areas for control of behavior